Small trimarans under 20'

Discussion in 'Multihulls' started by Doug Lord, Jun 24, 2012.

  1. waynemarlow
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    waynemarlow Senior Member

    At the moment the only proof of concept of the Fire Arrow is that of a model. As much as I would like it to scale up, I have serious concerns of the practicality of the foils system and of the small Ama buoyancy in in anything but ideal conditions.

    Take the Ama's. The volume is tiny in comparison to what is generally accepted, around 150 %. That limits the sail area to a relatively small high efficiency sail other wise you could quickly run into trouble just as you bare away from the upwind run, it's the one time all racing cats run into strife and with these very low volume out riggers, that will be magnified foils or no foils, add in waves or sea chop and those Ama / foil combination could be over whelmed creating the perfect Storm of submerged Ama with a sail beginning to fully power up.

    I'm not convinced of the centre foil being able to cope with the change in sea height and speed. The Moths show superb control by sailing fast and relying on speed to "average out " the rolling shape of the sea surface. The Fire Arrow design is quite a different beast, quite heavy and much slower. It will require quite sophisticated damping in the wands to prevent harmonic oscillation of the classic "too much movement at the wrong moment" of the aileron, light weight aircraft went through this and it hindered their designs for some time.

    I'm not saying it can't be done and the problems sorted, as in a way the design has merit, but until the design is moved onto a full size example, there are doubts.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    ==============
    The Fire Arrow is being carefully tested and the results so far are very encouraging. We know that the main foil wand system works because on the day of the last video the main hull could not have flown without lift from the wand controlled main foil. The wind was too light to fly the main hull.
    We know the UptiP ama foils work because there are pictures showing them lifting in two different load conditions and at two different speeds.
    The potential of the Fire Arrow foil system is just awesome and testing will continue with much more video this year.
    As far as the model test results being valid-they are, as shown by many others in a previous post, and because of the specific things being tested: foil area and placement ,CG position vs a vs the foils, rig position, beam, Wand controlled main foil system, UptiP ama foils, cross arm dihedral and vertical position of ama foils and more.
    So far they work perfectly. The only exceptions are the rudder sensitivity setting that wasn't right on the second video or the last video-but I know why. And the rig: it is extremely adjustable but I haven't got it right yet-in the last video it was only developing about 50% of the power it has.
    =====
    This is enough about my boat in this thread. If you want to ask questions or make comments about it, please do so in the thread. I will answer any further questions or comments in that thread,link below:
    http://www.boatdesign.net/forums/mu...f-righting-trimaran-test-model-36058-124.html
     
  3. mundt
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    mundt Junior Member

  4. Doug Lord
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    Doug Lord Flight Ready

    What boat is that?
     
  5. mundt
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    mundt Junior Member

    L7...
     
  6. waynemarlow
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    waynemarlow Senior Member

    Doug good move to keep anything to do with the Fire Arrow to its own thread, but will that also include the foil concept as well, it's still only proven at model size and that whole concept belongs in that model thread until proven at full size.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    I'll answer any Fire Arrow questions or comments in that thread. As to model testing ,apparently you have no clue. That's ok but people who are interested in a bit of info on model testing should checkout post 289, page 20 in this thread.
     
  8. waynemarlow
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    waynemarlow Senior Member

    There you go again, straight in mentioning models again;)
     
  9. Doug Lord
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    Doug Lord Flight Ready

    Attached Files:

  10. upchurchmr
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    upchurchmr Senior Member

    [​IMG]

    Main hull looks a bit like the Gougeon Splinter (25').

    [​IMG]
     
  11. Doug Lord
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    Doug Lord Flight Ready

  12. rcnesneg
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    rcnesneg Senior Member

    What do you guys think of the following trimaran:

    Basically a small version of a powered up maxi tri, comparable to an A class, but a trimaran.

    LOA: 18'
    Beam:14'
    Weight: 150 lbs (obviously a lot of carbon)
    Rig: A cat rig, carbon mast, height 30', A class sail with jib, canting up to 10 degrees. Sail area upwind around 250 sq. ft. Masthead spin for downwind.
    Vaka: Heavily rockered, rudder, but no daggerboard. No cabin or footwell.
    Amas: Medium volume with curved lifting foils/daggerboards and rudders(Capable of flying the main hull comfortably with foil assist). Probably the same length or longer than the main hull.
    Crew: 1, weight: 100-200 lbs, able to move about from one ama to the other on a trampoline.

    Cost: Open ended, say twice that of an A cat.

    Basically it would look like a small version of BMW oracles USA 17 with the fabric sail.

    This would use the same philosophy as the standard A-class cats, so no goofy stuff, except possible use of a wingsail.
     
  13. Doug Lord
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    Doug Lord Flight Ready

    I doubt you could do it with amas that long for 150lbs. Why did you choose 14' for the beam? Why would you make the mainhull "heavily rockered"?
     
  14. rcnesneg
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    rcnesneg Senior Member

    Ok, say 200 lbs then, and make the amas shorter, say 14 feet instead of the full 18. An A-class can get in at 165 lbs...

    I chose 14 feet because it is wider than a tornado, but not quite square, as the crew can move around, so I thought it was a good compromise.

    Heavily rockered main hull is for tacking and maneuverability. This is what I have in mind:

    http://www.juanpanews.com/wp-content/uploads/2012/03/ImageNews.jpg

    three more examples:
    http://www.boatdesign.net/forums/at...6d1321238848-trimaran-tornado-cat-bmw-usa.jpg
    http://cdn.streamlike.com/secure/Covers/68/11830.jpg
    http://www.seagypsypress.com/wp-content/uploads/2013/08/Mod-70-Trimaran-Spindrift-e1376010459782.jpg
     

  15. Doug Lord
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    Doug Lord Flight Ready

    Anyway you could reduce the size of that picture? It makes it difficult to read all the posts on the page. If you make the boat "highly rockered" and still want to fly the main hull you'd better check the "takeoff angle" of the boat with the 14' beam. Tris range from 10 degrees to as much as 26 degrees angle of heel as the main hull just lifts off. The boat in the picture is likely to be square*.
    * it's not square: 69.5' LOA X 55' beam MOD 70
     
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