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Discussion Starter · #1 ·
Got the plans to build a small wooden row boat. They call for marine grade plywood for the external shell of the boat. I was thinking of using pressure treated plywood. Has anyone built anything like this using pressure treated plywood over the marine plywood and what problems will I run into by doing so?
 

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Marine grade just means it was made with a water proof glue and has no voids in the laminates. Pressure treated is pumped full of toxic chemicals.

Is there any aluminum in your build? Pressure treated lumber is very corrosive to aluminum.
 

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Discussion Starter · #3 ·
Marine grade just means it was made with a water proof glue and has no voids in the laminates. Pressure treated is pumped full of toxic chemicals.

Is there any aluminum in your build? Pressure treated lumber is very corrosive to aluminum.
No aluminum but I was thinking of using brass screws. Other then that just pine wood into the pressure treated wood.
 

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I dunno what affect it has on brass if any.

Ive never purchased marine grade ply. That stuff is way expensive!
 

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From my youth helping a neighbor build a boat. Marine ply, water proof glue and marine plywood. Then we covered everything in and out with fiberglass. Three coats or resin.

It was a flat bottom boat that was designed for a 3 HP outboard. A transom of 3/4 marine ply, extra bracing and a 15 HP outboard was the regular motor. Up on a plane top speed was close to 30 by the speed wand.
 

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Discussion Starter · #7 ·
In my opinion pressure treated ply is junk. While very expensive, marine ply is what you should use.

GMC
My reasoning for pressure treated plywood was over marine plywood to keep cost down. If pressure treated plywood is junk what would another choice be and still keep cost down. This boat is just a fun project to build it more then if I will ever use it. If it ever sees the water at all it will just see if it leaks of floats. I plan on using planed down rough cut pine for the frame. My hobby is into more wood working then boating but also I like the looks of a nice finish job when I am done. For a finish I will use paint. Yes if I was to build a boat for use I wouldn't be using pine for the frame and I would use marine grade plywood.
 

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If you can hand pick your ply, standard luan will work for the boat, especially if you're glassing it afterward. It won't be as nice or as long-lasting (without maintenance finishes every couple of years) as a marine-grade ply boat but it will work just fine. I haven't found marine grade ply to be particularly expensive compared to pressure treated stuff, though. I guess it's all relative.

More importantly, for a boat, I wouldn't want to use pressure treated anything because it's pretty toxic stuff and doesn't look as nice either.

EDIT: I agree, brass screws won't be your best option for hardware. Check out some of the boat building forums, like kayakbuildersforum, or chesapeake light craft (clc.com) forums for some great advice.
 

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x3 on not using brass screws. The zinc will actually come out of the brass, leaving copper only which is weak. When I was working on my wood boat rebuild, silicon bronze was used.

The main reason marine plywood is used is because it doesn't have voids in it, which create weak spots and if you happen to put a screw in the void area it will collapse the outer layers.

If I remember correctly, the glue used in marine plywood isn't much different than the glue in exterior plywood.

Aircraft rated plywood actually has a test where it gets immersed and boiled.

Most pressure treated plywood I have seen has been of poor quality and looked like nothing more than sheathing grade. The chemicals would also likely affect the ability of finishes to stick. The new PT chemicals that replaced CCA are highly corrosive.

Steve
 

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I think you will answer your own question if you just go look at PT vs marine plywood, let alone lifting a sheet. It just doesn't make sense to invest all the work and use inappropriate materials just to save a few dollars. The project will suffer and so will you, using junk.
 

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I'm currently replacing wood flooring,cabinets and ledges in my fishing boat. Using marine ply then carpeting afterwards. Marine ply is a must. Do not use exterior ply due to treated with copper now. This will cause corrosion with aluminum contact. marine ply is a pleasure to work with too. Price is not that much more. 1/2" = $67/sheet. 3/4" =$85/sheet. Use nothing less than AB grade.
 

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I'm currently replacing wood flooring,cabinets and ledges in my fishing boat. Using marine ply then carpeting afterwards. Marine ply is a must. Do not use exterior ply due to treated with copper now. This will cause corrosion with aluminum contact. marine ply is a pleasure to work with too. Price is not that much more. 1/2" = $67/sheet. 3/4" =$85/sheet. Use nothing less than AB grade.
W/regard to the copper, I think you mean pressure treated plywood. As noted above, pressure treated plywood is junk from a structural standpoint. There are also corrosion issues with hardware/screws/nails - certainly brass wouldn't hold up. Don't know about bronze. Stainless is recommended for most pressure treated uses.

Above the waterline, for interior furnishings and other non-structural applications, you don't need marine plywood - good quality (A-B?) will be fine. Nothing wrong with using marine, just not necessary.

For your boat, remember, your labor will be the same regardless of the quality of the plywood. If you value your labor you will use the best quality plywood you can afford. But, no lower quality than A-B-X or you are wasting your time.
 

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Marine ply should be used for interior too. No voids and water proof glue. You're right about the labor factor. The pros say that the cd grade will de-laminate. Another issue is to make sure water proofing the ply is compatible with carpet glue and that is compatible with the carpet backing. Nothing but stainless hardware for me.
 

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Discussion Starter · #16 ·
I am sure glad I asked about the pressure treated plywood. It doesn't look like it is a good idea. I will look into seeing what else I can find. How about the idea I have about using pine for the boat frame? The hardware is something I just never gave any thought to. How would decking screws work? Now for a finish I was thinking I like the looks of a nice paint job, something like a high gloss exterior paint. Now the next question I have, would the wood be painted before I put things together or do you seal any place raw wood comes together with something? Then that brings me to the next question how do you seal wood from water leaks? Like I said before the reason I am building the boat is more to the enjoyment of building it more the using the boat and really have no idea what I will do with it when its done, maybe sell it? Yes I sure need some reading on boat building.
 

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Generally, pine is not a good wood for the frame. White oak is often used for that. Red Oak is not nearly as rot resistant as white oak.

For sealing joints, use 3M 5200 Sealant or BoatLIFE Life-Calk.

A good place to go for information is:

http://forum.woodenboat.com/

There are a lot of little details in building a wooden boat that determine if it lasts or not. A lot of proper ways don't cost more, but just use the right materials.

Steve
 

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I forgot to mention, a lot of older boats were built to seal from the wood swelling and sealing the gaps (like barrels do). If you are using plywood, then it will not swell enough to seal and you need to use sealer.

Steve
 

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I'd do some reading before starting to build. There's a lot of info on-line that would be useful for a beginner. For an idea on a boat design take a look at http://www.smallboats.com/bolger.htm The plans offered on that site are designed for beginners - you don't need to buy the plans, but the building techniques are useful.

Appears you are thinking of a plywood on frame construction. As noted, oak is probably best for frames. Fir would probably be better than pine - and is used a lot for small boat construction. Usually the members are glued with a good water proof wood glue and fastened with nails or screws. You'd paint after the boat is completely assembled (unless you have some inaccessible areas you'd want to protect - then do those prior to assembly).

There is also a "stitich and glue" building technique that doesn't use much in the way of frames and is easy and quick for beginners. Again, you can find lots of info on-line - including some web pages where builders document their boat building projects.

Have fun - building a boat is on my bucket list - haven't had time to do it yet, but I'm getting close.
 

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For what it's worth, I've built boats with luan and marine grade, and didn't see any difference in performance. I've also made frame for skin on frame boats with nothing but construction grade plywood. Seal them with the right sealant (marine epoxy works great but there are other options) and they work just fine for years. No need for fancy or expensive, though I will admit the nicer quality materials look better, generally.
 
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