sealing wood

PAR the boat I am repairing had aluminum tredplate over the deck.The fore deck was Oregan Pine and the aft deck was ply. The whole lot rotted away

 

Movement in boats can't be avoided, unless they're designed (and built to the plans) specifically to address movement. This movement pretty much guarantees that at some point, fasteners, glue lines and adjoining elements will work apart enough to permit moisture to get in between. Once this happens (usual out of sight until the worst is visible) the downward spiral of decay begins.

It's this reason that most of the old boat builders left their bilges and interiors finished bright. This way they could see when rot started to form or if a fastener was loose and staining the wood, etc. and they could get at it before major surgery was necessary.

 

The least expensive way to build is by skin-on-frame, like the way traditional native kayaks were built. I have built 8 kayaks this way using salvaged and remilled lumber, most cost about $50-60 in out-of-pocket costs. I use 9 oz raw nylon fabric (the most expensive part, about $30 worth), and then sealed with polyurethane floor finish or oil based paint. It is held together with small wood pegs and lashed joints; strong, light, flexible, inexpensive and fast to make. Even if you paid retail for everything used it would still cost less than $150 in materials. It also comes together faster than most construction methods because there very little fitting of parts together. Wood rot is seldom an issue since there are not many places to trap moisture, especially if you hang it in a garage or shop for storage. It is also a very light weight way to build, most of my kayaks weigh around 20 lbs.

I built a 14 foot sloop using this kind of construction for about $35 using all salvaged wood and supplies. I built it for a local $50 sail boat race where most people built crude rafts out of junk. We won of course since I built a real sailboat (some even accused us of cheating since the boat looks so good). It uses Tyvek house-wrap sails and a spinnaker made of disposable plastic tablecloths I got from a wedding we went to (I helped them clean up and saved them from the trash can). It uses a heavy plastic skin, but if you can find a cheap source of a fine weave synthetic fabric it should work fine. The whole sailboat weighs only about 100 lbs, I can carry on the roof of my Toyota Tercel without a rack, just a foam pad to protect the roof paint.

Even if you use ordinary 1/4 cdx plywood to build your boat you can wrap the hull in painted fabric. You wrap the outside of the hull tightly in fabric (hold in place with marine staples or wood strips at the gunwale) and paint it with an oil based paint. It will make a fine durable and waterproof hull without having to caulk any joints. Cotton fabric works too, but it will rot sooner than synthetic fabric (it should last several years, and then you just recover it).

Here is my daughter and I in Puget Sound with on first launch. Below you can see how it was built.

 

Some details of the mast construction please!

Beautiful work on the frame!