revamping an old daysailer or Pimp my laser

Discussion in 'Sailboats' started by solrac, Apr 10, 2006.

  1. CT249
    Joined: May 2003
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    CT249 Senior Member

    "CT249, you mean, using a windsurf mast "fixed" to the hull instead of the rotating ending used on a table? Think it will overcharge the flexion moment of the mast on the deck as it would be 200% more rigid, same as a beam cantilievered one end..."

    I've seen it done with low stays, connected to the mast at wishbone height. One poster here has it on his four-hull cat but I've forgotten his tag. Also look at the Australian Moth site, under developments I think, and you'll see some info about a guy called Greg Konnecke who used a standard windsurfer sail on a Moth.
  2. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    I do worry about side bend using a plain board rig though. The top is going to be sagging an awful long way off to leeward with the airflow tending to go upwards and thus greater tip losses. I think it was Andy Paterson who made the observation that if you really look at a top board sailor and rig then the rig tends to be upright. Its angled to windward at the bottom sure, but its upright further up as the side bend comes into play. If you add to that the belief in a lot of dinghy classes that slight windward heel can be of advantage then a stayed rig looks better on a dinghy if you can managed it.

    On the other hand of course a decent board rig gives you a light and well cut rig at moderate cost and effort, and that's worth a fair bit of efficiency!

    Oh yes, and that's looking like a sweet litle hull there:)
  3. solrac
    Joined: Feb 2006
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    Location: 34'54"35"47S - 56'07"48"98W

    solrac 100% sudaca

    well, thanks again for your input. still thinking it would be safer a stayed mast (for the proposed main use, kid's on sailing school, safe is the main concern, speed would be the second)
    Im actually on the test model cnc cutting, more news ASAP.
    thanks to all.
  4. tamkvaitis
    Joined: Aug 2005
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    Location: lithuania

    tamkvaitis sailor/amateur designer

    can anybody say how much, can be a plywood sheet twisted? is there a formula? I am talking about technique shown in the picture.
  5. solrac
    Joined: Feb 2006
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    Location: 34'54"35"47S - 56'07"48"98W

    solrac 100% sudaca

    think it depends on ply thickness, and the curvature radii:
    maybe a 3mm ply - about 30º on a 10/15cm diameter curve, maybe more on bigger diameter
    6mm ply - about 10º on a 40/50cm dia.
    9mm ply - gimme a break...:D
    I've seen long long time ago, here, (I was a child) an old carpenter who produced some nice multihull cats "bending" the ply to some impossible curves applying vapour. He used to have a concrete mold for hull & deck, and an enormous rubber bag inside filled with hot water, arranged the precut ply (wetted), glued them, and the evaporation process produced by the hot water & the pressure applied by the rubber bag made miracles.

  6. Skippy
    Joined: Nov 2004
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    Skippy Senior Member

    I don't know the exact math, but if you're talking about twist as opposed to simple curvature, it has to depend on the width of the piece. You can twist a narrow strip more than a wide sheet, since the edges of the sheet have to stretch more.
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