marine plywood

BobCT · Post by **BobCT** » Mon Mar 07, 2011 8:52 am

would you expect that all plywood on a boat is marine ply?

I'm in the process of replacing my engine seacocks and need to make up new backing plates. I have some factory plywood left over from my cabin steps. Do you think that it's marine grade? It's 6 ply.

If I go this route I'm going seal it with epoxy anyway.

I could do this in fiberglass or glass it in but the factory setup lasted 22 years and doesn't look like the wood was sealed at all.

I wound up removing the extra plug up in the mid cabin bilge. I tried to remove the plug and it snapped in 1/2 and was pink inside. I think with this and the macerator valve removed I might get that bilge dry.

There are lots of methods to remove old fittings but I found that between my roto-zip and dremel tool, just cutting chunks away is the easiest method. The engine seacocks only took about 20 mins per side.

Bob

Stripermann2 · Post by **Stripermann2** » Mon Mar 07, 2011 9:00 am

Why not use Starboard for the backers? It'll never rot, it's stronger and readily available.

vabeach1234 · Post by **vabeach1234** » Mon Mar 07, 2011 9:06 am

I think it's hard to get starboard to bond to resin. I'd look into that if you plan on glassing them in.

aweimer · Post by **aweimer** » Mon Mar 07, 2011 9:49 am

http://www.pbase.com/mainecruising/boat_projects

This site has a nice overview of replacing through hull fittings and backers.

Starboard is referenecd and highly NOT recomended. Its soft and there are bonding issues. Backer board is installed to strengthen the hull in this location, Starboard being more flexible doesn't provide that strength.

Interesting in the article, he suggests using 5/8" fiberglass backers, looks very nice. I have this as a spring project myself. I have a few that need to be re-caulked so i'm taking all the thru-hull's out this spring. Fiberglass backers though just seem too difficult to deal with. I will be using some nice solid oak with west systems on it.

BobCT · Post by **BobCT** » Mon Mar 07, 2011 10:00 am

I've heard the same about starboard as well but of course you'll find 100 people who have used it w/o any problems.

Also read that solid wood is not a great idea as it's more likely to crack. If I was going to go this route I would use Teak rather than oak. I think the plywood has proven itself to me based on what I removed.

Bob

Stripermann2 · Post by **Stripermann2** » Mon Mar 07, 2011 10:16 am

That's some good info Aaron. I would have thought that SB would be good due to it's composite. But the bonding issue has me thinking otherwise...

As Bob says, you'd probably find many who have used it for that application, with no problem.

Big D · Post by **Big D** » Mon Mar 07, 2011 10:41 pm

Don`t use Starboard. I would also not use solid wood; it can crack as mentioned but I`ve seen more often than not that solid wood will cup quite a bit over time. Use a good quality marine ply, it`ll last for years. If you encapsulate it with epoxy, give it a good thick coat and do not leave any wood exposed or it will rot very quickly as any moisture that gets in will be trapped. I wouldn`t think of a backer material that has to be replaced 10 years down the road as a bad thing. IMO replacing the backer material forces you to rebed the through hull at a time when it`s probably due anyway to maintain a quality seal.