34th America's Cup: multihulls!

Look closely Doug - there are T foil rudders ... so that setup with L main foils will fly steadily, don't need no stinking wands.

 

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I don't agree mon capitan: that would be like taking a Rave, Osprey or F3 and ripping the wands off and hoping it would rise just so far and sail along nice and pretty-ain't gona happen!

click

 

Except there it is right in front of your eyes.

 

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You know better than that these days! I think the SA guys have it right: lets see the video......

 

Would not boil down to lift off approach, in terms of design.

There appears to be some thing at the bottom of the windward rudder, as Gary suggests.

 

Ac 45 on foils

Can't see how its controlled but its for real: http://www.sail-world.com/USA/Ameri...show-off-hull-lifting-foil-developments/98900
On "normal" multifoilers like the Rave, Osprey, Hobie Trifoiler, Skat and even Rocker the rudders all have t-foils but altitude control is via some sort of surface sensor-a wand for most and a "feeler" on the Hobie. Thats what makes this so interesting: how does Oracle control altitude?
calling Tom Speer.......

Note that every catamaran that has ever been on foils 100% has been slower than its non foiling counterpart-latest example was "Rocker" developed prior to the last Little Americas Cup. Which is interesting in that cats that use "foil assist" to partially lift the boat are proven faster than their non foil equipped sisters and brothers.
Also note that the daggerboards holding the lifting foils are forward of the front beam, whereas on the "normal" 45 they are behind.......

click on image-last pix is Rocker on foils:

 

I agree that altitude control is required.

With the crew available on this size boat, manual control would be possible.

Given that an aiplane pilot controls both steering and altitude, I would be tempted to assign altitude control to the man on the helm.

If manual altitude uses the rudder for control, the entire boat Angle of Attack (AoA) would be adjusted (just like a traditional airplane). Putting the extra complexity all on the rudder makes sense to me given what is allready going on with the dagger boards (one goes up & the other goes down on each tack).

FYI, as I recall, the paper on Rocker indicated that they felt that the poor performance was due to four foils in the water all of the time. The photos of the Oracle boat show that they pull one dagger up & they can potentially fly one rudder a good portion of the time. They also seem to have a relatively small horizontal surface on the dagger.

I my assessment, this all adds up to potential for much higher top speeds without much loss in the less than optimum conditions.

This may be a case, where a plentifull supply of funds and talent can show that just because "no one made it work before" does not mean "it can not be done".

 

Good on yer P Flados - we'll make a believer of wand waving Doug yet.
It is safe and easy for a foiling multihull to lift off reach to broad reaching, hence the baggy and loose offwind sail in one of the shots; they're sailing well downwind and you can just sit around and enjoy the view (as the crew are doing) on this point of sail. Blunted (expert C Class sailor) is absolutely right about trimming the platform out via crew positioning ... and I can't see, if the foils are fixed along with T rudder (the latter at zero, or close to, angle of attack) that this method is not being used to work foils, rig and platform equilibrium - remember these are hyper skilled sailors, should be no problem for them.
One obvious observation: the T rudder lifting section is incredibly fine, meaning thickness, chord is also small, high aspect ratio, nice building. Those rudders would have minimal drag even in light airs. In a breeze, it is quite obvious, the foiling AC45 would be MUCH faster than the conventional version.
About bearing away and the T rudder (and stern platform area) pops up - doesn't happen - remember the foil is going 20 knots plus through the water (at zero angle) thin, thin foil, not huge lift, therefore it is like on rails, holding itself down simply through speed. It is only when you stop, or near stop that the T rudder will lift out and the crew get a high angle view of the onrushing water surface.

 

I wonder if there could be laser (or other optical), or perhaps even sonar range-finding devices taking the place of wands as sensors of distance to the water's surface. Also, I wonder if there could be some sort of fly-by-wire to the daggerboard foils adjusting lift/drag to compensate for LCG changes and pitch. Would such electronics be legal?

 

AC 45 on foils

Hi, Stephen. As I understand it moving the foils is illegal, flaps are illegal but I'd guess that electronics are ok if you can figure what to use them for. I'm wondering if they might use some form of movable ballast that slides fore and aft-don't know if that is legal. No way would crew movement be sufficient to control a 45' catamaran with a wing rig in pitch. They may have found a loophole in the rule that allows some control over the main foil-just controling the rear foil is not likely to work.
Sure will be interesting to see how they do it IF it flies in a "steady" state or if it pops up and down. Like they've said on SA: lets see the video!

 

Yes, movable intelligent ballast, read crew? On a featherweight boat. Or maybe there is something electronic in those blisters?

 

Just checked a copy of the preliminary AC 72 rule-no movable ballast, no movable flaps or any kind of flow control device.
Gary must be right(Nah) though I just can't believe a crew could control a 45 or 72' wingsailed cat in pitch.
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The only thing I see in this preliminary draft is that while the rule specifies that the "bilgeboard" cannot move more than 20mm at its lower loadbearing support there is no restriction, that I saw, on pivoting the daggerboard. If that is still true in the final rule then this may explain how they do it but it would have to be manuallly controlled. Pivot the daggerboard to change the angle of incidence of the main foil. The rudder foil will naturally "trail" the daggerboard: if you can move the daggerboard then you don't need to move the rudder foil.
Boats like the Rave and Osprey are controlled in altitude by "wands"(surface sensors) connected to flaps on the main(daggerboard) foils. While the rudder foil flap can be moved to "tune" the boats pitch angle it is not necessary to move the rudder foil or flap at all- the boat will foil just fine. The Rave was modified by a couple of guys to use a manual control system where a joystick controlled the main foil flaps instead of a wand-they said it worked well. On the AC 45, if I'm right about pivoting the board being legal, it would be a simple matter to design a system that allowed the board to be retractable and most importantly ,pivotable manually. Problem solved.....

 

Gooday guys. If I can stay out of that place (with all the bottles of oxygen in them) long enough to get to use my computer - - then I would say to all of you the - pics #1 & @2 - show 'wand' or 'warnd-type' apparatus protruding from the hulls into the water & another pic somewhere - shows 2 of them - forward of the front beam & between the hulls.

Question - did I not read something about th i14 cat - having a 'swist-handle tiller type to control the rudder foil attack angle ??? Gosh - that's only some very simple light-weight 90* bevel gears & very easy at that. Yes/no ???

Whilst what Doug observes - about rules - maybe true - from a pure development outlook - I'm positively sure they are the way of the future & I'm a convert of both foils & 'triming blade' extension trim-tabs - what ever one wants to call them. Further more I'm positive if I can get 'the boat I'm after' I'll fit some foils to both the c/b & rudder before I go acean racing & cruising. Also one can be assured that 'the-boat' will have a fairly large wing-mast fitted of at least 15 mtrs (50') high & probably 10% to 15% more plus be thicker than most people think is "the way to go" - as I'm not of that same poinion. As 'reefable' is not all that difficult nor weighs all that much more - I may well go for a reefing - wing-mast plus soft sail at the trailing-edge - which is also rather simple to make very effective.

Ooops - that's getting it - out-there - a tad - but I do believe it's very possible.

Also do look carefully & you'll see the 'wand' on the AC 45's

Ciao - one & all, james

 

Movable ballast.

Gooday Doug. I think if you check the records - you will find that 'THE BOAT" - USA 17 - was using water ballast to great advantage in winning the 2 races. Yes/no ???

As for 'moveable' ballast - of the crew - let me assure you & everyone else - that the crew 4 out of 5 - is enough - way, way back - say on the aft beam or that area - WILL have a very marked effect - on the 'pitch-poling' of the AC 45's - by the way - so would - moving the top of the mast aft by 660 mm (2') or more & would improve both tacking & jibbing as well as 80% of their down-wind performance. We were doing all that in both 'B' class & 'C' class back in the 60's & 70's I've been waiting for them to figure it out but - no one can contact them - in their insulated little iglo.

Ooops again. ha ha - ciao, james

 

SR as far as I know BMW Oracle USA17 trimaran didn't use water ballast. The Alinghi catamaran did but they were so completely outclassed on every point of sail it was hard to judge whether it offered much advantage. Not to mention the incredible racking in the platform on Alinghi under very minor wave action, sure USA 17 racked but it was much more controllable I guess you have to expect some in even a carbon platform thats 90' wide and incredibly lightweight.