Is Marine plywood a must? - SailNet Community
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post #1 of 42 Old 07-25-2019 Thread Starter
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Is Marine plywood a must?

I need to build a small shelf for an additional battery. My existing batter boxes are molded in fiberglass, in the lazarette, and stepped up the angled hull. Iíve made a template with curved bottom supports add a plan to screw in the sides of the existing battery ďtraysĒ. I need to make this in a couple pieces, then screw it into place, so that its secure, and strapped.

Marine plywood would be my default choice, however its hard to find where I am, and expensive to ship. This area of the boat is never wet. Iím considering just getting some A grade plywood, birch or something like that, and coating the pieces with bilge paint. If there are any voids in the laminate edges, Iíll fill them with epoxy or something.

Does this sound reasonable or should I really try and find some ďmarineĒ plywood? It needs to last.

Thoughts?
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post #2 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

ACX should last 10 years or so if it is well sealed with epoxy then painted.
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post #3 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

Yes,marine plywood is a must.

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post #4 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

Any decent plywood will hold up if you completely seal it with epoxy. That includes sealing the screw holes.
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Re: Is Marine plywood a must?

If you don't or can't get marine plywood, I would wrap non-marine grade plywood in a layer of glass. Great practice.


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post #6 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

My preference would be marine plywood, but a good 13 ply AB Baltic birch properly sealed, with a layer of glass on the corners, epoxied and painted might work in a pinch...as to the longevity of not using marine ply...that would be your call in the end.
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post #7 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

You could also use Starboard. Easy to work with and readily available.

https://www.homedepot.com/p/1-2-in-x...6333/202534579
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post #8 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

The only difference between marine ply and grade A ply of the same wood is that marine ply has no voids and more ply layers. Neither of them are rot resistant or waterproof or anything "marine-ish". Your application doesn't require the bit of extra strength more ply layers provide, and any voids are inconsequential.

You should consider glueing the pieces together when you screw them in place. Thickened epoxy is good, but you could use a liberal amount of a premium construction adhesive too. Edge sealing is good also, although the paint will do some of this.

Glassing isn't necessary, but a layer on the outside carried over to the existing box would tie everything together nicely.

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post #9 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

If you think you can keep your plywood dry and want to use regular ply, it should work. The same reasoning goes for having a cored fiberglass hull. They never delaminate because of water infiltration. Boats are wet. Wet plywood delaminates. Marine plywood delaminates more slowly. If the shelf is simply for an additional battery, is plywood even required? Others have suggested using Starboard. Red cedar might be cheaper, is rot resistant and won't delaminate.

On another point - why are you putting heavy batteries in the lazarette? Running cables all the way back there adds to the weight too. Would a more central location shorten the wiring and improve the boat's balance?

Last edited by paulk; 07-26-2019 at 09:20 AM.
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post #10 of 42 Old 07-26-2019
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Re: Is Marine plywood a must?

I used either marine or CDX 3/4" for a "box" / compartment to house 2 8D AGMs. The compartment utilized 2 existing fore-aft OEM plywood 14mm vertical panels. The "floor" was supported on hardwood cleats (oak) screwed to the OEM panels. The athwartship vertical panels... we also screwed to hard wood cleats. The Box was painted with bilgekote.
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