Marine Plywood & Bulkheads - SailNet Community
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post #1 of 20 Old 03-29-2011 Thread Starter
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Marine Plywood & Bulkheads

I am needing to replace many of Windsong's bulkheads and cabinets due to a lot of rot from years of neglected leaks.

I am having trouble finding a local supplier of marine plywood, and am not too excited about the price of what I have seen out there. I plan on using marine plywood, so don't get on my case too hard...I'd just like to see if the alternatives are suitable for above the waterline, and in theory, dry work.

So, must I use marine plywood for interior cabinetry and bulkheads? I plan on covering each piece of wood I use with epoxy to seal it up and prevent water intrusion, but I know that isn't 100% effective in the long run. I'd love to be able to save some cash and time by not having to find and use marine grade plywood, but if the argument for using it is compelling I will stick to that route.

(and before some smart guy says I should worry about the leaks first...yes, I've got that covered )

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post #2 of 20 Old 03-29-2011
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Supposedly, marine-grade and exterior-grade plywood used the same adhesives. The difference is that marine-grade plywood has no interior voids, while for exterior-grade plywood a certain percentage of "void space" is allowed. I would think that a good exterior-grade plywood, with a couple-three of layers of penetrating epoxy on all surfaces (maybe a layer or two extra along the edges) would be as strong and rot-resistant as you can get. Slap a nice-looking treatment (wood "door skin", Formica, or whatever) on the exposed surfaces and it would look like a million bucks.

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post #3 of 20 Old 03-29-2011
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I replaced my sole with standard plywood, sealed and potted of course.

Marine grade also has more/thinner ply which allows it to be stronger and lighter. Some say it will also rot slower because of having more ply. Boats were built before marine grade was around so I care not what others say about using/not using it. If it stays dry it should be more than adequate for a bulkhead.

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post #4 of 20 Old 03-29-2011
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I think your will find the marine plywood more stable due the larger amount of plys which is how they also make furniture grade ply before applying the veneer

I find SOME exterior-grade plywood is unhappy and try's to imitate a potato chip shape unless its nailed to house

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post #5 of 20 Old 03-29-2011
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If regular plywood's okay, why not just use OSB?
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post #6 of 20 Old 03-29-2011
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Quote:
Originally Posted by Siamese View Post
If regular plywood's okay, why not just use OSB?
I believe Chrysler boats did, didn't they?

Or was that press board?


I can tell you that my 1970 Oday does not have marine grade plywood at all! Nor did it ever.

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post #7 of 20 Old 03-29-2011
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Hi Beeresmith,

I would really encourage you to stick with marine ply. Bulkheads are structural. BS 1088 marine ply will stand-up better, due to better laminate schedule and minimal voids.

I have several sources of marine ply from whom I purchase. If you do not need a teak veneer, you can get Sapele or Okoume from Chesapeake Light Craft. While not local to you, they are top notch, very good to work with and are experienced at shipping anywhere.

If you would like to get a teak veneer -- which usually looks very nice on boats -- you can order sheets from Buck Woodcraft right there in Marathon FL. I've been very happy with the teak veneers I've received from them -- which I've used for cabinetry.

Yes, it's expensive compared to regular ply. But the real cost of most jobs is the time and effort. It rarely makes good sense to skimp on the supplies.


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post #8 of 20 Old 03-29-2011
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PT boats were built from marine plywood, must be good for something? .02
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post #9 of 20 Old 03-29-2011
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If it is for cabinets and not bulkheads exterior ply is ok. It would depend on the finish you want. Most exterior grade ply is fir and if you are going to paint it is very hard to get a good finish on fir. But if you are going to use a laminate no problem. For bulkheads marine ply is worth the extra. More plies, more stable, will take a paint finish well if not fir. Marine ply is not lighter though.

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post #10 of 20 Old 03-29-2011
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Exterior plywood is never going to look good unless covered with formica or some other such product. So factor that cost and time into the cost calculation. Most exterior plywood is of atrocious quality, the outer skins so rough and porous you would have to sand half of it away to get a level of smoothness for any kind of finish material. And with patches and voids all over the sheet you can never be confident that the area around the chainplate bolts is good solid material. Finally, most of it never lays flat and will drive you crazy.
There are reasons it is so cheap.
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