Re: 1983 Happy Traveler 16 foot stringer, transom, and floor repair
There is a huge debate on that very subject wabbie. You basically want a good grade of plywood that the resin will bond to.
There are those who swear by marine ply. But it is expensive and hard to get in some places. If you live near the coast, it is likely that it is common. The further inland you go, the harder it is to get. You can order it but the shipping is costly along with the cost of the ply itself. ($80-$100 a sheet + shipping)
Some like to use exterior grade treated ply. The trick with this stuff is you have to get dry sheets or buy it and let it dry or the resin can fail to bond.
Exterior grade MDO plywood is said to be the ticket. It is a fabricated form of plywood made with an exterior glue and is used to make road signs. I have no experience using MDO myself, but there are those who say it is the best option.
I used "marine grade" ply in my transom. But looking back at it I think I was duped by the retailer that sold it to me. For my stringers and deck I used plain old ACX ply from the home center. I was frustrated with the whole debate. ACX is a good quality plywood that has a sanded face on one side and a rougher side. Being that it is not one of the wonder plywoods that everyone seems to talk about, I spent extra time making certain that everything was sealed as well as I could get it. I concentrated on doing good glass work so water is kept out. I bet it will last for another 30 years or so. I will let you know.
I made the decision to go with ACX based on advice given to me by a friend who worked for a boat building company for 11 years. He is a co-worker of mine. He basically said "the core does not matter as much as the glass work, stop fretting over it. As long as you use a good quality plywood and seal it properly, it will be fine". My advice, go get some ACX at Home depot, get the glasswork done right, and be all means, don't fret over it.
