A small tri project

Discussion in 'Multihulls' started by Lurch723, Sep 25, 2017.

  1. Lurch723
    Joined: Aug 2012
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    Location: Devon UK

    Lurch723 Junior Member

    About 4 years ago I was persuaded to build an idea that was kicking around in my head.

    I wanted a boat that was long, thin but could still generate enough lift from its own hull form, possibly foil assisted. I chose a 49er rig as a donner because they are light and plentiful. However it did present drawbacks with regards rig tension and the amount required over a conventional wingmast beachcat donner.

    Here are some early mock ups, it's worth noting I drew the plans eventually the old fashioned way in pencil on drafting film and lofted all the dimensions by hand, and cut the measuring stations out of cardboard then transferred them onto stirlingboard for forming the hull shape.

    Its a two person crew, both on trapeze with a bowsprit and kite just to make things more interesting!
     

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  2. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Very interesting-good luck!
     
  3. Lurch723
    Joined: Aug 2012
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    Lurch723 Junior Member

    Well I've built it and started sailing it last weekend, so far we've found that in just 4 knots of wind with the kite up we are single trapezing off the outriggers with lots of apparent wind. There's no bow wave, no spray and the rear lifting foil when applied with positive AOA reduces the wake substantially.

    The hull ignores waves and is very controllable both directionally and in pitch. Acceleration is seamless but hard to quantify given the weather we've been testing it in so far.
     

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  4. UpOnStands
    Joined: Nov 2015
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    UpOnStands Senior Member

    Great work and clean build. Do you have forward foils? We would love some video. Chase boat not fast enough? ;)
     
  5. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Gorgeous boat-very impressive!
     
  6. Lurch723
    Joined: Aug 2012
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    Lurch723 Junior Member

    The boat is designed around a fulcrum that accommodates a wave piercing self levelling foil, but money and time are short so it will have to wait for another time. All the structure and bushings are there.

    My main foil is nearly 2m long and I can rake it through 25 degrees as the wind increases. The boat has got 37% less wetted area than a 49er but isn't as light as I would have liked, in fact if I built it again I think I could lose 30lbs easy. But it is very controllable with no lea or weather helm and very light to respond. It's not going to win any tacking duals but this is all about banging corners and lighting the touch paper.

    Here's some pics of the build
     

    Attached Files:

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  7. Cholsson
    Joined: Aug 2015
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    Cholsson Junior Member

    Looks Amazing! Want to see more :) any video?
    I rebuilt my 18ft trimaran this summer but failed to be finished. (With 49er jib)
    Is it carbon fiber in the hull?

    Chris
    www.chryz10.com
     
  8. Lurch723
    Joined: Aug 2012
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    Location: Devon UK

    Lurch723 Junior Member

    I know it's difficult to sea a boat project through to the end, I took 12 months off because it got too much. Cut yourself some slack Chris and when you feel re-energised have another go at it but without the pressure.

    No video for a while I've only got one more sail before we stop for the winter. But I'm as keen as the next person to get twin wiring on a quick reach or blast upwind into 4-5ft swell.

    Right the main hull is Corecell 80, with carbon laminates finished with sacrificial glassfibre. I got pretty much a 1:1 ratio of fibres to resin laid up by careful hand work. (An East German composites specialist showed me how) And it was light, but the weight came on later with some unnecessary superstructure and a couple of lofting errors.

    The outrigger hulls are made the way a 1950's aircraft fuse is made but with a modern twist. They are foam ribs with 1.2mm aircraft ply scarfed and skinned, then a layer of thin +-45 carbon overlaid. They came out very light and tough, so much so I added a kilo of 2 part poly expanding foam buoyancy to each hull in case they got holed.
     

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  9. Cholsson
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    Cholsson Junior Member

    Thanks! :) Yes I Will try to wrapp it up next year.
    Its an impressive build you have done. Fun with different tech as well!
    Is it for one or two persons? How do you raise the gennaker?

    Chris
     
  10. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    How about a few dimensions?
    Length, hull beam, overall beam.
    How far back is the ama bow from the main hull?
    Do you know how much this weighed?
    Is the cross beam demountable or do you have any kind of folding?
    Sail area?

    Looks very nice.
     
  11. Lurch723
    Joined: Aug 2012
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    Lurch723 Junior Member

    Dimensions - ehhh I remember those....ish

    The racks and hulls de-rig for boat parking and transporting very quickly by using lightweight alloy pins. Beam is 3.1 meters, length is just under 7m, weight - might weigh it over the winter but I can tell you it's somewhere in the 150lb region. The main hull is 460mm wide, I wanted to achieve that magical 14:1 ratio.
    The kite (using an old Tornado one for trial sailing) is 31m sq and stows in a spinnaker bag like a B14. and the rest is standard 49er - self tacking jib etc.

    The AMAs are there primarily for static roll purposes, but be under no illusion despite their diminutive volume they are a godsend for launching and recovery, and if that's not enough when the apparent wind dies they do a great job of keeping us dry! They are mounted as a crew trapeze rack would be on an 18ft skiff, so I can place crew weight directly over the aft lifting rudder foil for maximum efficiency, the lift from the rudder displaces the weight of one crew member at quite low speeds and ideal for upwind work.

    What's interesting when sailing it is the boat largely ignores the ama drag because of the way I designed them to function. I accepted they would be in the water a lot of the time so put the centre of bouyancy high up in the hull - so as they kiss the water little effect is felt until the crew realise they have too much roll on and trim out; it works very well.

    Early on in the development of these hulls I built a plug and floated it in a mates duck pond (a big one) with him sitting on it, I calculated It had 125kg of bouyancy, I looked at it and decided that was way too much drag hitting the water at 20knts at full chat so scaled the volume right down, with the effect of arm moment it turned out to be the right call.
     

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  12. Cholsson
    Joined: Aug 2015
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    Cholsson Junior Member

    Where are you sailing? I can are you have a Swedish main Sail (SWE 1068) from my neighborhood :)
     
  13. Lurch723
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    Lurch723 Junior Member

    The Swedish link is I bought the rig from Simon Hiscocks in Weymouth and I think this mainsail was sold off from London 2012 Olympics by one of the Swedish team. You may well have an ex Swedish Olympic 2012 49er flying around your local sailing club?
     
  14. Cholsson
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    Cholsson Junior Member

    I think you are right! I bought my 49er jib from another Swedish team marked "Rio2016" :)
    [​IMG]
     

  15. Lurch723
    Joined: Aug 2012
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    Lurch723 Junior Member

    This is great, we both have similar elements but they will work differently. The self tacking Jib works well btw, in a strange way your design is more pure Trimaran, as I conceived my design as a monohull with roll stabilisation, where as you have full length hulls. I really like your idea of full width beams too, it keeps the weight down and makes for a stronger and tighter design. it will be interesting to see how well it goes upwind?
     
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