Small trimarans under 20'

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

  1. Doug Lord
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    Doug Lord Flight Ready

    Maybe if he sat on the end of it? But that might hurt.......
     
  2. waynemarlow
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    waynemarlow Senior Member

    The boards are so so big and draggy looking that on first sight you have to say that in multihulls they would be a major source of drag as we already can do 20 knots without boards, I guess on monos that's the sort of speed they aspire to, rather than what they are already doing.
     
  3. Vantage475T
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    Vantage475T Vantage475T

    Quick update ref the Len Surtees Sting 600 - it has been delayed a bit further but Len is now aiming for launch in early July. He's uploaded some more photos onto the website Home | sting 600 https://www.sting600.net/ giving a better view of outriggers and folding beam system etc.
     
  4. Doug Lord
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    Doug Lord Flight Ready

  5. Vantage475T
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    Vantage475T Vantage475T

    I'm a clod. Been out of action for a short while and not caught up with everything yet...
     
  6. Doug Lord
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    Doug Lord Flight Ready

    No, not at all-its good to have it in both threads. The 600 is designed to be good as a regular tri and as a foiler.
     
  7. Dolfiman
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    Dolfiman Senior Member

    I like this idea, it seems that your boards mounting allows you to test various angles (as sketched attached) and I bet there is an optimum (about 15° to 20° ?) for which you can recover both more lift and a component contributing to the leeway resistance.
     

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  8. Doug Lord
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    Doug Lord Flight Ready

    Dolfiman, I'm using planing amas on my designs(Fire Arrow and WOLF) that are designed for incidental contact with the water at about 6-10* degrees where they would be close to flat. I never considered that these surfaces would contribute to lateral resistance-leaving that to the foils designed for that purpose.
    Do you think that if the planing surface was angled, as you suggest, the planing potential of the board on Waynes boat would be affected? Maybe delayed or higher drag than if they were flat?
    *13 was wrong!
     
    Last edited: Jun 27, 2018
  9. waynemarlow
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    waynemarlow Senior Member

    Dolfiman, yes they are adjustable to what ever you want, the boards are actually just a 3.6m windsurfer cut in half and then the cut section was slightly curved to give an asymetric hull shape, so that up wind hopefully we can get a bit of Hobie type going to windward. At the moment I have them set so that they are flat to the water as they enter the water. Its about 10 degrees by memory.

    The other reason for the flat inner hull shape was so that the Ama angle stay can be disengaged and the Ama swings up under the Tramp area for trailering.
     
  10. Dolfiman
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    Dolfiman Senior Member

    My suggestion is there, especially if it is easy to do : to test some angles instead to aim being flat exactly, just to see what happens, a "learning by testing" experience.
     
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  11. waynemarlow
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    waynemarlow Senior Member

    I'm not sure how an asymmetric hull would operate if it was inclined, your drawing shows a symmetric profile in the water and I would probably agree that you could play with angles, we used to over rotate my old F16 in choppy water and it make to weather better than if you kept it in the more normal inclination.
     
  12. Dolfiman
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    Dolfiman Senior Member

    I had not understand that you have used a half board when I drew my little sketch. And yes probably that an assymetric hull will be less relevant for an inclination test.
    But anyway it is a great idea to explore in my opinion, at least for under 20' trimaran in sheltered seas, to use board shape amas relying mostly on their dynamic lift (with let'say a buoyancy of just 50% of the total displacement, to debate) instead of classic amas relying quasi uniquely on their buoyancy lift of 150 % to 200%. So a lighter trimaran, potentially. In this perspective, the inclination issue is important, to maximise the lift effect, to recover a bit of leeway resistance, by light winds to reduce the wetted surface, upwind versus downwind performances, .... in brief to identify the best trade off.
     
  13. waynemarlow
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    waynemarlow Senior Member

    The whole intention of this little Trimaran was to explore the benefits of a slender single hull with ama's as a form of stabiliser, together with RM assistance from a trapeze, to minimise the size of the Ama. In practice it seems to work fairly well and I think once I can get the mast location a bit better, there's real fun to be had with the bonus of easy getting back on board when things do go wrong.
     
  14. Dolfiman
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    Dolfiman Senior Member

    Ok understood, that's different objectives. My suggestion was because myself I am working on this idea of boards as amas for small tris, how that can work with a high ratio of dynamic lift, with boards surfing on the water surface instead of hulls crossing through. But it is not yet mature in my mind.
     

  15. Doug Lord
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    Doug Lord Flight Ready

    "Two Stage ama"--
    Dolfiman and Wayne, I came up with an idea 10 years ago to use a planing ama as small as I could make it. For my boat it didn't have enough buoyancy to prevent the boat capsizing if it wasn't moving and was hit with a 10 knot gust. So I came up with what I still call a "curved piece"(which is exactly what it is ) that was large enough to double the buoyancy and prevent a knockdown in the conditions I just described. I learned I could increase the crossarm dihedral
    which works well for clearance and seating. The curved piece is attached to the crossarms and the ama hull is attached to the curved piece at the bottom and max forward.The ama hull is double ended so accidental immersion at slow speed would produce the minimum drag. The planing surface extends to the aft end of the ama hull. The two stage ama works well on the boat with an ama foil allowing the ama hull planing surface to have just incidental contact with the water.
    But on the second day of sailing the Test Model the ama foils were too small and the ama was more or less constantly in the water and surprisingly worked real well. Thought you guys might find the rationale and shape interesting with or without a foil.

    MPX-ama foil.jpg MPX-two stage ama 2.JPG MPX-Two Stage Ama.JPG
     
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