foiling mono hull sail boat new americas cup boats

[ozPE]

Hi,
I have been a sailor for 9 years including a double handed atlantic crossing and a structural engineer for 20. the new americas cup mono hull sail boats are one of a kind, i realize that these boats are not meant to go long distance but in harbor short fast match racing.
my question is really meant for naval architects / engineers but this is the closest i could find and i am sure there will be responses.
so these boats foil, hull lifts up the water, there is no keel hence the traditional righting moment is replaced by a couple produced by weight of the hull and lift produced by the foil (the moment arm is quite big). there is a video of a ETNZ boat tipping as it loses speed and as a result loses lift so the couple is replaced by hull weight x half the width of the hull (approx).
ok the question is this; during a race how do they manage to adopt to changing wind speeds during maneuvers thus changing overturning moment from the sails? (i am guessing by changing the angle of attack on the foils but would appreciate a more detailed explanation)
the other part is that the increase in wind speed contributes more to a transverse force than forward speed, so the change in the ratio of lift (speed) vs overturning moment is not 1:1 specially when going close haul.
here are some videos

https://www.youtube.com/watch?v=DKRmBaigV9Q

https://www.youtube.com/watch?v=7EqKjZgPv34

https://www.youtube.com/watch?v=bE65VtlkcY8

 

[3DDave]

That looks like fun. And I emphasize looking as I would not wish to be on that.

As you mentioned, it looks like the have a pair of outriggers with a hydrofoil on each but mostly deploy the down-wind one, so the weight of the hull, et al, is the counter balance.

I suppose they adjust to the wind by adjusting the pitch of the rear foil to change the angle of attack of the main one, whichever side is in the water. Since the weight is the same and the lever arm is the same, the moment remains the same, so they need to trim the sail for a constant side-force on runs.

When they come about, and the sails are no longer producing a moment, they put both down, which would tend to bleed off speed, but it also increases the available lift to compensate for the speed drop-off. Do it quick before the hull gets wet so that speed can be regained on the next tack.

It should be possible to get far more thrust than side load, particularly as the speed increases.

I don't know where I balance out, but it's not my money. On the one hand that is a very innovative, but ever so limited applicability design. On the other hand it represents a stupifyingly large amount of money which I concede might not feed orphans directly but is dispersed to a large number of engineers and craftsman and so still makes a positive outcome for society even though the end item has little utility beyond bragging rights.

This is one design that offsets my sadness they abandoned the old class (was it twelve-meter?) that really concentrated on the capability of the crew, but I'm good with watching as this heaves itself out of the water and can probably outrun some cabin cruisers.

Which reminds me of the guy who entered a sailboard long-distance race but, instead of a fixed sail, used a large sport kite and basically smoked the competition. Not only are the winds stronger higher up, but it pulled the board from the water, reducing its displacement. The result was a new rule defining what a sail was. Good job.

 

[rb1957]

foiling cats ? … how about those sailGP boats ? any time you hear the boat you know it's fast ! these boats will usually use only one foil, so much like the new AC boats.

me, personally, I don't think the look of these new AC boats … they look clumsy, deploying the new foil is bound to be something learnt (how to do it efficiently)

going to your questions … yes, they trim the AoA of the foils (whether they can on the new AC boats, without pitching the boat, I don't know) possibly they'll add a trim tab for small adjustments.

It amazes me how quickly foiling has entered the general sailing community.

another day in paradise, or is paradise one day closer ?

 

[GregLocock]

The main foils have dihedral, so as the device rolls the downwind foil produces more lift.

Rather more fascinating than these things are the single handed Moth class, a hydrofoiling dinghy. Bit of a workout!

https://en.wikipedia.org/wiki/Moth_(dinghy)#/media/File:Moth_Kiel2008.jpg

Cheers

Greg Locock


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[IRstuff]

Man, those things are ludicrously fast; the same team's 2012 entry had a record speed of 47.6 kt in a 21.8-kt wind.

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[ozPE]

thanks everyone.

3DDAve it makes sense that they have to trim the sails like you said because the moment is the same. i agree with you that these are some expensive toys similar to formula 1s, sometimes some new innovation comes out that spreads to wider public.

i do like the sailGP and the previous AC cats 50kn in 20kn wind, i don't think the new AC monos will get there without a wing sail although i would be happy to be proven wrong. it would be nice to see some reefable soft wing sails on production boats too.

 

[IRstuff]

These "boats" run upwards of $10M, but they have the absolute state of the art in racing technology

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