They're doing homework in 27 foot versions of the AC 75 for the 2021 America's Cup. Soft sails and 2 T foils. Not unlike a windfoiler banked to windward. If they articulated the mast they could get away with just one foil.

Thanks for posting Ian. Out of interest are the 27" just a proportionally scaled down version of the AC/75's

As an old Dinghy sailor I'm stoked to see foiling monos making gains on the foiling surfcats.
i haven't seen any speeds mentioned on these scale models though?
anyone have any idea if they are comparable to the cats?

Can't find the link but in my googling earlier today they were talking 40 to 50 knots for the full 75 footers. The foil arms are going to be one design to relieve each team of the task of developing their own. Sails designs seem to be open. There is a team experimenting with double skin sails.

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sausage said..
Thanks for posting Ian. Out of interest are the 27" just a proportionally scaled down version of the AC/75's

I now see the 27 footer was the Pommie prototype. The US proto is a 38 footer with half scale rig. The first full size 75 was scheduled to be launched in July.

I'm sure I read somewhere when they came up with this new rule that these boats will have a greater righting moment than the AC50's. I still find that hard to believe because the AC50's were doing wild stuff like wracking the platforms massively to get positive RM from the windward rudder and inverting the top of the wing etc; as an aside the SailGP 50's are allowed adjustable rudders so can cross trim them at will. That's all without taking into account the inherent platform width advantage.

You can't do that with a this new setup and a soft sail twin skin sail, while i'm sure they'll develop it really well is no multi element solid wing, not even in the same league efficiency wise.

Still it's an interesting rule and will push soft sail development and monohull foiling no doubt and the sheer size of the things will be wild. Even with the standard foil arms etc I expect the costs for this cycle will be bonkers compared to what could have been another cycle of AC50's with further developments etc.

Yes the righting moment doesn't look to be as much as on Cats, though I read somewhere that the T foils are ballasted? Also that the AC75s are about 20% heavier than AC72s but that the soft rigs weigh half as much. I also read somewhere that separation of the two longitudinal axis of the T foils is regulated to 4 point something metres with plus or minus ~1 mm tolerance. I'd think an advantage of the T foil's adjustability about the longitudinal axis is that they can trim out underwater mast lift and have the foil at the bottom do all the work. When using J foil daggerboards in cats you can't do this. The masts must be generating lateral lift at right angles to the lift at the bottom of the J. "The square on the hypotenuse is equal to the square on the other two sides" but when adding the lift vectors you don't square. To paraphrase Pythagorus "The induced drag on the hypotenuse is less than the induced drag on the other two sides."

Windfoilers can aim to do this. Have the mast freewheeling through the water not generating lift. A go pro aimed at the trailing edge of the mast would be interesting. I think the wake would clearly show when you were trimmed with the mast at neutral AOA.

Be interesting to see which direction the more everyday 18' skiffs go. Aus 299's photo looks about the size of a potential successor to the 18 footers whereas the superfoilers have already gone multihull with J dagger boards.

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CJW said..
I'm sure I read somewhere when they came up with this new rule that these boats will have a greater righting moment than the AC50's.

Found the rules.

drive.google.com/file/d/1jlbGdGZ-XERd63SGESoMamTgGZdRiPZJ/view

The port and starboard foils can each be 1175 kg. A useful bit of weight to hang out to windward.

Yes the smaller mules were a teaser but can't wait to see the AC 75 on water in Auckland