Meat Wad

Will they actually sail like the 3d animations?

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I doubt it. Yea, I do not care if this is in another thread..
It all looks and sounds great but what about "Match Racing"
What happens in a down speed tacking duel? or gybing duel?

Seems pretty wishful
 

 

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What I want to know is how the front boat covers the back boat up wind with these apparent wing monsters?

If you are covering on a tack and you then both tack the front boat can no longer cover? as it needs to be almost directly in front of the trailing boat?

As it was after the no look tack when OR rounded the first mark ahead.

So bye bye to tacking duels.

And yes they will sail almost exactly as their 3D animation.  Just they wont be sailed that way !?!

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19 minutes ago, Kiwing said:

What I want to know is how the front boat covers the back boat up wind with these apparent wing monsters?

If you are covering on a tack and you then both tack the front boat can no longer cover? as it needs to be almost directly in front of the trailing boat?

As it was after the no look tack when OR rounded the first mark ahead.

So bye bye to tacking duels.

WTF are you on about?Being directly in front of the trailing boat isn't where you need to be to cover. Upwind, it works exactly like conventional boats.

They won't sail anything like the video shows. If they are foiling upwind, they won't need or be able to fly the kites downwind as the apparent wind will be too far forward. Just like with the AC45's, we will only see the kites in light winds.

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^ It will be really interesting to see what the upwind foiling threshold is - if it happens.

OTOH, even without full foiling upwind, they will certainly be planing due to light weight and massive righting moment that increases with speed, so VMG should be impressive.

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1 hour ago, A Class Sailor said:

WTF are you on about?Being directly in front of the trailing boat isn't where you need to be to cover. Upwind, it works exactly like conventional boats

Please is this not true ?

 

Tacking.jpg

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3 hours ago, Kiwing said:

What I want to know is how the front boat covers the back boat up wind with these apparent wing monsters?

If you are covering on a tack and you then both tack the front boat can no longer cover? as it needs to be almost directly in front of the trailing boat?

As it was after the no look tack when OR rounded the first mark ahead.

So bye bye to tacking duels.

And yes they will sail almost exactly as their 3D animation.  Just they wont be sailed that way !?!

The wake trails at the apparent wind angle, so covering is no different than for the foiling cats.  You want to be to windward and ahead of your competition when going upwind.  Downwind, you can blanket your competition when you are ahead and to windward of their course.  .

I used to race a landyacht on the dry lakes of the Mohave Desert, and they presented a very neat demonstration of this effect.  The dust kicked up by the wheels would get entrained in the bottom vortex from the rig, so you could see the vortex being laid down by the yacht.  The vortex would sweep sideways over the ground, drifting with the true wind.  The yacht was laying down the head of the vortex at the speed of the yacht.  So the net effect was the vortex trailed from the yacht at the apparent wind angle.  From the perspective of the pilot, it did look like the dust was blowing back with the apparent wind.  But from the perspective of someone standing on the ground, the dust blew with the true wind and it was different dust coming off the wheel.

If you are directly to windward of your competition, they will be to leeward of your wake.  It may make sense to foot so as to draw ahead and place your wake on top of them.  Then you can resume Vmg sailing while gassing them.  If they stay with you.  They'll probably tack to clear their air.  

Tacking duels are still important.  It depends on how badly you want to defend your position.  If the advantage the competition can gain by splitting is small and the loss in tacking is large, then a tacking duel doesn't make sense.  When the course is narrow, there's not that much difference in wind between the two sides and the boats can't get a lot of leverage before they have to tack away from the boundary.  So it's better to let them go and just bounce off the boundary to meet them again.  But we saw in AC35 that the tacking in the AC50s was getting very good, so the boats could take advantage of small differences in pressure on one side vs the other.  As a result, they started to have tacking duels again.  If the course is wider, then it becomes more important not to let your competition split from you, and tacking duels become important even with a somewhat slower tacking boat.

It will be interesting to see how fast the AC75 supplied foil cant system moves the foils.  The AC50's could drop their foils very quickly.  The huge mass of the AC75 foils will need a lot of damping from the control system, and the battery capacity has to last the entire race.  As a result, the FCS may move the foils comparatively slowly. That's going to have a big impact on what the tacking performance will be.

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^ Thank you, much clearer.

So slow tacks, might be the suppressor of tacking duels. Although dropping a foil before tacking might speed things up?

And wide courses might encourage them.

Prediction on how close software will foretell performance?

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^

We will never know but I am guessing they will do better than most people think !?!

I guess if they fall off the foils often then they have not performed up to software predictions and I guess there will be lots of foxing particularly early on.

It will be interesting to see what NYYC bring to the table with all the USA resources in high performance foils in air and in water !?!

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5 hours ago, Kiwing said:

...It will be interesting to see what NYYC bring to the table with all the USA resources in high performance foils in air and in water !?!

There's not a lot of US technology in the NYYC challenge.  The Design Team is located in Spain and, AFAIK, all the lead personnel are European.  Some of the members are formerly from OTUSA, but I don't believe any of the OTUSA foil designers are on the team, at least not with regard to the hydrodynamics.  Some of the structural designers may be from OTUSA.  It's possible they may look to Airbus for help, but I think there's been a change in leadership at Airbus and I don't know if they are still interested in getting involved with the America's Cup.  I'd be very surprised if any of the US airframers got involved with NYYC.

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9 hours ago, Basiliscus said:

There's not a lot of US technology in the NYYC challenge.  The Design Team is located in Spain and, AFAIK, all the lead personnel are European.  Some of the members are formerly from OTUSA, but I don't believe any of the OTUSA foil designers are on the team, at least not with regard to the hydrodynamics.  Some of the structural designers may be from OTUSA.  It's possible they may look to Airbus for help, but I think there's been a change in leadership at Airbus and I don't know if they are still interested in getting involved with the America's Cup.  I'd be very surprised if any of the US airframers got involved with NYYC.

Yeah, it must have been a shock being equaled or bettered by some made-up on the spot software from Kiwistan. That can't have sat well.

Makes you wonder, maybe ETNZ should quit the AC and design planes instead?

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On 4/8/2018 at 2:50 PM, Kiwing said:

Please is this not true ?

 

Tacking.jpg

Your drawings are not very realistic. With the conventional yachts, the windward boat is not bow forward enough to be properly covering. The faster the boat goes, the more you need to be ahead, but upwind, it's not that much different because of the relative low delta between true and apparent. Downwind, it's as described by Basiliscus. Upwind, tacking battles can still happen but it will all depend on how much is lost in a tack. The faster these boats tack, the better chance of tacking battles. That is a far more significant factor than re-establishing close cover, which, if lost by the windward boat because the leeward boat gets a bit bow forward is easier to re-establish because of the speed gains from footing off slightly that aren't seen on slow leadmines.

 

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If the boats can look as good, or better than these bad boys look, I'll be happy.

 

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On 4/8/2018 at 11:34 AM, Meat Wad said:

I doubt it. Yea, I do not care if this is in another thread..
It all looks and sounds great but what about "Match Racing"
What happens in a down speed tacking duel? or gybing duel?

Seems pretty wishful
 

 

Hmm..

 

AC72s and AC50s didn't use Code zeros/ downwind sails. If these boats are as fast as we are told they will be, then they won't use them either.

 

Another vote for "I doubt it",.

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10 hours ago, sclarke said:

If the boats can look as good, or better than these bad boys look, I'll be happy.

 

Cool vids, I remember seeing them. But are these foils are totally different than the AC stuff?? It seems they are just there for stability lifting?

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57 minutes ago, Meat Wad said:

Cool vids, I remember seeing them. But are these foils are totally different than the AC stuff?? It seems they are just there for stability lifting?

Completely different. The foils are designed to prevent leeway, and provide lift and stability to leeward which is why Hugo Boss struggled once she broke her starboard foil. Still very cool. The 75's will (or should) perform more like a moth. It remains to be seen whether they will actually perform that way, but hopefully they can look as cool as the foiling IMOCA's.

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23 hours ago, sclarke said:

If the boats can look as good, or better than these bad boys look, I'll be happy.

 

a human will be steering instead of a computer...and yes, i think they will kick his ass in that much wind.

but yes, a great boat and vidy, thx!!!

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On 4/9/2018 at 11:44 AM, nav said:

Yeah, it must have been a shock being equaled or bettered by some made-up on the spot software from Kiwistan. That can't have sat well.

Makes you wonder, maybe ETNZ should quit the AC and design planes instead?

I thought the software came from Italistan? ;)

WetHog  :ph34r:

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On 4/9/2018 at 1:32 PM, Kiwing said:

Hull performance when healed to windward ???

Can it be made to work ??

heal to windward-page001.jpg

You're not taking it far enough.  The Design Rule makes no distinction between gravity and hydrodynamic down force on the windward foil.  It says the foil can only produce down force when fully down, fully up, or moving to a commanded position.  So take the windward heel further until the windward wing digs in while in the fully raised position.  Then the vertical lift comes from the wing, shaft of the leeward foil and rig, while the windward wing is producing side force and down force for additional heeling moment.  It's not clear from the Rule whether the teams will be able to tailor just what the fully raised position is, but they may be able to insert a mechanical stop to make the fully raised position favorable for creating additional heeling moment.

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It's going to be exactly the same. Actually, they will fail to build physical boats, so they will just sail simulators against each other, and it will be that same simulator!

I am interested in seeing what really happens. I hope no one gets killed.

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^ Just in case it was missed, Bernasconi made it pretty clear in that recent dodgy 'video' that the reason they had switched to pivoting foils rather than cased foils was to reduce the chance of serious crew damage.

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On 4/12/2018 at 2:10 AM, WetHog said:

I thought the software came from Italistan? ;)

WetHog  :ph34r:

five year old code base maybe

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On 4/7/2018 at 9:34 PM, Meat Wad said:

I doubt it. Yea, I do not care if this is in another thread..
It all looks and sounds great but what about "Match Racing"
What happens in a down speed tacking duel? or gybing duel?

Seems pretty wishful
 

 

Related image

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On 14/04/2018 at 5:02 PM, Basiliscus said:

You're not taking it far enough.  The Design Rule makes no distinction between gravity and hydrodynamic down force on the windward foil.  It says the foil can only produce down force when fully down, fully up, or moving to a commanded position.  So take the windward heel further until the windward wing digs in while in the fully raised position.  Then the vertical lift comes from the wing, shaft of the leeward foil and rig, while the windward wing is producing side force and down force for additional heeling moment.  It's not clear from the Rule whether the teams will be able to tailor just what the fully raised position is, but they may be able to insert a mechanical stop to make the fully raised position favorable for creating additional heeling moment.

5ae02a0596b98_Healing30towindward.thumb.jpg.0779f0069d455bd4dbabea068d7bba56.jpg How is this to talk about.

@Basiliscus  I will have to think long and hard to visualize what you are suggesting but am I on the right track?

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Yes, that's what I had in mind.

Now, consider what it looks like if the windward foil isn't raised so high - more of it will be in the water and it will be more effective.  Probably immersed up to the arm/wing junction would be best.  The Rule doesn't allow for much positive dihedral in the wing, but giving it as much as possible allowed by the envelope would help to generate more downforce.

AFAIK, there is no definition in the Rule of just what the maximum cant angle is.  The Rule only talks about downforce being allowed when the foil is at max [26.4(a)].  The Rule also says mechanical stops are permitted [20.2(ii)].  So, if one inserted a mechanical stop (which may need to be movable to meet the requirement of 12.7(b)), one could reduce the maximum cant angle.  That would allow less windward heel and move the leeward foil more to leeward for better righting moment.  Less heel also puts the stern foil deeper in the water.

The leeward foil can be set at any angle because it creates an upward force.  So the FCS can be commanded to put the leeward foil at its optimum position, whether that be with the wing horizontal or with more cant so the leeward wing contributes to side force.  It sounds crazy, but if the leeward wing were given less cant than horizontal, it would create a side force to leeward, requiring more side force to be generated by the windward foil and thus more downforce from the windward foil and more righting moment.  Whether this makes any sense at all would have to be determined by the VPP.

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5ae16761dcac6_healing30degtowindward.thumb.jpg.d708aeb07149d3ad21e5ac0786ca8584.jpgHow am I going.

Windward foil forces, Lee foil forces, rudder shaft forces, rudder foil forces all hydrodynamic forces (black)

sail forces (red), Gravity (green)  Not a lot of thought as to size but am I making progress?

 

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That is a cool notion, could they then do a scow hull and create a long flat touch down section in the hull for the full length of the boat for skimming/touch down and almost planning/liftoff mode.

Even further, could they then cant the rig to leeward Moth style as a form of control of this heel position or to achieve the best rig angle to the wind?

Between the adjustable foils and potentially canting rig they could create quite different modes of sailing to windward.

Crazy, or a potential reality?

AC windward heel1.jpg

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The sailrocket is still holding the record for the fastest sail boat, we are getting there...

Interesting theory anyway, quite difficult to determine if it's really an interesting configuration. In addition it looks good on paper and probably on flat water, but the venue is unlikely to provide such flat water thus the submerged height will vary/oscillate with time in the configuration drawed.

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Would sail shape be equally effective for windward/leeward heel?  Designing a sail around penetrating the oncoming air rather than pushing against it seems to call for different and potentially conflicting pressures.

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10 hours ago, Kiwing said:

5ae16761dcac6_healing30degtowindward.thumb.jpg.d708aeb07149d3ad21e5ac0786ca8584.jpgHow am I going.

Windward foil forces, Lee foil forces, rudder shaft forces, rudder foil forces all hydrodynamic forces (black)

sail forces (red), Gravity (green)  Not a lot of thought as to size but am I making progress?

 

Yes, although the force on the stern wing could be downward instead of upward.  It depends on where the c.g. is and how much pitching moment is created by the rig. 

I think you have the heel angle exaggerated, though.  If you consider the intersection of the arm and the 3.5 m circle, the c.g. of the foil and arm will be near that location and there's no point in raising that point higher than the arm pivot point, because that gives the maximum righting moment when the boat is upright.  I'd use that as the baseline max cant angle.  That should let you take out 15 deg or so of heel.  You should also put the pivots at the same height in the hull, and that will take out a little more heel.

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On 4/25/2018 at 8:13 AM, Kiwing said:

5ae02a0596b98_Healing30towindward.thumb.jpg.0779f0069d455bd4dbabea068d7bba56.jpg How is this to talk about.

@Basiliscus  I will have to think long and hard to visualize what you are suggesting but am I on the right track?

That would just look so awesome.

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They look ridiculous, and it won't be a quick fix if you hit something with those foils.

Looks like the worst of both worlds to me.

What was the point of changing from foiling cats again?

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What I don't get is stability at zero or near zero speed, unless those foils are reaaaallly heavy.

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On 27/04/2018 at 4:47 AM, Basiliscus said:

Yes, although the force on the stern wing could be downward instead of upward.  It depends on where the c.g. is and how much pitching moment is created by the rig. 

......

My limited thought would be that, due to the disaster of nose diving, they would balanced back with slightly more up force on the aft foil so as to have more down force available and allow the lee foil to be slightly more forward.  I guess at max speed everything neutral so less than max speed, slight up force on the aft foil ????  Have I got that right?

There is also a very controllable lee foil with righting moment and pinching upwind ability ???

Will these sails be as powerful as the wings on the AC50s were? Hence spare power to lift like sailrocket?

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On 4/26/2018 at 5:50 PM, Kiwing said:

5ae16761dcac6_healing30degtowindward.thumb.jpg.d708aeb07149d3ad21e5ac0786ca8584.jpgHow am I going.

Windward foil forces, Lee foil forces, rudder shaft forces, rudder foil forces all hydrodynamic forces (black)

sail forces (red), Gravity (green)  Not a lot of thought as to size but am I making progress?

 

So @surfsailor If you draw the sea level up and down on my diagram and rotate slightly various elements we are talking about this crucial transition are we not?

IMHO it is this transition that will determine the result of this round.  Moth sailors will have the most experience with this sort of sailing and it would be very interesting to hear their input.

Everything trying to get the boat hull out of the water,

Then a manageable Transition to only one foil in the water.

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21 minutes ago, Kiwing said:

So @surfsailor If you draw the sea level up and down on my diagram and rotate slightly various elements we are talking about this crucial transition are we not?

IMHO it is this transition that will determine the result of this round.  Moth sailors will have the most experience with this sort of sailing and it would be very interesting to hear their input.

Everything trying to get the boat hull out of the water,

Then a manageable Transition to only one foil in the water.

Nice drawing. My two comments are 1) I'd expect the rudder foil contribution to be much smaller as a percentage of the total, and  2) the leeward foil would already be canted to reduce leeway - this would increase the force generated by the rig, so both more lifting force (heave) and more drive coming from the sail. But as I noted in the other thread, there are so many possibilities and permutations that - until you run the models in anger - it's really hard to guess, beyond the fact that normal leeward heel will almost never be happening. There may well be counter-intuitive solutions that turn out to work. Really exciting stuff.

 

 

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Have any of you guys ever ridden a tricycle? They are diabolocally unstable. Any roll induces pitch variations.

Issue 1: These boats with three foils will be like tricycles. Even with only two in the water they will behave the same as tricycles.  Any roll will induce pitch variations and in the case of foiling, pitch variations will mean big issues with height control. Rolling to leeward will increase AoA of all foils and the boat will leap upward, the reverse for a roll to windward.

Issue 2: If they are sailed at fixed heal angles like moths, there are pitch implications from steering. Luffing induces a bow down pitch because the tilted rudder adds lift aft. bearing away induces a bow up pitch for the reverse reason. On moths its manageable, on the big boats maybe not.

Issue 3: If the boats are sailed healed the transition from healing one way to the other while tacking or gybing, brings out all the problems from Issue 1.

They will not have computers and powerful drives to retrim everything automatically during manoevres so I think the sailors will be making sure that the boats will be sailed plumb upright.

 

Separate issue, Windward down thrust from foil: All vertcal forces from foils induce drag. Adding downforce adds drag not only from the windward foil but since the leeward foil has to increase its lift by the equivalent value, its drag is also significantly increased. So the total drag goes up, maybe doubles. Big issues when you are looking for speed.   Secondly these boats will be sailed in waves, and having a windward foil close to the surface looks like a huge problem, if it gets close enough to ventilate, all downforce will be lost and the boat will capsize very rapidly.

 

I have a few doubts about the announced design concept but I think the people who dreamed it up know a lot more about it than any of us, they have the modelling, the numbers and have spent a lot more time on it. I think the boats might look and sail a lot like the graphic simulations released months ago.

 

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On 4/26/2018 at 6:13 PM, Lowgroove said:

That is a cool notion, could they then do a scow hull and create a long flat touch down section in the hull for the full length of the boat for skimming/touch down and almost planning/liftoff mode.

Even further, could they then cant the rig to leeward Moth style as a form of control of this heel position or to achieve the best rig angle to the wind?

Between the adjustable foils and potentially canting rig they could create quite different modes of sailing to windward.

Crazy, or a potential reality?

AC windward heel1.jpg

I think the idea of sailing it like a Moth is fanciful.  The Moth has a crew weight which is about twice the weight of the boat and has zero form stability so the crew can set the heel angle to anything they like.

The AC75 has a miniscule crew weight compared to the boat and it has relatively high form stability so if the crew hike out in a zero wind situation the heel to windward would be a few degrees at most.  This means that to achieve a significant heel to windward we would be entirely dependent on the foils which require the boat to be moving forward at speed.  We now have a situation of no form stability and a dynamic set of forces and reactions depending on the variability of the wind and the waves.  Unlike the Moth moving the crew about will have very little effect on the balance of forces so we are totally dependent on the control system .. good luck with that.

 

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@Phil S Thank you I can get your several points, which are all challenging.

However I am looking in Left Field for some ways to foil early which might be very risky but if you can get foiling early it would seem a huge advantage worth taking the risk for.

Where ETNZ got their winning advantage from last time?

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@Terry Hollis I am talking about the transition from non-foiling mode to foiling.  Trying to get the boat out of the water as a first stage to getting up on two foils then onto one with apparent wind increase.

Getting foiling early is a game changer? Right?

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22 minutes ago, Phil S said:

Have any of you guys ever ridden a tricycle? They are diabolocally unstable. Any roll induces pitch variations.

Issue 1: These boats with three foils will be like tricycles. Even with only two in the water they will behave the same as tricycles.  Any roll will induce pitch variations and in the case of foiling, pitch variations will mean big issues with height control. Rolling to leeward will increase AoA of all foils and the boat will leap upward, the reverse for a roll to windward.

Issue 2: If they are sailed at fixed heal angles like moths, there are pitch implications from steering. Luffing induces a bow down pitch because the tilted rudder adds lift aft. bearing away induces a bow up pitch for the reverse reason. On moths its manageable, on the big boats maybe not.

Issue 3: If the boats are sailed healed the transition from healing one way to the other while tacking or gybing, brings out all the problems from Issue 1.

They will not have computers and powerful drives to retrim everything automatically during manoevres so I think the sailors will be making sure that the boats will be sailed plumb upright.

 

Separate issue, Windward down thrust from foil: All vertcal forces from foils induce drag. Adding downforce adds drag not only from the windward foil but since the leeward foil has to increase its lift by the equivalent value, its drag is also significantly increased. So the total drag goes up, maybe doubles. Big issues when you are looking for speed.   Secondly these boats will be sailed in waves, and having a windward foil close to the surface looks like a huge problem, if it gets close enough to ventilate, all downforce will be lost and the boat will capsize very rapidly.

 

I have a few doubts about the announced design concept but I think the people who dreamed it up know a lot more about it than any of us, they have the modelling, the numbers and have spent a lot more time on it. I think the boats might look and sail a lot like the graphic simulations released months ago.

 

All great and interesting points, but we were discussing the takeoff transition, not steady-state foiling. Generating downforce with the windward foil would only be of value at low, sub-planing speeds - the boats are stability challenged (since there's no keel) so to my mind it makes sense to use every tool in the box to generate as much power from the rig as possible. With the hull in the water, the drag penalty for the induced additional displacement (from the foil downforce) will be relatively low, plus some of that downforce will be mitigated by the vertical component of the lift generated by the windward canted rig. As speed comes up, the both the heave and righting moment of the leeward foil will increase - the flap on the windward foil can be eased, and the boat should lift/rotate upwards around an axis defined by the CL of the leeward foil. In that scenario, turning downwind a little to coax the boat to launch will also momentarily increase the pitch because of the rudder cant, which will also facilitate launch. At some point, the windward foil and hull should be high and dry, and it's game on.

During steady-state foiling, I'm sure the windward foil will be raised, just like the graphic presentation. But I can still envision windward heel in lighter winds, especially going upwind - it unloads the leeward foil.

 

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1 hour ago, Terry Hollis said:

I think the idea of sailing it like a Moth is fanciful.  The Moth has a crew weight which is about twice the weight of the boat and has zero form stability so the crew can set the heel angle to anything they like.

The AC75 has a miniscule crew weight compared to the boat and it has relatively high form stability so if the crew hike out in a zero wind situation the heel to windward would be a few degrees at most.  This means that to achieve a significant heel to windward we would be entirely dependent on the foils which require the boat to be moving forward at speed.  We now have a situation of no form stability and a dynamic set of forces and reactions depending on the variability of the wind and the waves.  Unlike the Moth moving the crew about will have very little effect on the balance of forces so we are totally dependent on the control system .. good luck with that.

 

I think you are most likely 100% right, but trying to stay on the fanciful angle and ruling out crew weight as the major tool for creating the windward heal is there any chance that the following could happen.

So, the boat sailing to windward just transitioning from skimming and launching to foiling at say 15knots, both foils down and close to lift off, then at a yet to be determined speed, height and so on they start to lower the rig to leeward, whilst lifting the windward foil , maybe even having the mast on a track letting the base come to windward( a step too far maybe :)) could the leeward foil, the new mast base load direction, a windward foil flap control to create negative lift then create a rolling effect in heal of the hull and roll the whole schabang to windward moth style! Then a flat planing surface in the hull shape assists in planing/touchdown/foiling crossover whilst in this mode.

Yes I know, total rubbish and no chance but more than ever there could be some really crazy thinking(not from any of us) that comes up with a sailing mode on these boats that kicks ass and is totally out of the box and likely be a complete mind fuck to get the head around.

The whole boat has me pretty confused, can't wait to see what the hell happens on the water and what the design teams can come up with.

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On all foiling boats the ability to start foiling happens earlier (in less wind) when reaching than when working or running, just because the boat can go faster.  So when there is just enough wind you need to begin to reach to initiate foiling. Once foiling its relaitively easy to go where you want to, either upwind or downwind.

So the skipper needs to make  a decision when foiling is possible, bear away from a working lowriding course to a reach and take off after which a new much faster close hauled will be possible.  You rarely take off when close hauled unless its pretty windy and flatvwater. Even after a moth foiling tack a bear away is needed to build speed again.

My point is that there is no "transition from skimming to foiling while going to windward"

I still have concerns that in even moderate conditions, these boats will have difficulty getting enough speed with the hull in the water to take off. There just seems to be too much wetted surface and at low speed insufficient righting moment to power up the rig. The righting moment does not get big until both the hull and windward foil is out of the water. I still see the option of high power tenders towing the boats up to speed pre prep sygnal, then it would simply become a battle to see who can make an opponent crash off the foils.

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7 hours ago, surfsailor said:

Generating downforce with the windward foil would only be of value at low, sub-planing speeds…

You've got it backwards. At pre–foiling speeds, they will be able to generate all the RM they need by canting the leeward foil outward. Once foiling and the leeward foil has maxed its RM contribution, then it makes sense to look at adding RM from the windward foil.

I agree with Phil, these will likely be sailed flat, there's no reason to heel to windward. Moths and sailboards must heel to windward, it's a physical impossibility not to (except when going downwind or in very light conditions).

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1 hour ago, Phil S said:

 

My point is that there is no "transition from skimming to foiling while going to windward"

 

Yet that is exactly what OR's AC72 started doing on the windward legs in the second half of AC 34. I think you are underestimating the raw power and intrinsic dynamics of really big boats. Having said that, the extreme efficiency of the wings - especially at narrow angles of attack - will be very difficult to match with the rigs they've specified.

1 hour ago, Phil S said:

I still have concerns that in even moderate conditions, these boats will have difficulty getting enough speed with the hull in the water to take off. There just seems to be too much wetted surface and at low speed insufficient righting moment to power up the rig. The righting moment does not get big until both the hull and windward foil is out of the water. I still see the option of high power tenders towing the boats up to speed pre prep sygnal, then it would simply become a battle to see who can make an opponent crash off the foils.

The windward foil can be lifted at any time - meanwhile the hull will gradually unload (and unwet) as more and more of the boats total mass is born by the leeward foil. Lift increases with the square of velocity, so for example as the boat accelerates from 4-8 kts, the lift on the outside foil - and by extension, both the heave and the righting moment - increase by a factor of 4. (that's assuming the cant of the leeward foil remains constant). The lift coefficient can also be increased via the flaps. So you can see how - with both raw horsepower and lift increasing exponentially with speed, and wetted surface being shed - the boat could quickly transition to foiling, even at a relatively tight angles. As I noted above, the biggest constraining factor will be the rig. 

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26 minutes ago, RobG said:

You've got it backwards. At pre–foiling speeds, they will be able to generate all the RM they need by canting the leeward foil outward. Once foiling and the leeward foil has maxed its RM contribution, then it makes sense to look at adding RM from the windward foil.

I agree with Phil, these will likely be sailed flat, there's no reason to heel to windward. Moths and sailboards must heel to windward, it's a physical impossibility not to (except when going downwind or in very light conditions).

I'm thinking at low (sub foiling) speeds, where using both foils would effectively double the foil area. Most of the RM is speed-related, since it's being developed hydrodynamically, so at low speeds, more area is a huge benefit. Once you get close to the liftoff speed, you would obviously want to eliminate the down force on the windward foil (the equivelent of shedding weight), and by that point the leeward foil should be generating all the RM you needed.

For sure you could also do this at high speeds - kind of like the rudder differentials from the AC50s on steroids - since the increased downforce would be compensated for by increased lift on the leeward foil, but the loads across the platform would be insane - that's gonna take some serious engineering!

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The AC 72 definately needed to bear away to take off. We could hear Tom Slingsby called different modes. The needed to drop heading more than just several degrees to take off, then were abke to round up again once flying.

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@ surfsailor. Don't make me look up the Rule, but isn't foil downforce prohibited?

Related note: thinking about Basiliscus's supercritical section (delaying high speed cavitation), in seems to need a slotted flap for low speed, high lift work. That should mean the flap is pretty much unidirectional, i.e. quite poor at generating downforce

@Phil S. In fact, if the first simulation by the US team is to be believed, the boat wouldn,t be able to take off while going upwind at any wind speed

 

 

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6 hours ago, Phil S said:

The AC 72 definately needed to bear away to take off. We could hear Tom Slingsby called different modes. The needed to drop heading more than just several degrees to take off, then were abke to round up again once flying.

Ok, we’re splitting hairs a little here - yes, they bore away a little, but they still basically took off when they were close hauled on a tack - my point was they didn’t turn way off the wind as some are suggesting will be necessary with the 75s.

 

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5 hours ago, Xlot said:

@ surfsailor. Don't make me look up the Rule, but isn't foil downforce prohibited?

Related note: thinking about Basiliscus's supercritical section (delaying high speed cavitation), in seems to need a slotted flap for low speed, high lift work. That should mean the flap is pretty much unidirectional, i.e. quite poor at generating downforce

@Phil S. In fact, if the first simulation by the US team is to be believed, the boat wouldn,t be able to take off while going upwind at any wind speed

 

 

I’m sure downforce is prohibited once you are foiling - not doing so would basically allow the teams to load the platform and rig up until the boats literally exploded. This will be easy to monitor, since the windward foil would need to be in the water.  I was just noting that would potentially be fast.

At the bottom of the wind range, when both foils are in the water, it’s a different story. To get a beast like the AC75 going, you need a lot of thrust - power from the rig. But you can only apply as much thrust as you have RM available to keep the boat upright, and - unlike catamarans who develop their RM geometrically (the function of the leeward hull/leeward foil overlap), the AC75s ONLY develop RM from the foils (Sure, the hull has some intrinsic stability, but it’s still a 75’ dart with a massive rig) , which means it’s proportional to speed. So at very low speed - when you’re trying to get that thing moving - you have very little. So to me it makes total sense to augment that in any way possible so you can apply more power from the rig. 

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14 minutes ago, Rasputin22 said:

 

Too cool - and too crazy. There were some great vintage ice boats at Monmouth Boat Club in Red Bank  - some of them are huge, thinking like 50’, but i was a kid, so maybe I’ve got that wrong. We got a few rides, and later on I had one of Paul Mindich’s Free skates - a skate board with blades on the trucks and a windsurfer rig - those things were awesome.

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1 hour ago, surfsailor said:

Too cool - and too crazy. There were some great vintage ice boats at Monmouth Boat Club in Red Bank  - some of them are huge, thinking like 50’, but i was a kid, so maybe I’ve got that wrong. We got a few rides, and later on I had one of Paul Mindich’s Free skates - a skate board with blades on the trucks and a windsurfer rig - those things were awesome.

That stern steerer looks pretty Basiliscist to me.

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2 minutes ago, Rasputin22 said:

That stern steerer looks pretty Basiliscist to me.

Those things are pure 19th century Mad Max!

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@surfsailor .... "So at very low speed - when you’re trying to get that thing moving - you have very little. So to me it makes total sense to augment that in any way possible so you can apply more power from the rig."  Thank you.

This is the window that might decide this AC.  Can we go into Left Field and think about what is possible.

No Down force from the foils !  That could make it harder.  Larry created a rule that they thought would keep the foiling to  like the big tri for AC34 but someone thought outside the box and they pretty well foiled all the time.

Here the intention of the class rule might be to restrict full foiling to about 50% of race time (???)

Is someone going to bring Left field into this game and foil most of the time.  I hope they will !!

 

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9 hours ago, surfsailor said:

I’m sure downforce is prohibited once you are foiling - not doing so would basically allow the teams to load the platform and rig up until the boats literally exploded. This will be easy to monitor, since the windward foil would need to be in the water.  I was just noting that would potentially be fast....

Per the Design Rule: 

26.4  The foil shall not intentionally be used to generate net downforce (combining gravitational and hydrodynamic loads) unless:

(a)  the foil is at its fully raised position (maximum cant angle);

(b)  the foil is at its fully lowered position (minimum cant angle); or

(c)  the FCS is being commanded to drive the foil to a prescribed cant angle.

If the foil is not in one of these conditions and generates a net downward moment, the FCS shall not support the foil at a fixed cant angle and shall move the foil downwards.

Downforce is allowed, provided the foil is at its fully raised position.  The Rule does not specify what the "fully raised position" is.  Rule 20.3 allows the use of stops to alter the range of motion of a control system: 

20.3 Stops or locks acting on a single control function may be permanently in place (e.g. in the case of end stops on a hydraulic actuator), or if not permanently in place, may only be engaged and/or disengaged:
(a) directly by the crew;
(b) through a mechanically connected force input device; or
(c) by an ECC and/or HCC, providing the device is only capable of locking the control function:
     (i) in a maximum of two defined positions; or
     (ii) from moving at all, regardless its position.

The combination of Rules 26.4 and 20.3 mean the team can sail with a restricted value for the fully raised position, allowing the windward foil to dip into the water for hydrodynamic downforce.   

A foil section designed for a high incipient cavitation speed is almost symmetrical for the front half of the section, with nearly all of the lift at high speed coming from the aft half of the section.  It would be entirely feasible to create hydrodynamic downforce using flap deflection on such a section and still have good characteristics with positive flap deflection for takeoff.

They plan to use the FCS to enforce the restrictions on downforce:

26.5 If an FCS is frequently being commanded to drive the foil to a more raised position, and that foil is generating net downforce, the FCS may:
(a) reduce the operation of the cant movement, or drive the foil to a lowered position; and/or
(b) provide information to the Media System for the provision of racing penalties.

It will be interesting to see what happens when the FCS moves the foil to a lesser cant position than commanded by the crew, putting Rules 26.5 and 20.3 in conflict.  The crew may be operating the boat in a perfectly legal manner according to 20.3, but have the FCS invoke 26.5.  False positive indications in the FCS are a definite possibility as the heavy foil wing bobs up and down at the end of the foil arm, causing oscillating loads on the FCS actuator and requiring frequent compensation from the FCS to maintain position.  Uncommanded motion by design is a safety issue.  Since the FCS is a supplied item, it leaves the supplier open to a protest, lawsuit, or even criminal liability should injury or death result from the uncommanded motion.

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If you want to see what can result from a control system designed to move a control surface in an uncommanded manner, the crash of the Lockheed High Technology Testbed provides a cautionary tale.  There were seven fatalities.  The accident report says:  

PROBABLE CAUSE: "Disengagement of the rudder fly-by-wire flight control system resulting in a total loss of rudder control capability while conducting ground minimum control speed tests. The disengagement was a result of the inadequate design of the rudder's integrated actuator package by its manufacturer; the operator's insufficient system safety review failed to consider the consequences of the inadequate design to all operating regimes. A factor which contributed to the accident was the flight crew's lack of engineering flight test training."

It doesn't take a huge leap of imagination to substitute the FCS operating under Rule 26.5 into this paragraph.

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6 hours ago, Basiliscus said:

26.4  The foil shall not intentionally be used to generate net downforce (combining gravitational and hydrodynamic loads) unless:

Forgive me if I'm a bit behind the curve. during the last cup with the cats was this also in the rules?  It's my understanding the teams generated a lot of "foiling differential" specific components some supplied some not twisting and flexing ultimately resulting in large downwards forces from the upwind rudder giving the boat upwards of 250kg extra downforce.  Not "intentional just a happy coincidence that all the teams capitalised and optimised with some clever material engineering. I dare say similar non-intentional things will be very well engineered this time around as well. 

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In previous matches, the limitations against downforce were enforced by requiring the windward daggerboard to be retracted when established on a tack.  Downforce from the daggerboard was allowed for a limited time during maneuvers, and there was no attempt to measure it directly. 

AC72 Design Rule:
9.9 Daggerboards shall not be used to generate force for the purpose or effect of increasing righting moment when used on the windward side of an AC72 Yacht. This rule does not apply:
    (a) Prior to starting, as defined on RRSAC;
    (b) when the daggerboards are fully retracted (as per Rule 9.10)
    (c) when the windward daggerboard does not penetrate the surface of the water for more than 15 continuous seconds;
    (d) when the AC72 Yacht is within 300m of a mark, as defined in RRSAC;
    (e) when the AC72 Yacht is within 30 seconds prior to and after tacking or gybing;
    (f) when an AC72 Yacht is taking a penalty; and
    (g) when the effect is inadvertent as a result of a breakdown.
 For a protest against a Competitor under this rule to be upheld, it must be proven to the complete satisfaction of the Jury that this rule has been broken.

AC45 Design Rule:
11.14 Daggerboards shall not be used to generate force for the purpose or effect of increasing righting moment when used on the windward side of an AC Class Yacht. This Rule 11.14 does not apply:
(a) when the daggerboards are fully retracted (in accordance with Rule 11.6);
(b) prior to starting, as defined in RRSAC;
(c) when the windward daggerboard inadvertently penetrates the surface of the water for less than 10 continuous seconds;
(d) when the AC Class Yacht is within 10 seconds prior to and after tacking or gybing; or
(e) when the AC Class Yacht is taking a penalty.

Downforce from the rudder elevators was implicitly limited by the restrictions on elevator movement. This led to tactics like slack lower shrouds to increase racking of the hulls and unstable bending-twist coupling of the elevators to increase the downforce as much as possible.  

The AC75 is different from the catamarans because it depends on using gravitational downforce on the windward foil for stability.  This puts the authors of the Rule in the position of having to distinguish between gravitational downforce and hydrodynamic downforce, which is a very difficult thing to do, considering all the dynamic situations that occur when tacking and gybing.  You can bet that teams will be taking every opportunity to increase righting moment as much as possible within the Rule.

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i wonder if there will be a move in gusty, on/ off conditions where they start to foil with both main foils down, then raise the windward foil while they are foiling.

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1 hour ago, Basiliscus said:

The AC75 is different from the catamarans because it depends on using gravitational downforce on the windward foil for stability.  This puts the authors of the Rule in the position of having to distinguish between gravitational downforce and hydrodynamic downforce, which is a very difficult thing to do, considering all the dynamic situations that occur when tacking and gybing.  You can bet that teams will be taking every opportunity to increase righting moment as much as possible within the Rule.

Thanks for all the relevant info. I'm totally on the same page with you that the rule has enough cooked-in freedom in the foil design section to allow a flap that can produce downforce even though the pitch of both foils (windward and leeward) is the same. At low, sub-foiling speeds (0-8 kts) - where I think using downforce on the windward foil could be very effective for getting these unballasted boats up to launch speed - it would be extremely difficult to monitor.

Another thing - since the entire foil arm is articulated (rather than having the foil with adjustable cant attached to a fixed ama), you can rotate the entire hull/rig around the foil arm axis (without it getting any higher off the water) at will during steady state flight.  So a possible scenario at speed in higher wind would be heeling the boat to leeward - the downward component of the wing sail thrust would translate directly into RM. At speed, there will be no shortage of available lift from the leeward foil, so here would be another opportunity to potentially load the entire platform up until it explodes. You would need to move the CE down so that you kept as much lever arm as possible - the gantry at the top of the wingsail will allow them to invert the top just like the AC50s, so it's doable.

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44 minutes ago, david r said:

i wonder if there will be a move in gusty, on/ off conditions where they start to foil with both main foils down, then raise the windward foil while they are foiling.

This occurs in every foiling tack or gybe.  The Rule says the windward foil can produce downforce up to the weight of the foil when both foils are immersed.  But I see no way for the crew to know when the foil is producing downward vs upward hydrodynamic lift.  The authors of the rule may be expecting the FCS to be able to tell based on the force provided by the cant actuator.  But there are problems with that, too.

Let 0 cant angle be the measurement position, as shown in Figure 12.1 of the Design Rule, and the wing has the maximum 4 m span.  When the cant angle is 41.4 deg, the foil wings will be horizontal.  Figure 12.2 implies the maximum achievable cant angle is 123 deg.  Assume the c.g. of the foil and arm is on the Rule's 3.5 m circle for the minimum weight wing.  (The possibility of a team designing a much heavier wing is another complication for the FCS designers in limiting the downforce.)  Although 123 deg is achievable, the maximum righting moment from the weight of the foil looks to be closer to 90 deg cant because the foil is almost directly under the pivot in the measurement condition.  At that angle, the tip of the wing is almost 1.6 m below the measurement waterplane, so depending on the flying height the windward foil may be digging in even when trimmed for maximum righting moment without trying for any hydrodynamic downforce.  

But my point is to compare the moments about the arm pivot as seen by the FCS.  The FCS cannot sense the force on the foil, only the moment about the pivot.  Say the windward wing is immersed and horizontal (41.4 deg cant).  The pivot moment from gravity is 66% of what it is at 90 deg cant.  That means the foil can produce more than 50% of its weight in hydrodynamic downforce and still be within the same pivot moment (and FCS actuator force) as it is at the maximum gravitational moment.  By lowering the foil to the wings level position, the righting moment from the foil's weight has only dropped 20%, so there's a big gain in righting moment from lowering the foil and running with hydrodynamic downforce.  That gain is doubled because of the lift on the leeward foil that's required to offset the downforce. 

Of course, it's possible for the FCS to have a maximum pivot moment programmed as a function of cant angle, so the maximum pivot moment may not actually be a fixed value as I've assumed above.  But even then, although the Rule says a net downforce is not allowed, I don't see how it's possible for the crew or the umpires to know just what the net downforce actually is.  For example, the foil could be set at 51 deg cant and the boat sailed with 10 deg windward heel, leading the FCS to allow 12% more pivot moment that can be taken in downforce.  When the crew experiments with different cant and heel angles to see what produces the best performance, I don't see what will keep them from wandering into the negative downforce regime.  Especially when you couple that with the fact that maximum gravitational righting moment is not obtained at the envelope maximum of 123 deg cant, but closer to 90 deg cant.  That means the teams will want the "fully raised position" to be well below 123 deg cant, and the fully raised position will be anything the teams say it is making any amount of downforce perfectly legal.  

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35 minutes ago, Basiliscus said:

< snip >

But even then, although the Rule says a net downforce is not allowed, I don't see how it's possible for the crew or the umpires to know just what the net downforce actually is.

<snip>

The two ways I can see to prevent the use of hydrodynamic downforce would be:

1) to regulate the 3D shapes of the foils -  they would need to evaluate the foils at all flap positions

2) require the flap on the WW foil and LW foil to run off a single control - so both set the same.

 

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@surfsailor I don't think the boats are stable enough in light conditions, with both foils down to have both flaps worked from the same control, They need push up on windward and push down on lee foil and of course the boat would want nett push up.  So 2) is not possible IMHO.

If the team did not show their hand until racing started I don't think they would do 1) IMHO.

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@Kiwing  You could very well be right - but I suppose that at very low speeds they could be used purely as ballast, and then the windward one is could be out of the water (for maximum RM based on it's mass) by the time the leeward one was used to create lift. So many possibilities, and this is just sub 6 knots! LOL

In any case, as far as I can tell there is nothing  in the rule that constrains independent flap operation of the two foils (although I believe the flaps on either side of the 'T' need to operate as a unit).

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I have to say, to this (very) old control systems guy, writing a box rule around an FCS just seems nuts. Each FCS is going to be different but presumably equivalent, and each FCS is going to be proprietary to the individual teams. Then (for sake of argument) assume you have a crash caused by a design flaw in the Team X FCS. How do you inform the other teams of a potential flaw without exposing all the gory details and competitive features of the Team X FCS? Or assume (again, for sake of argument) that it is determined that the crash resulted from a flaw in the box rule, either by forbidding something that should have been allowed or allowing something that should have been forbidden. So then what? Do you change the rule? Is everybody now going to reset to a Rev 0 FCS at a late date to exploit the change? What if a team looks at the rule change and discovers "oops, the rule let those guys do xxx and they crashed, and we did xxx as well,  so do we revise our FCS or roll the dice?" 

I think that if you want to eliminate the possibility of an FCS arms race then the only practical way to do it is to develop a standard FCS, put it in a tamper-evident box and make everybody use it. Any other approach just seems to me to have way too much potential for descending into chaos. Or maybe not. People do roll 7s and 11s, but not usually for extended periods of time.

Cheers,

Earl

 

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^ Makes total sense to me. There are already so many variables intrinsic to this platform geometry that making FCS uniform across the fleet won't hold anybody back and - as you say - will allow the event authority to mitigate unforeseen safety issues. 

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1 hour ago, Earl Boebert said:

I have to say, to this (very) old control systems guy, writing a box rule around an FCS just seems nuts.  ...

I think that if you want to eliminate the possibility of an FCS arms race then the only practical way to do it is to develop a standard FCS, put it in a tamper-evident box and make everybody use it. ...

I agree with your first sentence. 

The standardized FCS is indeed the way they are going.  The FCS is a supplied item, along with the foil arm structure.  It's not clear what parameters the teams will be able to set in the FCS, if any.  Even with the standardized FCS, Rule 20.3 allows them to modify the range of motion of the FCS and establish their own fully raised position.

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2 hours ago, surfsailor said:

The two ways I can see to prevent the use of hydrodynamic downforce would be:

1) to regulate the 3D shapes of the foils -  they would need to evaluate the foils at all flap positions

2) require the flap on the WW foil and LW foil to run off a single control - so both set the same.

 

I don't think either approach will work.  The Design Rule allows the wing design to be totally open to the teams, provided it fits in the envelope.  If they tried to restrict the range of flap deflections, the foil could be mounted with negative incidence so as to produce downforce with zero flap deflection and rely on positive flap deflection for positive lift.

Requiring both flaps to be set the same would not work because the lift has to transition from one foil to the other during a tack or gybe.  With no rake control (and possibly slow cant control), independent flap control is the only way to keep the boat balanced through the maneuver.

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17 minutes ago, Basiliscus said:

I agree with your first sentence. 

The standardized FCS is indeed the way they are going.  The FCS is a supplied item, along with the foil arm structure.  It's not clear what parameters the teams will be able to set in the FCS, if any.  Even with the standardized FCS, Rule 20.3 allows them to modify the range of motion of the FCS and establish their own fully raised position.

Ah, thanks. I was (obviously) unaware of that. Do they specify what control loops are included?

Cheers,

Earl

 

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10 minutes ago, Basiliscus said:

I don't think either approach will work.  The Design Rule allows the wing design to be totally open to the teams, provided it fits in the envelope.  If they tried to restrict the range of flap deflections, the foil could be mounted with negative incidence so as to produce downforce with zero flap deflection and rely on positive flap deflection for positive lift.

Requiring both flaps to be set the same would not work because the lift has to transition from one foil to the other during a tack or gybe.  With no rake control (and possibly slow cant control), independent flap control is the only way to keep the boat balanced through the maneuver.

Fair enough. I was thinking #1 could work because they could evaluate the foils together, so that any AoA setting on the leeward wing that could produce enough lift to support the boat, the windward wing couldn't generate down force. 

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