Fly Baby - Marine plywood
scb
Baby. The plans suggest using marine grade plywood. I have located numerous
sources for aircraft plywood, but its pretty expensive and why argue with
the designer's choice of materials?
Any suggestions for sources and/or comments re:marine plywood.
Thanks
Scott
Frank Stutzman
Two things for aircraft plywood:
1) its certified for aircraft use. Probably not a big deal, but
at least the quality and consistancy is held to a tighter standard.
2) weight. I don't have the numbers, but I can't imagine marine plywood
being lighter than aircraft plywood.
I'm looking ath the Fly Baby plans as well. Alas, I can't see myself starting
one for number of years. Bowers design criteria was ease of construction
and costs. As I am considering some modifications that will add weight to
the project, I am willing to trade some weight for higher costs.
Aircraft Spruce has marine plywood, but unless you are really in the middle
of no where, I can't imagine you can't find a local source.
Frank Stutzman
Hood River, OR
Ronald James Wanttaja
scb <sbe...@tri-lakesonline.net> wrote:
>I am looking to start a first time project, particularly the Bowers Fly
>Baby. The plans suggest using marine grade plywood. I have located numerous
>sources for aircraft plywood, but its pretty expensive and why argue with
>the designer's choice of materials?
>
>Any suggestions for sources and/or comments re:marine plywood.
Well, Bowers has alternate suggestions, as well. To quote from page 9-2
of the plans: "The plywood does NOT have to be marine grade. It has
been found that a good grade of EXTERIOR fir plywood is practically the
equivalent of marine. While mahogany is preferred, fir is all right.
Minor differences in quality and strength will have no effect on the
integrity of the finished airplane because the 1/8" plywood parts are
considerably over strength anyway."
About a year and a half ago, I even bought 1/8" mahogany plywood from
the hardware/builder's supply store down the street (non-aircraft
project).
Ron Wanttaja
want...@halcyon.com
http://www.halcyon.com/wanttaja/
KeithF4281
about the only wood will be the wood vaneered panel) :) But...as a former
marine surveyor, I am familiar with marine ply, and my house is sided with
exterior grade ply. The marine will have (at least should have), finer grain
and no knots or imperfections (note "imperfection" is a relative term, since
nature is not perfect). Marine ply's other claim to fame is that the glue must
not delaminate when in contact with water or moisture. I'm not sure what this
does weight wise as it is not as critical on a vessel, but some of the best
vessels built of marine ply are epoxy saturated with the WEST system, which
prevents the rot from begining. I would suspect that aviation grade ply can be
gotten in thinner sheets,` most marine applications will use a thicker plywood
panel than that found in an aircraft. N.B. Just my thoughts, I am by no means
even a partial expert when it comes to aircraft grade ply. Warm Regards,
Keith
KeithF4281
my house. 10 years later, it is rotting where the panel meets the ground.
Obviously, there is constant contact with a moist area. I think a true marine
grade would have done a better job. Keith
David Munday
Wanttaja) wrote:
>In article <01bebf28$eb603360$aaf0f3d0@default>,
>scb <sbe...@tri-lakesonline.net> wrote:
>>I am looking to start a first time project, particularly the Bowers Fly
>>Baby. The plans suggest using marine grade plywood. I have located numerous
>>sources for aircraft plywood, but its pretty expensive and why argue with
>>the designer's choice of materials?
>>
>>Any suggestions for sources and/or comments re:marine plywood.
>
>Well, Bowers has alternate suggestions, as well. To quote from page 9-2
>of the plans: "The plywood does NOT have to be marine grade. It has
>been found that a good grade of EXTERIOR fir plywood is practically the
>equivalent of marine. While mahogany is preferred, fir is all right.
>Minor differences in quality and strength will have no effect on the
>integrity of the finished airplane because the 1/8" plywood parts are
>considerably over strength anyway."
Well that's pretty dispositive, but lat me add that the ply really
serves mostly to stick the spruce-to-spruce joints together, and to
keep those members loaded in compression from buckling. Marine or
Aircraft grade is probably only preferred since either is resistant to
rot. 1/8" is plenty, I've heard of people using 1/4" though that's
right off the scale.
______________________________________________________________________
David E. Munday E-mail: mun...@engr.uky.edu
Dept. of Mechanical Engineering Web: http://www.nku.edu/~munday
University of Kentucky Voice: (606) 257-3263
Lexington, KY 40506-0108 FAX: (606) 257-3304
Office: 202 D. V. Terrell Bldg.
Craig Wall
KeithF4281 <keith...@aol.com> wrote in message
news:19990625235739...@ng-fe1.aol.com...
Nope. Marine grade fir plywood is identical to exterior grade plywood
with one exception: the interior ply has no voids (they are all plugged) so
you don't suck a fastener down on one.
It's the same wood and same resorcinol glue, otherwise. There *are*
various "specialty" marine plywoods, but that isn't what we are talking
about here.
Exterior grade fir plywood is fine- you will have to toss a few parts that
turn out to have viods, so the wastage is higher, and in the fuselage skins
you will have to accept some voids, but you can plug the ones at the borders
by inserting plugs from the edge (so the nails don't cause depressions...and
they're only for gluing pressure anyway).
Craig Wall
Ron Natalie
resistant. The distinction from "normal" plywood is that the
glue is waterproof. You can get CCA PT plywood, but it's a
different beast.
mikepatt...@spammindspring.com
MP
Craig Wall
Ron Natalie <r...@sensor.com> wrote in message
news:377B7AD7...@sensor.com...
> Neither Marine or Exterior grade plywood is treated to be rot
> resistant. The distinction from "normal" plywood is that the
> glue is waterproof. You can get CCA PT plywood, but it's a
> different beast.
Exterior fir plywood and marine fir plywood use exactly the same
resorcinol glue.
My source is the Douglas Fir Plywood Association's book of boat plans.
Craig Wall
Ron Natalie
>
> Ron Natalie <r...@sensor.com> wrote in message
> news:377B7AD7...@sensor.com...
> > Neither Marine or Exterior grade plywood is treated to be rot
> > resistant. The distinction from "normal" plywood is that the
> > glue is waterproof. You can get CCA PT plywood, but it's a
> > different beast.
>
> Exterior fir plywood and marine fir plywood use exactly the same
> resorcinol glue.
>
Yes...that's my point. What makes exterior grade exterior grade
is the use of the waterproof glue, not because it is rot resistant.
To be rot resistant it has to either use rot resistant woods
(cypress, certain cedars, redwood) or use some kind of chemical
treatment. Neither of these is present in marine or exterior grade
plywood.
Craig Wall
Ah. It sounded like you meant that exterior plywood was "normal plywood".
Marine fir ply is the same as exterior grade except for the absence of
voids in the inner plys. And you are correct- neither is treated to be rot
resistant.
Craig Wall
Bruce A. Frank
When I lived in southern Chester County in Pa I once bought a sheet of
"rot resistant" marine plywood. It was pressure treated with copper
nathanate.
I am not questioning the fact that the marine and exterior use the same
glue but I have noticed something about the way they weather. When I was
about twelve my father had a stack of reclaimed house wood (beams, 2X4s,
and plywood) that he intended to use to build a backyard shop. The wood
had been stacked haphazardly for years and my father one day began to
sort and re-stack it. Some of it had rotted. Most all the exterior
plywood was partially delaminated (this was South Carolina-plenty of
year round rain--the plywood was stenciled "exterior BC"). I noticed one
piece of plywood was in much better shape. My father said that it was a
piece of marine plywood he'd had for more than ten years. The marine
plywood in the same stack as the exterior grade was still sound and
usable whereas almost none of the exterior grade was usable. The
exterior plywood had been salvaged from waste from the construction of
other houses in our neighborhood and was all younger than ten years.
This was also back in the day when even exterior grade plywood had very
few voids--in fact, I was fascinated by the fact that I could pull the
layers apart and dis-assembled several sheets. All of the internal knot
holes were patched in this exterior grade. (BTW, my father was not as
"fascinated" at the internals of the plywood because my delamination
party had spread slivers all over the lawn in the backyard. Even after
my cleanup the lawnmower spit splinters for the next three months.)
Was the glue used then(1960) different that that used today?
--
Bruce A. Frank, Editor "Ford 3.8/4.2L Engine and V-6 STOL
BAF...@worldnet.att.net Homebuilt Aircraft Newsletter"
| Publishing interesting material|
| on all aspects of alternative |
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While trying to find the time to finish mine.
Craig Wall
Bruce A. Frank <BAFRANK@**SpamBlock**worldnet.att.net> wrote in message
> I am not questioning the fact that the marine and exterior use the same
> glue but I have noticed something about the way they weather. When I was
> about twelve my father had a stack of reclaimed house wood (beams, 2X4s,
> and plywood) that he intended to use to build a backyard shop. The wood
> had been stacked haphazardly for years and my father one day began to
> sort and re-stack it. Some of it had rotted. Most all the exterior
> plywood was partially delaminated (this was South Carolina-plenty of
> year round rain--the plywood was stenciled "exterior BC"). I noticed one
> piece of plywood was in much better shape. My father said that it was a
> piece of marine plywood he'd had for more than ten years. The marine
> plywood in the same stack as the exterior grade was still sound and
> usable whereas almost none of the exterior grade was usable. The
> exterior plywood had been salvaged from waste from the construction of
> other houses in our neighborhood and was all younger than ten years.
> This was also back in the day when even exterior grade plywood had very
> few voids--in fact, I was fascinated by the fact that I could pull the
> layers apart and dis-assembled several sheets. All of the internal knot
> holes were patched in this exterior grade. (BTW, my father was not as
> "fascinated" at the internals of the plywood because my delamination
> party had spread slivers all over the lawn in the backyard. Even after
> my cleanup the lawnmower spit splinters for the next three months.)
>
> Was the glue used then(1960) different that that used today?
No, it's the same resorcinol, but BC exterior is a cheaper grade than the
AA that you'd normally compare Marine grade Fir plywood to. I suspect the
difference is (besides the obvious blems in the outer plys) that they don't
spend as much time compressing the plys while the glue cures. Cheap
plywood is clamped in stacks and banded to provide gluing pressure, which
resorcinol needs to give a full-strength bond. (Also, the faying surfaces
might not have been sufficiently decontaminated to get good penetration.)
AA and Marine ply are usually clamped in stacks between plattens with
hydralic presses.
Another reason might be that the laminations could be sufficiently
different in moisture content at the time of gluing in cheaper grades that
the differential swelling and shrinking could shear the plys at the
glueline. Ideally, the plys would be in the same state when glued together,
so that the expansion and contraction would be synchronized to minimize
stress.
I have built upwards of 30 small boats using AC Exterior Fir plywood and
have never had a problem with delamination, although dryrot is always
lurking if you fail to get all the water out during storage. The DFPA
(Douglas Fir Plywood Association) does recommend doing a test on each batch
of plywood used for critical applications where water is involved, however-
it involves repeatedly boiling a test piece in water to check for
delamination.
Craig Wall
Morgans
Bruce > When I lived in southern Chester County in Pa I once bought a sheet
of
> "rot resistant" marine plywood. It was pressure treated with copper
> nathanate.
If it is treated with copper, it is treated marine plywood, a different
beast than marine plywood.
the plywood was stenciled "exterior BC (snip)
Unusual. Most BC is not exterior rated. Are you sure your childhood
memory is correct?
AC is common, as is CDX. Read on.
Here is the rule for plwood and the types of glue. All grades of ply with
an A in the name use waterproof glue. The others need to be marked ext. for
that glue to be used.
> exterior plywood had been salvaged from waste from the construction of
> other houses in our neighborhood and was all younger than ten years.
To hod together for long, the end grain must be sealed.
Jim in NC