Planing Trimarans

Discussion in 'Multihulls' started by Doug Lord, Sep 30, 2006.

  1. Doug Lord
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    Doug Lord Flight Ready

    ===================
    I understand. I was just curious about what you would say.
    It's been my contention for a very long time that a monohull could be designed using foils and ballast to be self-righting AND faster than an equivalent length multihull using "foil assist"(like the ORMA tri's). Sort of have your cake and eat it too-but that's another thread entirely.....
    http://www.boatdesign.net/forums/sa...acing-monofoiler-design-discussion-15143.html
     
  2. tspeer
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    tspeer Senior Member

  3. cavalier mk2
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    cavalier mk2 Senior Member

    It does have water separation from the ama transom which is part of the planing definition, nice rooster tail. With a photo to show the amount of ama immersion the load it is carrying could be averaged and compared with the overall boat weight . The same process could be used on the main hull, if the amount displaced by both hulls is less than total boat weight and you have immersed transoms with definite wake/water separation you have the definition for partial dynamic lift/planing. More complicated calculations would then be needed for the if both hulls are planing how much is each carrying debate/free for all. It is a nice planing shape......If it doesn't help then it has to be considered like tail fins on a car? Racers don't usually want to carry extra weight......the foil lift could be measured would have to be measured by taking a run with and one without. The downwind picture in the ad shows the ama wave popping up just astern with the bow lifted, at higher speeds it should lengthen astern if it is planing. The lift from the foil might be forcing the stern down a bit too much? The Antrim would reward the careful sailor who measured the effects of various board depths etc...to find optimal course/speed settings but it makes it hard to tell how much if at all the ama planes with it down .
     
  4. Capn Mud
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    Capn Mud Junior Member

    Certainly be intersting to see som more pictures rear on, front on and from leeward side.

    The amas appear to be shaped for planing when the boat is flat. At this sort of angle of heal does that shape still plane as you get near the point of the elipse shape?

    Thanks for the pic Tom
     
  5. tugboat

    tugboat Previous Member

    hi-fdoes anyone else on here think that planing hulls are the wave of the future?
    i thought a very very slight v and stepped hull could work even if the ride might be a bit bumpy--it would take of in a good breeze. also what about a aerofoil as a deck? ie one designed to give lift as the vessel picks up speed??..
    the aerofoil would be mounted like a huge wing,and used as a deck instead of a trampoline, i.e. between the two hulls of a cat- set at an angle slightly dwonward to prevent too much lift and preventing a the boat from taking flight and a rollover. but would still add lift thereby reducing friction??
     
  6. cavalier mk2
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    cavalier mk2 Senior Member

    Sounds like a Nicol. Having control surfaces hooked up to a lift management system would a nice touch for such a wing. I think it would provide more lift for a hydrofoil because it is above the surface of the waves and in clear air.Close to the water a wing deck is functioning more in ground effect mode and is sheltered by the waves. When Hedley flew Vagabond 1 they had to wait for flat water to get the lift, otherwise in normal seas the wing was sheltered.
     
  7. tugboat

    tugboat Previous Member

    Cavalier mk2- any ideas on a lift management system forgive my lack of knowedge here --
     
  8. tugboat

    tugboat Previous Member

    yes the wing would run the risk of "plowing" it would have to have good freeboard on the hulls...to ride above the waves.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    Antrim 30

    ======================================

    Jim Antrim says:

    "The high buoyancy, planing geometry[ of the ama]
    is highly resistant to burying the bow at any speed."
    "...attribute this to a wonderfull synergistic effect between canted boards and the planing hull shapes.High static buoyancy, planing ama shapes and canted daggerboards form the holy Trinity of anti-nosedive safety."
    Jim Antrim
    Antrim 30+
    Address:http://www.antrimdesign.com/trimarans/erin/


    Click on the black and white image and then again on the resulting image for largest picture:
     

    Attached Files:

  10. cavalier mk2
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    cavalier mk2 Senior Member

    Hey tugboat, the aircraft industry has already done the research on control surfaces, flaps etc....With management of the foils as well as the sails like the Walker Wingsail the power/lift could be optimized. Foil borne a lifting wing would have a steady angle of attack. A hydrofoil boat also will keep the apparent wind forward which helps the wing lift. The downside is having a boat/machine the computer sails for you but that is what happens in commercial aircraft.
    Does anyone know if the Catri style ama tail fins produce less drag than the Antrim planing ama stern ?
     
  11. catsketcher
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    catsketcher Senior Member

    Those amas plane?

    I know Jim Antrim calls them planing but those amas look as planing a shape as my kayak. As I said I sailed a D2 sailboard a bit and they were flatter than this shape and I don't know if they planed - they sort of swooshed rather than planed - like the modern skiffs. Anyway he gets it wrong (not in design but at least in his writing about it) when he says that planing helps in nosediving.

    For one the boat looks pretty bow down to me which is pretty usual in Tom's shot. I get that. As for foils - I may incur Doug's displeasure but a small boat with forward mounted foils would not be my choice offshore as the foils could go negative in a big swell. The 60s do have foils like this so it is not an issue in big boats. They are more stable fore and aft. VSD capsized in the 80s when her bow foils went negative. So the Antrim (like the ORMA boats) has foils probably about the CE thrust line.

    The only flat bit of the ama is the stern and that is the last thing I would want to plane. Having powerful sterns is a no no in tri design. In fact if we look at Farrier's boats the floats are usually shortened to reduce volume aft. This helps stop overpowering the bow. The Antrim 30 has low volume amas aft which is normal.

    Here is why planing floats would be bad news. Planing relies on angle of attack to generate lift. Suppose you are off shore and your planing ama is generating lift because of its planing shape (so it is acting at a positive angle of attack to the waterflow) then you get to the bottom of a large wave and then the float must turn about 20 degrees to climb up the back of the next wave. If the ama planes it will slowly have to rotate itself so that its angle to the waterflow is always positive. This may be much slower than what is necessary to get the bows up and then the bows stuff which is not good. Do a thought experiment and substitute foils or surfboard for the ama. This is why you won't find any foils right up the front (unless they are active) What you really want is volume AND a lack of drag when the bow is immersed. And get that foil back near the centre of rotation so that if it won't increase rotational inertia in swells.

    Jim has designed more good boats than me but I think his writings on this aspect of the design may be aimed more at the general market and selling boats than picky guys around the world obsessed with details about boats - yeah us.

    cheers

    Phil
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Phil, I guess I don't understand how moving the center of lift of(lifting) foils aft would help in a seaway. Sounds to me like the conditions you described would not be conditions suitable for high speed foiling/"foil assist"? A 20 degree change in attitude?! Do you think an ORMA could handle that at foil assist speeds? ORMA tri's regularly flew 70% of the boats' weight in serious conditions-with serious problems in some cases-like the thing flying too high, ect. And most ORMA tris flew with no rudder t-foil which I would consider essential on smaller tri's using lifting foils.
    Back to planing: I don't think there is much voodoo in determining if a boat is planing-I think there may be some voodoo in an analysis that says if the ama has taken some of the load the planing main hull won't plane.
     
  13. Gary Baigent
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    Gary Baigent Senior Member

    When the Antrim boat heels, those dagger foils will be providing lift because the Antrim platform heels to what? - 20-25 degrees? in fact they will be doing most of the work in keeping the platform's bow up .... and will give the illusion to the PTB's, (planing tri believers) that the leeward aka is planing, along with the levered out main hull. In the Tom Speer photograph that leeward aka is pushed deep and kicking up a lot of fuss, and doesn't look like planing to me with that rooster tail, in fact it is ploughing. According to Gutelle, the wake aft of a planing hull will equal the shape of the hull forward, and the wake is smooth, not torn to pieces as in said photograph.
    A point on foils going to negative angle of attack and their placement forward; asymmetric foils still provide lift even at minus angles - you have to go a long way to a steep nose down before the defecation hits the fan - and at an angle that any conventional float and hull will be reaching the cartwheel point anyway. They also have to be placed forward and not central because if the latter, the boat will be rocking on them ... and that is a sure case for a nosedive.
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    When the Antrim boat heels, those dagger foils will be providing lift because the Antrim platform heels to what? - 20-25 degrees? in fact they will be doing most of the work in keeping the platform's bow up .... and will give the illusion to the PTB's, (planing tri believers) that the leeward aka is planing, along with the levered out main hull (which looks like it is planing but is, in reality, only half the boat). In the Tom Speer photograph that leeward aka is pushed deep and kicking up a lot of fuss, and doesn't look like planing to me with that rooster tail, in fact it is ploughing. According to Gutelle a planing hull has a smooth wake astern equal to the length of the hull/float forward - and that is no smooth wake.
    A point on foils going to negative angle of attack and their placement forward; asymmetric foils still provide lift even at minus angles - you have to go a long way to a steep nose down before the defecation hits the fan (and at an angle that any conventional float and hull will reaching the cartwheel position anyway. But agreed, at that oh no point, the foils will provide a tripping action. They also have to be placed forward and not central because if the latter, the boat will be rocking on them ... and that is a sure case for a nosedive.
     

  15. CT 249
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    CT 249 Senior Member

    Cav, re "The complete definition of planing I gave earlier did include wave separation and was a quote from Juan Baader who knew the difference."

    I really enjoy Baader's book and respect his knowledge. However, there are other people with equal or greater qualifications (formally and in practice) who do NOT agree with his definition.

    One problem I have with Baader's definition is that there are some craft where the transom runs free with a detached stern wake and appear to ride on their bow wave, but do this at a low speed when they do NOT appear to be planing as 99% of people would define it.

    Furthermore, as the sinker windsurfer example was meant to show, you can develop dynamic lift at very slow speeds, when planing is not involved. Surely the most basic Newtonian physics says that at any time when a fairly standard hull surface moves forward at an angle of attack in the vertical plane, there is SOME dynamic lift. That is, if the typical bow sections of a typical boat move forward at .00000001 knot, then SOME molecules of water will be displaced downwards. Once a single molecule is pushed down a single micron, we have SOME measure of dynamic lift and the boat is therefore "riding on its bow wave" and "using dynamic lift" to some extent.

    The other problem with Baader's definition is that it's either imprecise or impossible, because there's no clear meaning to his words "the hull detaches itself from its wave system, leaving its stern wave far behind and beginning to ride on its bow wave."

    And what is "detaching itself from the wave system"??? Look at any high-speed powerboat and one still sees a wave system that starts at a point on the hull and travels at the same speed of the boat. Again, it's very simple physics. Even a waterski has a wave system that starts at a point somewhere near the ski (so it's attached) and travels through the water at the same speed as the ski does. You can see the wave system clearly at the end of this video;

    http://www.youtube.com/watch?v=R-el1H3PUG0

    That vid is of the world waterskiing speed record being broken. If a ski isn't planing at 150mph+, when is it?

    Another good view of a high-speed wave system that has NOT been left behind comes a speed windsurfer comes at about 3 min into this video

    http://www.youtube.com/watch?v=HL2_ElienFI&feature=related

    So is the windsurfer not planing?

    Re "Go back a page or two. Sounds like your windsurfer was functioning more like a control foil when underwater".

    Yes, the board wasn't planing according to Baader's definition. It was planing according to some definitions, like the one you had given in the post I was replying to. The point is that the common definition "a craft is planing when it is being lifted by dynamic forces" can't really work, because some craft are being lifted by dynamic forces when they clearly aren't 'planing' as we accept it.
     
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