Because of resistance to puncture, isotropic properties and stiffness.
Foam sandwich doesn't work for small boats. To get sufficient resistance to
puncture, the skins must have a minimum thickness. For mechanical reasons,
we should use tri or quadriaxial while with plywood only biaxial is needed.
A sandwich panel made that way would be heavier than a plywood-epoxy-glass
sandwich.
Once you get around 27', foam sandwich becomes a valid choice. With
vacuum-bagging and aramids, we could build smaller units, donw to 20' but
the cost would be very high.

PS: about poplar, there are no fasteners in our boats . . .
--
Jacques
http://www.bateau.com

"Backyard Renegade" wrote in message

Why not make the panels of foam and skins, like vacume bagging?
Scotty

"Jacques Mertens" wrote in message ...
Because of resistance to puncture, isotropic properties and stiffness.
Foam sandwich doesn't work for small boats. To get sufficient resistance to
puncture, the skins must have a minimum thickness. For mechanical reasons,
we should use tri or quadriaxial while with plywood only biaxial is needed.
A sandwich panel made that way would be heavier than a plywood-epoxy-glass
sandwich.
Once you get around 27', foam sandwich becomes a valid choice. With
vacuum-bagging and aramids, we could build smaller units, donw to 20' but
the cost would be very high.

PS: about poplar, there are no fasteners in our boats . . .

I know.. I am building one of your boats now... but of course, I will
be using no poplar
Scotty 8-)


--
Jacques
http://www.bateau.com

"Backyard Renegade" wrote in message

Why not make the panels of foam and skins, like vacume bagging?
Scotty

I dunno ...the one and only guy (Homer, AK) I've met that has a lot of
vacuum bagging experience, as in "did it for a living down in Florida", said
it was not so easy to get right. I only met him just the once, and haven't
looked into it at all after that ...figured it might not be worth the
effort. What do you think?

Brian

--
My boat project: http://www.advantagecomposites.com/tongass


"Backyard Renegade" wrote in message
om...
"Brian D" wrote in message
news:QWscb.568478$YN5.404597@sccrnsc01...
And THAT is probably why I won't be able to find a lightweight plywood
for
the superstructure of my boat...the trade-offs aren't worth it. Denser
is
tougher, less dense is ...less dense, and all you get when you buy low
density wood. Anyone know of a marine grade foam core hardwood-veneered
product? Seems like I saw something like that somewhere. Note: Most of
this is academic and just fun to look into. I'm sure I'll end up using
standard marine ply of some kind in the end.

Brian

Why not make the panels of foam and skins, like vacume bagging?
Scotty


--
My boat project: http://www.advantagecomposites.com/tongass


"Backyard Renegade" wrote in message
om...
"Jacques Mertens" wrote in message
. ..
We are talking about two different things.
The plywood we are testing is not a buck a truckload, it is not
plain
cheap
wood.

Poplar is poplar is poplar. Maybe they put some expensive glue or
coating on it to dress it up but poplar still has bad qualities, it
soaks up water like a sponge and gets soft, it expands tremendiously
and distorts, it discolors (turns black with moisture), and it rots
easily, does not hold fasteners well, etc. However, it seems that you
have long before asking us, made up your mind and used it... So I will
leave it alone from here on...
Scotty


Anyway, I got at least one interesting response about a similar
experiment
(thanks Paolo) and since I am very stuborn, I will keep testing.
What keeps me going is the memory of all the people who were
laughing at
my
first boat designed for Airex. Foam for a boat hull? It will never
work
they
said . . .

--
Jacques
http://www.bateau.com

"Backyard Renegade" wrote in message
om...
"Jacques Mertens" wrote in message
...
The poplar plywood I am testing is listed here as "marine"
plywood:
http://www.worldpanel.com/eurolite.htm

I don't expect much distortion from a 5 ply 6mm ply with
melamine
glue,
saturated with epoxy and fiberglassed.
I am playing the devil's advocate here. I keep an open
mind about it and I am not ready to endorse it for such
applications. I
may
if my tests come out positive, I may not if I read about some
bad
experiences.

Thanks for your opinions and I would like to read more.

--
Jacques
http://www.bateau.com


Well, I still think it is a bad idea, if for no other reason than
that
the stuff is a buck a truckload up here in the NE and I have
*never*
heard of *anyone* using is locally for anything to do with
boats...
Scotty from SmallBoats.com

JM,

I was considering researching lightweight solutions for the
superstructure, not for the hull or structural components. See my boat
project web site below.

Brian

--
My boat project: http://www.advantagecomposites.com/tongass


"Jacques Mertens" wrote in message
.. .
Because of resistance to puncture, isotropic properties and stiffness.
Foam sandwich doesn't work for small boats. To get sufficient resistance
to
puncture, the skins must have a minimum thickness. For mechanical reasons,
we should use tri or quadriaxial while with plywood only biaxial is
needed.
A sandwich panel made that way would be heavier than a plywood-epoxy-glass
sandwich.
Once you get around 27', foam sandwich becomes a valid choice. With
vacuum-bagging and aramids, we could build smaller units, donw to 20' but
the cost would be very high.

PS: about poplar, there are no fasteners in our boats . . .
--
Jacques
http://www.bateau.com

"Backyard Renegade" wrote in message

Why not make the panels of foam and skins, like vacume bagging?
Scotty

On 24 Sep 2003 18:57:09 -0700, (Backyard
Renegade) wrote:

"Jacques Mertens" wrote in message . ..
We are talking about two different things.
The plywood we are testing is not a buck a truckload, it is not plain cheap
wood.

Poplar is poplar is poplar.

Well, no it isn't. The North American wood (Liriodendron tulipifera)
called variously yellow poplar, tulip poplar or tulipwood is neither a
poplar, nor a tulip. True poplars are in the Populus genus, and
include basalm poplar, cottonwood, swamp poplar, and some other
species, all of which are not very strong and not rot resistant.
Yellow poplar is heavier and stronger.

The Spanish-made plywood to which Jacques is referring is from another
species of the genus Populus. Poplars are grown widely throughout
Europe for use in construction lumber, furniture, and veneers. Poplar
plywood is popular because the logs peel well, and have few surface
defects. It looks nice.

This doesn't mean that any wood called poplar is suitable for boat
building, it just means that some woods called "poplar" are no more
"poplar" than Philippine "mahogany" is a mahogany. It turns out that
yellow poplar and true poplars are both not rot resistant, but only
one is really poplar.

snip

- Rick Tyler
--
"Ignorant voracity -- a wingless vulture -- can soar only into the
depths of ignominy." Patrick O'Brian

You don't have to vacuum bag foam necessarily.
For some interior parts, your cabin and especially for the roof, you could
use foam and fiberglass as if it was plywood.


--
Jacques
http://www.bateau.com



"Brian D" wrote in message
news:YVOcb.583066$o%2.266323@sccrnsc02...

I dunno ...the one and only guy (Homer, AK) I've met that has a lot of
vacuum bagging experience, as in "did it for a living down in Florida",
said
it was not so easy to get right. I only met him just the once, and
haven't
looked into it at all after that ...figured it might not be worth the
effort. What do you think?

Brian

--
My boat project: http://www.advantagecomposites.com/tongass


"Backyard Renegade" wrote in message
om...
"Brian D" wrote in message
news:QWscb.568478$YN5.404597@sccrnsc01...
And THAT is probably why I won't be able to find a lightweight plywood
for
the superstructure of my boat...the trade-offs aren't worth it.
Denser
is
tougher, less dense is ...less dense, and all you get when you buy low
density wood. Anyone know of a marine grade foam core
hardwood-veneered
product? Seems like I saw something like that somewhere. Note: Most
of
this is academic and just fun to look into. I'm sure I'll end up
using
standard marine ply of some kind in the end.

Brian

Why not make the panels of foam and skins, like vacume bagging?
Scotty


--
My boat project: http://www.advantagecomposites.com/tongass


"Backyard Renegade" wrote in message
om...
"Jacques Mertens" wrote in message
. ..
We are talking about two different things.
The plywood we are testing is not a buck a truckload, it is not
plain
cheap
wood.

Poplar is poplar is poplar. Maybe they put some expensive glue or
coating on it to dress it up but poplar still has bad qualities, it
soaks up water like a sponge and gets soft, it expands tremendiously
and distorts, it discolors (turns black with moisture), and it rots
easily, does not hold fasteners well, etc. However, it seems that
you
have long before asking us, made up your mind and used it... So I
will
leave it alone from here on...
Scotty


Anyway, I got at least one interesting response about a similar
experiment
(thanks Paolo) and since I am very stuborn, I will keep testing.
What keeps me going is the memory of all the people who were
laughing at
my
first boat designed for Airex. Foam for a boat hull? It will never
work
they
said . . .

--
Jacques
http://www.bateau.com

"Backyard Renegade" wrote in message
om...
"Jacques Mertens" wrote in message
...
The poplar plywood I am testing is listed here as "marine"
plywood:
http://www.worldpanel.com/eurolite.htm

I don't expect much distortion from a 5 ply 6mm ply with
melamine
glue,
saturated with epoxy and fiberglassed.
I am playing the devil's advocate here. I keep an open
mind about it and I am not ready to endorse it for such
applications. I
may
if my tests come out positive, I may not if I read about some
bad
experiences.

Thanks for your opinions and I would like to read more.

--
Jacques
http://www.bateau.com


Well, I still think it is a bad idea, if for no other reason
than
that
the stuff is a buck a truckload up here in the NE and I have
*never*
heard of *anyone* using is locally for anything to do with
boats...
Scotty from SmallBoats.com