AC 36 Foiling Monohulls

A rather grainy gybe video: Will on Instagram: “New @acup2021 prototype flying fast @sailing_anarchy” https://instagram.com/p/BlqMETahnDM/

Difficult to make things out, but there seems to be ventilation of the rudder half way through the gybe and the boat drops off foils. It then seems to get back up to speed and foiling again. The boat stays pretty flat throughout so foiling gybes may not be far off.

 

Good work by the INEOS team! Obviously, they made the configuration fly. But by some reason they need floats on the sides. Probably the stability from foil-weight and the main hull is not enough below some speed. They also have deck-spreaders, making the overall-beam more like a trimaran. It is getting closer the unballasted foiler, I suggested as an example in my post 285 before the AC-75 class-rule was published.
The experimental work, that INEOS is doing now, should have been done before the class-rule was decided! And the AC-organizers should also have taken (or let someone take) the logical next steps in the experimental work, i.e. trying a model of the configuration intended for the AC-75 without any extra floats or similar, before deciding such a strict class-rule as the present AC-75 rule.

 

Spithill on NZAC: it will be a beast of a boat-
Sailing: Jimmy Spithill predicts new America's Cup boat to take race to new level https://www.nzherald.co.nz/sailing/news/article.cfm?c_id=106&objectid=12099620

Excerpt--
"The speeds we could have… it'll be a beast of a boat. It's out there," Spithill said.
"This one will be another level."
"Will it work? That's the question. The America's Cup has always been at the leading edge of boats. Look at what's happened over the last decade. The AC72 kind of reminds me of this boat in that it is very, very powerful and never been done before."
"It's extreme, it's expensive, from first take, and what we are seeing, it's unstable, and it's going to be very, very physical."

 

The floats are necessary in the test model because they can't get enough ballast in the foils due to scaling. There were changes in the latest rules indicating that even the full sized boats will struggle to get enough ballast in the foils and that the arms are going to be heavier than first thought. Nothing that can't be overcome, but issues that mean this design may not scale well when applied to smaller boats.

The fact that INEOS has the boat foiling already is proof that confidence in the design was not misplaced. I admit to being as sceptical as anyone initially, and still think it's not a sensible design if "trickle down" is expected, but the fact that the INEOS boat is foiling already and looks close to pulling off foiling gybes is proof that the designers got it very close to spot on.

I expect that the main purpose of the test boat is to benchmark computer models with real world data and work out how best to sail them, likely they're entirely computer controlled with minimal human input (there appears to be only 2 crew on the boat). The AC75s will have "follow the ball" style graphics to indicate optimum settings for sail trim and anything else human controlled.

 

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That's true and all the more reason NZAC should have a fin keel like the Quant 23 and Gonet monofoiler. Would still foil and be very fast..... and the foils wouldn't have to be left in the full down position-in fact the full down position would never be needed and could result in much simpler mechanics.

 

If anyone complains this cup isn't innovative, he's lying. But it might be a technical unfeasible project.
I spoke with Larry Ellison about this and he said the old AC5o's were a much stabler platform for foiling.

 

It's definitely feasible especially since INEOS got the 28' version going so well. But the whole concept would be improved with a fin keel/bulb or canting keel.

 

I would rather take the opinion of someone that has sailed both boats (which is a very small number of people at present). The AC75 has a lot ofelectric power and computer controls not allowed on the AC50, so while it might theoretically be less stable, it might be easier to sail (noting that both classes are way beyond most sailors’ abilities). I don’t think anyone stepped onto an AC50 and had it sailing as well as the INEOS boat in such a short time, and that was after the AC72 and other multihull foilers had been around for awhile.

This report and follow up posts on the TF10 highlight how electronics and stored energy can make the boats much easier to sail.

 

In my opinion it would be necessary to build a smaller scale boat with canting keel and light canting foils and a boat with heavy canting foils. Make regattas. This should answer which is faster ?

 

I think that could be answered in simulations. The extra appendage is more drag so while it may make the boat more stable, it may not be faster by some criteria. Faster in a straight line may not be faster around a course, and a wing sail would make a difference too. I think top speed is limited by cavitation anyway, so faster is moot.

The boat is what it is, all boats are a compromise in some areas to meet design criteria, there have to be boundaries somewhere.

 

Bulb canting keel should fly above water.

 

It must be in the water prior to foiling and during tacks and gybes—it will have to tack/gybe with the boat. So that's another variable and another thing to get right (or wrong) making the boats even harder to sail.

A keel that cants to about ±90° requires some very unusual design parameters–the axis of rotation must be below the bottom of the hull*, and the optimum position will likely be exactly where the foils are. It would add a lot of additional weight for the fittings, machinery to move it and additional carbon in the boat to take the forces.

How will match racing go if there's a couple of tons of lead that must be swung 90° on every tack and gybe, in addition to trimming sails, swapping and setting the main foils and rudder? There are only 12 people on the boat, most of whom will be grinding like mad just to keep up with what they have now. And all just to provide some additional stability when the boat isn't racing. The AC75s don't need a keel.

Sorry, but this discussion is pointless. It's more interesting to discuss the actual boat.

* I think the closest you'll get is something like SpeedDream, which tilts to about ±80°, which would not be clear with the boat flat, even when foiling.

Also the YouTube video.
There was also "Q", but I think it used a semi—circular hull to rotate the keel, so totally different to an AC75. It had a nasty habit of getting stuck on one side or the other, causing the boat to capsize at least twice. It's disappeared into the abyss of seemingly good ideas that weren't.

 

They're one or two more versions of a 180 degree canting keel-but can't find the pictures:
Older thread with a lot of canting keel and flying canting keel debate:
Flying Canting Keel-Extraordinary Innovation! https://www.boatdesign.net/threads/flying-canting-keel-extraordinary-innovation.30806/page-16

Stravagnza sailing:




Stravaganza-Jo Richards , Guy Whitehouse :






"Q" pix by Nicole Scott :

 

Or why not keep the floats that INEOS used in their initial tests? I agree with Doug, that replacing the ballasted 120° stroke-angle foils with unballasted ones, that also require less stroke-angle, will make life much easier. The boats will still be expensive enough and challenging enough to sail anyway.
About scaling: don't expect it will be easier to balance the rig weight with the foils, when you scale up from 28" to 75". Both rig-weight and foil-weight will scale with L^3, while e.g. cross-sections in spars scale with L^2, so the stresses in the material scale with L. Hence, Young's modulus as well as tensile-strength shall scale with L, or if you already are using the best materials in the 28" size, you have to make the rig relatively heavier on the 75" version. (the cube-square law).

 

Some more video: Richard Leech https://www.facebook.com/groups/748354018542060/permalink/2136736729703775/

Apparently there's been at least one capsize due to the foils not being lowered for whatever reason. Also some good crashes, but no pictures or video that I know of.

The floats seem to only be required when the INEOS boat isn't being actively sailed. It doesn't accurately model the full sized AC75 in many respects, including articulation of the foils which don't seem to go into the fully down position.

The hull and rig don't appear to be scaled AC75 versions either, likely they're just "close enough" for the exercise (and perhaps at the right price as well). There is talk that the NYYC is using an MC38 as their surrogate hull, which should launch soon. It's probably a significant cost saving over building an accurate (roughly half size) model.