Offshore Foiling Revolution-Gitana

Gitana Mod 70 on foils!

Gitana picture by Yvan Zedda/Gitana; video-- https://www.youtube.com/watch?v=j2y2az8A124

The written stuff with the video-translated by Google and almost readable:

End 2013, the members of Gitana Team were embarking on an adventure just as exciting as complex transform Multi70 Edmond de Rothschild, a 70 feet originally built to run a crew on a monotype circuit, so that it becomes the first trimaran racing wheel. The project is ambitious . Just like Rome, was not built in a day , the transformation of Gitana XV will claim more than two years of research and innovation to achieve the goals it has set the team with five arrows. But in the opinion of all , the game was well worth the effort. Just a few days with his new appendages , the Multi70 Edmond de Rothschild has definitely taken off , with 43 ​​knots on the clock in 20 knots of wind , thus validating the efforts of an entire team supported by shipowners - Ariane and Benjamin Rothschild - passionate and committed .

 

Woohoo! Congrats to them! That flex at 2:48 is somewhat scary, the entire starboard ama is vibrating-pitching up and down. The bow must be moving at least 9 inches relative to vaka. I can't believe that would be healthy for the cross-bars and boat.

 

Gitana Mod 70 on foils!

I don't know-there was some movement but not very much as best I can tell. If it had moved a lot the altitude of the ama would have changed and I don't think it did change. Stiffness of a foiler platform is very important for that reason....
I still can't get over how good she looks.
It would be interesting to know how much wind she needs to foil-not foil assist but full flying. And the comparison between the main foil on this boat and the one on the big version of Macif is real interesting: the horizontal potion of the UptiP foil on this boat appears to be about twice as long as the same one on Macif.

 

I see the flex, watch the bow of the float. That is a lot, break out the Uni and apply quickly.

 

Those Gitana and Edmond de Rothschild turkeys - don't they realize, the poor ignorant creatures that they are - it is IMPOSSIBLE to foil without horizontal foils on the main daggerboard?
What you're seeing on these "uptuned" as opposed to "UptiP" MOD 70s is .... delusional, can't happen, photoshopped and a blatant visual lie; take it from "the one who knows" - you know, the toy red boat on a stand and occasional backwater hopping on a pond specialist, that these images are fantastical dream/nightmares? .... it is not OCCURRING.

 

Lite Air Foiling/automatic power on demand

No, no Gary-the Gitana is working great! You must have gotten yourself all mixed up when you tried to compare Gitana to my boat. The Fire Arrow has the advantage-because of the lifting foil and rudder T-foil on the main hull-of being able to fly in very light air which is ideal for a 20' and under sport trimaran. And the Fire Arrow system automatically increases RM when required.
No other tri currently sailing does these two things-that will change-you can bet on it.
But I wouldn't ,necessarily, expect a 70' ocean racer to need that kind of power and that wide a wind range. But who knows what the future will bring.......

 

There's a whole range of possibility available between the two extremes. I'd have thought a little bit of lift from a horizontal foil on the keel would help get the hull out sooner and keep it out for much more of the time so that there's less drag overall: the hull keeps touching down, and surely that's got to be scrubbing off a fair bit of speed. It shouldn't need the early lift that Fire Arrow's designed for though as it'll be seeking out better wind all the time by placing itself on the right piece of water. There's no reason though why Fire Arrow shouldn't also be available with a smaller main foil to optimise it for locations with better wind so that it suffers from less drag at high speeds. What we're actually seeing here is more evidence that Fire Arrow should work and that a full size prototype deserves to be built so that we can see how hard it is to flip it over: it could be the safest foiler design of the lot, and its performance needn't be poor.

 

Foils-Gitana type tri or larger

One of the most significant attributes of the Fire Arrow main foil is that it can develop downforce adding substantially to the RM of the boat. Whether that would be practical on a large tri is an open question. But the other advantages of keeping the main hull flying and early takeoff could be more likely to fit a large tri design. If major downforce wasn't required ,then the wand could possibly be eliminated for a surface piercing T-foil.
But the wand or an electronic altitude control system would probably be hard to improve on.
The cool thing about the Gitana MOD 70 is that it is just a prototype for a much larger foiling tri........

 

From The Foiling Week:

However, the incredible sensation of flight on such a machine, as pleasant as it is to be powered up at over 40 knots, is not Gitana Team’s only objective of course. Following the announcement made in May 2015, the five-arrow team also began construction of a maxi-multihull at the Multiplast yard in Vannes, south-west Brittany back in November. This craft, the twelfth in the history of Gitana Team, will reap the full benefit of the trials carried out on the Multi70 Edmond de Rothschild from 2014 to 2016. Indeed, Sébastien Josse and his men have been able to build the future on the water rather than solely at a desk.

 

It seems sensible when designing a mulithull foiler to put one main lifting foil on the outer hulls (i.e. two main foils) and design it to sail flat (since any heel to leeward is extremely inefficient when foiling). And if the windward foil is to produce downforce to assist in controlling heel, the best place to do that is at the windward hull where it has considerably more leverage (and therefore requires far less force) than in the middle.

The only parts that should be in the water are those parts of the foils required to support the boat, dragging along a centreboard and foil that's not doing anything is inefficient (so will require more power to initiate and sustain foiling).

If the intention is to foil in light breeze then simply increase the size of the sails and foils. Also, keep the boat absolutely flat or heeled to windward (hard to do on a multihull), where it's at its most efficient.

As far as I know, all successful muiltihull foilers are designed that way, so there must be more than simple logic to the design.

 

The Fire Arrow uses the main lifting foil because it is an oversquare platform* that would require 15knots + of wind to fly the main hull even with massive sail area. The lifting foil allows the boat to fly the main hull in a 5 mph breeze(model and fullsize) and the foil automatically creates downforce as required. Further, in rougher conditions it will keep the main hull in the air safely whereas the earlier foiling video of Gitana shows the main hull constantly touching down.
*LOA 19.5', Beam 22'

 

The difference in heel to leeward with the hull touching the water or just flying over the surface is small, so I find it hard to imagine that the losses from the extra bit of tilt are going to outweigh the reduction of drag from getting the hull out, but I'm sure they're looking at that: if I'm right, they'll see the speed going up every time the hull lifts out and they'll also see it fall again whenever it touches down. However, if it turns out that it's slowing down or not gaining speed whenever the main hull lifts off because the rig's tilting more to leeward, one way of fixing that would be to lower the foil on the ama so that there is no difference in heel angle.

If you're going to use downforce, the windward hull is clearly the best place to do it if you're trying to set speed records, but if it comes out of the water you're going to be upside down in an instant. Applying the downforce from a deeper foil on the central hull is much safer. The Gunboat G4 doesn't do the downforce thing, but we know it can be flipped over more easily than hoped, and when that happens it's a little inconvenient. A foiling boat with a cabin might be better based on Fire Arrow's foil arrangement, though having the ability to put the windward foil much deeper could be a viable alternative, adding a little drag for a lot of extra safety.

Okay, but that means you don't want to drag the centre hull through the water, and a centerboard + lifting foil which is actively keeping the hull out cannot be described as "not doing anything". If there's enough wind to keep the hull out without the lifting foil, then the lifting foil becomes extra drag, but it all comes down to how much time the boat spends with the hull on the water and how much off, while also taking into account the extra time it spends off the water due to the lift from the foil. If they can fly the main hull most of the time without a lifting foil on it, then they're better off without it, but I'd be surprised if that's the case: they're trying to keep it fairly level, and that means the main hull will keep touching down.

A lifting foil that keeps the hull out and automatically stops lifting when the foil comes out as well would be a simple way of helping keep the boat level. I expect to see changes with the design taking it in that direction, perhaps with sloping lifting foils to prevent bouncing.

 

Go sail a foiler and you'll very quickly discover how badly any leeward heel affects the performance of the boat (they become almost impossible to sail).

A central foil should lift the boat at exactly the same rate as the leeward foil, otherwise it will induce heel. Multihull foilers already have a foil that does exactly that on the windward hull.

Gitana appears to be designed to be sailed flat, as are all successful multihull foilers. When flat, both foils are in the water. If it needs to foil at lower speed, it'd have bigger foils and perhaps sails. Without hydrofoils, these boats will hit 20kn in 10kn of breeze, so achieving foiling speeds in relatively light air really isn't an issue. If they really wanted to foil in say 5kn (which is just a random number) they could very easily be designed to do so with their existing configuration.

But they aren't designed for low speed foiling, they're designed for very high speed which also means very high efficiency. In decades of development, no one who has built a successful multihull foiler has used a central T or designed the boat to foil heeled to leeward. Until someone does that, theories of its usefulness are just that, theories.

 

Leeward Heel in Multihull Foilers

"Leeward heel" making a multihull foiler almost impossible to sail is nonsense!! Look at the two foiling video's of Gitana! And see the last two still pictures below showing Gitana foiling at a small angle of heel. Look at the video's of Hydroptere and many other multihull foilers. And every picture below shows a multihull foiler sailing at an angle of heel and two of those pictures were taken during record speed runs!
The Fire Arrow is specifically designed to sail at an angle of heel from 10 to 17 degrees. Without that angle of heel the windward force* from the mainfoil when it generates downforce would be impossible. And without the designed in angle of heel it would be hard to keep the windward hull(and foil on the Test Model) clear of the water. The Fire Arrow foil concept is designed to allow foiling in the widest possible wind range from 5mph to above 25 mph(on the full size boat). The system allows the main hull to clear the water early and allows the RM to be automatically increased as the wind gets stronger. All the while keeping the boat flying and the mainhull clear of the waves.
*see sketch below

click: Note picture 3 of the Flying Phantom shows it sailing at record speed as does picture 6 of an Oracle AC45! Both are being sailed with a leeward angle of heel as is every foiler pictured below.

 

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And it's not just multihull foilers that successfully sail at a leeward angle heel. The Quant 23 is specifically designed to foil at a small angle of heel: