My Hydrofoiling yacht project

Discussion in 'Sailboats' started by TheUnlogicalOne, Jan 8, 2008.

  1. TheUnlogicalOne
    Joined: Jan 2008
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    Location: Victoria, B.C.

    TheUnlogicalOne Junior Member

    This if my first post here, but I have lurked around for a while. I hope no one minds a virtual project instead of a real boat.

    I like to doodle and design things for fun. I know I'll probably never have the time or knowledge to do it properly but I like to at least keep things semi-believable. I've been working on and off on a hydrofoil yacht that someone set me as a project. Unfortunately I've never sailed anything longer than about 3m (and quite badly at that).

    To this end I have two questions:

    1. What is an average displacement/mass for a 20m trimaran yacht? I'm just looking for a ball park figure for a middle of the road boat (if such a thing exists). If they don't what about a similar size mono hull? I guessed as a ballpark figure 20-25 tonnes.

    2. I only have a general understanding of hydrofoils and lack the intuitive understanding that I would expect comes from experience. For a hydrofoil like l'Hydroptere which uses angled foils on the front (this is so it self trims right?) wouldn't the ride get a bit bumpy in rough water with the constantly changing submerged area?

    If this is the case would adding a pivot at the top of the foil coupled with a shock absorber help? l'Hydroptere seems to have a similar structure but I have never noticed any deflection/movement in movies of it. In addition if the pivot were angled to the side the AOA of the foil could be decreased as it rose out of the water. Alternatively a linkage between a set of flaps and a straight pivot may be simpler. Does anyone think this would help damp out the movements of the ship? Intuitively it makes sense to me (although a variable damper connected to a computer might be needed for varying sea conditions) but I don't have enough experience to say.

    I've attached a few images of my project in it's current state. Please note that there are many things that I plan on rebuilding (such as bigger sails, bigger outriggers and completely new, larger foils). Unfortunatly both my modeling and design skills are suspect so who knows when anything will happen.

    Attached Files:

  2. Pericles
    Joined: Sep 2006
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    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

  3. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    I have often thought of such interesting concepts, then reality kicks in when I think of the number of sea-containers, logs and other flotsam, which could stop one very suddenly!
  4. Doug Lord

    Doug Lord Guest

    TUO- you might consider doing some research on . Some of the info on the big tri's is on the multhulls forum here.
    Note that Hydroptere is 80' wide and 59' long-very important! And Hydroptere uses movable water ballast brought in thru an intake on the rudder and pumped to eiher/or both ama's-up to 1760lb. per ama and some ballast in the main hull to aid pitch trim.

    Masalai,one of the things the Hydroptere project is developing is a combination radar/sonar designed to spot partially submerged objects and/ or objects just under the surface in time to avoid them. Such a system is a requirement, these days, for any kind of ocean going foiler,in my opinion.
  5. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member


    (i) Welcome aboard :)

    (1) It's hard to define such a thing as an "average" weight on such exotic boats. A 60' / 18.3 m ORMA tri might be around 6,000 kg when hanging from the load cell. (They're basically an empty carbon shell and a bunch of composite beams and stays, not much if any cabin space.) A liveaboard, ocean-cruising multi of similar LOA could be as much as 30,000 kg.

    (2) The foils on something like l’Hydroptère that flies all hulls all the time must do more than just lift the boat clear of the water. They have to be able to precisely balance the overturning moment of the sail plan, and to provide just enough resistance to leeway for the boat to track reasonably well. I hate to think how many pages of equations and gigabytes of computer models it took to get them the way they are on that boat. Damping, again, is a matter of tremendous math and simulation.

    Crazy-cool 3D renderings, btw. I don't think your CAD modelling skills are suspect. Or your patience, for that matter.

    Attached Files:

  6. Chris Ostlind

    Chris Ostlind Previous Member

    Total agreement on that. I spend a lot of time in Rhino doing rendering and you've really done the whole thing there.

    On the weight thing... I have not run any numbers, but a preliminary eyeballing of the design would lead me to believe that the boat has too much wetted surface, too much possible weight and too little sail area available to be a functionally ball-parked virtual foiling boat.

    I do get that virtual boats do not have to behave to the laws of physics, but you did say, semi-believable. Matt touched on that very softly with the numbers for a cruising design as opposed to a full-tilt foiling machine.

    As a, what-if, design study exercise, it succeeds... brilliantly. That's made the more so by your wonderful rendering skills and attention to detail.

    Hat's off to you, Grand Master Unlogical One.


  7. TheUnlogicalOne
    Joined: Jan 2008
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    Location: Victoria, B.C.

    TheUnlogicalOne Junior Member

    Thanks for the input everyone. I had thought about the debris problem but didn't have a solution. The pod on the rudder might be a good location for a forward looking sonar. As for, I've looked around before (but mainly at the pretty pictures). I'll have another look through.

    As for water ballast, it was always my intention to have it in some form. I figured that the sails could also be connected to a computer which could adjust them individually to help stability in quickly changing wind.

    I had considered adding control surfaces to the forward foils but decided against it (i can't remember why). Is it necessary to do so? I had thought the angle and the fact they are surface piercing would sort all that out.

    Most of the ship was designed using the "It Looks Sort of Right" (TM) method, but I tried putting the hull into Delftship. I don't know how accurately I managed but with those sails it should do around 12-13 kt in a 15 kt wind. It's meant to lift off at around 9 kt (I think, the foil area from the top is about 6 m^2.
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