Fake Marine Grade Plywood
 

I just bought two sheets of "marine grade plywood" . I had a friend pick it up. Now that I am looking at it, it is five ply and has multiple footballs and areas of filler in the top layer. Is there anyway possible that this is the correct material or suitable for a transom repair? I have a couple sheets of birch plywood from Lowes that is 12 ply and looks much better. Any input is appreciated.

A friend`s dad invented the glue for marine ply. Not all ply is created equal. A high quality fir ply can be much better than HD marine ply. Not everyone wants or can afford Meranti.

Plywood!
 

Follybob, Find an old '67 Seacraft bowrider and cut the floor out of it. Carl treated the 9 layer weldwood glued Marine fir plywood with styrened resin somehow to make it last 50 years. Amazing!

So you guys think think this wood is ok? I just don't see how this was $92 per sheet.

No, we are not saying it's OK, but it might be the best you can get today. APBA Marine plywood was the best, but I haven't seen it in decades. Water proof glued multi-lamanate plywood without voids was what Carl Moeslay used in the 60's and it's still holding up pretty well. Give the composites 50 years and lets see how they are doing. Back in the '60's when "Made in America" was not driven by Wall Street investor ROI we made stuff that lasted a lifetime. Detroit and Peoria Iron still rules! Would you rather have a Preius or an Olds 442, a Doosan or a Caterpillar, a Bayliner or a SeaCraft?

Well said Terry :)

I would be ok to use, just make sure you seal it up real well. Now far as the money you spent on it, I would be upset. For $92 a sheet you could have gotten something better. It sounds like you ended up with a "AC" or "BC" grade marine 5 layer ply. I don't know what type of wood it is, but Douglas Fir will be better than pine. Most good Marine Ply will be 7 Layer "AB" Douglas Fir. The important thing is that it has the exterior or water resistant glue. This will help it keep from delaminating if it dose get moisture in it. If you have a fair amount of "footballs" on one side then it probably is "AC" grade. It will have one good side and then a side with filled flaws. The "A" side will be cleanest void free side, where the "B" side will have minimal filled smaller flaws of voids. The "C" grade will have filled voids or knots that have been cut out and filled in with the football pieces. Long as it is sealed well and has the proper fiberglass lay up you will be fine. Less voids will be slightly stronger and cleaner to lay up on but its just a transom not a piece that is open to be seen. Now the 5 ply layers would be upsetting, If I paid that much I would of expected 7 layers. The biggest difference between $30 a sheet "AC" exterior douglas fir sheeting and "AB" marine douglas fir is that the marine wood will have the 7 layers vs the 5 layers plus the "B" second side vs the "C" second side. If I was to pay $80-$90 a sheet I would expect at least 7 layers and "AB" grade.

Here is a link to a site that will tell you the differences in marine plys:

https://www.marine-plywood.us/douglas%20fir.htm

https://www.marine-plywood.us/mahogany_okoume.htm

https://www.marine-plywood.us/mahogany_meranti.htm

https://www.marine-plywood.us/mahogany-meranti-aquatek.htm

Meranti is a good clean wood and comes in loyds 1088 grade and BS6566 grade which is superior to the "AB" grade woods but it is not as strong for structural applications. It is better suited for stich and glue boats or cold mold type construction. Okoume is a better choice for transoms and stringers, it can come in the better 1088 stamped grade and it is much stronger than Meranti or fir but has less rot resistance than douglas fir . It will have cleaner surfaces than the birch you talked about in you first post and be much better if you want to spend the $160-$180 a sheet for it. The birch is not a good choice, Baltic Birch is usable in marine applications but that is different from the birch at the big box stores. Most people just use the "AB" douglas fir marine grade for structural stringers, bulkheads and transoms. On a budget the $30 a sheet "BC" Fir is not much different and probably what you got sold to you now, just for a lot more.

You could take back what you got and try to find a 7 ply douglas fir "AB" grade but I wouldn't let it worry me to much. What ever ply you use make sure you seal it with a vinyl ester resin thinned with styrene. It will last as long as you will live either type of sheet you use. Sealing it up is the key. Hot coat it several times and let the wood soak the supper thin resin up, especially the edges, they are the most important. Laminate it well and don't leave any spots uncovered for water to inter in cause it will wick water up fast. VE works best cause it can be thinned a lot better than epoxy Because it is styrene based. Polyester resin is styrene based too but it is also pours and can yield water absorption over time. If you want to use epoxy that is fine, just use the VE to hot coat the plys then epoxy is fine to use after that.

Thanks for all the input, it sure is nice to have this resource!i will let ya know how it goes.

LBI's price for Divinycel H80 at $118 has to be for a 2x 4' sheet, right? Not a 4 x 8?

Because that would be really interesting.

http://www.lbifiberglass.com/CORING/coring.html#986

Pretty much covered already, but the term "marine grade" is a general term, the veneer thickness, veneer number, and face quality can vary quite a bit depending what its purpose or intended use. A plywood that will be used for cold molding or wood boat construction needs to be MUCH higher quality than a plywood that will be covered in lots of fiberglass.

Its sounds like you have some lower quality fir plywood, which so long as it has very few voids and is made with a proper glue - will work just fine for a transom or core.

In my former business, I inventoried and sold everything from B/C fir to BS1088 Okoume, and each has its use. I built my skiffs and runabout with BS1088 Okoume, I used B/C fir on the transom/frames of my seacraft. I also used BS1088 meranti for my deck (so I could use less glass and save weight)