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jalmberg
04-21-2013, 05:19 PM
I'm about to build a galley for my boat. I'm planning to use plywood for the two half-bulkheads that will make up the sides.

I am planning to use marine ply because if I ever get a lot of water in the boat ever any water in the boat, I don't want the ply to get messed up.

Only problem is, I have no thru-hulls and have never had more than an inch of water in the bilge. I'd need about 18" of water in the bilge to get the bottom of the bulkheads wet, so it's pretty unlikely.

Is marine ply overkill for interior use?

wizbang 13
04-21-2013, 05:36 PM
yes , I think so . overkill
acx

Peerie Maa
04-21-2013, 05:46 PM
Exterior grade may be OK, as long as the glue is waterproof. The wood may not get wet enough to rot, but it is still a damp environment.

jalmberg
04-22-2013, 07:26 AM
All right... consensus with no debate! How rare is that? Exterior ply with waterproof glue it is.

Thanks.

wizbang 13
04-22-2013, 08:09 AM
if the glue is not waterproof , it is not exterior ply

kc8pql
04-22-2013, 08:53 AM
^ +1. Waterproof glue is what makes ply exterior.

jalmberg
04-22-2013, 09:06 AM
if the glue is not waterproof , it is not exterior ply

Got it. Never knew that, but I've been reading up on plywood this morning. I'm constantly amazed by how much I don't know...

Peerie Maa
04-22-2013, 09:57 AM
Got it. Never knew that, but I've been reading up on plywood this morning. I'm constantly amazed by how much I don't know...

There are varying quality of exterior ply as well, some may have voids where the inner lams don't butt up tight. Those voids become condensation traps and rot. Examine the edges carefully after confirming the WBP stamp.

holzbt
04-22-2013, 04:03 PM
If this will be painted you might want to consider MDO plywood. It's the stuff with the resin paper faces used by sign painters and available at most real lumber yards.

jalmberg
04-24-2013, 10:00 AM
If this will be painted you might want to consider MDO plywood. It's the stuff with the resin paper faces used by sign painters and available at most real lumber yards.

H'mmm. Okay. I will look into that, too. Thanks.

Dan McCosh
04-24-2013, 10:23 AM
Our bulkheads were made from three-ply interior ply in 1936. It has been problematic ever since. Much of it ended up with bubbled sections, particularly at the lower end. Some of it was submerged at one point. The replacements have been MDO ply, which has been ideal because a: it is designed for exterior use in all weather, which is why it is called "sign board". b: the surface is a nice texture, free from checking problems, and easily painted. It is even available pre-primed. Definitely the best for new bulkheads.

jalmberg
04-24-2013, 10:29 AM
I heard the word 'MDO' before, but didn't really know what it was. Been doing some reading, and it does look good for the purpose.

wizbang 13
04-24-2013, 10:32 AM
I use it for my artwork, it's good stuff. One can get it "one side" or both sides.
The 3/8" is usually more expensive than the 1/2" .

jalmberg
04-24-2013, 10:51 AM
That brings up a good question: how thick? I've been thinking 3/4" for the two sides, and 1/2" for the top and front. I'm going to paint it and edge it with some mahogany that I picked up for free.

The galley is going to be fairly small... about 24" wide.

Dan McCosh
04-24-2013, 10:54 AM
I've never seen 3/4 mdo; most of it seems to be 1/2 ins., which is quite stiff, and should be adequate.

jalmberg
04-24-2013, 11:45 AM
Yes, I found a local yard that has double-sided 3/4" and one sided 1/2".

The 1/2" is probably strong enough, but I'm thinking the added thickness will be easier to grab onto, as a hand-hold. I'm not sure, but I'm leaning in that direction.

George Ray
04-24-2013, 03:35 PM
The advantages of a higher priced ply are the higher ply count and a surface that will take a good finish. Some 3/4" CDX pine sheathing may be only 4 ply , ..... 3/4" AC of Fir or some S. American wood will be 5-7 plies, ...... , 3/4" Marine will probably be 11-ply, 3/4" Baltic Birch is about 13 plies.

The higher ply count will make the material much better suited for interior sculpture such as if you wish to cut a hole in a corner for a hand hold and then shape/smooth and stain/paint. Having said that if it is just a structural sheet that will be camouflaged by various coatings and trim pieces the run of the mill exterior play should do a great job and some of the S. American woods that are showing up in the big box stores exterior AC ply racks does seem to take a finish much much better the venerable fir ply of old.


DuckWorks on Plywood:
http://www.duckworksmagazine.com/03/r/excerpts/iabbs/april.htm

Baltic Birch:
http://www.woodworkingseminars.com/wp-content/s7334.pdf

Few Marine ply prices:
http://www.boulterplywood.com/MarinePlywood_4.htm

Bluegill
04-24-2013, 06:24 PM
I have never seen MDO in any store/lumberyard, etc.

WX
04-24-2013, 10:19 PM
Don't forget to seal the edges of the ply with epoxy. If you have any TPA (timber preservative agent) then mix a bit of that into the epoxy as well. I epoxy coated all the ply in my boat and used exterior grade.

Soundman67
04-24-2013, 11:28 PM
MDO is sometimes called Crezone.
if the lumberyard doesnt list it under one name sometimes they can find it listed under the other.

Jay Greer
04-25-2013, 12:30 AM
I have always built bulkheads either of raised panel in frame or three layers of T&G white cedar the center core being laid on the diagonal. This is much lighter than plywood, more pleasant to work and less prone to rot if even at all.
Jay

jalmberg
04-26-2013, 07:25 PM
I have always built bulkheads either of raised panel in frame or three layers of T&G white cedar the center core being laid on the diagonal. This is much lighter than plywood, more pleasant to work and less prone to rot if even at all.
Jay

I like this idea, too, but I'll be darned if I can figure out how to build a T&G panel in this shape:

http://photos.identry.com/blog/waterline/IMG_1502.jpg

Actually, this pattern isn't quite finished... I still need to cut out a piece in the upper right corner, so the galley has a 6" 'bulwark' around the counter. But you get the idea.

How do you build a frame to this kind of complex shape? Must be a nightmare.

jalmberg
05-01-2013, 02:48 PM
Probably another dumb question: Am I right in thinking that all MDO is exterior grade? I've been reading, and that seems to be the case, but the guys at the lumberyard just shrugged and said they don't sell a lot of it. I don't see any markings along the edges.

J.Madison
05-01-2013, 07:07 PM
For a galley it would be great but for bulkheads that receive chainplates I would be skeptical of its tension strength. Never used it though. Anybody have info on the strength properties of the stuff? Especially in tension?

wizbang 13
05-01-2013, 07:18 PM
In the fifties , boats were built of it .
Of course, ply in general was better then.
The stuff I use ( paintings/artwork) , is def fir , with maybe some hemlock in the cores.


Related, maybe not , I have cut Woodwinds main bulkhead open , and closed it back up , four times. For maximizing ventilation in the tropics, and for holding heat in the PacNorthwest. A real sawzall re model each time. Fancy joinerwork does not lend itself to this type of modification. How many boats I go aboard , someone says , "watch your head on that such n such" ( nicely fit piece of teak, usually), I 'm thinking to myself, "that would last about 2 minutes on my boat. "