Boat Building Glue

I am thinking about building a 19' flat bottom plywood on frame boat with plans from Spira International. This would be my first venture into boat building and I have several questions.

Could I use a glue like TiteBond 3 to glue & screw my frames and plywood coverings? Also, what would be the best screws to use, Stainless, or could I use coated deck screws? I only plan on glassing the bottom to the waterline and the boat would be kept on a trailer when not in the water.

 

Welcome to the forum.

If you want your boat to last in a very damp climate such as yours, the Pacific Northwest, you must seal the wood entirely. My choice for sealing and gluing would be epoxy, then a strong UV blocking finish over it. Titebond 3 works well but if it is on exposed wood the epoxy won't hold well to it. Coated deck screws will eventually rust, expanding as they do so, creating cracks which will lead to rotting wood. I would use stainless steel or bronze fasteners.

 

Use the normal stuff

Even if you're lake sailing or motoring in the desert you need to look at a few things.

First it must be completely sealed or you go the paint/varnish route. You can't mix them (doesn't mean paint over a sealer). The problem here with wood is you get a pocket of not sealed this becomes a pocket of not protected at the transition. The long term effect is a goo normally called dry rot.

If you are going to en-bed the screws you have a different problem where in lesser salt water you may not have a problem. However the projected time a screw under epoxy is hard to predict. A metal screw under polyester is an ever expanding shaft of rust that will split you wood or ... It's REALLY hard to undo this kind of mistake.

You can build with glues other than epoxy or polyester resin. You will want to google the 'boil test' to verify the glue isn't prone to breaking down due to water.

Wooden Boat has done a number stories on why boats build without modern sealers work out quite well. I hope this helps.

 

I disagree in that it MUST be sealed with epoxy. I strongly recommend it, but many millions of boats survived successfully without any goo's on them.

Marine epoxies do not pass the type one boil test BTW, so aren't considered WBP, by some authorities (like the US Navy), but unless you're intending to moor over active, underwater volcanoes, you can be assured it in fact is waterproof.

TiteBond III isn't a structural glue and it does pass the type one WBP test, but just barely. It will soften with emersion and it'll creep under load too. I use TiteBond III frequently, but not in underwater applications or heavily loaded structural elements.

There are other glues and adhesives, though they can't do what epoxy does, all things considered. With a Spira design, the PL's will do, though technically more costly per ounce than discount epoxies, it's a one part formulation, so easier to handle.

Stainless is the sensible way to go. Galvanized will do, but you'll eventually see rust stains at each fastener. Coated deck screws are tough, but the coating comes off when inserted, leaving a mild steel fastener to rust. Many Spira design don't need full encapsulation. Follow the plans and use his recommendations.