Small trimarans under 20'

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Kites and a tacking version of the SailRocket rig can virtually eliminate the need for conventional righting moment. One kite powered cat I've read about uses foil downforce to hold the boat in the water. It will be interesting to see the rig Paul Larsen comes up with for his ocean racing boat.
On my Fire Arrow trimaran, it's the skippers choice whether to uses mainfoil downforce or to reef the rig.

 

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Richard, do you know what happened to the 3m class? I read an article once that they had something like 10 active boats.

 

I can just imagine what would happen if for some reason the cat lost contact with the water while the kite was at full power... That would be impressive to watch.

 

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One of my books shows exactly what happens: the boat flys! The picture, if I remember correctly, is of "Jacobs Ladder". I'll see if I can find it.

Comment about picture: " On one occasion during the launch sequence of the kites on JACOB'S LADDER, excess power could not be reduced quickly enough and Ian Day became the first sailor to stand a catamaran on end whilst under sail! "

 

In all the years I knew Dr. Sam I never heard of this happening to a Rave, Osprey or SKAT. I've never seen any mention of such an incident with the Hobie Trifoiler or Long Shot.
Have you ever heard of or seen an incident like you describe?
If so, do you have a link?

 

The only thing that comes to mind is Hydroptere at 1:37 in this video.


https://www.youtube.com/watch?v=VS9bX_fTBJE

I'm not sure if it's even using the windward foil for downforce. This may be completely unrelated, but I suspect it would look like a much faster version of that. Perhaps it isn't as bad as we would think, in which case, I guess once you get a fast cat on foils in the groove, you could just power up to the max the boat can handle and it will just dig in and scoot along. I would like to see it actually happen. How do you plan to do that with just uptip foils on the amas?

 

Not even close-Hydropteres foils don't pull down on the windward side*. But that makes me think: as much research as I have done since 2000 w/o video of a Rave or Trifoiler "pulling loose" with the windward foil must say something....
It just doesn't happen. I have heard of a guy foiling a Rave in Spain who didn't heed the never exceed speed and broke the main crossbeam!
* Hydroptere uses about 1700lbs(?) of water ballast in the windward ama.

 

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What do you mean "just uptip foils on the amas? I thought you understood how my boat works. The good thing, the revolutionary thing about uptip foils is that a single foil can control the altitude of the hull(ama) it is attached to regardless(for the most part) of speed. It does that(for the most part) by leeway coupling, that allows the leeway of the vertical portion of the foil to work to increase lift of the horizontal portion. Uptip foils at the beginning were somewhat different than what is used on the 32 ,Nacra and FP in that they required AOI(angle of incidence) adjustment if the speed of the hull they were attached to rose above or sank below their effective speed range. Since then it has been learned how to design the foil so that it can have a minimum amount of adjustment. The UptiP ama foils I designed for the Fire Arrow have not yet required adjustment and you can see a photo illustration of how well they control ama altitude in pictures A & B on the last page of my thread. That takes care of the lee ama-the windward ama is almost never in the water.
So, we come to the main wand controlled foil that uses dual wands because of the width of the boat-when the boat heels the leeward wand is always wet. The wand length is set(now) to allow the main hull to fly about 3" and to sail at about a 10 degree angle of heel. The wand controls the altitude of the main hull and the angle of heel of the whole boat. Should the angle of heel increase beyond the "set point" of the dual wand system, the wand causes the flap to rise creating downforce. Downforce can be used as just a momentary gust response, as a way to power up the boat ,or as an indication that it is time to reef.
I hope that helps you to understand.....ask questions if you don't.

Notes on the Fire Arrow system:
1) main hull altitude and therefore the angle of heel of the whole boat can be adjusted by changing the length of the dual wands, no adjustment required of the UptiP ama foils.
2) The mainfoil begins to unload as soon as the main hull flys, reducing induced drag,
3) the mainfoil and the rudder foil ,working together, give the Fire Arrow much greater pitch control than a "normal" trimaran,
4) The mainfoil and rudder foil working together control the ride angle of the UptiP ama foil so that it stays at about the same angle of attack automatically.

 

We saw Jacobs Ladder performing in the 1983 Weymouth speed trials. We were there on our Gwahir catamaran, probably the only people ever to live on board their boat during the speed trials.

I don't know what happened to the 3m class, too slow and heavy and took long to rig is my guess. I know there are a couple still around in the PNW but I have not seen one

RW

 

This has happened to me personnally. I have a speedsailer, a bi-directional version of sailrocket, built back in 98-2000, and it uses a foil to create negative lift to resist the sail forces. The forces that can be generated are very large (no heeling moment), but the moment the foil loses grip the acceleration to leeward is vicious and uncontrollable (no capsizing because there's no heeling moment).

This was also a common problem on the old windsurfers, where we could apply very high forces through the skegs, but the instant the foil emerges an uncontrolled spin-out occured. Modern skeg design has reduced this considerably, primarily by increasing immersion.

Fundamentally, if you have an arrangement where the foil force reduces as the applied force increases, then you will be vulnerable to this. With my foil, the downforce is proportional to both speed and applied force, which controls the AoA, but in a highly non-linear manner and only up to a lower limit of immersion, at which point all lift is lost. The violence of the event depends on the proportion of RM being provided by the downforce, and thus I suspect the proportion is relatively low for the boats you mention. In my speedsailer the forces being generated are about 8 times the weight of the vessel, hence very rapid acceleration when the force disappears.

 

Very interesting-thanks. Any chance you could post pictures of your boat?

 

Do the ama foils adjust angle of attack or just the main hull foils?

 

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The ama foil angle of attack is controlled by the mainfoil and rudder foil working together. The ama foil cannot substantially change it's angle of attack on its own other than the slight variations caused by waves.
The wand changes the effective angle of incidence of the mainfoil by moving the flap which can affect its angle of attack(the relationship of the foil to oncoming flow). The AOI(angle of incidence) which is the relationship of the foil angle when set up with flap neutral to the static waterline is 2.5 degrees for the main foil, zero for the rudder foil and +6 for the ama foil. AOI is always measured in referance to something on the boat-like the static waterline. The AOA(angle of attack) changes with all the foils based on speed and waves and is constantly changing.The best measure-or reference to- angle of attack is the pitch angle of the boat measured when its flying(referenced to the static waterline). That's why when talking about foil setup you always refer to the angle of incidence because it doesn't change unless you change it or in the case of the wand controlled foil unless the wand moves the flap-but even then you refer to the fixed angle of incidence of the mainfoil with flap neutral for setup purposes.
Pitch attitude of any hydrofoil changes from takeoff to cruise with a nominal pitchup of around 6 degrees for a light air takeoff to a cruise anywhere from near zero(parallel to the static waterline) to +3 degrees for cruise in lite air.
You can estimate angle of attack by adding the pitch angle to the angle of incidence.

 

So the only way to create downforce on the uptip foils on the amas is to pitch the whole boat down? Won't that pitch both ama foils down? I would think something like the kitefoiler, two independent wands and L foils, one on each ama, would be most effective. Then one wand is saying to increase lift, while the other wand is saying to increase downforce, so you have up on one side and down on the other.

Check out this video: Kitefoiler K2. Especially at 0:37


https://www.youtube.com/watch?v=Yjm9nvxOWGQ

 

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On my boat you would never,ever, want downforce on the UptiP ama foils. Downforce can only be generated by the wand controlled main foil.