Bieker B6

[Presuming Ed]

So, on the front page (yeah, yeah, heard all the "There's a FP?" jokes before. Enough already), there are renderings of the sexy new Bieker B6 international 14. Looks top notch (to my non-14er eyes). Interesting that he's going with a gybing board. Theres an article in Seahorse this month from Dave Hollom about the theory behind gybing boards, and why he doesn't necessarily believe in them.

A rough synopsis of the article.

• Gybing boards aren't – unequivocally – the answer. In classes that allow them, they go in and out of fashion.
• How close to the wind we can sail depends on the combined hydrodynamic and aerodynamic lift/drag ratios.
• Hydrodymanic lift is a reaction force, equal and opposite to rig forces. We can't increase lift because we can't power up the sails more, and we can only do that if we can increase righting moment.
• Leeway doesn't matter. If we were actually concerned with minimising leeway, we would increase appendage area. But we have actually been decreasing appendage size.
• Drag from the canoe body is always there. If we can generate some lift by yawing the canoe body (sailing with some leeway), the lift generated might be beneficial. "If the rise in drag due to canoe body yaw, for a certain lift force, is less than that produced by the larger foils necessary to produce the same lift force, ..it will pay to produce that lift on the canoe body."
• "Because of its length the canoe body runs at a far lower Froude number than the liftiong foils so that the induced drag caused by any lift it generates may well
  be less than a similar amound of lift produced by on the shorter chord foils, which will be running at much higher Froude numbers. It isn't, therefore, altogether unreasonable to expect that canoe body lift is notas inefficient as one might initially think. Indeed, it may well be, comparatively, very efficient.
• Gybing boards might offer one advantage. By gybing the main board, the rudder isn't directly downstream of it, so that it is moving out of the downwash and has some separation and is thus starting to work as a bi-plane.
• Boats with gybing boards can sheet sails further out = a larger slot. The benefits of a larger slot are unclear.

(More next month, apparently - "Smaller foil plus larger trim tab....a superior solution?")
 
It's all very interesting. And way beyond me. Thoughts from the knowledgeable? Boat does look good, though.
 

 

[joe.bersch]

Here's what I can say empirically about the gybing board and how it worked on my Bieker 5. My observations are limited to one gyber, on one boat. On the other hand, the boat is one of those shown in Dave Hollom's photos (Paul Bieker's former boat) and I am the future owner of the B6 currently under construction. Because of my experiences on the B5 I insisted on the B6 also utilizing the gyber, although the centerboard trunk can accept a fixed board if that is the preference of the buyer.

In moderate breeze of 10-14 knots, we have shown consistently good speed and pointing ability. From the perspective of the helmsman, when the gyber is "on" (gybing) you can feel the lift of the centerboard very clearly. Maximum benefit seems to be sensitive to adequate leech tension. In the lighter ranges, we also find a benefit from slight leeward heel of 2 or so degrees. The boat clearly feels more powered up with the gyber on than it does with it off. In the Gorge, we actually find benefit from the gyber upwind well into breezes around 20 knots, but generally lock it off because it is too scary maneuvering at the start and when bearing off at the weather mark.

On occasions when we find ourselves with only average speed and point, the first thing we look for is whether we forgot to unlock the gyber before the start. On most occasions we find the gyber locked. After unlocking, we immediately feel a change in the feel of the boat and our pointing ability. We have also done extensive tuning off the racecourse against other top boats testing whether the gyber does or does not work. Our conclusions have been unequivocal that a properly functioning gyber provides a definite benefit. I don't know or care why, but nobody will convince me that a gyber does not work. Whether it is real or just perceived doesn't really matter to me. It just is.

The most important thing to emphasize is that gybers don't win races. This point is proven time and again by our sailing mates Steve and Alan who are the only top boat on our coast who don't use one. They most recently demonstrated in Hawaii that solid foundational sailing skills will time and again trump the best little speed gimmick out there. In spite of this, I think even they are considering a winter upgrade to incorporate a gyber into their program. I am confident to say that we would benefit more from spending the time we fiddle with our gyber actually sailing than we do from the gyber itself. But that is another story.

Joe

 

[Irrational 14]

Once you go with a Gyber, you don't go back. I'm with Joe on this... it's just fundamentally better across the board. We've done our own testing as well - there is a noticeable difference in the right conditions. Somewhat accelerated in proper trim. We've also noticed that the Gybing Board is beneficial on longer legs. Short course stuff, not so much. Sydney and Hawaii are some examples. There are also some drawbacks to the system if not engineered or maintained properly. Overall, it's good to have in your kit. Oh, and thank you SEAHORSE for posting a pic of my boat without asking. Andy - you wanker.

Paul

Team Newport Adhesives & Composites 2011

USA 1168

 

[BalticBandit]

My experience is sailing a non-gybing Bieker in a fleet of other Biekers both gybers and non-gybers.

What I observed was that the gybers tracked roughly the same "course made good" as the non-gybers, but they were "pointed lower" (ie bow down compared to the non-gybers). And this let them make gains in the LULLS. In the lull where I would have to "nose down" to keep flow and speed, they were just able to sheet on the main a bit more and keep speed and height. Thus they would periodically "hop" to weather a bit, AND leg out.

Now here's where I think Hallom is in frog country.

# Hydrodymanic lift is a reaction force, equal and opposite to rig forces. We can't increase lift because we can't power up the sails more, and we can only do that if we can increase righting moment.
He is presuming that "powering up the sails more" necessarily has the same balance of vectors between driving and heeling vectors. This clearly IS NOT the case. If I can sail 45 degrees lower (beam reach) I can ease my sails so that the driving vector is significantly more aligned with my CMG and reduce my heeling vector. If I can do this, I can power up my sail more until the reduced heeling vector is back at equilibrium.

Now if I can point my bow down 3 degrees lower than you can, I DO get a change in the balance of driving vs. heeling vectors - and that gives me the ability to have more power on (and this is what my experience in the lulls against the gybers indicates)

# Leeway doesn't matter. If we were actually concerned with minimising leeway, we would increase appendage area. But we have actually been decreasing appendage size.
Again this presumes something that is not a fact. you can get similar amounts of lift from smaller appendages if your speed is higher. And you do so with a lower price of drag. So raw appendage size is a functional tradeoff of drag, vs lift across a broad range of speeds, so it is a net compromise that has been aimed at the higher speed end of the spectrum. Thus appendage size doesn't tell us squat about the importance of leeway



# Drag from the canoe body is always there. If we can generate some lift by yawing the canoe body (sailing with some leeway), the lift generated
might
be beneficial. "If the rise in drag due to canoe body yaw, for a certain lift force, is less than that produced by the larger foils necessary to produce the same lift force, ..it will pay to produce that lift on the canoe body."

Yes it "might be beneficial" - but again this is a tradeoff between a foil surface optimized for generating lift vs. a canoe body who's lateral resistance is based on purely static drag effects (like pushing a flat plank through the water at an angle). And as we have seen from moths, a lifting foil works far more effectively as a way to combat (and even overcome) leeway, than a full length hull. (and we saw this in the movement away from full keel hulls to high aspect fin keel hulls. So while there still is drag from the canoe body, it is simply surface drag. The leeway drag is reduced, and that is a net drag reduction.



# "Because of its length the canoe body runs at a far lower Froude number than the liftiong foils so that the induced drag caused by any lift it generates may well



be less than a similar amound of lift produced by on the shorter chord foils, which will be running at much higher Froude numbers. It isn't, therefore, altogether unreasonable to expect that canoe body lift is notas inefficient as one might initially think. Indeed, it may well be, comparatively, very efficient.

Ibid my immediately preceding comment. Again the canoe body is not a lifting foil, thus its "lift" comes in the form of turbulent drag at the edges and NOT from any actual induced lift. So the resistance generated by the canoe body is not close to optimized, whereas the foils are. Hallum would be taking a step back from the frog box if he suggested that I-14 planforms would work better if the canoe body itself was shaped like a lifting foil - but we know such shapes are slow



# Gybing boards might offer one advantage. By gybing the main board, the rudder isn't directly downstream of it, so that it is moving out of the downwash and has some separation and is thus starting to work as a bi-plane.

Actually if this is true there is an additional effect here. If indeed the board's slipstream reaches back to the rudder (I'm not convinced it does) then by altering that configuration by a mere 3 or so degrees means you now have a 2 foil system with a slot. And we KNOW that such systems generate more lift than unslotted ones.



# Boats with gybing boards can sheet sails further out = a larger slot. The benefits of a larger slot are unclear.

Again as I discussed above, sheeting sails further out has benefits other than a larger slot. The most significant being that a larger component of the net lifting vector becomes aligned with the CMG of the boat. The secondary effect being that since this means the heeling component is reduced, we can increase the power of those sails until the heeling vector is restored. But that also means an increased driving force

So I think Hallum is doing a lot of "maybe, what if" arm waving. And yes it is true that other fleets with gybing boards have seen them come and go. But there are other issues at play there. The 5oh is limited in board length and aspect ratio by the trunk. Furthermore since it lacks an extending sprit, the ability to automate the gybing/lockout of the board for upwind/offwind increases the complexity of rounding requirements. I don't know how many times we would bear off and forget to lock out the gybing until well down the leg when the skipper noticed control of steering was "clunky". Also retrofitting a 5oh sometimes results in weird stressors on the CB Box because it was not designed to carry those loads at those points

I don't know about other classes that have had gybing boards, but I suspect the 'retrofit' aspects of it are non-trivial as part of why they come and go out of fashion.

Given my druthers, I'd go for a gyber every time

 

[skiffman]

very off topic, but does anyone know how long the courses/races will be at the worlds in weymouth this year? Not so keen if there 2 hour boatspeed races

 

[ADK]

I haven't really gotten around to thinking through all the details enough to be convinced whether or not a gybing board helps and when, etc... However, in the process of building a boat, I don't think it really matters. Unless there's something I'm missing, I don't see why you would build a dagger board case into a new 14 that couldn't accept a gybing board. It's just a rectangular case. The only possible difference is that you'd probably want to reinforce the sides of the case a bit more than if you weren't using a gybing board. I see the following advantages to using a rectangular case (with HDPE inserts for either a gybing or non gybing board):

1) It simplifies the build of the boat by making the case a bit easier to build

2) It allows you to very easily change to a different foil section. If my B3 had been built that way originally, it would have been much easier to fit my current board in it. So much so, in fact that I'm considering cutting out the existing case and putting in a rectangular one.

3) It would allow you to use a gybing board if you wanted.

Maybe I'm missing something, but I don't see any downsides to building the boat that way.

One of the things that I think is really nice about the gybing board setups that I've seen is that they're so simple. Once you have the rectangular case (and even retrofitting that isn't too big a deal), it's just a matter of getting a few pieces of HDPE waterjet cut to shape and bolting them together. I would expect it to be about a $100 conversion - cheaper if you could get a couple boats together and cut several sets of inserts since you'll be running into minimum job charges for the water jet. That's a pretty cost effective modification on a boat where just a new set of foils will run you $1600 or so.

All that said, I really applaud everyone involved in this project for putting the effort into showing that there's no reason a competitive 14 has to be either pre-preg or $50k. I've felt for quite awhile that it would be possible to build a competitive boat with hand layup techniques like they're using but that it would take a world class crew racing it to get anyone to actually believe that it was competitive. Nice work guys!

 

[JimC]

As I've said before I can't see how they can possibly work as advertised. The board must check out at the same angle of attack to the water no matter what. So what you are doing is basically rotating the hull relative to the course of the boat. This must have some effects, at least on a two sail boat.

Look at this pic: the blue boat has the hull rotated 3 degrees compared to the red boat, and the sails sheeted at the same angle to the wind. Look how different the two jibs relationship to the mainsails are... I fdind it hard to believe that will not make a difference.

Incidentally Bethwaite suggests that a gybing board is more likely to move the rudder into the wake of the daggerboard rather than out of it. Who's right, maybe both, there'll be a big "it depends" about it I reckon.

/monthly_02_2011/post-60-065465100%201297369388_thumb.gif

 

[TingTong]

I've had to re-read Seahorse a few times after your post, and then drawn out the vectors etc.. I believe you may be wrong! Beyond the assumptions, which clearly can always be challenged, I see nothing wrong with hOllom's analysis.

DOI i tried a gybing board, having seen the USA boats test and find benefit in them, and spent so long trying unsuccessfully to get it to work that i missed half a summer's sailing and other useful development. They are certainly not the panacea of 14 design. Just ask Archie.

-Now if I can point my bow down 3 degrees lower than you can, I DO get a change in the balance of driving vs. heeling vectors - and that gives me the ability to have more power on (and this is what my experience in the lulls against the gybers indicates)

No you don't. Hard to explain without several pint glasses, a newspaper, and some cough sweets, but the vectors (including course) simply rotate around the hull. You only get the benefit you speak of if your course also alters, ie going onto a reach (many 14 sailors enjoy this, but seldom reach the top mark first).

You may be onto something though. Because the hull rotates relative to these vectors, it may provide a little bit of stability by the bow lifting against the heeling force - essentially it is further from the ballast (in way of the heeling force) than the leeward chine.

Also the sails can be sheeted more aggressively which may or may not be a good thing, though a traveller would achieve just as much.

-Yes it "might be beneficial" - but again this is a tradeoff between a foil surface optimized for generating lift vs. a canoe body who's lateral resistance is based on purely static drag effects (like pushing a flat plank through the water at an angle).

This is exactly his point. What he is trying to do is demonstrate that if the hull is allowed to contribute a small amount of lift, it may do so more efficiently than by adding foil area (or increasing lift coefficient). The curves could intersect anywhere, but your assertion that it MUST be at 0deg hull leeway is unlikely to be true. Of course you require either a gybing board or an infinite selection of daggerboard thicknesses to find the optimum. I think his description of canoe body lift is excellent - clearly a hull moving through the water with some leeway will create lift differently from a plank going sideways.

-Actually if this is true there is an additional effect here. If indeed the board's slipstream reaches back to the rudder (I'm not convinced it does)

of course it does. think how far a rig's slip stream extends. These are big effects, though i hvave no idea if a 3 deg rotation would push you in a good or bad direction...

-then by altering that configuration by a mere 3 or so degrees means you now have a 2 foil system with a slot. And we KNOW that such systems generate more lift than unslotted ones.

Sadly not a slot, as such. The purpose of a slot is to re attach flow to a highly cambered foil system. We're talking biplanes here, not slots.

 

[TingTong]

p.s. I think this boat looks glam. I think aiming for a sustainable price is great, and hope more follow suit.

 

[TingTong]

very off topic, but does anyone know how long the courses/races will be at the worlds in weymouth this year? Not so keen if there 2 hour boatspeed races

if someone knows how to move this and start a new thread, then please feel free.

I am NOT chief organiser or anything (thoiugh i believe i am the USA liaison so please contact me if you need to know anything)

Weymouth can be whatever we want it to be, i suppose. The bay is as good as you can get for a regatta venue. Huge. Sheltered from the prevailing wind and swell. Not too tidal.

With ?100 boats in the fleet i expect the course to be quite large, but nothing silly. There are few directions where it becomes one-sided. From the north (hills) it is shifty, from the south east it is a very slow oscillation, from the south west there are some funnelling effects but a decently placed course will stop it being one sided. If it breezes up too much we can sail inside portland harbour, which is completely sheltered from waves, but typically with a very steady wind. If you want certain death (quite literally) you can sail into portland race, which is perfectly capable of sinking large ships....

Jim saltonstall did some great venue guides, i'm sure there's one for weymouth if you google it.

Essentially, while the beats will be appropriate for the fleet size, all but the likely candidates will have their heads out of the boat and take the escalator up the middle (or slightly left).

Ashore at portland they have all the facilities you's want, but the "soul" is in weymouth. It's a long walk but a pleasant cycle around the harbour. If the yanks bring over a few extra wall-mart beach cruising bikes, i'd happily have one. Most of the socials will be in weymouth, which is packed with pubs etc.. There are even donkey rides on the beach and a high speed ferry to the channel islands if the unique genetics of portland aren't enough for you already.

POW race will be a 2-3 hour boat speed race though, but you can't wimp out on that.

 

[joe.bersch]

The sailing conditions sound great although I understand it is not likely to be warmer than Seattle. If all goes well, B6-H2 Hull Number 1 will be in Weymouth. This depends only on whether we can get enough US boats to fill a container. There are at least four spots open in the container. Anyone want a B6 delivered to Weymouth?

 

[SimonN]

You can write as much theory as you like, but simple 2 boat testing tells the true story. I have fitted gybing boards to a number of dinghies and have tested those boats both with the boards gybing and the boards locked. I have always found that having the board gybing produces the faster boat. I don't care how people want to try to rationalise it, I wil, always sail with a gybing board in a dinghy if it is allowed by class rules.

I do have a theory as to why these things yo yo about. Take the 14's, as an example. I believe that the Americans were totally convinced by gybing boards, but Archie isn't. Just because Archie has won the last 2 worlds doesn't mean he is right. I have watched Archie sail and train and I am sorry to say he is in a different league at the moment. He doesn't actually need the fastest boat to win. The fact that his total package is probably the fastest around also doesn't mean it wouldn't be faster with a gybing board. However, people use this as evidence that gybing boards aren't a panacea. Of course they aren't. For starters, it is far easier to make a gybing board that doesn't work than one that does. You cannot simply take an existing board section and profile and make it gybe. Next, even when you do get it right, it probably won't gain you much more than you would lose in 1 bad tack. Archie loses less than anybody tacking! But I can tell you from personal experience that in some classes, the difference between top 2 or 3 at the windward mark and 20th is a matter of metres and that is when every little bit helps, and I usually need all the help i can get because I don't have the natural talent of somebody like Archie. And until I do, I will stick with gybing boards.

And finally, consider this. If you were building a boat that only had to sail on 1 tack, you would build it with an assymetric c/board. A gybing board gives you a very similar effect. In fact, if you look at C Class cats, they do use assymetric boards and pull the windward one up. On C's, when you change from symetrical to assymetrical foils, you have to move the board further forward because the reduction in leeway means you don't have the bow contributing as much to the prevention of side slip. Something must be working!

 

[mark1234]

So, here's a somewhat non-sequitur observation. With the exception of ones that are designed to work well upside down, pretty much every aeroplane in the world sets the main wings at about +4degrees to the fuselage line - because that's (typically) the optimal AOA to get the wing into the best L/D 'bucket', hence what they fly in cruise. They *could* also derive lift from having the fuselage(body) at a small AOA, but don't, and they tend to care rather about efficiency. It's kinda equivalent to the 'one tack' boat above.

With no figures to back it up, my gut suggests that the average dagger/centreboard is working at pretty low AOA, therefore there's likely to be a win in running a smaller foil at a higher AOA, irrespective of where the hull part is pointed. A smaller foil will also (usually) be shorter, bringing the centre of lateral resistance up, and closer to the centre of effort - thereby reducing the heeling moment arm, and letting you live with a bit more grunt from the bits in the air. Most of the boats I've decent experience of (RS600, 49er, 18's) work better with the board somewhat 'up' in a breeze even upwind, both due to reduced heeling moment, and the reduced drag.

 

[Daniel Holman]

Haven't read the seahorse article, but wrote a spiel in (hopefully) plain english about why they work on the DC Canoe thread a couple years in a previous incarnation as "Danny Boy."

http://forums.sailinganarchy.com/index.php?showtopic=65915&st=125

It goes without saying that the gybing board is a small piece of the bigger technical pie with the 14, and a gyber is caught in the noise of variance in gear and sailing ability until you reach the pinnacle. Apart from the pegasus program from a few years back it is unlikely that it has been possible to control these variables sufficiently to see a difference.

As another post mentions, being able to set / quantify / adjust it correctly would be pretty important to its success.

Also a very valid point was made with regards length / complexity of course sailed - prob not worth having if crash and burn short course racing.

I have a 50% mature 14 design and were I building one, FWIW I would have a gyber in a heartbeat.

Although I imagine that for a long time my I14 sailing sailing skills would let me down. Even more than David Hollom's.

Dan

 

[Daniel Holman]

Post #146 BTW.

Mark 1234 you are right on - about 3-4 deg sees the foils in the optimum tradeoff between frictional drag (reduces with reduction in foil area) and induced drag (increases with reduction in foil area). The plane fuselage would want to be at 0 deg to incidence, else it would be inducing drag.

Lifting the dagger / cb on a "fast" boat in breeze works because

1) "fast" trap boats respond to sailing faster once overpowered, therefoe you need to reduce area to keep the foils working at optimim Cl, else they will be working at, say 2 deg leeway and suffering a WSA penalty.

2) This also shifts CLR aft which helps balance things up when the sails are feathering and effectively shifting Cp and therefore CoE aft.

3) Brings CLR upwards a little which means that you can generate more sail force (thus driving force) for a given righting moment.

"slow" hiking boats which work best with the "stab and flap" style of sailing in breeze go at the same speed once powered up regardless of breeze, so since RM is the same once powered they work best without lifting the dagger. Sometimes it helps to lift a Centreboard a bit though - as 2) above, mitigates the weather helm brought about by the CoE moving aft as the sails feather (esp bad on a una rig)

Dan

 

[BalticBandit]

-Now if I can point my bow down 3 degrees lower than you can, I DO get a change in the balance of driving vs. heeling vectors - and that gives me the ability to have more power on (and this is what my experience in the lulls against the gybers indicates)

No you don't. Hard to explain without several pint glasses, a newspaper, and some cough sweets, but the vectors (including course) simply rotate around the hull. You only get the benefit you speak of if your course also alters, ie going onto a reach (many 14 sailors enjoy this, but seldom reach the top mark first).

no the vectors don't quite rotate. Because you ease the sail. this has two effects. First just easing sheets changes the SHAPE of the sail. Softsails get fuller (ie thicker chord) when you ease the sails. - And by itself, that would be an advantage. But that's not the only benefit.

 

for sails the lift vector hovers around 60deg to the planar angle of the sail. With an AoA of 30deg (again these are approximations, varies from sail to sail wind etc.) to the Apparent wind, your actual singleton lift force vector operates at about 120deg to the TwA (90deg Awa). Upwind the lateral resistance of the hull lets us break this down into

• a normalized Drive vector D Length 1 , (L x cos(60))
  
• a Summed normalized Vector L length 2 that is the true lift vector,
  
• a normalized heeling vector H length SRT(3) =1.73. (L x sin(60))
  

Now on a close reach, the AWA on the sail is still 30deg, but the AwA on the hull is now around 60deg. The lateral resistance now lets us break this down into:

• a normalized vector D Length SQRT(3) driving the boat,
  
• a Summed normalized Vector L length 2 that is the true lift vector,
  
• a normalized heeling vector H length 1.
  

So by sailing the boat LOWER by 30 degrees, the heeling vector gets reduced by 43%... and this is obvious because when we crack off and ease sails, we can't trap as hard...

 

Ok so if we could increase the power of our sails on the close reach by 43%, we now would trap just as hard, but have about 240% of the drive power that we have close hauled and trapping equally hard.

 

SO if instead we crack off 5 degrees, so our AWA on the sail is still 30 deg. but our boat's angle is 5 degrees lower. So the Heeling vector is now 11% less and our drive vector is 14% greater.

• a normalized Drive vector D Length 1.14 , (L x cos(55))
  
• a Summed normalized Vector L length 2 that is the true lift vector,
  
• a normalized heeling vector H length 1.63. (L x sin(55))
  

So if the gybing board lets the hull sail 5 degrees lower and generate the same amount of lateral resistance, we can power up the sails an additional 6% ON TOP of the improved drive.

 

Now in practice we are looking at more like a 3% difference in angles and the geometry is a bit more complex, but you get the ideal.

 

-Yes it "might be beneficial" - but again this is a tradeoff between a foil surface optimized for generating lift vs. a canoe body who's lateral resistance is based on purely static drag effects (like pushing a flat plank through the water at an angle).

This is exactly his point. What he is trying to do is demonstrate that if the hull is allowed to contribute a small amount of lift, it may do so more efficiently than by adding foil area (or increasing lift coefficient).

And he is wrong. Because absent a gybing board, there is no such tradeoff available. With a non-gybing board, the lateral contribution of the hull is fixed.

Sadly not a slot, as such. The purpose of a slot is to re attach flow to a highly cambered foil system. We're talking biplanes here, not slots.

Um no. the purpose of a slot is to reduce the rate of decelleration of flow on the latter part of the foil, and thus allow a longer period of high speed flow over the leading element. By injecting flow into the low pressure side, you increase pressure without dropping flow speed, and thus you generate more lift on the leading element.

 

[solosailor]

What the hell is going on here.....! Great technical explanations, ideas/theories, solid arguments and examples to back up each and no name calling nor asinine comments. I don't think I can handle this thread.

 

[TingTong]

I'm not trying to disagree here, just trying to understand what might be going on. If i understand something i'm more likely to get some benefit from it...

I get the idea of the heeling force rotating forward. Same total magnitude though, so the reaction must come from somewhere. There must be a greater separation between the ballast (crew) and the reactionary lift from the hull - crew can't move, so hull lift must move forward. Anyway, unless you have fried my brain with your evil maths, this is the closest i have seen to an adequate explanation of the main source of benefit of a gybing board.

Not so sure about fuller sails - this is achievable anyway, if needed.

I still find hollom's analysis very useful, and am sure 0deg yaw cannot be optimal. As you say, a gybing board is a good way of finding this, but it may be achievable without - perhaps trying a longer, thinner board for example (or copying someone else who has). I wouldn't say the lift from the hull is fixed. It will vary with speed (Fn, planing/non-planing), height of board etc., in fact it is rather unfixed - best way to fix it is to adjust your gybing board to maintain a constant yaw of 0deg / no lift.

I saw too much gynae today to think more about slots, but i'm sure you're right, though at those separations isn't the d/b's effect on the rudder going to be more signifiant than vice versa?

Anyway, it doesn't matter, i'll have you all with my trim tab... Should be ready to go in a few weeks (yes, the board is specially (but basically) designed for it.

p.s has anyone heard of gybing boards being used in cat rigged monohulls? Might help quantify the perceived benefit in a wider slot (sorry).

 

[TingTong]

What the hell is going on here.....! Great technical explanations, ideas/theories, solid arguments and examples to back up each and no name calling nor asinine comments. I don't think I can handle this thread.

last time i bothered with this site is soon left. i rejoined under a different (secret) name since it looked like it had grown up a bit. if people cant be honest (even if critical) or civil then we'd all be better off having a fight down the pub (which i would lose). the old slagging matches were no good to anyone, even if that was the main aim.

To maintain an off -thread theme. I will shortly be forwarding more info (official and unofficial) about the Weymouth Worlds to all the USA emails that i have and ask them to cascade further.