Transom and floor replacement - standard plywood.

[ShoestringMariner]

Hi guys, I have to replace th floor and transom on my 1976 starcraft.

I have some 3/4” exterior plywood (sheathing) Not PT either. I plan on sealing the exposed transom area with epoxy and varnish, and or paint. The flooring will be covered with either marine grade carpet or marine vinyl flooring, more than likely the latter.

My question is, is exterior sheathing too coarse for this? I don’t want to see rough grain showing through vinyl flooring etc.

also, what would you use to seal the wood? Epoxy? Spar varnish?

I know a lot of people use marine grade plywood, but if I understand correctly, Starcraft only used exterior grade plywood on these boats to begin with, and untreated that . I am replacing the wood for the first time in 42 years, so for my purposes I’m thinking marine plywood would be overkill,,,

 

[Scott Danforth]

get sanded exterior grace (ACX)

 

[CrazyFinn]

I know a lot of people use marine grade plywood, but if I understand correctly, Starcraft only used exterior grade plywood on these boats to begin with, and untreated that . I am replacing the wood for the first time in 42 years, so for my purposes I’m thinking marine plywood would be overkill,,,

They didn't use marine grade because it would have cost more, and served no real purpose. Left exposed and untreated, marine grade is really no more rot resistant than regular exterior grade plywood. It often has thinner/more plies for strength (and pliability), and is void free - but that only really matters if you are building a wood boat. Back in our racing days we were running wood tunnel hulls, and the outer skin was very thin plywood for weight savings - in that case being void free was very important!

As structural components on a fiberglass or aluminum boat, marine grade just helps you spend more money.

 

[ShoestringMariner]

Thanks guys. Whats the best sealer to use if I'm laying marine carpet? Will the glue act as a sealer? I might use vinyl, so I assume only the underside of the floor needs sealing in this case. but not sure about carpet

 

[kcon]

I think you should seal both sides of the plywood with resin and fiberglass, I'm sure there's other (likely less effective) methods to seal it though - I don't believe carpet adhesive is one of them.

 

[CrazyFinn]

Will the glue act as a sealer? I might use vinyl, so I assume only the underside of the floor needs sealing in this case. but not sure about carpet

In my opinion, both sides need to be sealed - with something other than glue. Otherwise the carpet/vinyl will simply trap moisture in there and make it rot faster.

Polyester resin and fiberglass cloth will do the job (with poly, you need the cloth). Epoxy would probably work as well - but I would probably use the poly resin, and some thinner cloth for strength. Top and bottom... That will also hide any roughness in your plywood.

 

[AShipShow]

Agreed on coating with resin and glass... The less prevention you take now, the shorter the time till you have to redo all your work.

 

[mickyryan]

coat with resin and glass and if you want you can also use lanco ultra roof sealer, its a real thick acrylic paint thats 100 % waterproof for up to 50 hrs, then you can glue on top of that, they also make a thickened product that you can fill areas where it might be rough from layup. you can paint over it so i feel the adhesive would stick just fine .

 

[Woodonglass]

The 2nd link below might be of interest.