Glen-L.com

Hallo
What makes marine plywood marine?
Amir

While many plywoods have exterior glues, for me the defining criteria that I demand is solid inner cores of quality woods. While the cross layers do not have the ability to be continuous in its width, which in a sheet of plywood means eight or so feet of a run, its important that the junctions of the inner veneers going cross grain to the faces be butted and without voids. There are some that do have a percentage of slight inperfections, you will find that the dollar amount per sheet by comparision to other generic or oriental stuff rarely have any voids at all when you cut into them or attempt to cut scarfs.

What Oyster said plus, in practical terms, marine grade :

Will not come apart in when wet.
Will be less likely to snap or fracture when bending.
Costs more.
Worth every dime!

Now I have some 'marine grade' douglas fir I tossed because it was not well made... so 'marine grade' does not always mean quality.

I've use BS1088 Meranti Plywood (which is 'marine' stuff) and I've been very happy with mine. Others have had issues with even the BS1088 standard, with variations in sheet weight and the like.

Just be cautious about 'deals' and try to deal with a supplier that cares and will stand by the product.

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Ian (aka Iggy)
My Malahini Build

Can't remember what my previous build marine fir plywood was as far as plies,but this current build had 5 pies on the 1/4" (6MM) as opposed to 3 plies for exterior plywood.

The faces are much smoother also,and as others have pointed out,no interior voids, and I like the way it bends and feels more stable.

I used BS1088 Okume Marine ply this time.

There is a weight difference in the different types also,so depending on where it's used,and what type of boat, that can be a deciding factor

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Plywood is simply plywood without voids in the inner layers that is built to a standard spelled out by one of a couple rating systems. It is glued together by a non-water soluable glue. There are many types of marine plywood and their rot resistance varies greatly. On it's own, without paint or epoxy coating, it is not exceptionally rot resistant in most cases. What marine plywoods bring to the table is exceptional strength per thickness compared to CDX or ACX plywoods and a very smooth finish surface for applying paint, varnish or epoxy.

Treated plywood is plywood that has been treated with chemicals, CCA and ACQ being the most popular, to render it long term rot resistant. Unfortunately it is usually done on cheaper CDX grades of plywood. It is difficult to get paint to stick to for marine use and I imagine that it would probably have issues with epoxies as well. It is highly corrosive to aluminum and non-galvanized steel. I personally wouldn't use treated wood on a boat.

Simple test to check the quality and suitability of your plywood. Cut some square pieces small enough to fit in a pot. Fill the pot with water and put it on the stove with the samples floating in the water. Turn on the heat and put a lid on it. When the water comes to a hard boil, turn the heat on so it continues to boil softly. Check the plywood once an hour and be sure the water level does not get too low. Continue doing this for 72 hours or until the plywood delaminates. You can see the delamination begin when small gaps begin to appear between the layers of the plywood. If you samples have not begun to delaminate in 48 hours you have good plywood. If they don't delaminate in 72 hours you have great plywood!

Why boil? Someone once asked me what the point of boiling was unless you planned to sail near an underwater volcano. The purpose of boiling is to act as a time accelerator. You could accomplish the same thing by not boiling, but letting the water soak in the water for a year or so. Me, I'd prefer to do the test a little quicker, so I boil.

Regards,

Bill

_________________
We don't stop playing because we grow old, we grow old because we stop playing! Ben Franklin
Any day spent messing with boats, is a good day! me

Um, boiling water for 72 hours???

Expect a spike in your gas bill and an irritated spouse if you use this method.

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Jeff

My Celerity build.

Weigh every sheet you buy to ensure uniformity. I learned that the hard way.

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Andy Garrett

"When all else fails, follow the instructions." -Dad

Jprice said:



This is the Philippines! I have no wife, but I do have a maid and cook. They were none to happy with me for tying up the stove for so long, but they got over it and there really wasn't much odor. The water took on a nasty brownish tint though. In my test I was also testing some 1 1/8 laminations I'd made up with the local laminating epoxy to give it a test as well. So, I had a full pot!

Regards,

Bill

_________________
We don't stop playing because we grow old, we grow old because we stop playing! Ben Franklin
Any day spent messing with boats, is a good day! me