Marine Grade Plywood alternatives

I know this topic has been gone over a few times but I can't seem to find a straight answer. Living in the middle of PA, I can't find marine plywood anywhere. I can special order it from a place locally, but with tax and shipping, I'm looking at close to 200 for a sheet of plywood! I don't want to spend a ton on this restoration project as the boat is already 20 years old. I'd like to make it serviceable for another 10 or so years before moving on to my next boat if that makes sense.

I have a local lowes that sells an exterior grade plywood called sumauma. Its 9 ply and is rated for exterior use with waterproof glue. It also claims in the description to not have any internal voids. Its $88 a sheet here locally. I'm coating the thing with epoxy as its for a transom core.

https://www.lowes.com/pd/3-4-IN-4x8-Sumauma-Hardwood/1002938070

Thoughts?

If thats not a good one to use, any other readily available plys that can be used? I've seen Maple and Oak, higher end plys around here as well.

I, too, looked at marine ply when I needed.to redo decks a couple years ago. The price scared me off. Instead, I used exterior-rated BCX ply.

The real difference between BCX and marine ply is that marine ply is supposed to be free of voids while BCX will have voids, sometimes numerous voids depending on supplier quality. Marine ply will usually also have higher quality face veneers. Since I was covering up the ply with a covering, I didn't really care. I did fill some surface voids with Bondo before coating the ply with fiberglass resin. I paid particular attention to edges to preclude water absorption into the plies.

I wouldn't use the plywood shown from the link to Lowe's. It's not intended for exterior applications. You could probably use any kind of plywood if you're coating it in epoxy and making it water proof or water resistant.

Going to add a flavor with ACX..it is just cleaner....................But BCX will work great as well.

You might see if any yards near you carry MDO, the material that highway signs are made of. It cuts and works like plywood but it's much stronger and more water resistant than even marine plywood. Not cheap but not $200 per sheet either, usually around $80 per sheet for 3/4".

I used ACX with epoxy coating (gluvit). Has held up great. There are other epoxy coatings and the fiberglass resin is good, too. 3/4" is going to be heavy. I would look to make shorter spans and use thinner sheets. If for floor, consider using foam boards for support. If it was for lay-up for a transom, than that is fine.

I typically use 5/8" BC plywood, or 3/4 inch, depending.

In an aluminum boat, even 3/4 inch CDX is generally plenty strong enough, it's just not great to work with.

The big thing is that you want to saturate the wood thoroughly, especially the edges, with whatever waterproofing you choose.

In the long run, preventing rot is your most important goal when replacing the decks. Almost any plywood will be strong enough when it's new but when it starts to rot...

Thanks fellas. Its for a transom that needs to end up 1.5" total thickness on this boat. My concern with lesser quality plys is that if there are voids in it, it could trap moisture in there and rot up. Maybe it doesn't work that way once sealed however? Quality plys are hard as hell to find around here it seems... lol.

These guys do not have any ACX or BCX ?
https://trianglebuilding.com/building-supplies


I have family out your way.

I am going to be beefing up a transom . I have been considering Thermo-lite board . I will use it for the flooring but I am unsure about its strength for the transom . The one I will use for the transom if Thermo-lite isn't strong enough is Coosa board . These are expensive products but it will be a one and done and never worry about them again .
https://www.spaceagesynthetics.com/thermo-lite-board-product-line/
https://coosacomposites.com

muskyhunter1978 said:

Thanks fellas. Its for a transom that needs to end up 1.5" total thickness on this boat. My concern with lesser quality plys is that if there are voids in it, it could trap moisture in there and rot up. Maybe it doesn't work that way once sealed however? Quality plys are hard as hell to find around here it seems... lol.

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If your focus is price and something that will last until the next boat, I would go with exterior grade ply. Glue two 3/4 together. Coat liberally with epoxy resin. And Bob's your uncle.

ripdmup said:

These guys do not have any ACX or BCX ?
https://trianglebuilding.com/building-supplies


I have family out your way.

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Believe it or not, not. Best they have is CDX. They tried to sell me on some OSB stuff called advantex that is for wet areas like bathrooms, etc.

LDUBS said:

If your focus is price and something that will last until the next boat, I would go with exterior grade ply. Glue two 3/4 together. Coat liberally with epoxy resin. And Bob's your uncle.

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Believe it or not, I do have an uncle bob... great guy...

Head South to the Collage town.........................I have to pre-order at my Lumber yard, that is if I want to stay local

muskyhunter1978 said:

Thanks fellas. Its for a transom that needs to end up 1.5" total thickness on this boat. My concern with lesser quality plys is that if there are voids in it, it could trap moisture in there and rot up. Maybe it doesn't work that way once sealed however? Quality plys are hard as hell to find around here it seems... lol.

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If the the original transom was treated ply, you likely have "worm tracks" and possibly pin holes in the rear skin.

FuzzyGrub said:

If the the original transom was treated ply, you likely have "worm tracks" and possibly pin holes in the rear skin.

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Yes, I have another thread where i'm updating everyone on the saga of this boat. It was treated ply OEM and the thing got damp from a couple leaking through bolts (original owners bolted a ladder on there and used ZERO sealant it looks like. The bolts came out with my fingers... it left water get in between the wood and skin and I have a bunch of corrosion holes, etc. I've ground, scrubbed and cleaned all that damage out, am replating the inside of th skin with new metal and putting new, sealed wood back in it. its a job, but should give me a nice boat for a while.

muskyhunter1978 said:

its a job, but should give me a nice boat for a while.

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There's a couple of fantastic youtube videos about thinning resins to "prime" the plywood and get good penetration. They were fiberglass related videos from a boat builder.

I went through this last summer at 170 for a sheet of 1/2 marine grade. I worried and researched and looked into composites and really worked myself up about it. In the end, I wrote the check and I wish I would have just done that to begin with. That stuff is sexy! If it's a boat your keeping, just get the good stuff and gripe about availability and cost from the captain's seat. I invested a lot of time I could have invested working on the boat. You've probably got bigger things to worry about.

That said, if it was a boat I didn't have heirloom kind of feelings for, BCX and Old Timer's Formula application method (boiled linseed oil, spar oil based urethane varnish, mineral spirits applied quite liberally) would be plenty good. The wood you selected is Exposure 1, waterproof bond, but not something to leave out unfinished. Well... marine ply as far as I know doesn't really want to be out uncovered either. I ended up putting over half a gallon of OTF over marine ply, and don't feel like I need to worry about it for a long time. Keeping it dry will make any wood last much longer.

Once you get past the wood choice, now you can agonize over the wood finish! (ie, epoxy or OTF).

Oh, and here's one thought I never finished when I was going through BCX, Marine grade, Composite, Epoxy, Spar mixture... modify some aluminum car ramps from Harbor Freight. I really know how spend time in the rabbit hole. That's why I say just get the marine grade and move on. You may not have this problem, but if I don't reel mine in, nothing ever gets finished! lol. Good luck!

It is your nickel and your boat..... How long do you anticipate owing it? For me I chose marine plywood, in the thickness the matched the original plywood. I then used four coats Old Timers Formula to seal it, replaced the carpeting and never looked back. The extra I spent on the plywood was a drop in the bucket in comparisn to time and money invested in a great toy. It took me over a year and and $6000 to outfit a toy that matched a new $25,000 boat. Remember it IS a toy, and how you play with it is up to you...