Plywood flat bottom

Discussion in 'Boat Design' started by manich, Aug 13, 2011.

  1. manich
    Joined: Aug 2011
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    Location: Bradford

    manich New Member

    Hi all,

    Ive recently returned from Malta where the harbours are full of home made boats of all descriptions,there were even inflatables which appear to have been fibreglassed/laminated over.This got me thinking i could do better than most of these,and I remembered I had a left over tin of cureit premium roofing resin and some chooped strand matting in the garage.My plan is to build a flat bottom craft from 12mm ply,reinforced in the areas of stress,and laminate it.(then let the brother in law test it out!)

    Any advice,tips or indeed plans most apreciated

  2. erik818
    Joined: Feb 2007
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    Location: Sweden

    erik818 Senior Member

    I assume you want to build a simple boat that you expect to survive a limited number of years, that you don't care about resale value and that you do it mostly for the fun of building a boat yourself.

    The plywood is the structural element in a plywood boat hull. Whatever you apply to the surface is for protecting the wood. If the boat is usually on land and is in the water only when used, paint will be enough to protect it. Needless to say, the plywood needs to be of a quality that withstands water. 12 mm sounds right for a small boat if you use plywood of reasonable quality with WBP glue, e.g. underlayment plywood. If your ambition for the boat is higher and you want to minimize the weight, use plywood intended for boatbuilding.

    I see no good reason to use the left-over resin and chopped strand matting. Chopped strand matting is used to build thick layers that are "structural" and serve the same purpose as the plywood. If you use both chopped strand matting and plywood you will just get a heavier boat. If the goo you have is polyester, my experience is that you should keep it as far away from a wooden boat as possible.

    Best method to join the plywood panels is to tape the seams from the inside (woven glass fibre strips and epoxy). There are several books describing how to work with plywood and epoxy/glass; Devlin´s boat bulding by Samuel Devlin is one. There are also several internet sites that supply free or low cost plans, which will increase the likelyhood that the boat you build will be to your satisfaction. There are several threads on this forum concerning boat plans of the type I assume you´re interrested in.

    Good luck,
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Erik I think this poster wants to use roofing patch (tar) on this boat. There are two basic types of this sort of goo in a can: one is asphalt based the other I'm not real sure about. The asphalt stuff can't be painted over and dries to a semi hard, not especially rigid coating. The other stuff, which may be a polyurethane, has similar physical properties, but it can be painted over.

    In any case neither would be very good as a glue, but could be used as a sealant in mechanically fastened joints. This stuff (roof patch) isn't intended to absorb much dynamic movement, so it'll fail pretty quickly on a boat, but it is cheap.
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