What wood to use on inside of fiberglass boat?

I bought a fiberglass boat at an estate auction last September. The motor was kept covered and fired up first try. (Thank God). But the boat was left uncovered, so all the wood inside is rotten. What kind of wood should I use to replace it? It looks like it was plywood covered with carpeting. Should I use Marine Plywood or just get exterior plywood and seal it with something?

 

Marine plywood is superior and stronger, pound for pound, and lacks voids that will make it warp in bad ways. It would still need to be sealed, preferably with epoxy, to keep it from absorbing moisture and making it heavier, before re-carpeting.

 

you might consider buying pressure treated exterior grade plywood available at most lumber supply yards. It is not as high a quality as marine ply but it will resist rotting. the floor in this kind of boat is not structural to the hull but rather to keep the occupants off the uneven bottom of the hull. so rot resistance is more important I would think than strength, especially if you are going to store it outside. Paint it with 4 coats of exterior paint before you install it to prevent corrosion that might happen where the treated wood makes contact with metal, and to improve the appearance. On the top side you can even put a coat of friction type paint for walkways, it has some kind of fine aggregate in it to give it a non-slip surface. You do these things it will likely outlast the boat, and you only have to do it once.

 

I guess the first thing for me to do is see if anyone around here actually has any marine plywood. I know Lowes doesn't, I already checked. Depending on its availability and price, I might have no choice but to use the exterior kind. I'll post updates as we get her fixed up. Thanks for the help guys.

 

My First Supplier Many Decades Ago

http://www.dixieply.com/nashville.shtml

Dixie has AB marine plywood.

 

I have a question. If I have to seal it either way, what is the benefit of using the Marine plywood? I'm going to do some calling tomorrow to see if any of the lumber yards in my area carry it or can get it. Maybe from that Dixie supplier.

 

a lot, but not all, of Ace hardware stores carry a limited selection of marine plywood.

Marine plywood is stronger for any given thickness, and a cleaner appearance and little to no voids between the layers that can cause creases or kicks if bending it to a shape. the voilds can also collect and trap water if used on the external part of the hull and hasten internal rot. With treated plywood, trapped moisture will be of little issue, you can fill any edge voids with caulk before you paint it, and since it will not be submerged when you use it, the small voids are not likely an issue. The only consequence is appearance, and a little extra weight.

 

There's treating plywood (PT, polyurethane, polyester, etc.), then there's stabilizing plywood, which is a whole different beast.

Treated plywood doesn't prevent moisture gain, just potential issues, like rot. Stabilized wood prevents rot and also keeps the wood dimensionally stable, so it can't swell with moisture gain. This is a huge difference from an engineering point of view.

If plywood is used in the structure and you want it to last for generations, you have to stabilize it or just expect a certain level of routine repair. On the other hand if you just want a down and dirty skiff, screw the epoxy and go fishing, realizing it'll probably not last nearly as long.

Lastly, carpet in boats has kept me in business for decades. I hope folks and factories continue putting it in their boats, so I'll have something to replace in a decade.