America's cup boats

[Steve_D]

These boats amaze me.
But why do they not just fall on their nose when they lift up onto the foil?

The foil is in line with the base of the mast. The centre of pressure of the sail must be some way up the mast, perhaps a third of the way up, so why does this not just push the boat nose over.

Once it is up on the foil how is the boat kept level? A powerboat has trim tabs to keep it planing level and outboards will have power trim.

Thanks
Steve

[tank slapper]

They can adjust the angle of the lifting foil for trim. I expect they are also quite a lot heavier toward the stern, in addition to the weight of the crew being there.

[ALawson]

As well as the other weights they shouldn't have on board!

[Penguinracer]

The foils' horizontal surface has a fixed angle of attack (unlike a foiling International Moth which has a variable pitch lifting section controlled by the bow-mounted speed-sensing "wand") but they can change the rake of the entire foil which of course will change the angle of attack of the lifting surface. These boats were not intended to foil (hence the fixed-pitch horizontal section) but the teams have obviously experimented to overcome this.

[Hard-Drive]

The AC72s also have a horizontal foil on the rudder, which although is essentially fixed, will obviously damp pitch oscillatons.

I've got a foiling Moth...the wand is not speed sensing, it's height sensing...when the boat is too low it will adjust the foil tab for max lift, and vice versa. However the lifting foil is always horizontal, and can be creating a lot of lift even if just below the water surface.

Here's the clever bit on the AC72...even though the foil looks L shaped when raised, when it's dropped it essentially becomes V shaped due to the curve on the vertical section of the board. When the Moth is too high, the wand is telling the flap to kill the lift, but the whole foil is still in the water. When the AC72 is too high, is essence your big immersed V becomes a smaller v because you have less foil in the water. Less immersed foil = less lift, and the whole thing sinks a bit until equilibrium is restored.

In dinghy circles, Cherubs are just starting to experiment with V foils...

[CoopR]

They are amazing bits of technology, and the stories around the competitions and how the winners/challengers decide the rules is bizarre.

I was lucky enough to spend a week kitesurfing with one of the designers of these boats. Fascinating stuff to hear how they work around the "only one foil" and other rules rules. Also didn't know that there are no electrics allowed for any of the pumps or mechanical gears at all, the whole hydraulics systems have to be manually charged and pumped. The guys who do that are beasts!

[prand]

Didn't one of the boats actually flip in trials, due to mast/hull failure, which is what contributed to the death of Andrew Simpson? Some incredible forces being pushed through the boat for sure.

Amazing things to watch in flight though. Nice to see NZ in front, though our chap Ben Ainsley in the US team must be scratching his head how to make up a 6-0 defecit.

[Hard-Drive]

Oracle flipped, and Artemis flipped, killing Bart. However at this stage in development both boats were non-foiling, this was before they fitted lifting foils.

[sawman]

prand said:

Didn't one of the boats actually flip in trials, due to mast/hull failure, which is what contributed to the death of Andrew Simpson? Some incredible forces being pushed through the boat for sure.

Amazing things to watch in flight though. Nice to see NZ in front, though our chap Ben Ainsley in the US team must be scratching his head how to make up a 6-0 defecit.

I am not sure theres enough time left in this for oracle, new zealand seem to have a great overall package - their speed upwind and through the tacks is telling.

[TTwiggy]

As a (very part time and amateur) cruising yachtsman, I'm wondering if these foils will make their way onto cruising yachts at any time soonish? The idea of doing a Transat at, say, 30kts under sail alone is intriguing!

[Hard-Drive]

Unlikely. The enemy of foiling is weight, so it works with lightweight dinghies, and also cats as neither have ballast. In dinghies, Moths, Cherubs, 12s, 49ers, RS600s,18s and even the humble Laser and Optimist have foiled with varying degrees of success at some point...the Moth still being the only class that gathered any momentum probably due to the fact that it was so minimalist in the first place and lent itself to flight.

However foils are being used to counteract heel (kinda like a sideways keel out to leeward underwater developing lift, but not ballasted) so who knows, anything might be possible, but any "cruiser" would be unrecognisable by current standards.