Differences between exterior and marine plywood
Dave Carnell
Product Standard PS 1-74 of the Product Standards section of the
National Bureau of Standards.
Both use the same glue and have to meet the same standards such as boil
test, vacuum-pressure soak, heat resistance, etc.
Marine grades have to be A-A, A-B, B-B, HDO, or MDO. Repairs in marine
grades have to be of wood with exterior glue and set by a combination of
heat and pressure. Marine requires a minimum of 3 plies to 3/8", 5 for
over 3/8" to 3/4", and 7 for over 3/4".
Exterior A-C and B-C can have wood or synthetic putty patches. Minimum
nomber of plies is 3 to 3/8", 4 for over 3/8" through 1/2", 5 for over
1/2" through 7/8", and 6 for over 7/8".
In a nutshell you get better construction and comparable durability in
marine compared to exterior A-C or B-C.
Exterior plywood came into general use in the 1930s, as I remember.
Around 1940 the Douglas Fir Plywood Association did a good bit of
promotion of exterior type plywood for boatbuilding. They commissioned
a number of boat pland for pram dinghies to knockabout sloops. I had
them all at one time, but have now only the 7'-9" Pram Dinghy designed
by C. P. and E. D. Burgess. Through the years I have built five of
those. The sailboats were most designed by a Charles MacGregor, as I
remember.
I have built boats of exterior grade plywood, either A-C fir or B-C pine
over the last 50 years and have never had a failure in the plywood.
Exterior plywood, of which marine plywood is one grade, is a most
satisfactory material for boatbuilding.
<http://home.att.net/~DaveCarnell>
William R. Watt
Dave Carnell (davec...@worldnet.att.net) writes:
> Exterior plywood and marine plywood in the U.S. are made to U. S>
> Product Standard PS 1-74 of the Product Standards section of the
> National Bureau of Standards.
>
> Both use the same glue and have to meet the same standards such as boil
> test, vacuum-pressure soak, heat resistance, etc.
I've found what looks like very good luaun exterior grade plywood. Nice
one sided finish and no edge voids. However I've seen exteror grade spruce
and GIS fir I would not want to use due to the many edge gaps and to the
poor surfaces. The good side had many filled in knot plugs and on the
standard side they weren't filled.
What I've read is that gaps in the middle ply are where rot starts. I used
some on a boat deck and had screw heads dissappear into the gaps.
Apparently there are not only gaps in teh middel play which can bee seen,
but gaps in teh application of the glue which can't. Glue gaps may nto be
important when using full sheets but when cutting sheets up for boat
buliding glue gaps may end up at an edge where delamination could be a
problem.
I guess like most wood, one has to look over the plywood one uses on a
boat before selecting the pieces to use.
My understanding is that there are no gaps in either the wood or the glue
in marine plywood. Just for liability reasons I imagine the manufactuers
would take extra care with something they are selling as marine ply. It
sure is expensive compared to exterior grade in these parts.
On a historical note I read recently that the resin glues (urea and
resorcinol) were invented during the 1930's. And that resorcinol was the
first "truly waterproof" glue. Its use became widely known in boat
building circles after it was used in the construction of PT boats in
WWII.
>
> Exterior plywood came into general use in the 1930s, as I remember.
> Around 1940 the Douglas Fir Plywood Association did a good bit of
> promotion of exterior type plywood for boatbuilding. They commissioned
> a number of boat pland for pram dinghies to knockabout sloops. I had
> them all at one time, but have now only the 7'-9" Pram Dinghy designed
> by C. P. and E. D. Burgess. Through the years I have built five of
> those. The sailboats were most designed by a Charles MacGregor, as I
> remember.
>
> I have built boats of exterior grade plywood, either A-C fir or B-C pine
> over the last 50 years and have never had a failure in the plywood.
> Exterior plywood, of which marine plywood is one grade, is a most
> satisfactory material for boatbuilding.
>
> <http://home.att.net/~DaveCarnell>
>
>
>
--
------------------------------------------------------------------------------
National Capital FreeNet www.ncf.ca Ottawa's free community network
Pat Ford
<davec...@worldnet.att.net> wrote:
<snips of a relatively thorough discussion of plywood classification>
However the most important criterion is not addressed. Marine is not
supposed to have voids. Voids will create fairness problems. If rot
starts in a void it can shoot up to eight feet quickly.
>In a nutshell you get better construction and comparable durability in
>marine compared to exterior A-C or B-C.
>
>Exterior plywood came into general use in the 1930s, as I remember.
>Around 1940 the Douglas Fir Plywood Association did a good bit of
>promotion of exterior type plywood for boatbuilding. They commissioned
>a number of boat pland for pram dinghies to knockabout sloops. I had
>them all at one time, but have now only the 7'-9" Pram Dinghy designed
>by C. P. and E. D. Burgess. Through the years I have built five of
>those. The sailboats were most designed by a Charles MacGregor, as I
>remember.
>
>I have built boats of exterior grade plywood, either A-C fir or B-C pine
>over the last 50 years and have never had a failure in the plywood.
>Exterior plywood, of which marine plywood is one grade, is a most
>satisfactory material for boatbuilding.
I don't understand what "Exterior plywood, of which marine plywood
is one grade, is a most satisfactory material for boatbuilding."
means. I can't decide if it is simply a poorly written sentence, an
ignorant assertion or a troll.
If it means that exterior and marine fir plywood are equivalent in
durability that is certainly mistaken. However, if you were asserting
that they are both more or less bad I would have to agree. Marine fir
is bad. Exterior is just garbage.
If you want to build a "throwaway" boat, I suppose exterior fir would
work.
The sad thing is that uninformed readers will take the original
message seriously. It is a sadly mistaken opinion cloaked in an
apparently reasoned post.
Again-Don't believe anything you read on Usenet--at least until you
double check it. ---that includes my statements.
Antique and Classic Boat Society
Pacific Northwest Chapter
Free Classic Boating Ads for All
http://www.halcyon.com/pford/acbsx.htm
sailor
Obviously, you have no idea who Dave Carnell is. His methods and
experience are highly respected amongst the boat building community.
What he says about plywood is right on the mark. Check out his website:
http://home.att.net/~DaveCarnell/
In article <383850f7...@news.halcyon.com>, pf...@halcyon.com (Pat
* Sent from RemarQ http://www.remarq.com The Internet's Discussion Network *
The fastest and easiest way to search and participate in Usenet - Free!
Jacques Mertens
I like to read different opinions from each of them.
--
Jacques Mertens
Boat Plans OnLine
http://www.bateau.com
sailor wrote in message <0a0133f8...@usw-ex0107-042.remarq.com>...
Mike Goodwin
Greg Rinaca <greg...@lcc.net> wrote in message news:383AC279...@lcc.net...But don't lose sight of the difference between factual information and opinion.
Dave Carnell consistently presents factual information here.Greg Rinaca
Pat Ford
wrote:
First, Mr. Rinaca-please don't use html when posting to a newsgroup.
This can usually turned off in your editor.
Uh, where is the factual information in Mr. Carnell's presentation?
Dave Carnell presents as fact (ie: antifreeze as a miracle cure for
rot, no difference indurability between fir exterior and marine
plywood) conclusions which have little basis. He presents as proof
andecdotal evidence but little hard fact. Certainly this is the case
with his curious assertions regarding fir plywood.
I have been a professional boatwright doing high quality classic
boats for over 25 years. However, I don't ask you to believe me simply
on the basis of my pronouncements here.
Check it out! Ask professional boatwrights if there is any difference
between exterior and marine. When you tell them Dave Carnell's
theories it should bring a smile to their face.
Again, don't believe me, investigate.
>Greg Rinaca
>Jacques Mertens wrote:
Antique and Classic Boat Society
Bill S. Roberts
marine fir stamped both PS1-83 and PS1-95 that had voids. This stuff had the
APA stamp on it, and was junk. I wouldn't have used it for a concrete form.
I have copies of the standards that I purchased from the APA. For cheap boat
renovation on a budget, I have recently bought the MDO here on Puget Sound
for about 32.00/sheet, and when I cut panels to fit found no voids, and it
works fine. This MDO was a compromise, which best fit my individual needs.
For the type of work Pat does(I've seen it, first class, artisan level),
then Lloyds rated ply or equivalent is the only choice. His quality of work
is show quality. For the majority of el-cheapo homebuilt boats, AC or the
MDO seems to have a place too. And latex paint on the el-cheapos works great
too, I've done it. And it's sitting outside and to MY eye, looks super. Not
to get off track, but look at the current BOatbuilder mag and read what Renn
Tolman says on this. I love the part about "I build boats and prefer to
leave the epoxy on the boat...However, I wouldn't let latex NEAR Pat's work,
it's in a different market segment. Gold-plater stuff, and for those with
the time or the income, it is arguably more near "as good as it gets" than
the extMDO2sides/sys3/latex deck I installed in my Skagit. ANd if my boat
were parked next to one of Pat's restorations at the Bellevue waterfront,
nobody would notice mine. But it puts a smile on MY face:)
I just replaced the decks in a Skagit glass cruiser with the MDO, and she's
better than new. If I look at the ply used in my 23' Skippercraft
Wavemaster, it is Crezon faced ply, MDO. Both fir and mahogany, the fir
being labeled "hot press". ANd this boat is a '61, having been well cared
for, she's in great shape. Where there was water intrusion due to the blue
tarp syndrome, and some delamination, I'll be installing a patch using
modern techniques. But of all the square footage on this boat, only 1.5
square feet need renovation. So System Three and some new ply(you guessed
it, MDO!) will perform as they always have for me, a one-time repair.
I think that the difference of opinion between Pat and Dave presents an
opportunity for the rest of us to learn there are many ways to get to the
same spot, on the water. Each has his place in the forum, and I've learned
from BOTH men.
Hey Pat, what do you know about Skippercraft boats made on Vashon Island by
Larsen Marina?
--
Bill
Whidbey Island(Coupeville), WA
bi...@pugetsound.net
Dave Carnell <davec...@worldnet.att.net> wrote in message
news:3836E0D0...@worldnet.att.net...
> Exterior plywood and marine plywood in the U.S. are made to U. S>
> Product Standard PS 1-74 of the Product Standards section of the
> National Bureau of Standards.
>
> Both use the same glue and have to meet the same standards such as boil
> test, vacuum-pressure soak, heat resistance, etc.
>
> Marine grades have to be A-A, A-B, B-B, HDO, or MDO. Repairs in marine
> grades have to be of wood with exterior glue and set by a combination of
> heat and pressure. Marine requires a minimum of 3 plies to 3/8", 5 for
> over 3/8" to 3/4", and 7 for over 3/4".
>
> Exterior A-C and B-C can have wood or synthetic putty patches. Minimum
> nomber of plies is 3 to 3/8", 4 for over 3/8" through 1/2", 5 for over
> 1/2" through 7/8", and 6 for over 7/8".
>
> In a nutshell you get better construction and comparable durability in
> marine compared to exterior A-C or B-C.
>
> Exterior plywood came into general use in the 1930s, as I remember.
> Around 1940 the Douglas Fir Plywood Association did a good bit of
> promotion of exterior type plywood for boatbuilding. They commissioned
> a number of boat pland for pram dinghies to knockabout sloops. I had
> them all at one time, but have now only the 7'-9" Pram Dinghy designed
> by C. P. and E. D. Burgess. Through the years I have built five of
> those. The sailboats were most designed by a Charles MacGregor, as I
> remember.
>
> I have built boats of exterior grade plywood, either A-C fir or B-C pine
> over the last 50 years and have never had a failure in the plywood.
> Exterior plywood, of which marine plywood is one grade, is a most
> satisfactory material for boatbuilding.
>
Davthzlt
some a/c pine it was a lot heavier i have built several workboats i.e large
crab skiffs that work evry day during the crab pot season .in the lower
chesapeake bay the norfolk end.i hav,nt been building but for 12 -13 years i
built theese using a/c fir and polyester resin two are still going after 7
years they may be trhow away boats but they hav,nt been trhowed away yet
D.W.Johnson
Greg Rinaca
If you don't see factual information in Dave Carnell's posting on the
differences between exterior and marine plywood, then I don't think I
can help you. However, I would think that you should be able to
understand this type of information that Mr. Carnell is presenting; it's
not technical and it is simply stated. Maybe it hasn't occurred to you
that some folks build boats that are quite different than those with
which you are involved.
Greg Rinaca
Pat Ford wrote:
>
> On Tue, 23 Nov 1999 10:36:09 -0600, Greg Rinaca <greg...@lcc.net>
> wrote:
>
> First, Mr. Rinaca-please don't use html when posting to a newsgroup.
> This can usually turned off in your editor.
>
> Uh, where is the factual information in Mr. Carnell's presentation?
> Dave Carnell presents as fact (ie: antifreeze as a miracle cure for
> rot, no difference indurability between fir exterior and marine
> plywood) conclusions which have little basis. He presents as proof
> andecdotal evidence but little hard fact. Certainly this is the case
> with his curious assertions regarding fir plywood.
>
> I have been a professional boatwright doing high quality classic
> boats for over 25 years. However, I don't ask you to believe me simply
> on the basis of my pronouncements here.
> Check it out! Ask professional boatwrights if there is any difference
> between exterior and marine. When you tell them Dave Carnell's
> theories it should bring a smile to their face.
>
> Antique and Classic Boat Society