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

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    Dolfiman, I found these two papers when I was trying to learn how to calculate lift for a planing surface like a windsurfer(Fire Arrow) :
    PS- I was given a "rough" tip years ago that a windsurfer planing surface area would be in the vicinity of half of the lift of an equivalent hydrofoil. So, for instance, a Moth with a 180lb crew, 66lb hull+ rig and a 1.1sq.ft. main foil would lift(at 80% total load) about 178.9lb per sq.ft.. A windsurfer would lift about 89lb per sq.ft. according to the tip. I think I wound up with an approximate lift on my planing amas of around 67 lb of per sq.ft. @ 4 degrees angle of incidence of the planing surface at the inception of planing. On my amas it's not critical because most lift comes from the ama foil-the planing surface is just back-up for incidental contact with the waters surface only.
     

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    Last edited: Jul 4, 2018
  2. Dolfiman
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    Dolfiman Senior Member

    Thanks, very helpful info and documents,
    The figures which are mentioned in Jim Drake document are not annexed to it ?
     
  3. Doug Lord
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    Doug Lord Flight Ready

  4. Dolfiman
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    Dolfiman Senior Member

  5. Lurch723
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    Lurch723 Junior Member

    BE3197A1-CE53-4172-938F-023A6A684211.jpeg C94D49DE-F519-407D-BA84-2DF37FCC53E6.jpeg I managed to sail my design a couple of weeks ago in a good f3-f4 of breeze. I’m only running a rudder lifting foil for the early tests and the results are impressive. No figures as I’m not datalogging at the moment.

    It points well and the modified 49er rig allows for very precise trim by controlling the leech tension on the main sheet.
    Across wind on a beam or above we are both wiring and dumping power as too much drives the bows down, but because I designed in a lot of forward bouyancy she simply adopts that attitude and continues to sail predictably. With the front main foil fitted it’s going to go totally bananas as we will be able to use all the power and keep accelerating.

    On a broad reach there’s no need for a kite, single wiring with main and jib sheeted in it demonstrated that it’s an apparent wind sailing machine - very impressed and again very controllable. Again with the front foil on I believe we will be twin wiring on 2 sails.

    On a run with the kite up we were single wiring and going very deep, again no lee or weather helm but were covering the bay at such a rate it was over far to soon. So that’s the good stuff...

    The bad stuff is I need to change the sheeting position to allow the use of only one tiller extension as I had a lot of problem with the redundant tiller locking off the helm on the bridle. One of my trampolines came lose and I need to fit a different kite halyard cleat and another block on the self tacking jib. The 49er rigging procedure is terrible, I hate it and would dearly love to fit a carbon F17 mast and main but it’s too much money for now.
     
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  6. Doug Lord
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    Doug Lord Flight Ready

    Are you talking about a single lifting foil in each ama or a single lifting foil on the main hull forward?
     
  7. Lurch723
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    Lurch723 Junior Member

    Rudder foil is a Cucifix foil that I can adjust on the fly from my tiller extension, the main lifting foil which I have yet to fit isdeigned to put the boat into a skimming or just bourne mode. One of my questions I wanted the answer to was what was the smallest surface area I could plane on and I believe this boat did just that, it also wave pierced beautifully and just kept going, ignoring waves and not slowing.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    Will the main foil be attached to the daggerboard on the center hull?
     
  9. Lurch723
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    Lurch723 Junior Member

    Sorry about that - not very concise of me, just forward of the centreboard and forward of the CofG on the main hull so it’s pitch stable and responsive to rudder lift trim. I’m using H105 as the section so it’s one of Toms.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Lurch, on at least 90% all foilers the forward foils/ daggerboard(s) are located just forward of the CG. If that was true in your case it would save you from having a second strut for the forward foil (which will negatively affect maneuverability) as well as save substantial weight and reduce crew workload to just having to retract one forward board rather than two. As long as you have about 80% of the weight on the forward foil you'll be fine in pitch.
    Just to be sure I'm understanding you: your boat will be like an F101 except with a second vertical fin forward of the daggerboard/centerboard, is that right? Will you use wand altitude control on the forward foil or try to control altitude with only the rudder foil?

    F101 2-8-17.jpg
     
  11. Lurch723
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    Lurch723 Junior Member

    Sort of Doug, this is an experimental foiling platform so I’ve designed an undersized foil with 2 struts (which are hinged on both sides of the hull -a T foil with another upright) that should produce enough lift to breach at about 18knots of boatspeed. I want to monitor the boats performance on all points of sail compared to not running it, then the next step is to go to a surface piercing v foil and see how it works. I’m trying to leave T foils and wands alone until I’ve played with v foils enough.

    I’m not too concerned about it’s ability to change direction quickly as it’s designed very much as a distance racer. Besides tacking it is a bit like my old Hurricane, you sail it through the tack in an arc rather than stuffing it into a turn like I would in say a Laser or a 505. There is no right and wrong just different approaches to achieve a similar goal.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Well, best of luck! Hope you'll keep us abreast of developments......
     
  13. Corley
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    Corley epoxy coated

  14. Doug Lord
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Corley, where'd you find it?
     

  15. Corley
    Joined: Oct 2009
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    Location: Melbourne, Australia

    Corley epoxy coated

    It came up on Facebook in the Small Trimarans group. One of the guys there Gregg has recently purchased the boat and is going to restore her.
     
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