difference between marine grade plywood and regular?

[Mark]

Whats the difference?

[Jim Conlin]

If you search deja.com
http://www.deja.com/home_ps.shtml
for "marine plywood", you'll find that this subject has been covered here.

Mark wrote:

> Whats the difference?

[Glenn Ashmore]

OK, once more into the breach. This subject is almost as contriversial
as guns on boats.

Marine and exterior plywoods have similar glues but there are two
primary differences that apply to all marine rated plywoods in
comparison to exterior rated. .
1. There are at least 2 more plys in marine plywood over 1/4" thick.
2. The interior plys are fitted better resulting on fewer voids.

For domestic fir plywood that is as far as it goes other than the face
veneers are usually A/B on marine and A/C on exterior. When it comes to
imported BSB rated plywood like meranti and okoume, there are more
differences. There will be 4 to 6 more plys glued together under more
pressure, even less voids and better face veneers that do not raise
grain or check as badly as fir and pine faced ACX..

The net result is that marine plywood bends more evenly to a fair curve
than exterior, has a slightly better ultimate strength and there is less
possibility for water intrusion into interior voids.

From a practical standpoint, if the boat will be trailered and stored
dry, has no critical curves and weight is not an issue, good old ACX
will do fine. OTOH, if it will soak in water for its lifetime, has has
fine lines or weight is critical, marine is the better option.

I include weight in this comparison even though ACX and marine plys of
the same species weigh about the same with marine fir being slightly
heavier than ACX fir.. The reason being that some imported woods,
particularly okoume, are much lighter for the same thickness as the fir
and pine used in ACX.

Mark wrote:

> Whats the difference?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.mindspring.com/~gashmore

[Trevor Rabey]

a good question. mainly, its the the glue, not the wood.

Mark wrote:

> Whats the difference?

--
Trevor Rabey
Phone Mobile: 0407213955
mailto: tra...@ozemail.com.au
PO Box 704 Vaucluse NSW Australia 2030

[paul1martin]

In article <903b0k$oe9$1...@imsp026.netvigator.com>,
"Mark" <markv...@epsi-highpressure.com> wrote:
> Whats the difference?
>
Waterproof glue, no voids, number of laminates, sometimes wood and
finish.

--
warm seas and dry decks to ya,
pm
From Mark Twain:
"Twenty years from now, you will be more disappointed
by the things you did not do than by the things you did do.

Sent via Deja.com http://www.deja.com/
Before you buy.

[ProCareJax]

>This subject is almost as contriversial
>as guns on boats.

<snip>

Hmmmm....now why would guns on boats raise such a fuss? Nothing wrong with a
fella that wants to protect his and his families (ass)ets is there?

I didnt think so. :-)

Have a nice day.

Dave (I'd rather be caught with it...than without it) Reid

[David Carnell]

Exterior plywood uses the same waterproof glues and passes the same boil
tests as marine plywood. The only differences are in the number of
plies and the veneer quality. My 16' utility skiff of ź" A-C exterior
fir plywood has lived in the water (salt) for 18 years now and is going
strong.

[William R. Watt]

"Mark" (markv...@epsi-highpressure.com) writes:
> Whats the difference?
>
>

as far a price and performance go figure a boat made of exterior grade
will last about half as long as one made of marine and for a small open
boat whose cost is all hull, cost will be less than 1/3 of marine

I belive the average age of a wooden boat to be about 50 years, and of a
marine ply boat 25 years, and an exterior grade ply boat about 15 years.

If an exterior grade boat is kept any length of time count on more
maintenance. Initially seal edges well and try to fill voids.

I think that's about right.

--
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National Capital FreeNet www.ncf.ca Ottawa's free community network

[John McCoy]

On Thu, 30 Nov 2000 21:35:42 -0500, Glenn Ashmore <gash...@mindspring.com> wrote:

<a good answer to a very FAQ>

Can you title that "FAQ - difference between marine & regular plywood"
and post it about once a month?

John

[sfk...@mindspring.com]

Please if I could add something from personal experience regarding luan vs.
pine Home Depot plywood. I built a small sailing pram from plans I bought
from a very popular web site. The designer said luan plywood was OK for this
small boat and that is what I used. This fall I managed to strike a coral
head at fairly high speed for this boat (down current and on a beam reach).
The daggerboard case and keel were both broken in rather badly and the boat
nearly sank as a result. The luan plywood had outer veneers that were not
much thicker than paper and the nominal 1/4" thickness was actually hardly
more than 3/16". I also built a 15' small power boat from plans from the
same site. I used BC pine plywood with 3 ply of equal thickness and although
it is listed as 1/4" plywood it is nearly 5/16 of an inch thick. There is no
comparison regarding strength as the pine is many times stronger, although
heavier, than luan.
I plan to use the marine tech boatbuilding plywood from McEwan Lumber
for my next boat unless they come up with meranti exterior glue. Home Depot
recently got in meranti, but it was for interior use only and 5.2 mm in
thickness ( around .200" of an inch). Also this is from the perspective of
an amateur and I learn a lot from Glenn's posts.
Warmest regards,
Frank
Big Pine Key/Lake Worth

[John Kohnen]

There's a boatbuilding plywood FAQ here:

http://www.boat-links.com/plyfaq.html

It's a bit old, but plywood hasn't changed much lately has it? ;o) I
suppose either Craig or I should update it though.

--
John <jko...@boat-links.com>
http://www.boat-links.com/
In this world of sin and sorrow there is always something to be thankful for;
as for me, I rejoice that I am not a Republican. <H. L. Mencken>

[Steve]

It's the same glue but the wood has no voids in marine ply. Quality control
over the glue process is much tighter.

steve
s/v Good Intentions

[Maguire]

Not to be argumentative, but I don't see how the fact that your sailing pram
was made of luan has any bearing on the outcome of "strik(ing) a coral head at
fairly high speed." I would guess the outcome would have been the same for ANY
plywood of approx. 1/4-inch.

Maguire

[Jacques Mertens]

Sorry to hear about your accident, especially since I believe this is one of
our designs but I should not blame the Lauan plywood for the grounding!
Lauan or not, its is possible to sink any boat. Not so long ago, I saw a
steel boat that sunk on a reef off Great Inagua.
Lauan is OK for a small dinghy that does not live in the water but the same
boat will have a stronger hull if made from marine fir and much stronger if
made from Okume.
Boat building ply is unsanded marine fir, not much stronger than your BC
pine.
There is no miracle: you always get what you pay for.
In this case, it was probably wise to choose cheap plywood. It is cheaper to
crash on a reef with Lauan . . . you would almost certainly have experienced
the same damage with an Okume hull but at a greater cost.
May I suggest (with a smile) buoyancy foam for your next landing craft?

--
Jacques Mertens
Boat Plans OnLine
http://www.bateau.com
<sfk...@mindspring.com> wrote in message
news:90b0q8$agh$1...@nntp9.atl.mindspring.net...

[sfk...@mindspring.com]

My point was exactly the opposite of what you have stated. I gave a
comparison of the two materials of nearly equal cost in the hope of being
helpful. I am in the process of testing the BC pine on a sailboat of
different design. (weighted leeboard and kick up rudder). The pine ply at
about 7 MM with far heavier outer plys is much stronger. That is what I have
said. I don't recall mentioning anything about what the results would have
been if I were using something else. So if your post was not meant to be
argumentative then I must have missed it's point.
Frank