"Marine Grade" plywood


So my dad wants me to make a couple of replacement bumpers for his boat trailer. Basically they are pieces of plywood covered in outdoor carpet. He's insisting that they be made from "marine grade plywood", in spite of my suspicion that he has no idea what "marine grade" even means or if the originals were even made therefrom. (from it?)
IAE, I'm tempted to use good old pressure treated ply but for the fact that I've heard the new stuff corodes metal screws and this gets bolted to metal. Any thoughts?
Thanks, JP
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wrote:

True "Marine Grade Plywood" is made from the Pine Trees that surround Parris Island, South Carolina; is tough as nails, needs no finish beyond its natural resistance to outside influence, and will stand on edge, as though by magic, whenever someone says, "Goodnight, Chesty."
Actually, the above is all bullshit and MGP is really a grade of ply that has no voids in the ply and is bonded by an adhesive that will resist delamination according to the ASTME spec. that applies to its specific use.
Don't use the PT.
It ain't the real deal.
Semper Fi.
Tom Watson - WoodDorker tjwatson1ATcomcastDOTnet (email) http://home.comcast.net/~tjwatson1/ (website)
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Tom Watson wrote:

Maybe so, but I like it.
As far as the actual application is concerned, use 3/4" CDX plywood.
Laminate as many thicknesses as required using epoxy.
When the piece is the correct size, coat all exposed edges with 3 coats of epoxy allowing 24 hours between coats after filling any voids with microballoon thickened epoxy fairing compound.
Attach the carpet with stainless steel screws or monel staples.
Attach with S/S bolts.
Have fun.
Lew
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Lew has it right. Someday you might have to replace the carpet on the bunks but the structure won't rot or de-laminate.
Patrick Fischer Olalla WA

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When doing things for my father, I often will ask him why he wants it done that way. In the absence of overwhelming reason NOT to, I tend to accede to his wishes.
He put up with me during my extended smartass period. Still does.
Patriarch
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"Marine grade" is one of those terms which the marketing weasels have made essentially meaningless. About all you can be certain about with "marine grade" is that it's made with waterproof glue (which means it's equivalent to any exterior grade ply). Marine _should_ mean it's made with more, thinner plys, and it has no interior voids, but the stuff you get from Home Depot isn't made that way. If you really want marine quality ply, you have to look for BS1088 rated plywood.
For your boat trailer, any exterior grade ply should be fine. It's not a structural application, you don't need the extra strength that a true marine ply would provide. If your dad is worried about rot, coat them with epoxy - you'd have to do that with any ply, marine or not, to get a long life out of it.
John
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JP, It sounds to me that you mean - 'bunks' not bumpers. The long 'planks' covered with a 'carpet' that support the boat hull.
If that is indeed the case . . . go ahead & use PT 2x4's. This is the stuff I use to replace rotted or weakened {from rusted bolts, etc.}ones. I've even made 'auxiliary bunks' from scratch with the stuff. Use all Stainless Steel hardware & fasteners. A bit more in cost, but they will last practically forever, and the bunks will last longer as well . . . especially if it is a 'Salt Water boat'.
Regards & Good Luck, Ron Magen Backyard Boatshop {PS - PT comes in 3/4 ply. Heavy as hell and not exactly cheap . . . but will do the job. Or just use the cheapest EXTERIOR ply you can find. I've used a full sheet as the 'deck' on my utility trailer for about 5 years . . . just looks dirty and no delamination.}

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Jay Pique wrote:

What would you do if Dad was a paying customer?
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