Rotatable Hull(ROH) Multifoiler

Came up with this a couple of years ago and thought I'd mention the concept here now since I can't afford to patent it-and because I think it has a great deal of potential.
I was impressed by Yves Parlier's l'hydraplaneur which for those that don't know is an Open 60 multi with a difference: it is a cat with two stepped planing hulls looking somewhat like seaplane hulls.In the original article in Seahorse the boat was supposed to have some form of "variable geometry" to mitigate the negative effects of the steps at low speed. The article said the area of highest drag for the boat was between about eight knots and twenty knots with drag above twenty dropping to a fraction of the drag of a "normal" displacement multihull at that speed. In sailing against the ORMA tri's the boat showed flashes of speed but was basically crushed in the two races I'm familiar with.
Since I've designed and sailed numerous multihulls both full size and radio control the idea kind of interested me but I wanted a way to eliminate problems with the step at low and moderate speeds.What I came up with is this:
I envisioned a trimaran test boat 18' LOA with an 18' beam. The main hull would have a hydrofoil on the daggerboard and one on the rudder. But the amas are the key to this concept: they ROTATE! At slow-moderate speeds the ama is an 18-20/1 displacement hull but as the boat approaches a still to be determined "rotational" speed the windward ama is rotated 180°; the boat then tacks and the other ama is rotated .The bottom of the rotated ama is a stepped hull designed to reduce drag above a certain speed. The two foils are designed both to lift the mainhull early AND to possibly add to RM as max speed is approached.They also function to assure pitch stability given the massive sail carrying power of the boat.There is a lot of room for experimentation with the foils since it is possible that their area could be kept quite small. The test boat would be designed to utilize two crew trapezing off the
windward ama.
I've built a small balsa model just to work out the geometry and it works out quite nicely.It is a weird looking hull with the displacement hull deck the bottom of the stepped planing hull! Next thing would be a fully functional rc model but that is quite a ways off. I think it is a beachcat killer with real high potential speed.Great applications on larger versions as well. I showed the model to Eric Sponberg who thought it was interesting and seemed to think the engineering could be done at a reasonable weight.
But right now it's just an idea....

[icetreader]

Doug,

It sounds like an intetresting concept, and now I'm frustrated because you didn't post any illustration of your idea

BTW, have you thought of sending the USPTO a provisional patent application? -It costs very little, requires no professional editing, and could buy you some time to inquire about the market potential of this thing, technical issues and prior art in this field.

Yoav

Here are the balsa concept models:

[Gary Baigent]

Doug - wouldn't it be simpler to roll the amas only 45 degrees - the stepped hull would be, so to speak, the ama's leeward (or windward) side. This is still a very complicated thing to design and engineer aka/ama connections but not as difficult as your half rotation.

Maybe, but I think I've figured out a real solid way to connect the rotating hulls to the boat-not like the models. How do you think this kind of hull would perform if the planing hull was first used at speeds of 12-15 knots on up with the two hydrofoils on the main hull providing pitch control?

[Gary Baigent]

Yves Parlier's cat was a rocket in stronger winds (37 knots recorded during a black squall in one image in Voiles et Voiliers) and obviously the stepped hulls worked extremely well (although the hulls threw huge quantities of water and spray everywhere) - and if you can sort out the rotating float engineering, there is no reason that the stepped amas will not break surface contact, drag will go way down and your boat will also perform well. Yes, the two lifting foils in the main hull will do their job but you will not want the boat rocking while at speed - so the floats will have to be set from a flat main beam, no dihedral.
But remember those two main hull foils are going to drag in light airs and you won't be able to alter that by much. You are going to solve drag problem in light airs with the combination of displacement/stepped floats ....... but foils in floats are not a bad solution because they can be lifted. Parlier's cat was no good in the light as you know. You end up going round in circles and everything is a compromise? Not trying to depress you though Doug - I mean it is an original idea of yours - maybe a 4 metre model first.

[Samnz]

Its a very cool idea!

I thought of doing a fairly close thing on my boat, but not a stepped float and no foils on the main hull, it is rather a float like a windsurfer, on edge in the light breeze and rotated flat in the heavy breeze.

Only reason I didnt pursue this option is in Auckland we never seem to race in a steady breeze so would allways be rotating from on to the other... not ideal

Thanks Samnz.
Gary, this system will be tried on my "experimental platform"(highly modified 19'6" Hobie Miracle main hull-now 21') which I am building now-the amas will be able to be unplugged if they don't work. The boat should be 275lb. all up with 182 sq.ft SA upwind and 14' of beam. The hydrofoils should fly the main hull in very light air.
I'm not sure that the planing amas have anything to offer over foils like the Rave but may be better than a partially immersed ama + curved foil. or "foil assist". I appreciate the comments,Gary-thanks. I have a nagging curiosity about how well this will work...
One design issue is to get the ama planing area right to take over-say at about 12-15 knots boat speed. But the downside is that the thing will have to be capable of tacking and starting off at much lower speed. If this thing is designed right it should allow a fairly small ama keeping weight low. And the interaction between the daggerboard hydrofoil, rudder hydrofoil and displ./planing ama should be fascinating.
If anyone thinks of other considerations or problems/advantages I'd like to hear them....

[Chris Ostlind]

Originally Posted by Doug Lord

... And the interaction between the daggerboard hydrofoil, rudder hydrofoil and displ./planing ama should be fascinating.
If anyone thinks of other considerations or problems/advantages I'd like to hear them....

On some level it may, indeed be fascinating, but the real question for a boat like this will always be...

What's the purpose, other than fiddling for fiddling sake?

If you keep adding complex technical issues to a boat, then you will soon reach the point where the craft operation leaves the realm of the sailor capabilities. Let's point to the automotive industry, where there are a whole host of technical systems functioning in the cars typically sold to the public... most in a passive state with no need for operator input. You know, the stuff like ABS, traction control, auto-coupling/decoupling of all wheel drive, cabin climate controls, air pressure sensors at all four corners and the ubiquitous, engine management system.

In that segment, you do have a parallel for heavily technical machines. But, the dividing factor here is that the complex cars are going to be sold to waiting buyers as a profit generating product. I do not see a boat like this as viable in the commercial sense.

People don't need boats such as this, whereas, current modern, developed civilization puts cars at, or near, the top of the heap for machines that are necessary. If one wants to go faster on a boat, one simply moves up in size with less stuff to go wrong, it will likely be priced in a similar range and it will be a whole lot easier to sail by comparison.

If it's purely an exercise, just to see if it's possible, then hey, have a run at it. It's your time and your money.

[Samnz]

Originally Posted by Chris Ostlind

On some level it may, indeed be fascinating, but the real question for a boat like this will always be...

What's the purpose, other than fiddling for fiddling sake?

If you keep adding complex technical issues to a boat, then you will soon reach the point where the craft operation leaves the realm of the sailor capabilities.

I guess the purpose is allways the same, to win!

If its fast enough you can make other things more simple, like the rig to compensate the extra controls for the floats/foils.