Differences in marine ply?

[CCrew]

Re: Differences in marine ply?

"One of the worst..IMHO..things is to run fasteners into the edge grain of ply. Ply is most vulnerable to rot in the edge grain and has the least fastener strength."<br /><br />Interesting statement. If indeed true (and I have no grounds to disagree) that means that subsequently screwing the deck to the stringers would be fastening it into the weakest strength area....<br /><br />-Roger

 

[FLATHEAD]

Re: Differences in marine ply?

Let me throw this out there,,You could always scab a piece of one by two along the top of the stringer to accept the screws for the deck.

 

[airman]

Re: Differences in marine ply?

If you really want to protect the boat, get a really good cover for the boat. Not just a camper top but a cover that gets the whole boat. As to my experience, it really does make a difference what you use so choose carefully. I replaced the transom in my 19'Glassply 5 yrs ago. I also replaced some flooring. The transom was marine ply, sealed with 2 coats of epoxy sealr then glassed in. The flooring was replaced with standard exterior ply, unsealed and glassed in. I'm replacing the flooring again. The transom is still good. I'm also making a good cover.

 

[kenneths]

Re: Differences in marine ply?

One thing I don't see here is 1/2" is no-longer 1/2".....it's 15/32". I replaced my boat floor (1/2"), with 5/8"...truely 19/32".<br /> As for glassing the wood, you gain zero unless you do both sides, because you have compression in one side and expansion on the other-I'm not talking about resin only, I'm talking Glass too.<br /> As for water-proofing, there is nothing better or more effective than oil-based floor paint, thined 50%, and apply 3-4 coats per side, drying between coats, and no, you don't need marine grade-the ONLY difference is the glue used to laminate, and if you are sealing both sides, this has no relavance.

 

[Columbia]

Re: Differences in marine ply?

I disagree that the ONLY difference between marine ply and regular is the glue. The main difference is the voids/knotholes are filled in marine ply on all plies...in theory. They used to select for 'perfect' plies in the old days so all plies were an 'A' face but that fell out years and years ago and 'footballs' are typical now on inner plies. Thus, when you cut through there should be no areas to backfill nor to collect rainwater...so to speak...and no built in weaknesses due to said voids. I can agree with the paint application, some folks will 'fill' the outer ply with linseed oil and I've heard some say should be boiled and some say should be raw. The glue line limits penetration to the next ply for the most part in my experience.

 

[crab bait]

Re: Differences in marine ply?

is that your PRETTY boat there OLD SAILOR..??<br /><br />that's one thing that is the same in marine an exterior plywoods... is the glue...the same in both

 

[baba]

Re: Differences in marine ply?

Are all of you scarfing sheets of plywood, or is there a place to buy longer sheets, like 20'?

 

[Columbia]

Re: Differences in marine ply?

Two answers: Yes, that boat is/was my old Benford 22. I finished it from a bare hull in the late '70's for the most part. I sailed her ten years, no engine, before selling. Saw her the other day because I'm having a half model built for the wall and needed some pics for detail for the model maker. Geez..and stronger words..she is mildewed, neglected, and varnish is gone to hell and rigging has failed and.....sad to tell.<br /><br />The 16' marine ply I have on the side wall of the garage came from a plywood mill in Vancouver WA. Maybe there's a mill in your region doing marine ply....<br />

 

[crab bait]

Re: Differences in marine ply?

supposely,, the only place east of the mississippi river that can sarf plywood is harbor sales .. but there machine is broke an can't afford to fix... <br /><br />the only one in the country is in LA...

 

[BillP]

Re: Differences in marine ply?

More thoughts...<br />Just like any woodwork, edge fastening plywood is not an issue if you use the right size fasteners. I used #14 x 3" flathead screws spaced on 18" centers to secure 3/4" pt ply decking to the 3/4" pt ply stringer edges. I pilot drilled and "buttered" up with thickened epoxy before setting the deck down and screwing together. The glue or the screws would have done it alone but I used screws to give a 100% mechanical clamp and the epoxy for 100% water proofing. The extra labor and cost was miniminal over the cheapest way.<br /><br />Marine ply...it is MUCH stiffer than exterior ply, regardless of wood grade. I have ordered both marine and exterior plys in the same identical grades so it isn't like you can't get top quality exterior ply. Yes, I paid more for the exterior but it was still less than marine. The difference was I could bend the exterior around a hull and the marine was very difficult or impossible to bend. Use marine if you are looking for the stiffest ply because all the other are in 2nd place. <br /><br />I also bought and paid big bucks for the WEST brand 5'x5' imported wood sheets they sell for "WESTING" over old hulls. The stuff is NOT waterproof and needs epoxy to survive. I have a sheet hanging in the rafters and it has delaminated by just the humidity in the air. It is thin (I think 4mm) and bends easily but I will never use it again, or any other that isn't glued with waterproof glue. WEST's printed material is also very outdated (by 15 yrs) concerning pt ply use.