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For a few projects I need some plywood. What type is marine plywood? Does it have a particular name? Since I am buying a sheet for the big piece I need for the little dinner table in my c-22 I will use the rest for a new step and some other projects. What should I shop for (wood type) ?
 

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I used resin for bulkheads and stuff, especially the end grains...sand them finely first...

I used strutural exterior grade stuff as the marine ply down here is either non existant or beyond ridiculous price wise...

not the best option but we did really seal them up and pay attention to end grains where water damage occurs...
 
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I may be wrong but shouldn't marine grade plywood have waterproof glue and not "water resistant"? Douglas fir might not be bad for a table inside the boat but if you use it outside I've heard it will check in a few years no matter what.

Yup just checked the APA states waterproof glue for marine grade plywood, so that stuff at Home Depot is either described wrong or not marine grade.
 

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Over Hill Sailing Club
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Depending on use, "marine" ply is usually not necessary for many things, especially if it's getting glassed. Plywood quality varies tremendously. Some AC or BC ply will actually be better and denser than marine grade from crappy mills with poor QC. "Cabinet" grade 12 ply is nice for its outer veneer but can be real crap as well from the wrong supplier. Rot is also a consideration. I have used .60 CCA (underground grade) ply for bulkheads. The stuff will NEVER rot and glass adheres to it just fine once roughed up. I believe the glue used in all commercially produced outdoor/marine plywoods is the same. It's the care taken in the layering, plugging, and, heat and compression stages of production that seems to make all the difference.
 
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yeah ply discussions are like oil threads...

true real marine grade is instantly noticeable compared to all others

what I have noticed most is not the gluing differences but basically the VOIDS and quality of wood notice that in those ads they talk about voids allowed...its that which makes it strong or not, the denser and less voids the better.

I did not use the ply that looks like chopped wood but one that had very dense layers and looked and felt heavier than the real cheap stuff

again structural grade ply for construction

I beleive that this is fine...if sealed well and or glassed and no problem

its also really strong

we made a mount for my outboard bracket using this same ply but sandwiched with epoxy and sealed again on the outside...Id bet it will last as long as a plastic or nylon mount...

really really strong
 

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HDO or MDO (high or medium density overly) can be had. It's what they make road sign out of, water proof glue, and conforms with the Federal standard PS 1-95. Chip board OSB would be a good option, waterproof glue and on voids.

Now just to go kind of OT...I have see some honeycomb plastic materials for replacing coring material in decks. Is there a non wood structural option here, instead of using plywood?
 

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for bulkheads? and interior stuff I thought people these days were using the g10 stuff...
 

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I had a heck of a time finding marine grade ply. None of the Home Depot stores in my area had it, and they had no interest in finding it. I finally had to special order it from a lumber yard. I used it to make new hatch boards. No delamination, but after a couple of years, they still checked and deteriorated on the outside. I don't know if that's because I wasn't dilgent enough with keeping up the polyurethane coating, or due to the quality of the wood. I made a new set last summer out of the same wood, but this time I painted them instead of finishing them bright. We'll see how they hold up.
 

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hatches have hard lives mostly because they are flat and in direct sunlight...I find ply if in vertical positions last a lot longer...

guess it makes sense for many materials...

anywhoo

heres hoping middle range ply works

I actualy thought about completely glassing my bulkheads but opted not cause of concerns about being too stiff creating stress cracks elsewhere on decks, hull etc...

I think bulkheads and other structural pieces, shouldnt be considered life of boat items but repleaceable at specific intervals kind of like chainplates and rigging are...

anywhoo
 

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Wandering Aimlessly
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I've used 1/2" oak plywood (as well as some 1/4") on the interior. So far (8 years) it's held up well.
 

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Over Hill Sailing Club
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I've dying to try some OSB sheathing in a marine environment. The stuff is tough as nails and can be left outdoors for years without deteriorating. It's ugly so is of no use for exposed surfaces but laminated over, it seems it would be good for deck underlayment or bulkheads. I'd even be tempted to try it for countertop base material. I used it on my house for floor sheathing. Down at the local lumberyard, they have used it for flooring in outside work areas and it has not deteriorated after years of heavy use, getting soaked, etc.
 

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what is osb murphy? thanks
 

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The OSB idea is similar to a lot of the engineered wood products like Microlams and Parallams. The idea is to take small directionally laid out, overlapping wood pieces of various sizes and then pressure-laminate them together with an adhesive. The results of these processes is truly remarkable. I have a few chunks of large Parallam beams left over from a post and beam building I put up that have sat outside, used for blocking up stuff, for 10 years with 0 delamination. In the picture above, you can see that the strands of wood are long, longer than cheap chipboard which it shouldn't be confused with.
 
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A little secret to tell. At Home Depot in my area and north of the 49 parallel, they have marine plywood of another name. Comes in 1/2'', and 3/8' sheets, 5'X5', for about $55.
There must be 7 to 9 plies, beautifully made. At the boatyard it is left outdoors for years.
Sand it and it looks good. The trade names are ,Russian plywood and or, Birch plywood.
So most of the readers should ask for the latter name. Eh! The kicker is that, the glue is better than marine grade.
 
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