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#1 furling

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Posted 27 September 2010 - 10:58 AM

Pitch poling is a feeling usally only reserved for multihull sailers, do the rules allow anything to be put in place to avoid this? given that the winds may be up to 30+ knots wouldnt it be wise to have something in the bow that when pushed too far, instead of killing everyone it will merely bury in and slow down allowing the cat to continue racing, wouldnt this be more desirable or does larry want to go that extreme and the person with the biggest gonads wins?

#2 josselin

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Posted 27 September 2010 - 11:05 AM

you mean something like this ?

http://www.sailingan...aCapsizeNet.jpg

it use to happen with Orma 60 and it was part of the game!!
It will be part of the AC 34 I hope!

Would you suggest that we add a keet to the multihull so that it can't pitchpole???:lol:

#3 furling

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Posted 27 September 2010 - 11:34 AM

no not a keel but something like hobie uses on its cats to stop pitch poling, may give you the extra seconds you need to regain control, although the x40`s have nothing but we see them going over time to time and close calls often..



#4 the loose cannon

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Posted 27 September 2010 - 12:28 PM

something like hobie uses on its cats to stop pitch poling,

There is nothing that a hobie uses to stop pitch poling.

From a design perspective, adding anything in the bows (like a waterplane) only adds drag and further exacerbates the pitch pole (slowing down the hulls while the rig still wants to go faster - thus starting the cartwheel.)

The only solutions to pitchpoling are light weight (so that the hulls are always popping up above or punching through the waves, smaller rig (so It can't force the cartwheel), or longer hull length to create the longitudinal buoyancy required to prevent the hulls from being pressed down into the water (like the current generation of maxi singlehanders, and most notably BP5.

#5 DRIFTW00D

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Posted 27 September 2010 - 01:04 PM

Aside from chopping off the old design and getting lifting foils under the low side and a set of new wave piercing bows.
Just do not let it happen.

That said do not cleat the sheets in extreme conditions.

Seems I read about auto sheet releases to at least avoid the cleated sail problem.
But at night racing in calm winds everything up is a big problem when a strong front with storms is lurking near. To this problem RADAR and satellite weather for images of cells in the area could save you life.




#6 Who's your daddy

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Posted 27 September 2010 - 01:09 PM

Seems like Monomunchers balls have just shrunk now he has got the balls out multihulls he has been rabbiting about for months :D

#7 Xlot

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Posted 27 September 2010 - 01:29 PM

The only solutions to pitchpoling are light weight (so that the hulls are always popping up above or punching through the waves, smaller rig (so It can't force the cartwheel), or longer hull length to create the longitudinal buoyancy required to prevent the hulls from being pressed down into the water (like the current generation of maxi singlehanders, and most notably BP5.


That, and narrow/faired bow topsides

#8 davidprobable

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Posted 27 September 2010 - 02:12 PM

pitch poling is the only reason for ac34 to use multihulls to maximize reality show people on the viewer list...........its all about tv revenue and potential death/injury that drives viewership.......

#9 s2 alter ego

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Posted 27 September 2010 - 02:21 PM

The only solutions to pitchpoling are light weight (so that the hulls are always popping up above or punching through the waves, smaller rig (so It can't force the cartwheel), or longer hull length to create the longitudinal buoyancy required to prevent the hulls from being pressed down into the water (like the current generation of maxi singlehanders, and most notably BP5.


Compared to USA17 AC72 is very narrow for its length making pitchpole less of a problem. Even greater difference when AC72 is compared to orma60s.

AC72 has a wing, therefore they can reverse the angle of attack above the hounds producing a significant bowup moment on demand, should they ever need it.
That would also reduce apparent windspeed by slowing the boat down further helping to avoid pitchpoling.

Light platform weight does not help to resist pitchpoling with a heavy rig in a chop.

There is no restriction on using T-foil rudders on heavy weather, is there ?
If not that would help too as long as those remain in the water instead of being lifted above water.

#10 s2 alter ego

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Posted 27 September 2010 - 02:27 PM

pitch poling is the only reason for ac34 to use multihulls to maximize reality show people on the viewer list...........its all about tv revenue and potential death/injury that drives viewership.......

Almost, but it's a perceived risk instead of real risk that counts.
As long as the audience believes there is a great risk involved it makes no difference even if there really wouldn't be any risk at all.
Risk of a collision or near collision leading to flipping sideways is far more propable than pitchpoling due to simply pushing too far when sailing without any other boat nearby.

#11 MauganNacra20

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Posted 27 September 2010 - 02:37 PM

Those bow foil things only work until you hit a certain angle and then they became pitchpole fins, driving you deeper.

The best thing that can be done to prevent pitchpoling is putting T-foils on the rudders.

The X40's are prone to flipping and such because they 1) have shallow rudders that come out of the water easily, and 2) have a hydraulic mainsheet that doesn't release fast enough.*

*this is what I've been told by people who sail them.

#12 jalani

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Posted 27 September 2010 - 02:55 PM

T - foil rudders as on the F16 Stealth, AO F14 and others would be the best solution. They can be pushed very, very much harder than standard rudders.
Mind you if they 'let go' there is absolutely no chance that the boat won't pitch-pole :D

#13 coxcreek

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Posted 27 September 2010 - 09:44 PM

Inverted T rudder foils have saved me many times when buried in blue and white water to and above the mast base - boat nearly stops, tough on the rig and fittings but the stern doe not come out., well not far anyway ... and that is a huge plus for multihullers.

#14 laser 173312

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Posted 28 September 2010 - 07:55 AM

Isn't there a requirement for a deformable crash structure in the bow. May be a clever designer could use that to help stop pitch-poling.

#15 Alpha FB

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Posted 28 September 2010 - 08:42 AM

pitch poling is the only reason for ac34 to use multihulls to maximize reality show people on the viewer list...........its all about tv revenue and potential death/injury that drives viewership.......


Yes, it is indisputable that a large crash/wipeout with personal injury is the only way to guarantee the AC makes the headline news - but surely this is not what anyone wants (apart for some ghouls we don't want involved in the sport anyway)...

However, to get more people interested in following the whole thing, it needs to be obvious that it is not easy sailing the boats around the course. While watching a tactical battle between two old school IACC's gets it going for someone who can be troubled to understand the difference in wind on either side of the course, tidal currents and what not. For this, the great unwashed are not ready...

On the other hand, watching the clips of those Extreme 40's in Cagliari makes it clear that it takes skill, balls and lightning reflexes to control one of these boats - and these things any viewer can understand and learn to appreciate...

#16 hoom

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Posted 28 September 2010 - 09:01 AM

...

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#17 mad

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Posted 28 September 2010 - 10:47 AM

pitch poling is the only reason for ac34 to use multihulls to maximize reality show people on the viewer list...........its all about tv revenue and potential death/injury that drives viewership.......

Whinge, fucking whinge

#18 Boybland

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Posted 30 September 2010 - 03:45 AM

The easiest way to stop pitchpoling is to have the big fat guy who paid for it all sitting in the stern.

#19 Stingray

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Posted 30 September 2010 - 04:00 AM


The only solutions to pitchpoling are light weight (so that the hulls are always popping up above or punching through the waves, smaller rig (so It can't force the cartwheel), or longer hull length to create the longitudinal buoyancy required to prevent the hulls from being pressed down into the water (like the current generation of maxi singlehanders, and most notably BP5.


Compared to USA17 AC72 is very narrow for its length making pitchpole less of a problem. Even greater difference when AC72 is compared to orma60s.

AC72 has a wing, therefore they can reverse the angle of attack above the hounds producing a significant bowup moment on demand, should they ever need it.
That would also reduce apparent windspeed by slowing the boat down further helping to avoid pitchpoling.

Light platform weight does not help to resist pitchpoling with a heavy rig in a chop.

There is no restriction on using T-foil rudders on heavy weather, is there ?
If not that would help too as long as those remain in the water instead of being lifted above water.

Care to expand on those, please?

How does narrow/long help avoid pitchpoling?

Has anyone actually taken advantage of reverse aoa to feather a wing? The BOR guy who answered when asked about it said that, while it was theoretically possible, they had not ever tried to go completely reverse on the tip to create that effect.






#20 cheshirecat

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Posted 30 September 2010 - 04:48 AM

How does narrow/long help avoid pitchpoling?

Because speed or lack of is the enemy. It's to do with the apparent moving aft loading up the leeward bow slowing it down, drag going up and cycle repeating.
Long narrow enables speed to be kept up so apparent keeps forward. Lack of weight aft helps as I found in the T cat when trying a 90kg FD crew out in a breeze actually caused the L bow to dig when rounding - or so I mentioned to him as he flew past still on the wire.

Compared to a dinghy it's quite hard gettting a Cat round a top mark and down fast - you can't do all the usual tricks to take the load and drag off the rudder/hull.
Also it's harder for the lead boat on stbd to defend against a port tack attack in a cat than mono racing, especially when nearing the top mark.

Maybe SimonN or someone could come in here and bring us uptodate as it was 96 when I was last active on the travelling circus

#21 Basiliscus

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Posted 30 September 2010 - 06:14 AM

...
AC72 has a wing, therefore they can reverse the angle of attack above the hounds producing a significant bowup moment on demand, should they ever need it.
That would also reduce apparent windspeed by slowing the boat down further helping to avoid pitchpoling...


Easier said than done! Twist control is comparatively slow compared to sheeting the whole wing, so sheeting ("traveler" in USA 17 parlance) would be the way you'd react to fast changes.

Twist changes the basic lift distribution. But the change in moment due to a change in wind speed or angle of attack is not affected by twist (the additional lift distribution). It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort. The hydrostatic analogy might be center of buoyancy and center of flotation. The total buoyancy acts through the center of buoyancy but any change acts at the center of flotation. So if you're using twist to lower the center of effort and balance the boat, beware! Because the gust is going to hammer you at the higher aerodynamic center.

The good news is changes due to sheeting also act at the aerodynamic center instead of the center of effort. So the reaction will probably be to sheet first, and adjust twist or camber second.

The other problem with depowering downwind is the rotation of the wing is limited by the shrouds. It is more effective to sheet in on the main element and let the flaps out to leeward until the trailing edge reaches the shroud than it is to blade the whole wing out with the flaps flat until it's against the shroud. But that's an unnatural act, and it depends on how quickly the flaps can be deflected from their normal position to dump lift. Dumping the flaps through a given angle while holding the main wing fixed is approximately 80% as effective as dumping the whole wing through the same angle with no change in camber. And the flaps can be dumped to leeward through a greater angle than the whole wing, thus ending up in the configuration with inverted camber mentioned above. So we may see the development of control systems that allow the flaps to be dumped rapidly, even if they have to be pumped back up more gradually afterward.

The wing is twice as high as the length of the boat. I think there will be danger of pitchpoling even with control of the wing above the hounds.

#22 Mal106

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Posted 30 September 2010 - 10:07 AM

You have to realize however that in a fast multi, there will be no problem with shrouds and the sail. The relative wind angle will almost never get beyond 40 degrees so there will always be room to wash out however much of the upper portion of the wing it takes to avoid a pitch pole or capsize. My guess is that even with human power there will be enough control of the wing that righting and pitchpole protection will be not a problem in the design winds. Negative AOA will never be needed as the righting moment of AC72 will be huge. I do wonder about control of the gennie, pictured all the way to the aft beam, and the staysl which is also pictured as huge. Both are pictured as greatly over trimmed.

Foils are not needed like on a small soft sail cat because the wing gives such good control over righting moment.

This, of course assumes that there is no crew error or equipment failure. The consequences of either of those will be considerably greater than with a lead hauler.

#23 Xlot

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Posted 30 September 2010 - 10:27 AM

It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort.


Erm ... you would really complete your daily good deed if you expanded on that. I understood the aerodynamic center was related to an airfoil's pitching moment, i.e. it's something that moves in the longitudinal plane. Whereas in terms of pitchpoling (and capsizing) the critical factor should be the location of the wing's center of effort in the vertical plane, no?

#24 Mal106

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Posted 30 September 2010 - 10:44 AM


It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort.


Erm ... you would really complete your daily good deed if you expanded on that. I understood the aerodynamic center was related to an airfoil's pitching moment, i.e. it's something that moves in the longitudinal plane. Whereas in terms of pitchpoling (and capsizing) the critical factor should be the location of the wing's center of effort in the vertical plane, no?

You are correct. As long as the gust is in the same direction as the prevailing wind, within reason the twist lowered center is the aerodynamic center. I say within reason because there is always the possibility of an area of the wing going from a stalled situation to providing lift. Highly unlikely but if for example the upper portion of the wing were stalled and a gust cleared that stall; righting forces could be quickly overcome and a capsize or pitchpole could easily be the result. Pitchpole can for all practical purposes be considered a capsize on the longitudinal axis.

I have taken a few rides around the mast on a trap myself but we shouldn't glean too much from a soft sail cat and apply it to a wing sail. Sheeting, downhaul and traveler on a soft sail cat as they apply to sail control pale in the light of what control is available on a well designed wing in speed, magnitude and righting moment.

#25 Mal106

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Posted 30 September 2010 - 11:24 AM

Just as an example of what can be done with a wing sail to avoid pitch pole. AC72 will be able to configure the sail by removing panels as needed to suit the race conditions. The very top of the sail has the most effect on righting moment to prevent capsize and keep a hull flying to reduce drag. The wing will always be used to maintain this balance at the point where a hull just flies. As the sail loads due to a wind increase, the very top will be washed out or twisted downwind to maintain the height of the hull above water. This takes place long before capsize or pitchpole is possible. If pitchpole or capsize were thought to be a threat, it would be a simple mod to include a spoiler, blow out panel or force the top of the wing to a controlled break and fold over. The wing can and will be canted into the wind to compensate for the heel angle caused by the flying hull such that lift is maximized by having the sail perpendicular to the wind. It might even be over canted to allow for some lift reducing wetted area and hydrodynamic drag. Boat balance and thus rudder drag can be controlled by leaning the mast fore and aft.

The wing on USA 17 was absolutely crude compared to what is possible. Look to the C class to see what current wing development is like but even the C is crude verses what is possible. The surface has just been scratched. Imagine a sharply curved wing where drag is minimized, forward lift is maximized, vertical lift is maximized all regardless of the wind. This could be done by changing camber, thickness, bend (think 90 degrees), chord, length; all on the fly. If you really go off the deep end you could go back to a mono hull by moving the rig for balance. If the wind were sufficient, all that would be in the water is one fin. The wing would lift the rest clear and control would be provided by changing the balance by moving either the sail or the fin fore and aft. I'm way off the deep end as this is obviously not today's reality.

#26 blunted

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Posted 30 September 2010 - 02:16 PM

Just as an example of what can be done with a wing sail to avoid pitch pole. AC72 will be able to configure the sail by removing panels as needed to suit the race conditions. The very top of the sail has the most effect on righting moment to prevent capsize and keep a hull flying to reduce drag. The wing will always be used to maintain this balance at the point where a hull just flies. As the sail loads due to a wind increase, the very top will be washed out or twisted downwind to maintain the height of the hull above water. This takes place long before capsize or pitchpole is possible. If pitchpole or capsize were thought to be a threat, it would be a simple mod to include a spoiler, blow out panel or force the top of the wing to a controlled break and fold over. The wing can and will be canted into the wind to compensate for the heel angle caused by the flying hull such that lift is maximized by having the sail perpendicular to the wind. It might even be over canted to allow for some lift reducing wetted area and hydrodynamic drag. Boat balance and thus rudder drag can be controlled by leaning the mast fore and aft.

The wing on USA 17 was absolutely crude compared to what is possible. Look to the C class to see what current wing development is like but even the C is crude verses what is possible. The surface has just been scratched. Imagine a sharply curved wing where drag is minimized, forward lift is maximized, vertical lift is maximized all regardless of the wind. This could be done by changing camber, thickness, bend (think 90 degrees), chord, length; all on the fly. If you really go off the deep end you could go back to a mono hull by moving the rig for balance. If the wind were sufficient, all that would be in the water is one fin. The wing would lift the rest clear and control would be provided by changing the balance by moving either the sail or the fin fore and aft. I'm way off the deep end as this is obviously not today's reality.


This all sounds fantastic until the gybing bit..... Let me assure you that a rig that is essentially twice the height of the length of the water line has substantial pitching leverage available to it. When you are sailing your angles downhill, yes, you can wash it out a bit, if not a lot with twist and de-cambering, but as you bear away for what ever reason, you still have this big powerful thing way overhead wanting to always go forward. even in barn door mode. On a bigger yacht, crew mass will be next to useless in trimming down the sterns. so you have a couple of choices, one, go through a gybe at warp speed to try and minimize appearant wind mid gybe, Two, over trim the thing completely and center it in the boat with the breeze blowing over it backwards, this can actually work, for a few seconds.

With any approach the scary part is when the wing "hooks up" or flow gets re-established. You usually try to do it concisouly and where you want it to happen. It's when it happens in an unanticipated manner that it casues problems, it's like hitting the turbo button, the boat takes off instantly, so you better hope you're pointed in the right direction and not entering the back face of a big wave. This is in fact one of the easiest heavy air mistakes to make with a wing. a new wing trimmer goes down hill in the big stuff, everything seems kind of calm, because they actually have it over trimmed and its stalled, then they ease in a puff because that's what people do and wham!, it hooks up, your thrust triples and the boat takes off, or wipes out.

With the inverting of the wing tip, yes, it can work, but if you are doing that downhill you are also slowing the boat down as the vectors are pretty much pointed aft at that point, at least the mast tip ones. This is a race and people tend to like to go faster not slower in a race, so it's a tricky balance. again, none of that will help when you have to do the inevitable gybe. That is where all the forces of nature conspire against your survival.

#27 pitchpoledave

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Posted 30 September 2010 - 03:21 PM

pitch poling is the only reason for ac34 to use multihulls to maximize reality show people on the viewer list...........its all about tv revenue and potential death/injury that drives viewership.......



HOGWASH

#28 pitchpoledave

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Posted 30 September 2010 - 03:30 PM


It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort.


Erm ... you would really complete your daily good deed if you expanded on that. I understood the aerodynamic center was related to an airfoil's pitching moment, i.e. it's something that moves in the longitudinal plane. Whereas in terms of pitchpoling (and capsizing) the critical factor should be the location of the wing's center of effort in the vertical plane, no?



I heard some comments about CAANAN that it could reverse camber the top of the wing? Is that what this is for? Can you do it fast enough at PP time or is it on all the time in windy conditions?

#29 blunted

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Posted 30 September 2010 - 03:40 PM



It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort.


Erm ... you would really complete your daily good deed if you expanded on that. I understood the aerodynamic center was related to an airfoil's pitching moment, i.e. it's something that moves in the longitudinal plane. Whereas in terms of pitchpoling (and capsizing) the critical factor should be the location of the wing's center of effort in the vertical plane, no?



I heard some comments about CAANAN that it could reverse camber the top of the wing? Is that what this is for? Can you do it fast enough at PP time or is it on all the time in windy conditions?


yes, no, no and finally, no.

MC

#30 Mal106

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Posted 30 September 2010 - 03:50 PM

I'm obviously not an expert on wings on sailboats but at least on a beach cat gybing is the simple one and I would imagine it the same with a wing sail. There is no sailing downhill. Remember that the boat is going 1.5 to maybe 3 times the wind speed. This means that there is never a relative wind from behind so there is never a forward force at the top of the wing due to wind behind it just due to the forward component of lift. This forward component is quite small because the boat is not dragging lead nor is it bang up against the displacement rule like the lead hauler would be pulling the wind astern. As the cat slows in a gybe this forward force becomes even less. Never from behind? well maybe if the start goes similar to a beach cat start where the boats are parked on the line. I doubt that will happen in a match race like it does in a fleet race.

The main factor that makes the PP happen in a small cat and maybe an AC cat is the boat being overpowered forward. The drag of the hull(s) being too high for the forward moment on the sails. This practically never happens on a beach cat when the boat is slow because the hulls don't develop the drag until at speed. The boat is nearly PP proof slow because hull inertia is minimal so the boat accelerates until hull drag becomes a problem. At speed you end up as far aft as you can get and the sterns lifting and the bows digging. Real nice videos of this with the Extreme 40's and Eighteen foot skiffs.

Having said all that I do wonder about quick maneuvers and the center of gravities being much MUCH higher than the lead haulers where it is well below the water line. A sharp turn into the wind in a very high performance lead hauler actually stands the boat up with the action of the CG below water where as the multi can capsize due to this same force. To correct overpowering force heeling a lead hauler using rudder only takes a turn into the wind. With a cat, it takes a turn downwind. I can't tell you how many mono sailors (including myself) when introduced to a cat capsize trying to save the boat by turning into the wind even when they know better. It's an uncontrollable reaction.

Quick story illustrating pitchpole and acceleration. I was goofing with a GPS on a Prindle 18; 2 up one on the wire (didn't need to be, just goofing around). The P-18 is a relatively low performance boat so downwind is sailed at about 90 deg of relative wind. We were hit with the first gust from a thunder storm. The boat accelerated smoothly from 8 kts or so to 18+ so fast that it actually forced the guy on the wire off the boat. Luckily he landed on the stern but was soon back forward as one hull buried itself and the boat decelerated. We didn't PP due to the extreme buoyancy of the P-18 hulls and the dumb luck of both of us being as aft as we could be. A lead hauler would have broached immediately or blown out the rig. The high performance boat protects the rig by accelerating rather than absorbing the force of a gust. I suspect the AC45 and 72 would behave like the Prindle only more so. I would predict those guys are going to have to hang on in gusty conditions at near design wind speed.

#31 catsailordude

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Posted 30 September 2010 - 04:13 PM

I'm no scientist, but a 130 foot mast/wing on a 72 x 46 foot platform seems like too much power. It's great that top panels can be removed for the conditions, but conditions usually change throughout the day. Also, if there is going to be tight racing in windy harbours, wouldn't it be better if the design sacrificed a small amount of power in favour of being able to do safer maneuvers in rough conditions. Why is flying a hull in 5 knots important? If the hull flying threshold was 8-10 knots, the boats could be pushed harder and maneuvered more agressively in 25 knots. I am afraid that this box rule will further the myth that high performance multis are not safe in heavy air, when if fact any boat optimized for 5 knots of wind (mono or multi) is not good in heavy air.

#32 Mal106

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Posted 30 September 2010 - 04:33 PM

I'm no scientist, but a 130 foot mast/wing on a 72 x 46 foot platform seems like too much power. It's great that top panels can be removed for the conditions, but conditions usually change throughout the day. Also, if there is going to be tight racing in windy harbours, wouldn't it be better if the design sacrificed a small amount of power in favour of being able to do safer maneuvers in rough conditions. Why is flying a hull in 5 knots important? If the hull flying threshold was 8-10 knots, the boats could be pushed harder and maneuvered more agressively in 25 knots. I am afraid that this box rule will further the myth that high performance multis are not safe in heavy air, when if fact any boat optimized for 5 knots of wind (mono or multi) is not good in heavy air.

That's where you need to start altering your thinking from sailboat to airplane. You change the shape of the wing to suit conditions just like an airplane. With the same length wing an airplane can fly at speeds of 120 to almost 600 kts. The wing sail can easily do 5 to 30 boat speed and wind speed by changing the sail's shape and much more is possible.

Flying a hull is critical because the drag of a the boat is nearly cut in half with one up. It is also the perfect way to judge how much the wing is powered up. A boat needs to be optimized for the race conditions. We don't want to see the wimpy no starts we did in 33. Having said that there is a certain safety in a high performance boat that is not present with a displacement hull. As I said earlier the rig is protected by the boat's light weight. Additionally the structure is protected by there being no huge forces involved in varying wind speeds as long as the boat is in control. If not in control; failures won't just be blown spins and broken spars but total mess.... It's going to be quite interesting and I suspect some teams will run back to the monos after early sails on AC45.

#33 mili

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Posted 30 September 2010 - 04:34 PM

I'm no scientist, but a 130 foot mast/wing on a 72 x 46 foot platform seems like too much power. It's great that top panels can be removed for the conditions, but conditions usually change throughout the day. Also, if there is going to be tight racing in windy harbours, wouldn't it be better if the design sacrificed a small amount of power in favour of being able to do safer maneuvers in rough conditions. Why is flying a hull in 5 knots important? If the hull flying threshold was 8-10 knots, the boats could be pushed harder and maneuvered more agressively in 25 knots. I am afraid that this box rule will further the myth that high performance multis are not safe in heavy air, when if fact any boat optimized for 5 knots of wind (mono or multi) is not good in heavy air.


+1 Me too, I'm no scientist , sounds logic.

#34 blunted

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Posted 30 September 2010 - 04:34 PM



The main factor that makes the PP happen in a small cat and maybe an AC cat is the boat being overpowered forward. The drag of the hull(s) being too high for the forward moment on the sails. This practically never happens on a beach cat when the boat is slow because the hulls don't develop the drag until at speed. The boat is nearly PP proof slow because hull inertia is minimal so the boat accelerates until hull drag becomes a problem. At speed you end up as far aft as you can get and the sterns lifting and the bows digging. Real nice videos of this with the Extreme 40's and Eighteen foot skiffs.


So I'll ask, how high is the mast on said yacht, relative to it's LWL? the taller the rig, the more pitching moment available. On a C-cat it's about 1.85:1. I know we have higher skinnier rigs then most other boats. On an AC72, it's even higher I think, perhaps in the order of 1.95:1 which is a tall rig.

Keep in mind how high/heavy your crew mass is relative to the yachts overall mass and available sail area. The bigger the boat, the less the crew can do to save it, they become totally ineffectual. On a C-cat, crew mass is perhaps 55% of total displacement. a quick reading of the AC 72 rule says crew mass only accounts for 15% of all up displacement. On you prindle, perhaps crew mass is similar to the C-cat because its a small heavy boat with two moderate size guys on it. But on the Prindle, your sail area is also, well, very small, so it's easy to man handle the boat around the course.

So on an AC72, you have 3.8 KG of crew per sq meter of wing.

On a C-cat you have 6.1 KG of crew per sq meter of wing

On a Hobie 18, sailing with the same crew as the C-cat you have 7.8 KG of crew per sq meter of sail area. Not to mention a way heavier platform which also wants to stay on the water and a shorter rig, 30% shorter rig.

So sure, you can keep a "beach cat" from pitchpoling. because you can grunt it through a maneuver. Sailing a wing boat is a very different proposition, way lighter platform, gets to hull speed in 14 knots of TWS with no problem, much higher rig, higher CG, lower mass of crew per sq meter of SA. When you stall the wing it instantly stops pushing you efficiently through the water (Higher AWS through the maneuver), then there is the risk of it "hooking up" on the far side of the gybe.

#35 mili

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Posted 30 September 2010 - 04:37 PM


I'm no scientist, but a 130 foot mast/wing on a 72 x 46 foot platform seems like too much power. It's great that top panels can be removed for the conditions, but conditions usually change throughout the day. Also, if there is going to be tight racing in windy harbours, wouldn't it be better if the design sacrificed a small amount of power in favour of being able to do safer maneuvers in rough conditions. Why is flying a hull in 5 knots important? If the hull flying threshold was 8-10 knots, the boats could be pushed harder and maneuvered more agressively in 25 knots. I am afraid that this box rule will further the myth that high performance multis are not safe in heavy air, when if fact any boat optimized for 5 knots of wind (mono or multi) is not good in heavy air.

That's where you need to start altering your thinking from sailboat to airplane. You change the shape of the wing to suit conditions just like an airplane. With the same length wing an airplane can fly at speeds of 120 to almost 600 kts. The wing sail can easily do 5 to 30 boat speed and wind speed by changing the sail's shape and much more is possible.

Flying a hull is critical because the drag of a the boat is nearly cut in half with one up. It is also the perfect way to judge how much the wing is powered up. A boat needs to be optimized for the race conditions. We don't want to see the wimpy no starts we did in 33. Having said that there is a certain safety in a high performance boat that is not present with a displacement hull. As I said earlier the rig is protected by the boat's light weight. Additionally the structure is protected by there being no huge forces involved in varying wind speeds as long as the boat is in control. If not in control; failures won't just be blown spins and broken spars but total mess.... It's going to be quite interesting and I suspect some teams will run back to the monos after early sails on AC45.


Sounds logic too, where's the truth?

#36 the loose cannon

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Posted 30 September 2010 - 04:58 PM

Sounds logical too, where's the truth?

The truth is that the picture of the planform for the AC72 is for a light air configuration. If you are going to race these boats in SF with an average wind speed at or above 15kts (help me here - 18 average in the places they will race? It's been a while since I raced there.) the rig will be unarig wing upwind and it will not be full planform. Either a wing that can shed sections (can't imagine the engineering nightmares there) or multiple wings to address wind ranges.

Drag wise you will want to be unarig upwind in any breeze that you can fly the hull consistently, and you may be leaving the screecher/blade furled above a certain wind speed on the downwind leg as well....

#37 Mal106

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Posted 30 September 2010 - 05:07 PM




The main factor that makes the PP happen in a small cat and maybe an AC cat is the boat being overpowered forward. The drag of the hull(s) being too high for the forward moment on the sails. This practically never happens on a beach cat when the boat is slow because the hulls don't develop the drag until at speed. The boat is nearly PP proof slow because hull inertia is minimal so the boat accelerates until hull drag becomes a problem. At speed you end up as far aft as you can get and the sterns lifting and the bows digging. Real nice videos of this with the Extreme 40's and Eighteen foot skiffs.


So I'll ask, how high is the mast on said yacht, relative to it's LWL? the taller the rig, the more pitching moment available. On a C-cat it's about 1.85:1. I know we have higher skinnier rigs then most other boats. On an AC72, it's even higher I think, perhaps in the order of 1.95:1 which is a tall rig.

Keep in mind how high/heavy your crew mass is relative to the yachts overall mass and available sail area. The bigger the boat, the less the crew can do to save it, they become totally ineffectual. On a C-cat, crew mass is perhaps 55% of total displacement. a quick reading of the AC 72 rule says crew mass only accounts for 15% of all up displacement. On you prindle, perhaps crew mass is similar to the C-cat because its a small heavy boat with two moderate size guys on it. But on the Prindle, your sail area is also, well, very small, so it's easy to man handle the boat around the course.

So on an AC72, you have 3.8 KG of crew per sq meter of wing.

On a C-cat you have 6.1 KG of crew per sq meter of wing

On a Hobie 18, sailing with the same crew as the C-cat you have 7.8 KG of crew per sq meter of sail area. Not to mention a way heavier platform which also wants to stay on the water and a shorter rig, 30% shorter rig.

So sure, you can keep a "beach cat" from pitchpoling. because you can grunt it through a maneuver. Sailing a wing boat is a very different proposition, way lighter platform, gets to hull speed in 14 knots of TWS with no problem, much higher rig, higher CG, lower mass of crew per sq meter of SA. When you stall the wing it instantly stops pushing you efficiently through the water (Higher AWS through the maneuver), then there is the risk of it "hooking up" on the far side of the gybe.

First you are absolutely correct in that crew weight is likely negligible on AC72 and nearly so on the 45. I doubt either will use trapezes. In our discussion I think we can ignore crew weight on the big boat.

Second as to pitch poling a beach cat. My point is not that you can move crew weight to prevent it nor maneuver your way out. It is going to happen; there is nothing you can do about it short of going home. A heavy sailor on a H-14 is a perfect example. There is a wind where the boat cannot be sailed, where you just have to let the sail twist off and carefully luff along. As soon as the boat is powered up the sail overpowers the hull and even with the crew at the aft corner the boat pitchpoles. The problem is hull drag and the maneuver is a capsize in the forward direction.

The ratio of sail area to boat weight is important but in a boat that either cheats the displacement rule due to an extremely narrow hull (cat) or a hull that planes (18 ft skiff) or both (AC72?) the tendency to pitchpole is not a problem as the additional force even with a long moment simply goes into accelerating the boat not turning it over on the forward axis.

When you say a boat gets to hull speed in 14kts true you are talking about a different boat than any high performance cat or planing hull or both. For those boats there is no such limit, just a slight drag rise at 1.34X^1/2 the LWL in the cat and a big hump easily overcome on the planing hull. Even the lowly Prindle I mentioned earlier sails around at 2 to 3 times hull speed.

Imagine an ice boat. Nearly nil friction so no chance of a PP. Now a beach cat; just a matter of what wind speed will do it as the drag goes up. The AC72; likely both boats are somewhere in between. Now remember the controllable nature of the wing on top of that. The ability to almost instantly remove lift from the critical area up high; and the boat becomes nearly PP proof as long as it is in control. Add to that the fact that the wind will never be from behind and a PP becomes only a remote possibility in design wind speeds.

#38 Mal106

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Posted 30 September 2010 - 05:19 PM


Sounds logical too, where's the truth?

The truth is that the picture of the planform for the AC72 is for a light air configuration. If you are going to race these boats in SF with an average wind speed at or above 15kts (help me here - 18 average in the places they will race? It's been a while since I raced there.) the rig will be unarig wing upwind and it will not be full planform. Either a wing that can shed sections (can't imagine the engineering nightmares there) or multiple wings to address wind ranges.

Drag wise you will want to be unarig upwind in any breeze that you can fly the hull consistently, and you may be leaving the screecher/blade furled above a certain wind speed on the downwind leg as well....

Exactly, and well said.

The problem upwind in a breeze will be wind drag. The wing will need to be thin with very little camber similar to flattening a soft sail when overpowered but more so. Down wind the boats are so efficient that the problem will be the same but less so. Camber will increase slightly to deal with a relative wind of 40 deg rather than the upwind 20 or 30. As the wind drops the pictured fore sail will be added. Either it or the staysl may well be used upwind in a falling breeze as well if needed to keep a hull flying. I suspect like USA17 fore sails will be furled and lowered if not in use. A furled fore sail is simply too much drag....

#39 s2 alter ego

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Posted 30 September 2010 - 05:29 PM

It seems the number of quotes are limited nowadays for some reason. Threfore I'm numbering the parts of text I'm responsing to.


...
AC72 has a wing, therefore they can reverse the angle of attack above the hounds producing a significant bowup moment on demand, should they ever need it.
That would also reduce apparent windspeed by slowing the boat down further helping to avoid pitchpoling...

1) Easier said than done!
Twist control is comparatively slow compared to sheeting the whole wing, so sheeting ("traveler" in USA 17 parlance) would be the way you'd react to fast changes.

2) Twist changes the basic lift distribution. But the change in moment due to a change in wind speed or angle of attack is not affected by twist (the additional lift distribution).

3) It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort. The hydrostatic analogy might be center of buoyancy and center of flotation. The total buoyancy acts through the center of buoyancy but any change acts at the center of flotation. So if you're using twist to lower the center of effort and balance the boat, beware!

1) For boats existing at this time I agree it's easier said than done, but I see no reason why that would have to apply any future boats wing wings as well, especially since the number of crew and dimensions of the wing allow one wing trimmer being positioned inside the wing, sitting on the boom box would make a perfect place for a rapid adjustment of camber. There isn't necessarily any airbourne center"hull" for wing trimmers anyway in AC72 cats.

2) For changes in agle of attack I agree 100%, and as long as change in true windspeed cause significan't changes in aw_angle as well as aw_speed, then I agree on that case too.
I also think we agree that sailing downwind in heavier air is exactly the kind of conditions when any change in tws results the most change in apparentwindangle.

However I didn't suggest sailing continuously with reversed aoa at the top, just using that as a response for gusts as a last line of defence, which avoids the problem as it means the wing wasn't having too much twist before the gust, thus giving room for a lot of more twist as a gust response.

3) That is exactly what I did NOT suggest. Therefore no problem here.

Because the gust is going to hammer you at the higher aerodynamic center.

The good news is changes due to sheeting also act at the aerodynamic center instead of the center of effort. So the reaction will probably be to sheet first, and adjust twist or camber second.

The other problem with depowering downwind is the rotation of the wing is limited by the shrouds. It is more effective to sheet in on the main element and let the flaps out to leeward until the trailing edge reaches the shroud than it is to blade the whole wing out with the flaps flat until it's against the shroud. But that's an unnatural act, and it depends on how quickly the flaps can be deflected from their normal position to dump lift. Dumping the flaps through a given angle while holding the main wing fixed is approximately 80% as effective as dumping the whole wing through the same angle with no change in camber. And the flaps can be dumped to leeward through a greater angle than the whole wing, thus ending up in the configuration with inverted camber mentioned above. So we may see the development of control systems that allow the flaps to be dumped rapidly, even if they have to be pumped back up more gradually afterward.

Now you are making my point more clear than I did. thanks for that. :)

The wing is twice as high as the length of the boat. I think there will be danger of pitchpoling even with control of the wing above the hounds.

I don't think they should use that high wing in the heavy air days. The rule allows reducing the number of elements from the top, bringing down the wing height for those conditions.
Also I haven't seen any rule preventing to lower hounds as well for those conditions, therefore still allowing significant amount of wingarea above the hounds in heavy air as well.

Of course that assumes the truewind doesn't change from 5 knots to 30 knots during the same day ...

#40 Mal106

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Posted 30 September 2010 - 05:36 PM


pitch poling is the only reason for ac34 to use multihulls to maximize reality show people on the viewer list...........its all about tv revenue and potential death/injury that drives viewership.......



HOGWASH

Amen, Total hogwash!

#41 pitchpoledave

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Posted 30 September 2010 - 05:46 PM





The main factor that makes the PP happen in a small cat and maybe an AC cat is the boat being overpowered forward. The drag of the hull(s) being too high for the forward moment on the sails. This practically never happens on a beach cat when the boat is slow because the hulls don't develop the drag until at speed. The boat is nearly PP proof slow because hull inertia is minimal so the boat accelerates until hull drag becomes a problem. At speed you end up as far aft as you can get and the sterns lifting and the bows digging. Real nice videos of this with the Extreme 40's and Eighteen foot skiffs.


So I'll ask, how high is the mast on said yacht, relative to it's LWL? the taller the rig, the more pitching moment available. On a C-cat it's about 1.85:1. I know we have higher skinnier rigs then most other boats. On an AC72, it's even higher I think, perhaps in the order of 1.95:1 which is a tall rig.

Keep in mind how high/heavy your crew mass is relative to the yachts overall mass and available sail area. The bigger the boat, the less the crew can do to save it, they become totally ineffectual. On a C-cat, crew mass is perhaps 55% of total displacement. a quick reading of the AC 72 rule says crew mass only accounts for 15% of all up displacement. On you prindle, perhaps crew mass is similar to the C-cat because its a small heavy boat with two moderate size guys on it. But on the Prindle, your sail area is also, well, very small, so it's easy to man handle the boat around the course.

So on an AC72, you have 3.8 KG of crew per sq meter of wing.

On a C-cat you have 6.1 KG of crew per sq meter of wing

On a Hobie 18, sailing with the same crew as the C-cat you have 7.8 KG of crew per sq meter of sail area. Not to mention a way heavier platform which also wants to stay on the water and a shorter rig, 30% shorter rig.

So sure, you can keep a "beach cat" from pitchpoling. because you can grunt it through a maneuver. Sailing a wing boat is a very different proposition, way lighter platform, gets to hull speed in 14 knots of TWS with no problem, much higher rig, higher CG, lower mass of crew per sq meter of SA. When you stall the wing it instantly stops pushing you efficiently through the water (Higher AWS through the maneuver), then there is the risk of it "hooking up" on the far side of the gybe.

First you are absolutely correct in that crew weight is likely negligible on AC72 and nearly so on the 45. I doubt either will use trapezes. In our discussion I think we can ignore crew weight on the big boat.

Second as to pitch poling a beach cat. My point is not that you can move crew weight to prevent it nor maneuver your way out. It is going to happen; there is nothing you can do about it short of going home. A heavy sailor on a H-14 is a perfect example. There is a wind where the boat cannot be sailed, where you just have to let the sail twist off and carefully luff along. As soon as the boat is powered up the sail overpowers the hull and even with the crew at the aft corner the boat pitchpoles. The problem is hull drag and the maneuver is a capsize in the forward direction.

The ratio of sail area to boat weight is important but in a boat that either cheats the displacement rule due to an extremely narrow hull (cat) or a hull that planes (18 ft skiff) or both (AC72?) the tendency to pitchpole is not a problem as the additional force even with a long moment simply goes into accelerating the boat not turning it over on the forward axis.

When you say a boat gets to hull speed in 14kts true you are talking about a different boat than any high performance cat or planing hull or both. For those boats there is no such limit, just a slight drag rise at 1.34X^1/2 the LWL in the cat and a big hump easily overcome on the planing hull. Even the lowly Prindle I mentioned earlier sails around at 2 to 3 times hull speed.

Imagine an ice boat. Nearly nil friction so no chance of a PP. Now a beach cat; just a matter of what wind speed will do it as the drag goes up. The AC72; likely both boats are somewhere in between. Now remember the controllable nature of the wing on top of that. The ability to almost instantly remove lift from the critical area up high; and the boat becomes nearly PP proof as long as it is in control. Add to that the fact that the wind will never be from behind and a PP becomes only a remote possibility in design wind speeds.


One thing that I noticed the other day while doing some extreme reaching in a Nacra Infusion is that the the faster the boat went the higher the bows were and I think it was due to water pressure. It really surprised me and I was waiting for the PP but it didn't happen. So I think that the same effect can happen downwind in the 45/72 if there is enough boat speed. The killer will be punching into a wave and decelerating.

#42 Mal106

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Posted 30 September 2010 - 05:48 PM

Alterego and Basicillicus. You are still thinking monomoran and soft sails. There will never be a problem with the shrouds as the apparant wind will never be that far aft. Additionally due to internal shape and structuree much more of the wing can be cantilevered which puts the shrouds lower. Think a really big mast. Hell the shrouds could be eliminated totally and the wing cantilevered form the deck up. I suspect the weight penalty would be too stiff but it's possible.

There will practically never be a need for reverse camber. With the wind always ahead a flat wing (0 camber) will always be sufficient to bring the forward component of that section of the wing to less than 0....

#43 F18 VB

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Posted 30 September 2010 - 05:51 PM

I'm no scientist, but a 130 foot mast/wing on a 72 x 46 foot platform seems like too much power.

It's less powered up than a Formula 18 sailing under main alone.

A formula 18 is 18' long, 8.5' wide, and displaces about 750 lbs with crew. It has a 30' mast with 17 m^2 main. (F18 also has a jib and spinnaker)
AC72 is 72' long, 45' wide, and displaces 15,500 lbs without crew. It has a 130' wing with 260 m^2.


For pitchpoling I suggest healing moment over righting moment:
A * H / (L * D)
For an F18 it is .038
For an AC 72 it is .030

For normal capsizes:
A * H / (W * D)
For an F18 it is .080
For an AC72 it is .047


Big sailboats are generally more stable because the righting moment scales with the forth power while healing moment scales with the third power.

#44 Mal106

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Posted 30 September 2010 - 05:57 PM






The main factor that makes the PP happen in a small cat and maybe an AC cat is the boat being overpowered forward. The drag of the hull(s) being too high for the forward moment on the sails. This practically never happens on a beach cat when the boat is slow because the hulls don't develop the drag until at speed. The boat is nearly PP proof slow because hull inertia is minimal so the boat accelerates until hull drag becomes a problem. At speed you end up as far aft as you can get and the sterns lifting and the bows digging. Real nice videos of this with the Extreme 40's and Eighteen foot skiffs.


So I'll ask, how high is the mast on said yacht, relative to it's LWL? the taller the rig, the more pitching moment available. On a C-cat it's about 1.85:1. I know we have higher skinnier rigs then most other boats. On an AC72, it's even higher I think, perhaps in the order of 1.95:1 which is a tall rig.

Keep in mind how high/heavy your crew mass is relative to the yachts overall mass and available sail area. The bigger the boat, the less the crew can do to save it, they become totally ineffectual. On a C-cat, crew mass is perhaps 55% of total displacement. a quick reading of the AC 72 rule says crew mass only accounts for 15% of all up displacement. On you prindle, perhaps crew mass is similar to the C-cat because its a small heavy boat with two moderate size guys on it. But on the Prindle, your sail area is also, well, very small, so it's easy to man handle the boat around the course.

So on an AC72, you have 3.8 KG of crew per sq meter of wing.

On a C-cat you have 6.1 KG of crew per sq meter of wing

On a Hobie 18, sailing with the same crew as the C-cat you have 7.8 KG of crew per sq meter of sail area. Not to mention a way heavier platform which also wants to stay on the water and a shorter rig, 30% shorter rig.

So sure, you can keep a "beach cat" from pitchpoling. because you can grunt it through a maneuver. Sailing a wing boat is a very different proposition, way lighter platform, gets to hull speed in 14 knots of TWS with no problem, much higher rig, higher CG, lower mass of crew per sq meter of SA. When you stall the wing it instantly stops pushing you efficiently through the water (Higher AWS through the maneuver), then there is the risk of it "hooking up" on the far side of the gybe.

First you are absolutely correct in that crew weight is likely negligible on AC72 and nearly so on the 45. I doubt either will use trapezes. In our discussion I think we can ignore crew weight on the big boat.

Second as to pitch poling a beach cat. My point is not that you can move crew weight to prevent it nor maneuver your way out. It is going to happen; there is nothing you can do about it short of going home. A heavy sailor on a H-14 is a perfect example. There is a wind where the boat cannot be sailed, where you just have to let the sail twist off and carefully luff along. As soon as the boat is powered up the sail overpowers the hull and even with the crew at the aft corner the boat pitchpoles. The problem is hull drag and the maneuver is a capsize in the forward direction.

The ratio of sail area to boat weight is important but in a boat that either cheats the displacement rule due to an extremely narrow hull (cat) or a hull that planes (18 ft skiff) or both (AC72?) the tendency to pitchpole is not a problem as the additional force even with a long moment simply goes into accelerating the boat not turning it over on the forward axis.

When you say a boat gets to hull speed in 14kts true you are talking about a different boat than any high performance cat or planing hull or both. For those boats there is no such limit, just a slight drag rise at 1.34X^1/2 the LWL in the cat and a big hump easily overcome on the planing hull. Even the lowly Prindle I mentioned earlier sails around at 2 to 3 times hull speed.

Imagine an ice boat. Nearly nil friction so no chance of a PP. Now a beach cat; just a matter of what wind speed will do it as the drag goes up. The AC72; likely both boats are somewhere in between. Now remember the controllable nature of the wing on top of that. The ability to almost instantly remove lift from the critical area up high; and the boat becomes nearly PP proof as long as it is in control. Add to that the fact that the wind will never be from behind and a PP becomes only a remote possibility in design wind speeds.


One thing that I noticed the other day while doing some extreme reaching in a Nacra Infusion is that the the faster the boat went the higher the bows were and I think it was due to water pressure. It really surprised me and I was waiting for the PP but it didn't happen. So I think that the same effect can happen downwind in the 45/72 if there is enough boat speed. The killer will be punching into a wave and decelerating.

Exactly. That was the boat climbing over its bow wave on its way to a plane or in the NCRA's case a partial plane. The waves will be no problem because 1 the bay is quite sheltered so there won't be enough fetch to get big waves and 2 the boat will have wave piercing bows like almost all modern high performance multis including A5 and USA17 from AC 33 and your Infusion. Those bows minimize deceleration in two ways: by limiting the direct force on the boat thru a sharp entry and by limiting the wasted energy expended in pitching the boat by floating the bows upward thru the use of minimal buoyancy and an inverted entry forward.

Sailing your infusion will really give you a feel for what the big boats will be like. Imagine that with ten times the power and effeciency.

#45 s2 alter ego

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Posted 30 September 2010 - 06:07 PM

Alterego and Basicillicus. You are still thinking monomoran and soft sails.

Wrong, we both sail multis on the water, and in addition as far as I know, landyachts/dirtboats for Basiliscus, and iceyachts for me occassionally.
On ice or land, there is no practical limit on speed in most conditions, on the water there is in heavy air, and for AC72, it's more likely significantly less than 50kts rather than more.

There will never be a problem with the shrouds as the apparant wind will never be that far aft. Additionally due to internal shape and structuree much more of the wing can be cantilevered which puts the shrouds lower. Think a really big mast. Hell the shrouds could be eliminated totally and the wing cantilevered form the deck up. I suspect the weight penalty would be too stiff but it's possible.

There will practically never be a need for reverse camber. With the wind always ahead a flat wing (0 camber) will always be sufficient to bring the forward component of that section of the wing to less than 0....

How far aft do you think shrouds are located from mast step ?
What angle from the centerline would that be from mast step ?

What downwind vmg are you thinking AC72 will achieve in 30 knots true ?
At what boatspeed will that happen in at steady state ?
At what twa ?
And how much will the boat slow down during a gybe at most ?
What's the awa at that point ?

Do the math and then come back, I never suggested any reversed aoa at wing top in light winds, when v_boat is something like 3 X tws !
But I would definately expect downwind vmg dropping below 30 kts during a gybe in 30 kts true even in flat water and most certainly so in chop !

#46 s2 alter ego

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Posted 30 September 2010 - 06:30 PM

It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort.

As long as the gust is in the same direction as the prevailing wind, within reason the twist lowered center is the aerodynamic center.

Only if by prevailing wind you mean apparent wind, in in that case that's misleading.
The gust changes truewind first , and boatspeed later if at all, depending how fast the boat was going to begin with, among other things.
As a result the apparent wind changes direction, the more the closer the downwind vmg is to the truewindspeed.
At 30kts true, the change in aoa for a given wing trim and course sailed is most certainly significant in magnitude and requires some quick and correct reaction by the crew.

The increase/decrease in aws on the otherhand does increase/decrease all aero forces equally at all heights, and would act at center of effort if there were no change in aoa due to change of awa.

#47 Mal106

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Posted 30 September 2010 - 06:31 PM


Alterego and Basicillicus. You are still thinking monomoran and soft sails.

Wrong, we both sail multis on the water, and in addition as far as I know, landyachts/dirtboats for Basiliscus, and iceyachts for me occassionally.
On ice or land, there is no practical limit on speed in most conditions, on the water there is in heavy air, and for AC72, it's more likely significantly less than 50kts rather than more.

There will never be a problem with the shrouds as the apparant wind will never be that far aft. Additionally due to internal shape and structuree much more of the wing can be cantilevered which puts the shrouds lower. Think a really big mast. Hell the shrouds could be eliminated totally and the wing cantilevered form the deck up. I suspect the weight penalty would be too stiff but it's possible.

There will practically never be a need for reverse camber. With the wind always ahead a flat wing (0 camber) will always be sufficient to bring the forward component of that section of the wing to less than 0....

How far aft do you think shrouds are located from mast step ?
What angle from the centerline would that be from mast step ?

What downwind vmg are you thinking AC72 will achieve in 30 knots true ?
At what boatspeed will that happen in at steady state ?
At what twa ?
And how much will the boat slow down during a gybe at most ?
What's the awa at that point ?

Do the math and then come back, I never suggested any reversed aoa at wing top in light winds, when v_boat is something like 3 X tws !
But I would definately expect downwind vmg dropping below 30 kts during a gybe in 30 kts true even in flat water and most certainly so in chop !

Sorry I must have plucked a bad string. Didn't say you didn't sail them just that you weren't thinking them.

The only math I'll do is your 30kt downwind example. Say the boat is all the way down to 1.5 wind speed and it looses 1/2 it's speed in the gybe, IMHO a gross overstatement. That results in a whopping 8kts from astern. With the reduced drag due to reduced speed that is negligible. As to the shroud angles, all boats are designed such that that is not a problem as long as the boat is sailed efficiently. I have no reason to think AC cats will be any different. In fact the downwind shroud could be loosened or removed. Neither would be needed because the amount of flattening needed to unload the top of the sail would be no problem. Shroud interference is simply not a factor.

#48 s2 alter ego

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Posted 30 September 2010 - 06:42 PM

The only math I'll do is your 30kt downwind example. Say the boat is all the way down to 1.5 wind speed and it looses 1/2 it's speed in the gybe, IMHO a gross overstatement. That results in a whopping 8kts from astern. With the reduced drag due to reduced speed that is negligible. As to the shroud angles, all boats are designed such that that is not a problem as long as the boat is sailed efficiently. I have no reason to think AC cats will be any different. In fact the downwind shroud could be loosened or removed. Neither would be needed because the amount of flattening needed to unload the top of the sail would be no problem. Shroud interference is simply not a factor.

The situation isn't worst at the moment the cat is going ddw during a gybe, but just at the time it begins to accelerate again, and that's at least 20 degrees off that point of sail.
How about you calculate the twa=155degs as well as twa=150 degs cases just after the gybe is complete.
What's the awa & aws for the tws=30kts case ?
Do you really still think the complete wing can be feathered inside the shrouds at all heights at those points in question even with zero camber at all heights ? ! ?

#49 s2 alter ego

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Posted 30 September 2010 - 07:16 PM



The only solutions to pitchpoling are light weight (so that the hulls are always popping up above or punching through the waves, smaller rig (so It can't force the cartwheel), or longer hull length to create the longitudinal buoyancy required to prevent the hulls from being pressed down into the water (like the current generation of maxi singlehanders, and most notably BP5.


Compared to USA17 AC72 is very narrow for its length making pitchpole less of a problem. Even greater difference when AC72 is compared to orma60s.

AC72 has a wing, therefore they can reverse the angle of attack above the hounds producing a significant bowup moment on demand, should they ever need it.
That would also reduce apparent windspeed by slowing the boat down further helping to avoid pitchpoling.

Care to expand on those, please?

How does narrow/long help avoid pitchpoling?

You trim the "sailplan" for heelingmoment to fly the hull. That means heelingmoment sideways will always match rightingmoment sideways.
When a boat has higher longitudinal stability / sideways stability compared to another boat (=orma60) , it also has more longitudinal stability in reserve for a given direction of aerodynamic force in the same point of sail than the other boat (think orma60)

So it can have aeroforce pointing more forward than an orma60 can without pitchpoling. As long as awa is well forward it means only waveaction can cause a pitchpole, not a gust alone, since aeroforce is then never far enough forward, but always has a sideways component as a limitingfactor.
That doesn't apply in high winds or during gybes, when awa is not as far forward all the time, but higher length/beam is still a benefit reducing the risk.

Has anyone actually taken advantage of reverse aoa to feather a wing? The BOR guy who answered when asked about it said that, while it was theoretically possible, they had not ever tried to go completely reverse on the tip to create that effect.

As far I know, no ,

And I would not expect any reversing untill a rigid wing high performance multi is sailed towards the limits in higher winds.
As far as I know, USA17 haven't done that. It was sailed hard only in conditions allowing vmg downwind exceeding truewind, and not in 30kts true as AC72 is required to do by the rule.

#50 blunted

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Posted 30 September 2010 - 07:17 PM







So I'll ask,



When you say a boat gets to hull speed in 14kts true you are talking about a different boat than any high performance cat or planing hull or both. For those boats there is no such limit, just a slight drag rise at 1.34X^1/2 the LWL in the cat and a big hump easily overcome on the planing hull. Even the lowly Prindle I mentioned earlier sails around at 2 to 3 times hull speed.



My reference to hull speed was on the C-cat, 22.5 knots or 4.5 * the square root of LWL, is a decent estimate for "hull speed" in a long slender, displacement mode boat, like a C-cat. Which is not unlike the hulls of say, BOR 90. So when I say we go hull speed in 14 knots TWS, I mean a C-cat will do 20 knots downhill in 14 knots TWS. So no, I am not talking about a high performance cat that you are speaking of.

If I follow your suggestion you are talking about psudo-planing style boats, if not full planing of course in speaking about skiffs, never dropping speed that much etc etc etc, also having lifting bows etc etc.

#51 Mal106

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Posted 30 September 2010 - 07:33 PM


It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort.

As long as the gust is in the same direction as the prevailing wind, within reason the twist lowered center is the aerodynamic center.

Only if by prevailing wind you mean apparent wind, in in that case that's misleading.
The gust changes truewind first , and boatspeed later if at all, depending how fast the boat was going to begin with, among other things.
As a result the apparent wind changes direction, the more the closer the downwind vmg is to the truewindspeed.
At 30kts true, the change in aoa for a given wing trim and course sailed is most certainly significant in magnitude and requires some quick and correct reaction by the crew.

The increase/decrease in aws on the otherhand does increase/decrease all aero forces equally at all heights, and would act at center of effort if there were no change in aoa due to change of awa.

You are obviously correct. Thanks for keeping me straight.

When you do a vector analysis of a gust as a fraction apparent of wind speed, however, the change in AOA is minimal but as you pointed out it is there and must be corrected for. Corrected for for efficiency but not likely for PP avoidance. If the gust continues speed increases and the apparent wind shifts forward again. That's why I used the qualifier, "within reason".

#52 s2 alter ego

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Posted 30 September 2010 - 07:42 PM

My reference to hull speed was on the C-cat, 22.5 knots or 4.5 * the square root of LWL, is a decent estimate for "hull speed" in a long slender, displacement mode boat, like a C-cat. Which is not unlike the hulls of say, BOR 90.

Just one more example why I avoid using word hullspeed.
Some, like you it seems, use it as a practical top speed of the boat, while others use it only to describe the situation when waves made by the hull have same length as the boat, like in all litterature of naval architech...

So when I say we go hull speed in 14 knots TWS, I mean a C-cat will do 20 knots downhill in 14 knots TWS.

If there would be c-class race in Freemantle or SanFrancisco, and if the rules would allow sailing there in 30 kts true, and if you had a shorter wing than in alpha optimised for those conditions, do you think your top speed would increase by how much ?

Have you done any comparisong with canaan wing and alpha wing on the same platform regarding top speed, and if so, how much difference was there ?
What is the difference in height in those 2 wings again ?

#53 Mal106

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Posted 30 September 2010 - 07:52 PM

Incidentally here is an almost example of the bent wing mono with displaced rig providing lift I was fantasizing earlier...

A little too much lift in this case.

#54 rule69

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Posted 30 September 2010 - 08:02 PM

My reference to hull speed was on the C-cat, 22.5 knots or 4.5 * the square root of LWL, is a decent estimate for "hull speed" in a long slender, displacement mode boat, like a C-cat. Which is not unlike the hulls of say, BOR 90. So when I say we go hull speed in 14 knots TWS, I mean a C-cat will do 20 knots downhill in 14 knots TWS. So no, I am not talking about a high performance cat that you are speaking of.


Maybe better to use a term like "top speed", "best sustainable speed", V max or something else because the term "hull speed" almost always causes confusion. I know smart, accomplished folks have used the term the way you are even in print but it has also been defined by other respected folks also in print in different incompatible ways. The result is typically a bunch of confusion and an argument when the term is used.

#55 blunted

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Posted 30 September 2010 - 08:02 PM


My reference to hull speed was on the C-cat, 22.5 knots or 4.5 * the square root of LWL, is a decent estimate for "hull speed" in a long slender, displacement mode boat, like a C-cat. Which is not unlike the hulls of say, BOR 90.

Just one more example why I avoid using word hullspeed.
Some, like you it seems, use it as a practical top speed of the boat, while others use it only to describe the situation when waves made by the hull have same length as the boat, like in all litterature of naval architech...

So when I say we go hull speed in 14 knots TWS, I mean a C-cat will do 20 knots downhill in 14 knots TWS.

If there would be c-class race in Freemantle or SanFrancisco, and if the rules would allow sailing there in 30 kts true, and if you had a shorter wing than in alpha optimised for those conditions, do you think your top speed would increase by how much ?

Have you done any comparisong with canaan wing and alpha wing on the same platform regarding top speed, and if so, how much difference was there ?
What is the difference in height in those 2 wings again ?

Freemantle, that would be fun and yes, we would develop a radically different boat for such a contest. We would trade off masses of light air performance to do something very different I think. This is the trick of it all, what are your venues going to be for the boat? What are your limits? So yes for SF, We would build a boat that could probably hit 30, but it would suck in light air, by a wide margin.



The "Top speed" of all the boats, as they are 25' long is alarmingly similar, 22.5 knots. We have made them all go faster than that in ideal conditions but we rarely exceed that number on a daily basis. They are all displacement hulls, so that's pretty much how fast they go.

PL has been made to go faster, say 25 plus, by us on a few occassions, which speaks to the efficacy of curved foils and adjustable rudder spoilers. Steve's new boat should and does go faster than that, but again with some costs at the lower wind range.

#56 Surf City Racing

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Posted 30 September 2010 - 08:05 PM


My reference to hull speed was on the C-cat, 22.5 knots or 4.5 * the square root of LWL, is a decent estimate for "hull speed" in a long slender, displacement mode boat, like a C-cat. Which is not unlike the hulls of say, BOR 90.

Just one more example why I avoid using word hullspeed.
Some, like you it seems, use it as a practical top speed of the boat, while others use it only to describe the situation when waves made by the hull have same length as the boat, like in all litterature of naval architech...

So when I say we go hull speed in 14 knots TWS, I mean a C-cat will do 20 knots downhill in 14 knots TWS.

If there would be c-class race in Freemantle or SanFrancisco, and if the rules would allow sailing there in 30 kts true, and if you had a shorter wing than in alpha optimised for those conditions, do you think your top speed would increase by how much ?

Have you done any comparisong with canaan wing and alpha wing on the same platform regarding top speed, and if so, how much difference was there ?
What is the difference in height in those 2 wings again ?


In the configuration that the Cs raced in the LAC, I think SF on a typical day would chew 'em up and split 'em out in big wad of carbon slivers. Perhaps that's another discussion as to how the design will be optimized for wave conditions in The Bay.

As my friend Jay says, "you can pitch anything." But at a typical, let's say F18 event, you don't see much pitchpoling, the modern designs and rig tuning have that pretty much under control.

#57 Mal106

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Posted 30 September 2010 - 08:11 PM


My reference to hull speed was on the C-cat, 22.5 knots or 4.5 * the square root of LWL, is a decent estimate for "hull speed" in a long slender, displacement mode boat, like a C-cat. Which is not unlike the hulls of say, BOR 90.

Just one more example why I avoid using word hullspeed.
Some, like you it seems, use it as a practical top speed of the boat, while others use it only to describe the situation when waves made by the hull have same length as the boat, like in all litterature of naval architech...


Correct me if I'm wrong but when you define hull speed as the waves made by the hull have the same wave length as the length of the boat the formula is always 1.34 times the square root of the waterline length. Only when you have a boat with very light displacement and long length do you substitute a larger constant because the drag rise occurs at a higher speed. Even then it has little or no relation to top speed because the boat climbs over it's bow wave and planes. Even my lowly Hobie 18 will do that.

What is the shape of a C cat's bottom? Is it flat(ish) with little or no rocker? I ask because I think the primary reason for A5 being so much slower than USA17 was the excessive rocker. The boat pitched badly and didn't seem to have the lift the heavier and bulky BOR boat did.

Is your experience with C cats building, sailing or both. I think there are some pretty neat job openings for such experience if a lot of teams take up the challenge and I hope they will.

#58 the loose cannon

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Posted 30 September 2010 - 08:11 PM

...Picture of monoslug pearling in I believe the solent.

Always loved that picture and all the more so for the fact that the bowman was underwater plastered against the foredeck by the water pressure.

#59 s2 alter ego

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Posted 30 September 2010 - 08:46 PM



Just one more example why I avoid using word hullspeed.

1) Correct me if I'm wrong but when you define hull speed as the waves made by the hull have the same wave length as the length of the boat the formula is always 1.34 times the square root of the waterline length.
2) Only when you have a boat with very light displacement and long length do you substitute a larger constant because the drag rise occurs at a higher speed.
3) Even then it has little or no relation to top speed because the boat climbs over it's bow wave and planes. Even my lowly Hobie 18 will do that.

4) What is the shape of a C cat's bottom? Is it flat(ish) with little or no rocker? I ask because I think the primary reason for A5 being so much slower than USA17 was the excessive rocker. The boat pitched badly and didn't seem to have the lift the heavier and bulky BOR boat did.

5) Is your experience with C cats building, sailing or both. I think there are some pretty neat job openings for such experience if a lot of teams take up the challenge and I hope they will.

1) the definition I gave is always valid. The speed of the wave of a given length does vary a little bit in very shallow water compared to deep water, but telling you 1.34 is wrong constant because of that would be splitting hares when talking about boats in general, but it is relevant for toy boats in shallow water changing at leats the last digit.

2) I don't substitute in any higher constant in those cases as like I said, I try avoid using that expression in the first place.
3) Planning is another expression to be avoided. That too has far too many interpretations to be of any use. Does it simply mean higher froude numbers or does it indicate significant dynamic vertical forces directed upwards ? There is no common answer to that Q, thus beter not to start yet another silly debate about the issue, just avoid using it is my advice, and you are free to ignore that advice if you wish ... :)

4) More rocker you seem to think. Why don't you look for yourself ; plenty of pics in multihullAC forum. For example in the: " Fred is in so much trouble thread."

5) I have nothing in common with C-cats in practical level, though I hope I would. I have just studed what ever has been made public in theory.
But Blunted has plenty of practice in C-cats, ask him nicely if you want to know something or go check out the thread mentioned in above.

#60 Mal106

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Posted 30 September 2010 - 08:59 PM








So I'll ask,



When you say a boat gets to hull speed in 14kts true you are talking about a different boat than any high performance cat or planing hull or both. For those boats there is no such limit, just a slight drag rise at 1.34X^1/2 the LWL in the cat and a big hump easily overcome on the planing hull. Even the lowly Prindle I mentioned earlier sails around at 2 to 3 times hull speed.



My reference to hull speed was on the C-cat, 22.5 knots or 4.5 * the square root of LWL, is a decent estimate for "hull speed" in a long slender, displacement mode boat, like a C-cat. Which is not unlike the hulls of say, BOR 90. So when I say we go hull speed in 14 knots TWS, I mean a C-cat will do 20 knots downhill in 14 knots TWS. So no, I am not talking about a high performance cat that you are speaking of.

If I follow your suggestion you are talking about psudo-planing style boats, if not full planing of course in speaking about skiffs, never dropping speed that much etc etc etc, also having lifting bows etc etc.

Yes; I'm quite sure that will apply to the 72 and likely the little boat as well but cheating the displacement rule and thus loosing little speed n gybes does not depend solely on the boat's capability to plane. It also depends on how narrow the boat is in relation to its length and inversly proportional to its displacement. A good example is my Prindle or a Hobie 16. They both cheat the displacement rule easily but have a sharp entry through the whole length of the boat so they do it by being light and narrow almost exclusively: little lift and no planing. The Hobie 18 exhibits these characteristics and likely cheats displacement rule on that merit alone but it also has a relatively rounded bottom and lifts quite a bit at speed so its no doubt a combination. The other end is well represented by the 18 foot skiff. In the displacement mode it will go about 6 knots. No cheating there. It is so light flat and overpowered, however, that it easily climbs over its bow wave and planes. I've messed with the math but not enough to speak to the magnitude of each mode just that it exists alone or in combination.

Design of the hulls of the race 72 will surely result in compromises in an attempt to maximize lift and thus righting moment as well at speed; Minimizing drag with little rocker, the aforementioned lift and by minimizing side forces instead passing them on to the high aspect board. All this while trying to make it turn and stay together; it's certainly going to be interesting. For awhile the mono hull folks are going to get in the way but it won't take them long to get it.

#61 Mal106

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Posted 30 September 2010 - 09:38 PM



Just one more example why I avoid using word hullspeed.

1) Correct me if I'm wrong



4) More rocker you seem to think. Why don't you look for yourself ; plenty of pics in multihullAC forum. For example in the: " Fred is in so much trouble thread."


Dang you S2; I spend way too much time on this stinkin box already already and you go and give me a free snort.

I just came over here to get away from the shall we say "stogeyness" of the AC forums at Scuttlebutt and see what a site with this name would think about the Cup. I was, frankly, a little disappointed with similar sour grapes seen at the Butt. Not quite as many but quite adamant even to the point of rudeness.

Back on track, seriously, thanks for pointing me that way. The more rocker comment was really too much rocker and referring to A5. The C hulls look like long lean H-18 hulls. There even seems to be a little rocker. I suppose acceleration and maneuvering needed in match racing requires it though I suspect it hurts top speed. For the 72 hull, I'm expecting less rocker than A5 but some, a similar length to width as the C, wave piercing bows like A5 and fairly sharp chine angles. I suspect the relatively flat bottoms to be at whatever angle they decide to sail on. I suspect there will be a speed where the rocker is only forward and the boat planes, I know I hate to use that word too but don't know no better, only using the rocker in maneuvering, accelerating and when the flotation is required in a wave.

Any thoughts?..........blunted nicely?

#62 Scarecrow

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Posted 30 September 2010 - 10:59 PM

Mal,

take a deep breath and consider who you're talking to, you don't seem to relise Blunted's roll in both the LAC and AC33. Do some research on the old C cat threads and you'll see that Orion (built between Alpha and Canaan) has reduced rocker and it proved slower, also have a good look at the majority of the photos, the hulls are a lot rounder than you seem to think, primarily as wetted surface is the principle resistance driver on these hull shapes.

With regards to the original thread question it is worth noting the evolution of hulls in the F16 and F18 classes. Early in their development, both these classes headed towards the A class reduced freeboard and bow volume. Newer designs have gone in the opposite direction with increased forward freeboard. Expect AC72 boats to go in a similar direction if not more extreme given their huge power and lack of usefull movable ballast.

#63 Mal106

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Posted 01 October 2010 - 12:15 AM

Mal,

take a deep breath and consider who you're talking to,

I would hope that I treat everyone here and everywhere with a goodly amount of respect until they prove to deserve otherwise. If I did otherwise in this thread; I sincerely apologize. On the other hand on a forum I do believe posts must stand on their own. I will share experiences occasionally but only with a good FWIW qualifier. That's about my best deep breath.

I haven't watched the F-16 and 18 classes much recently and hadn't noticed that change. The "A" obviously went the other way during later development. Both BOR and A-5 seem quite light in forward buoyancy with solid wave piercing bows. Did the 16 and 18 increase fwd buoyancy because the tramp was getting too much of a wash, for resistance to burying a bow or what? I don't usually support any sort of conspiracy theory but occasionally a mfr will change something simply to sell the leaders a new boat and sometimes the leaders will build their own with a change. Because they lead, they win and the change is thought to be faster and it is, but not necessarily due to the change.

This is going to be an interesting AC; particularly to a multihuller. I just hope the mono sailors will play along and not turn their backs on the Cup because of the number of hulls on the boats. That seems questionable if you watch the forums.

#64 Basiliscus

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Posted 01 October 2010 - 12:20 AM


It is possible to generate negative lift at the head and lower the center of effort. However, when the gust hits, it acts through the aerodynamic center, not the twist-lowered center of effort.


Erm ... you would really complete your daily good deed if you expanded on that. I understood the aerodynamic center was related to an airfoil's pitching moment, i.e. it's something that moves in the longitudinal plane. Whereas in terms of pitchpoling (and capsizing) the critical factor should be the location of the wing's center of effort in the vertical plane, no?

I'm using the term "aerodynamic center" in the context of the vertical plane as well as the horizontal section plane, because I don't think there's any other accepted term in yacht design for the distinction between it and the center of effort.

The center of effort is defined to be the heeling moment (or pitching moment, depending on the context) divided by the lift. This is the same as the concept of center of pressure for an airfoil. If the moment went to zero at the same time the lift went to zero, then this would be the same as the aerodynamic center. If the wing had no effective twist (zero lift lines of all sections were parallel), then this would be the case. However, things are different with a twisted wing.

If you sheeted out a twisted wing until there was no net lift, then there would still be a heeling moment because the head would be pushing one way and the foot would be pushing the opposite way. When you calculate the center of effort, it is at infinity because you have the heeling moment due to twist divided by zero lift! Suddenly the concept of center of effort isn't making much sense.

When the wing is operating below stall (linear lift range), then the change in the lift distribution will be pretty much the same for a change in the sheeting of the wing (angle of attack), whether the wing is twisted or not. It's just that the change at a given section will have a different starting point when wing is twisted. So it makes sense to consider the height at which the change in lift is centered in order to give the same change in the heeling moment. This is the aerodynamic center in the context of heeling moment, just as it is when considering pitching moment in the context of section aerodynamics. So now we have the lift acting at the aerodynamic center producing a heeling moment and we have an additional heeling moment that is due to twist. If you look at it this way, the effects of angle of attack and twist are decoupled. The local lift at the head can go negative if the twist is large enough or the angle of attack is low enough, but that doesn't change anything - it's only a matter of degree.

If the head is twisted off, then the heeling moment due to twist will be a restoring moment, and will oppose the heeling moment due to angle of attack. At any given moment, it will be as though the center of effort is lowered. But the center of effort will be going up and down as the lift changes, which again kind of defeats the whole purpose of being able to think of the lift as acting at one fixed point. So it may be more useful to think of the lift as acting dynamically at the aerodynamic center, and being controlled by sheeting the wing in and out. Then use the twist as a means of heel trim, because it will be slower to effect the twist than to sheet the wing.

When a gust hits, it will have two effects (assuming the shear is similar in the gust). There will be an increase in apparent wind speed, which will affect both the heeling moment due to twist and the heeling moment due to angle of attack, and the apparent wind angle will increase, which increases the angle of attack. If there's a lot of twist, the heeling moment will be greater than what one might expect because the change in relative wind angle will be acting through the aerodynamic center and no getting a corresponding offset from the twist.

#65 rule69

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Posted 01 October 2010 - 04:05 AM

...
When a gust hits, it will have two effects (assuming the shear is similar in the gust). ... and the apparent wind angle will increase, which increases the angle of attack. If there's a lot of twist, the heeling moment will be greater than what one might expect because the change in relative wind angle will be acting through the aerodynamic center and no getting a corresponding offset from the twist.


Forgive me for being more dense than I usually am; I've applied an after work beer and no food. Is the key here just that as the apparent wind angle increases with a sail twisted to have negative lift at the top the neutral lift section moves up and thus the center of force moves up?

#66 blunted

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Posted 01 October 2010 - 01:29 PM

For the sake of clarity here is a shot where you can get a good idea of the underwater shape of BOR on the hulls. if you look closely around the dagger foils you can see below the water line the shape is thatof a semi circle, E.g. Lowest wetted surface area approach. towards the stern things are flattened off a little.

Attached File  GGVLC3-D6_0115.jpg   700.78K   84 downloads

#67 blunted

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Posted 01 October 2010 - 01:41 PM

here is a nice stern shot, allowing you to see how the hull is trimmed flat towards the transom.

I'll let you debate the reasons why that is done.

Attached File  771973100_WINGDAY5_0230.jpg   348.18K   36 downloads

Here you can decide how much rocker it has...

Attached File  771973100_WINGDAY3_0116.jpg   235.44K   36 downloads

#68 blunted

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Posted 01 October 2010 - 01:46 PM

Now one of our good friends for comparison

Attached File  alinghi-sailing-sunglasses.jpg   62.23K   13 downloads

#69 blunted

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Posted 01 October 2010 - 01:49 PM

And to compare rocker...


Attached File  IMG_1265_office.jpg   607.91K   16 downloads

#70 blunted

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Posted 01 October 2010 - 01:53 PM

Here you can see Alpha's rocker..

Attached File  Alpha reaching 001.jpg   143.85K   8 downloads

#71 blunted

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Posted 01 October 2010 - 01:56 PM

A little bit of Orion... here's what you get with narrow bows.

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#72 blunted

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Posted 01 October 2010 - 01:58 PM

Orion's rocker can be seen here

Attached File  IMG_3542.jpg   726.84K   19 downloads

#73 Xlot

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Posted 01 October 2010 - 02:14 PM

Well, Blunted obviously belongs to the Steve Killing school with significant rocker, semi-circular sections and comparatively narrow sterns. This is the traditional method aiming at minimum wetted area I'm quite familiar with, originating I believe in US Navy research in fast displacement craft back in the Thirties. The drawback is limited pitch dampening, and the rudder being exposed the moment the bow goes down.

Steve Clark's Aethon pushes the envelope of the more recent consensus with little rocker, semi-elliptical sections, flat exit resulting inevitably in more wetted area and a wider max. girth: he goes for power and pitch dampening at the cost of more drag.

As for WZ, Blunted should know but the picture of the old hulls at Core (cannot re-post it at the moment, but the cradles are quite revealing) would say forward sections are definitely flattish - as is the AC45 plug.

#74 Mal106

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Posted 01 October 2010 - 02:53 PM

Nice shots; thanks for posting. During the build up to 33 and the races I payed way too much attention to the courts, the Deed and the politics of the race rather than boat design and had little time for even that.

The last picture of A5 really reveals the rocker, what little there is of it, extending quite far aft; perhaps all the way aft. I think that factor likely explains the pitching movement that far exceeded that of BOR in both races. Additionally rocker seems to me to be a liability at anything above hull speed (13 kts give or take). BOR seemed to have little or no rocker toward the rear and was much smoother in its motion. My guess is that that was one reason A5 was slower. Maybe rocker is a worthwhile trade off for acceleration through hull speeds or maneuvering in reducing the long moment arms of the extremes of the hull. Think tacking a no board beach cat where you get as much of the bows out of the water you can.

I am surprised that the flat toward the stern of both boat's hulls didn't seem to make an attempt at angling the lift (flat) either straight up at the design sailing angle or even slightly more to help the board with leeway. That would also provide a finer entry and more rocker when the boat is flat and slow as well. Maybe not the leeway since the board has a huge advantage in doing that job with a very high aspect and small wetted area in comparison to the hull.

The new boats are going to have so much power that I expect hull design to swing much more toward power boat hulls. Harder chines, flatter bottoms providing vertical lift to reduce wetted area at speed with minimal deference to sailboat hydrodynamics. They obviously have to have the longest hulls possible due to the engine being high up on the boat, not below it like a power boat. The long hulls will provide enough buoyancy at extremely narrow widths so they will indeed be narrow. It sounds like the boards will not be movable except up and down and may well be one design. That takes away some innovative possibilities for maneuvering but is likely a good idea. Think shifting it 4 or 5 degrees to windward as you bring it up in a tack or varying it's AOA over it's length and adjusting it up and down as needed.

I always thought that BOR made a huge sacrifice being a tri and having to haul around the huge bulk and aerodynamic drag of the center ama. I think they didn't anticipate the engine in early planning and needed a place to put all the manpower that would be needed to handle sails on a 90 foot unlimited canvas boat. The hulls might have been slightly better than A5 but only the wing could make up that huge deficit of the middle hull. Sail area was a good characteristic to discuss when they were soft but to use that measure when comparing a soft sail to a wing it is totally inadequate. The Wright Bros Flyer wing was basically a full battened sail operating at fast sailboat speeds and look how quickly it gave way to a fat wing. Low speed aerodynamics are well known. The trick will be 6 to 30 kts wind speed and 0 to whatever boat speed and making the wing adapt and maneuver the boat.

How ridiculous are my thoughts on the subject? It's certainly going to be an interesting ride......

#75 Mal106

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Posted 01 October 2010 - 03:22 PM

More great pictures as I was hunting and pecking......superb. Again thanks. I particularly liked the view they gave of the wing's extreme camber downwind. For just two elements, or are they three? they really looked good. The flap looked to be at a high enough angle that it could have used a slot. Does one open up at the high angles downwind? How are they controlled? One line and the wing takes what is needed for the main sheet trim or is the flap individually controlled? Why no separate elements at the top? Sorry.... I'm loosin it.

Amazing design and construction for a two up boat. Damn me for not going to Connecticut for the LAC!

#76 MR.CLEAN

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Posted 01 October 2010 - 03:27 PM

Got a link to our 'tv guide', blunted,? so that this poor refugee from the cold, dark abyss of the interwebs can step into the light?




#77 blunted

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Posted 01 October 2010 - 03:34 PM

Got a link to our 'tv guide', blunted, so that this poor refugee from the cold, dark abyss of the interwebs can step into the light?


Mal, I suggest you take a few minutes, hours, days, whatever you need to catch up on some material over here at this thread.

http://forums.sailinganarchy.com/index.php?showtopic=101656

By popular concensus we have all stopped posting there as we kind of flogged that horse real good for the time being.

I think it will satisfy your appetite for wing and C-class hull ideas, questions, thoughts, theories, debates etc etc etc. It pretty much covers the waterfront on boats with wings, or as much as you could hope for in one thread. It's only 1800 posts, you'll be through it in no time.

Cheers

MC

#78 coxcreek

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Posted 01 October 2010 - 10:50 PM

For the sake of clarity here is a shot where you can get a good idea of the underwater shape of BOR on the hulls. if you look closely around the dagger foils you can see below the water line the shape is thatof a semi circle, E.g. Lowest wetted surface area approach. towards the stern things are flattened off a little.

Attached File  GGVLC3-D6_0115.jpg   700.78K   84 downloads


Somewhat off subject but that shot (who took it?) is a work of art of a work of art.

#79 Xlot

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Posted 02 October 2010 - 12:40 AM

As for WZ, Blunted should know but the picture of the old hulls at Core (cannot re-post it at the moment, but the cradles are quite revealing) would say forward sections are definitely flattish - as is the AC45 plug.


This is the picture - courtesy of a proud SA parent whose name I don't recall:

Posted Image

see what I mean?

BTW, there's a very nice article by Steve Killing in the just-out SH magazine, with a very revealing superposition of Alpha's, Orion's and Canaan's profiles - and Canaan has (even more) rocker than Alpha! This is quite counter-current, Killing is adamant that the key is wetted area ..

#80 Mal106

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Posted 04 October 2010 - 06:41 AM

Mal, I suggest you take a few minutes, hours, days, whatever you need to catch up on some material over here at this thread.

http://forums.sailin...howtopic=101656

I think it will satisfy your appetite for wing and C-class hull ideas, questions, thoughts, theories, debates etc etc etc. It pretty much covers the waterfront on boats with wings, or as much as you could hope for in one thread. It's only 1800 posts, you'll be through it in no time.

Cheers

MC

Minutes? YGBSM! Hours? No way! Days? Except for a few hrs. of sleep, 6 hrs. of sailing (38 ft lead hauler) and all too little interaction with the family ... 3 (days). Satisfaction, no way, it just whetted my appetite for more.

That has to be the best thread I have ever had the pleasure of being obsessed with. Aside from the gushing platitudes on the great personalities of those involved and the openness, honesty, and advanced nature of the class; all of which can only be understated; there was more wheat and less chaff than I could have imagined. Words cannot describe. I enjoyed it more than anything I could have done out of the air or off the water with my pants on.


First, I wouldn't dare pollute that thread with my questions or musings so I'll say here congrats to you and Fredo; my sympathies to Steve. Sometimes results don't properly reward effort or ability but even his remarkable expertise and skill pales in the light of his giving, sharing and super attitude in the face of such adversity. Fredo's generosity in the loan, charter, whatever of his boats was simply amazing. Anything else I could say of the event and all its participants would only be, again, understated as words, at least mine, don't work..

I busted my butt trying to figure out what controlled what even trying to trace some of the lines in pics and watching multiple videos stopping and repeating trying to see who and what moved what. Too bad your demonstration was near the end but thanks for doing it. It likely saved my sanity but I'd still love to see them moved and traced to their relative movements.


I'm sure there are a bunch of things that have been tried and rejected as lacking (weight, reliability, too complex to control, draggy etc.) but I wonder about the following specifically:

1 Have the wings been canted to be perpendicular to the wind like your night charge?

2 Has anyone used fences, an end plate, or a little forward sweep (rigidity?) to reduce spanwise flow? Particularly in the light of heel used to fly a hull. Spanwise flow is a double whammy due to its loss of power and increased down force.

3 Has anyone tried an asymmetrical wing (each element) overcoming the obvious difficulties of making it self tacking rather than the whole wing rotating in a tack or gybe a la "Windmill" which is arguably illegal in max beam?

4 Have there been efforts to actually change the shape, on the fly, of individual elements of the wing to adapt to different wind speeds. Thicker in light winds and thinner in heavy winds even if still symmetrical.

5 Since center of pressure must be moved lower in higher winds; has any one tried a sliding section at the top such that not only the heeling moment can be removed but also the drag of a feathered (twisted off) section? The area lost by the sliding tip could even be recovered with added area down low even with a relatively simple sliding flat panel increasing flap area down lower in winds high enough to require retracting the tip.

6 Has anyone tried a truly planing hull with hard chines and a flat bottom aft, maybe even with a step such that pitching is reduced by two entries each with a flat bottom aft.

I wonder about several references to max speeds even the mention of asymptotic to some maximum. I would think that the limit hasn't been near reached. I realize that incremental speed increases get less and less as the class develops but I can't imagine anything would be in the way of the increasing trend; certainly not yet. The relative performance of the competitors (boats) in this regatta supports that premise.


Though my main interest is in the AC, you have converted me to a C junkie as well. The class' implications for the Cup are obvious. Some were surprised by the number of AC rock stars in attendance or looking over the class before the regatta. Now that I know something about the class I'm surprised that there were so few. After watching those gorgeous boats; I can't imagine the sour grapes aimed at the choice for the next Cup. A "C" class scaled up to 72 feet with a crew of 11 pulling the strings ...... it's gonna be a hoot! Throw me in coach!

I would really like to hear more about the night sailing you did on USA 17. I can imagine it being like an alley cat on a leash. Have you written more on the subject or given interviews other than the taste I saw with Spittie?

#81 blunted

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Posted 04 October 2010 - 01:27 PM


Mal, I suggest you take a few minutes, hours, days, whatever you need to catch up on some material over here at this thread.

http://forums.sailin...howtopic=101656

I think it will satisfy your appetite for wing and C-class hull ideas, questions, thoughts, theories, debates etc etc etc. It pretty much covers the waterfront on boats with wings, or as much as you could hope for in one thread. It's only 1800 posts, you'll be through it in no time.

Cheers

MC

I enjoyed it more than anything I could have done out of the air or off the water with my pants on. Glad you liked it.



I'm sure there are a bunch of things that have been tried and rejected as lacking (weight, reliability, too complex to control, draggy etc.) but I wonder about the following specifically:

1 Have the wings been canted to be perpendicular to the wind like your night charge? Yes, SHC has tried it, we have also tried it, we chose not to do it this August for a number of reasons.

2 Has anyone used fences, an end plate, or a little forward sweep (rigidity?) to reduce spanwise flow? Particularly in the light of heel used to fly a hull. Spanwise flow is a double whammy due to its loss of power and increased down force. Not exactly, sort of, not really though

3 Has anyone tried an asymmetrical wing (each element) overcoming the obvious difficulties of making it self tacking rather than the whole wing rotating in a tack or gybe a la "Windmill" which is arguably illegal in max beam? Wingmill and Otip, no others to the bset of my knowledge, I will defer to SHC on that one

4 Have there been efforts to actually change the shape, on the fly, of individual elements of the wing to adapt to different wind speeds. Thicker in light winds and thinner in heavy winds even if still symmetrical. Well once you put camber in, its not symmetrical, its assymetric and yes we change the shape all the time, Camber, flap twist, forward twist.

5 Since center of pressure must be moved lower in higher winds; has any one tried a sliding section at the top such that not only the heeling moment can be removed but also the drag of a feathered (twisted off) section? The area lost by the sliding tip could even be recovered with added area down low even with a relatively simple sliding flat panel increasing flap area down lower in winds high enough to require retracting the tip. We have contemplated it, but given that we all generall y agree to not sail / race in more than 20 knots TWS, it's not entirely an issue. Canaan's wing can still be handled in that blow, if with difficulty. A different configuration would be faster in heavy air, but you have to trade off against what everyone else is sailing with. Don;t want to get caught short on the water on the big day.

6 Has anyone tried a truly planing hull with hard chines and a flat bottom aft, maybe even with a step such that pitching is reduced by two entries each with a flat bottom aft. Not really that far, I have this argument with Steve Killing and he is pretty clear that cats are generally just too long and skinny to plane properly. I on the other hand think you can do it, and SHC is obviously half way there with a bit of a hybrid. The trade off is of course lighter air, anything up to 15 knots and displacement sailing may well be faster in a C-cat. So if the venue is right, it's possible a flat bottom boat could well do better then a curvy boat.

I wonder about several references to max speeds even the mention of asymptotic to some maximum. I would think that the limit hasn't been near reached. I realize that incremental speed increases get less and less as the class develops but I can't imagine anything would be in the way of the increasing trend; certainly not yet. The relative performance of the competitors (boats) in this regatta supports that premise. When I refer to max speed again, I am just saying thats how fast that type of hull in displacement mode, wants to go. I have no doubt whatsoever that you can make a 25' boat go faster, again, it's about setting around the whole course with the net fastest time.


Though my main interest is in the AC, you have converted me to a C junkie as well. The class' implications for the Cup are obvious. Some were surprised by the number of AC rock stars in attendance or looking over the class before the regatta. Now that I know something about the class I'm surprised that there were so few. After watching those gorgeous boats; I can't imagine the sour grapes aimed at the choice for the next Cup. A "C" class scaled up to 72 feet with a crew of 11 pulling the strings ...... it's gonna be a hoot! Throw me in coach!

I would really like to hear more about the night sailing you did on USA 17. I can imagine it being like an alley cat on a leash. Have you written more on the subject or given interviews other than the taste I saw with Spittie? check out the bmworacle web site, or search "wingnuts" on youtube. In short it was a lot of work, long cold nights, more than a little pressure to not screw it up, huge learning and a very very very unique experience. Most people who saw the boat for the first time, Larry included simply said "Holy shit!" because it was so immennsely huge. It really defied description. The scale of the whole enterprise was remarkable. The boat on a bad night was an angry beast. We had a couple of scary experiences, it was of course our goal to not have them...
On balance it was a huge amount of fun, working with that team was fantastic, great guys and gals, very professional, exceptionally good at what they all did, it was an honor.



#82 mili

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Posted 04 October 2010 - 04:48 PM

Quote:


1 Have the wings been canted to be perpendicular to the wind like your night charge?

2 Has anyone used fences, an end plate, or a little forward sweep (rigidity?) to reduce spanwise flow? Particularly in the light of heel used to fly a hull. Spanwise flow is a double whammy due to its loss of power and increased down force.

3 Has anyone tried an asymmetrical wing (each element) overcoming the obvious difficulties of making it self tacking rather than the whole wing rotating in a tack or gybe a la "Windmill" which is arguably illegal in max beam?

4 Have there been efforts to actually change the shape, on the fly, of individual elements of the wing to adapt to different wind speeds. Thicker in light winds and thinner in heavy winds even if still symmetrical.

5 Since center of pressure must be moved lower in higher winds; has any one tried a sliding section at the top such that not only the heeling moment can be removed but also the drag of a feathered (twisted off) section? The area lost by the sliding tip could even be recovered with added area down low even with a relatively simple sliding flat panel increasing flap area down lower in winds high enough to require retracting the tip.

6 Has anyone tried a truly planing hull with hard chines and a flat bottom aft, maybe even with a step such that pitching is reduced by two entries each with a flat bottom aft.




"All I wanted to know about C Cats and was afraid to ask"

#83 eric e

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Posted 04 October 2010 - 09:34 PM

#6 sounds like yves parlier's hrdraplaneur

planing hulls modelled on flying boat hulls with a big step half way along

seem to remember it was very quick on a reach

but not so quick going to weather



#84 furling

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Posted 04 October 2010 - 10:25 PM

#6 sounds like yves parlier's hrdraplaneur

planing hulls modelled on flying boat hulls with a big step half way along

seem to remember it was very quick on a reach

but not so quick going to weather




I guess being planing hulls then the one on the top of the wave has to lift the other vice verser, emagine the twist on the beams, would be awsome in flat water

#85 Mal106

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Posted 05 October 2010 - 01:03 PM

I guess being planing hulls then the one on the top of the wave has to lift the other vice verser, emagine the twist on the beams, would be awsome in flat water

That might be some sort of #7. Controlled flex between hull angles; sort of an independent suspension if you will. Not really smart enough to figure out how efficient that would be vice pulling the opposite hull up with it but it certainly could smooth the ride and that's usually more efficient. Might even be able to harness that motion to transfer the energy into some sort of kenetics as in a roll tack or pumping sails.

Definite planing hull look at the entries; maybe a little less at the sterns but the two masts are definitely one way to keep the center of pressure low and the righting moment under control. I'm sure it takes a bunch of wind to drive it.


Blunted; Thanks so much for your thoughts.

The only one I may not have been clear on is the "removable" top section. I meant that it be on the boat at all times. It could be raised and lowered with a halyard and slide over the next element down. In even 20 kts it could be lowered vice keeping the drag of it twisted off. Likely would always be used downwind to sail deeper and never up wind in a breeze where the sail had excess power.

I'm going to dig through your references on the night watch. I'm a big fan of BOR and you are surely one of the maybe not unsung but less sung heroes. What a different AC it would have been if you hadn't been successful. It was sure a high consequence job.

#86 blunted

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Posted 05 October 2010 - 01:46 PM


I guess being planing hulls then the one on the top of the wave has to lift the other vice verser, emagine the twist on the beams, would be awsome in flat water

That might be some sort of #7. Controlled flex between hull angles; sort of an independent suspension if you will. Not really smart enough to figure out how efficient that would be vice pulling the opposite hull up with it but it certainly could smooth the ride and that's usually more efficient. Might even be able to harness that motion to transfer the energy into some sort of kenetics as in a roll tack or pumping sails.

Definite planing hull look at the entries; maybe a little less at the sterns but the two masts are definitely one way to keep the center of pressure low and the righting moment under control. I'm sure it takes a bunch of wind to drive it.


Blunted; Thanks so much for your thoughts.

The only one I may not have been clear on is the "removable" top section. I meant that it be on the boat at all times. It could be raised and lowered with a halyard and slide over the next element down. In even 20 kts it could be lowered vice keeping the drag of it twisted off. Likely would always be used downwind to sail deeper and never up wind in a breeze where the sail had excess power.

I'm going to dig through your references on the night watch. I'm a big fan of BOR and you are surely one of the maybe not unsung but less sung heroes. What a different AC it would have been if you hadn't been successful. It was sure a high consequence job.


You might want to have a closer look at the draft rule. It is pretty clear about the platform not wiggling for any reason other than basic stresses, E.g. no kinetic hulls.

Likewise with the current wing rule draft, it's pretty prescriptive about how big the wing must be. To my mind there are contradictory elements about the mid-september rule in this regard, E.g. if you take off the tip what happens to "sailing weight"? Do you add sand bags to make up for the tip being gone?

To answer your idea of hoisting and lowering a wing tip. It's really not required for upwind / downwind. Upwind the wing can be feathered very effectively, much more so than a soft sail. I am very rarely worried about sailing any wing upwind in weather, the only limit is when you get blown over backwards, not sideways. If we get caught out in big breeze and do not have a quick exit, the survival strategy is to sail upwind as it is the safest way to go. If I wanted to get rid of area it would be downhill not uphill, and then I am only loking to get rid of height.

Plus with your raising and lowering concept, it's not like a wing is a fat mast with two tracks on the back face on which you attach a fairing, the whole wing has thickness and is self supporting, just like an airplane wing. How do you get one fat part past another fat part in plan view?

Something to chew on.

MC

#87 blunted

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Posted 05 October 2010 - 02:13 PM

Mal I was also thinking about your reefing idea having additional issues, namely the flap on the back of the wing. If you are going to "lower" your tip, you would want to do both the main element and the flap. Lots of craziness to sort out when doing that, I'll let you try, perhaps you'd have more luck than me.

I also got the sense that I should throw up the basic wing sketch to clarify it for some who might be confused.

Included is a sketch of a section of a wing, in 4 different modes. Here you can see how you take something fundamentally symetric and make it assymetric by inducing camber, or folding the wing bits.

More camber equals more power, less camber equals less power. keep in mind that you can twist your flap all the way up the wing, so you can have camber (Power) at the bottom of the wing, and you can have zero camber (Flat depowered wing) at the top. Much like a soft sail, only much much cleaner.

At zero angle of attack (Think AWA), the wing I have shown here would have less drag than a mast half the thickness of the front element. Never mind if that mast had a flapping piece of cloth behind it.

Hope this helps your understanding of how a wing basically works.

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#88 furling

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Posted 05 October 2010 - 02:20 PM



I guess being planing hulls then the one on the top of the wave has to lift the other vice verser, emagine the twist on the beams, would be awsome in flat water

That might be some sort of #7. Controlled flex between hull angles; sort of an independent suspension if you will. Not really smart enough to figure out how efficient that would be vice pulling the opposite hull up with it but it certainly could smooth the ride and that's usually more efficient. Might even be able to harness that motion to transfer the energy into some sort of kenetics as in a roll tack or pumping sails.

Definite planing hull look at the entries; maybe a little less at the sterns but the two masts are definitely one way to keep the center of pressure low and the righting moment under control. I'm sure it takes a bunch of wind to drive it.


Blunted; Thanks so much for your thoughts.

The only one I may not have been clear on is the "removable" top section. I meant that it be on the boat at all times. It could be raised and lowered with a halyard and slide over the next element down. In even 20 kts it could be lowered vice keeping the drag of it twisted off. Likely would always be used downwind to sail deeper and never up wind in a breeze where the sail had excess power.

I'm going to dig through your references on the night watch. I'm a big fan of BOR and you are surely one of the maybe not unsung but less sung heroes. What a different AC it would have been if you hadn't been successful. It was sure a high consequence job.


You might want to have a closer look at the draft rule. It is pretty clear about the platform not wiggling for any reason other than basic stresses, E.g. no kinetic hulls.

Likewise with the current wing rule draft, it's pretty prescriptive about how big the wing must be. To my mind there are contradictory elements about the mid-september rule in this regard, E.g. if you take off the tip what happens to "sailing weight"? Do you add sand bags to make up for the tip being gone?

To answer your idea of hoisting and lowering a wing tip. It's really not required for upwind / downwind. Upwind the wing can be feathered very effectively, much more so than a soft sail. I am very rarely worried about sailing any wing upwind in weather, the only limit is when you get blown over backwards, not sideways. If we get caught out in big breeze and do not have a quick exit, the survival strategy is to sail upwind as it is the safest way to go. If I wanted to get rid of area it would be downhill not uphill, and then I am only loking to get rid of height.

Plus with your raising and lowering concept, it's not like a wing is a fat mast with two tracks on the back face on which you attach a fairing, the whole wing has thickness and is self supporting, just like an airplane wing. How do you get one fat part past another fat part in plan view?

Something to chew on.

MC

what about like a car radio areal that slides into itself, just the top 2 sections could have less internals or no flaps as it is smaller at the top, or is it possible to moor the wing safely, the wing could be lowered down into the water, perhaps a type of key if the wing was turned 180 degrees and just lowered down under the water, maybee just half of the wing submerged, just throwing it out there! Forgive my madness

#89 Mal106

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Posted 05 October 2010 - 03:15 PM

Good points. I was really more speaking of the "C" more than the AC. Even with the AC my take on kenetic hulls is that the hulls cannot be moved not that they can't be allowed to move.

My movable mast tip would be either a hard shell slightly larger than the top of the element below with mast end sliding inside that below or a more likely a thinner section that extends out from the top section. The lower section would provide support around the perimeter for the over sliding section and the sliding portion of mast would hold the top in place. The section between could still be mylar; with only leading and trailing edges as a carry through. The thinner retracting section would be even easier depending on how thin it were made. Any decrease in wing area attained could be regained down low with an extendable flap. Aircraft change the size of the wing at the root end rather than at the tip either by the flaps sliding out or the wings sweeping. In the case of the aircraft flaps, however, drag is a desired result not a nasty consequence. Drag reduction is the prime mover in sweep as well but no need to even consider compressability; the "C" is fast but not there yet.:unsure: Back to the C and reality; this would do the same at the tip where drag upwind is critical. I hadn't thought of the problems down hill being as you described but when overpowered there; particularly when transferring true wind speed into sailing deeper; you are in something of a coffin corner when it comes to depowering. The retractable section would shine there but if 20 kts is agreed upon and not a problem; I suppose it is a moot point. The "tripping over backward" you mentioned is no doubt a result of that excess drag provided by even a totally washed out tip providing a bunch of drag at that extreme moment. You know it's got to be slow. Getting rid of the tip would cure that. The trouble with feathering is that, even though the excess heeling moment is relieved; nothing is done about the parasite drag which is in almost exactly the wrong direction. It is there even if the top section is at 0 AOA.

As to assymetry; obviously the more the wing can conform to the ideal in various conditions and points of sail; the more efficient it is. I suppose 3 elements along the chord and I assume one slot has gotten you to a point of diminishing return but before the wing, the sail then the wing, then the two element wing and so forth. My whole discussion there was aimed at the next steps. 4 elements, more? all the way to actually varying the camber, and maybe slots, within the elements. You even seem to have done that to an extent with the ability to vary twist with the leading edge of the lower element. I suppose the ultimate is the wing that can vary camber, aspect and cross section as the situation dictates. The "C" does only camber but not because the rules don't allow more. I really think the next step is to vary aspect with an extendable flap and retractable tip. It still could be and might have to be, by the rules, one string.

The AC is another animal and one reason the C is so progressive in comparison. I really think those writing the rules think of all the really extreme innovations (that they have no idea how to do) and block them in the rules. The wing keel was even criticized after the fact but you can't swing a dead cat and not hit a boat with a wing keel now. TNZ's bussel, the fore and aft rudders and so forth were a few that got through. A team with an innovative idea dare not talk about it, not just because it would be copied but because the rules will be changed to outlaw it. This is why DoG matches and the C are so interesting to me. How about 22mX15.5mX4.4m and 7200kg minimum .... period? I suppose that would kill most chances of good match racing but it sure would spur innovation. The DoG would eliminate the min weight but that is the only way it has even a chance at being nothing more than a $rms race.

#90 blunted

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Posted 05 October 2010 - 03:49 PM

Good points. I was really more speaking of the "C" more than the AC. Even with the AC my take on kenetic hulls is that the hulls cannot be moved not that they can't be allowed to move.

My movable mast tip would be either a hard shell slightly larger than the top of the element below with mast end sliding inside that below or a more likely a thinner section that extends out from the top section. The lower section would provide support around the perimeter for the over sliding section and the sliding portion of mast would hold the top in place. The section between could still be mylar; with only leading and trailing edges as a carry through. The thinner retracting section would be even easier depending on how thin it were made. Any decrease in wing area attained could be regained down low with an extendable flap. Aircraft change the size of the wing at the root end rather than at the tip either by the flaps sliding out or the wings sweeping. In the case of the aircraft flaps, however, drag is a desired result not a nasty consequence. Drag reduction is the prime mover in sweep as well but no need to even consider compressability; the "C" is fast but not there yet.:unsure: Back to the C and reality; this would do the same at the tip where drag upwind is critical. I hadn't thought of the problems down hill being as you described but when overpowered there; particularly when transferring true wind speed into sailing deeper; you are in something of a coffin corner when it comes to depowering. The retractable section would shine there but if 20 kts is agreed upon and not a problem; I suppose it is a moot point. The "tripping over backward" you mentioned is no doubt a result of that excess drag provided by even a totally washed out tip providing a bunch of drag at that extreme moment. You know it's got to be slow. Getting rid of the tip would cure that.

As to assymetry; obviously the more the wing can conform to the ideal in various conditions and points of sail; the more efficient it is. I suppose 3 elements along the chord and I assume one slot has gotten you to a point of diminishing return but before the wing, the sail then the wing, then the two element wing and so forth. My whole discussion there was aimed at the next steps. 4 elements, more? all the way to actually varying the camber, and maybe slots, within the elements. You even seem to have done that to an extent with the ability to vary twist with the leading edge of the lower element. I suppose the ultimate is the wing that can vary camber, aspect and cross section as the situation dictates. The "C" does only camber but not because the rules don't allow more. I really think the next step is to vary aspect with an extendable flap and retractable tip. It still could be and might have to be, by the rules, one string.

The AC is another animal and one reason the C is so progressive in comparison. I really think those writing the rules think of all the really extreme innovations (that they have no idea how to do) and block them in the rules. The wing keel was even criticized after the fact but you can't swing a dead cat and not hit a boat with a wing keel now. TNZ's bussel, the fore and aft rudders and so forth were a few that got through. A team with an innovative idea dare not talk about it or the rules will be changed to outlaw it. This is why DoG matches and the C are so interesting to me. How about 22mX15.5mX4.4m and 7200kg minimum .... period? I suppose that would kill most chances of good match racing but it sure would spur innovation. The DoG would eliminate the min weight but that is the only way it has even a chance at being nothing more than a $$rms race.


Well the c-cat twists the main element, it also has assymetry in the main element in that the integral flap, that we call #2, deflects and controls the slot size, so yes the main element actually has adjustable / variable camber. On top of that, the main element also twists as well as the flap. a c-class wing is a good deal more sophisticated than my sketch above.

I think, well I know, from my perspective, that the wing on the C-cat is as complicated as I would want to make it right now. Any more complicated, and it's going to start to weigh a lot more. All else being equal (Which it often is not) the lightest boat is going to win, if you have the lighest boat, that doesn't blow up, you are even more likely to win. It takes a while to develop a reliable, robust wing boat, that can be used day after day, without hundreds of hours of work between sailing sessions

So to me it sounds like it's time for you to build a wing. As my prof in school always said, "show me don't tell me". I imagine any of the ideas your speak of could in fact be worked out, they just take time, patience, money and a starting point that floats. That's where all the compromises begin.

If you want to see a complicated multi element wing, you need look no further than the yellow pages wings, it was often said that only Lindsay cunningham cuold actually figure out how to properly operate and tune the thing becasue it was so complicated. For each element you add to the machine, it gets exponentially more complicated and there is a corresponding rise in the potential for failure.

Just sayin....

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#91 Mal106

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Posted 05 October 2010 - 04:02 PM

And we haven't even touched on boundary layer and I don't mean that that takes place like Steve was describing between the surface and the top of the sail; I mean that between the wing surface and the free stream above. Any quick free source of sucking or blowing on the boat? Other than, in my case, the skill of the sailor.

And all your comments on complexity, weight, durability and the ability to control and practice with it are, of course, right on the money.... now anyway. Later, who knows? It's easy to talk the talk but to walk the walk is another matter. I really wish I could build a wing but the C and the AC are two places where I, regrettably, must remain an interested spectator. Anybody got an old used A cat they want to trade for 3 beach cat's and a couple of tired old sunfish?

Oh and to an aviator as myself; that wing is gorgeous! Yours that is; the yellow one; not so much.....




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