34th America's Cup: multihulls!

I don't think automatic control systems are necessary. The AC72s and smaller catamarans have demonstrated that the boats can be made inherently stable in flight.

The current Design Rule takes an extreme position with respect to stored energy, such that accumulators are not allowed in the supply side of the hydraulic systems. No responsible mechanical engineer would design such a system were it not dictated by the Rule. The crews can pump the hydraulic system up to maximum pressure, but as soon as anything moves, the pressure drops immediately. This means you can lose pitch control if the other board is being raised/lowered, or the wing adjusted, etc.

Allowing accumulators up to a certain size would go a long way toward making the control system design more tractable. The crew would still be providing the average power with the accumulators smoothing out the peak demands. This doesn't change the essential character of manual control in an athletic contest.

The other thing that can be done is to allow movable flaps on the foils, for sensible control of flying. Prohibiting such devices did not prevent flying, and instead of reducing cost, they increased the difficulty of developing a flying boat. The foiling cat is out of the bag, so teams should be allowed to design means of control that are safe and effective.

The daggerfoil carries a vertical load on the order of 6 tons and a horizontal load on the order of 3 tons. The horizontal load, in particular has a long lever arm because much of the board can be out of the water, concentrating the load on the bottom of the board. So the loads at the bearings are very high, and there's a lot of friction. It's a big ask to be able to achieve rapid, precise control with so much friction, especially when the supply pressure to the actuator is fluctuating over a large range.

The hinge moments of a flap would be a small fraction of the moments on the board bearings, so the control system could be smaller, simpler, more precise, and safer.

 

Agreed, when the cup is here in Auckland for next defense and challenge?? the foiling rule should be loosened up, flaps, reasonable stored power, and whatever multihull (or monohull) type you want, just a broad box rule, say 65x65, or keep it 72x72?
It's not the boats that are the great expense, just the huge crowd to keep them sailing and running.

 

based on a moth and must fit in 40' container should be the ticket

 

i also agree, i have no problem with the foiling cats, i think theyre fantastic. I hope next time they allow full freedom with the control systems should they choose to stay with a foiling multihull rule. But the rules for this race, should not be changed, especially not so close to race day...

Doug, i dont have a problem with oracle testing and tweaking their boat with rudder elevators, makes perfect sense. But its just a little convenient that a rule change allowing it on race day has been proposed now dont you think?

"Umm.... we cant control the boat we built safely, so wed like to change the rules so we can be safer... please???" :/

If i had the power of descision, my reply would be "if you could not design your boat to safely fly on foils within the current rule, then in the interest of safety your boat should not be flying at all"

 

Thanks for this comment Tom. I agree with your technical considerations and I think that is the path the AC will go, should they keep the foiling vessels for the future formats.

You seem to be the right person to discuss with about one thing which I am still trying to understand. Back in my post #1751 (http://www.boatdesign.net/forums/multihulls/34th-americas-cup-multihulls-34612-117.html#post636884) I have asked how did they arrive to use daggerboards for foiling, given that AC class rule defines daggerboards in this way:

Section 1, item 1.4.e
"daggerboard means a retractable appendage primarily used to affect leeway. The term daggerboard is synonymous with bilge board, centerboard, lifting keel and sliding keel"​

Doug has replied to this saying that what is not explicitly prohibited is to be considered allowed. But I am seeing the 1.4.e as an explicit prohibition of using daggerboards for purposes which are more important than leeway control.

Now, as you said, currently daggerboards carry approx. 6 t of vertical load, which is twice the amount of horizontal load. The way I read these numbers, it means that daggerboards are no more primarily used for leeway control. The whole design philosophy of these boats is currently centered on the foiling capability, which is so important for the victory that all boats are currently flying on foils (which are - daggerboards).

Of course, daggerboards are still necessary for the control of leeway - but is it still their primary function or can we say that the leeway control currently has at least the same level of importance as the generation of vertical lift? Everything in their design reflects this other primary purpose - their shape, their usage, their structural design - in which case, the item 1.4.e of the Class Rule is violated.

I am primarily interested in understanding these technical nuances and not in arguing against foiling (so Doug, you can sleep easy ). The logical process of rules interpretations and reading between the lines is something still so much above me (I am too much an engineer when reading the Class Rules), and I think this is a fascinating example from which one can learn something.

Cheers

 

Everyone assumed the boats wouldnt foil but they did it within the rules hence you end up with a foiling boat ( only works in x windspeed) but you cant have any of the controls you need.

 

That is the part I am trying to comprehend. It might be all about the interpretation of the word "primarily" in the rule 1.4.e , but I'd like to hear it from an informed person, with the first-hand info.

For reference, once again, this is the current version of AC72 Class Rules: http://noticeboard.americascup.com/...AC72_Class_Rule_v1-1_incl-Amendments-1-14.pdf

 

if a boat goes fast enough it will lift on the bottom of your dagger board,
remember the first windsurfer..

 

from Sailing Scuttlebutt today

"Ian Burns (AUS), Design Team Coordinator, Oracle Team USA – 7th campaign:
No one really contemplated flying when the rule was created. So, the biggest surprise is that the boats fly so well, and fast. Wing development has almost become less of a priority compared to daggerboard and rudder development because of flying."

Fresh is an old (cat) Hobie man himself

 

Apart your wording, which is not clear (what is the "bottom" of a daggerboard?), you are apparently describing something that exploits a collateral effect of high speed - which is not the case here. Here we have daggerboards specifically shaped and engineered for generating lift twice as big (according to Tom Speer, whom I trust when it comes to technical info) as anti-leeway force.

This confirms the considerations in my previous two posts about which is the primary function of daggerboards currently used. Which imo puts a question mark over the compatibility of foiling daggerboards with rule 1.4.e (see previous posts).

 

Yes true, i'm just pointing out like a original windsurfer it generated enough speed that it had the potential to do something that it wasnt designed to do
how the board is allowed to be an L board, I couldnt say
When a cat is healed a vertical board is supplying lift so how do you write that out of the rules...

 

Yes, Powerabout, with his last sentence:
"When a cat is heeled a vertical board is supplying lift so how do you write that out of the rules?"
is on the money and is what you should consider.
For example, if the boards were angled inwards, or the hulls were also angled inwards, (this maybe illegal under present rule, don't know, too lazy to look it up, just an example) then straight or near straight or S or C boards/foils or a combination of these shapes, would provide vertical and horizontal lift at the same time. I mean the boards can also be cranked athwartships (and fractionally fore and aft too) as long as they don't protrude outside overall beam ... which the cheaters right now are attempting to change at the last minute with their rudders.

 

I have stood by and watched all the rule crap with F18 and F16 and its problamatic to make a rule when you know the intent but someone will interpret to where you didnt think.
Rules get voted on by the sailors, just takes a smarter one to see the loophole.

 

One can only assume that in the definition of the "daggerboard" they simply took a legacy definition without thinking about defining a more detailed and up to date version in light of all the new lifting foils used on modern multis. They could have written out the ability to foil right there. They probably didn't want to tho, or they would have.

Thinking along the lines of the orma tris where they allowed some lift but not enough to completely foil....

 

Nacra C 20 not quite foiling but tons of lift, can pop into the air ( fund when they do)