Boat and yacht decks and hulls are commonly cored to
save weight.

What are the various types of core material?

What are the characteristics of each?

Lashes for terse answers. Points for detailed answers.

On Jun 14, 8:27 pm, Bart wrote:
Boat and yacht decks and hulls are commonly cored to
save weight.

What are the various types of core material?

What are the characteristics of each?

Lashes for terse answers. Points for detailed answers.

Bob's 35s5 has a lightweight honeycomb core...made out of re-cycled
cardboard.

Characteristics....tends to swell when exposed to moisture.

Joe

"Bart" wrote in message
ups.com...
Boat and yacht decks and hulls are commonly cored to
save weight.

What are the various types of core material?

Airex foam
End-grain balsa
Plywood
Metal honeycomb


What are the characteristics of each?

Airex: a near-perfect core material, won't absorb water, quite rigid,
fairly lightweight, far cheaper than balsa or honeycomb, provides insulation
factor.

End-grain balsa: very lightweight, expensive, labor-intensive, low-tech,
will absorb water, quite rigid, some insulative properties.

Plywood: cheap, heavy, absorbs water like a sponge, very rigid, good
backing for major hardware like winches, cleats, did I mention cheap?

Honeycomb: rigid, very expensive, won't absorb water, but if damaged during
construction water can flow into the cells, no insulative properties, high
tech and the lightest in weight of the bunch.

There are probably others, but less significant in terms of commonality.

Max

Bob's 35s5 has a lightweight honeycomb core...made out of re-cycled
cardboard.



Joe doesn't sail enough to know the difference between a main and a
genoa. Now we can see how much he knows about boats and how they're
built. Beneteau hulls are NOT CORED, Joe. The honeycomb elements are
her bulkheads and floor sections above the structural grid.
Good work for today, Joe!



RB
35s5
NY

On Jun 14, 11:02 pm, "Maxprop" wrote:
"Bart" wrote in message

ups.com...

Boat and yacht decks and hulls are commonly cored to
save weight.

What are the various types of core material?

Airex foam
End-grain balsa
Plywood
Metal honeycomb



What are the characteristics of each?

Airex: a near-perfect core material, won't absorb water, quite rigid,
fairly lightweight, far cheaper than balsa or honeycomb, provides insulation
factor.

End-grain balsa: very lightweight, expensive, labor-intensive, low-tech,
will absorb water, quite rigid, some insulative properties.

Plywood: cheap, heavy, absorbs water like a sponge, very rigid, good
backing for major hardware like winches, cleats, did I mention cheap?

Honeycomb: rigid, very expensive, won't absorb water, but if damaged during
construction water can flow into the cells, no insulative properties, high
tech and the lightest in weight of the bunch.

There are probably others, but less significant in terms of commonality.

Max

Hey Max! Good answer--worth 2 points, athough not as
funny as Joe's who get's 1/4 pt for his humor. A dozen
lashes to the Swab for being such a lame swab.

My understanding is balsa has far superior adhesion because
the end grain is rougher. Foam can suffer from extensive
delamination due to freezing--as water continues to propagate
in the layer between the laminates. Does anyone have
any experience with this?

Most builders don't properly seal the edges of the
core in areas where hardware is attached. Ensuring
water does not get into the core is not that hard to do,
but unfortunately most builders skip this step, and
few owners want to take the trouble to remove every
but of deck hardware to re-do what builders fail to do
--put solid glass or epoxy filler to seal the edges of
the laminate to prevent water intrusion into the core.
I caught one guy installing a thru-hull on my boat
skipping this step!

I've found that balsa even if rotten can still function
for a surprisingly long time in that condition. I'm just
starting to re-core the deck of my Etchells and found
quite a bit of rot, with virtually no weakness in the
deck. I attribute this to the curved shape of the
deck and coaming which the enhanced strength
of the deck.

I'm going to re-core it with balsa, although I have a
source of left over foam core that I could get my
hands on cheap--albeit I don't think it is the right
thickness for my application.

By the way, I've seen Nomex honeycomb in both
aluminum and epoxy coated paper, although I don't
know if the later is every used in boats. Does any
one know about that?

Bart

What are the various types of core material?


Maxprop" wrote:
Airex foam

There are a lot of different types of foam. "Airex" is a brand name.

End-grain balsa
Plywood

Not really a core material IMHO. You can put fiberglass skins over
plywood and not gain a thing structurally over straight plywood..


Metal honeycomb


Many different types of honeycomb too.


What are the characteristics of each?


Airex: a near-perfect core material, won't absorb water, quite rigid,
fairly lightweight, far cheaper than balsa or honeycomb, provides insulation
factor.


Lower shear strength though. Some types of foam are easy to bond,
others less so. There are also lots of different densities of foam
with different properties such as higher impact resistance etc etc.

If one is going to build a foam core structure then it makes a lot of
sense to do some homework and shop around.


End-grain balsa: very lightweight, expensive, labor-intensive, low-tech,
will absorb water, quite rigid, some insulative properties.


You forgot the best property of end-grain balsa: very easy to get an
excellent bond to the skins with very high shear strength. And it has
pretty decent impact resistance.

The worst thing about end-grain balsa IMHO is that you can't screw
anything into it. Foam core can have lightly loaded screws right into
it, no problem. Balsa core you can't risk letting in any water, ever.


Plywood: cheap, heavy, absorbs water like a sponge, very rigid, good
backing for major hardware like winches, cleats, did I mention cheap?


Actually balsa core will absorb water more quickly than plywood.
However, plywood has long capillaries running thru the wood to wick
water all thru the structure, so the saturated area will spread
rapidly. End-grain balsa tends to rot out in small patches directly
around water penetration.


Honeycomb: rigid, very expensive, won't absorb water, but if damaged during
construction water can flow into the cells, no insulative properties, high
tech and the lightest in weight of the bunch.


Honeycomb *can* have great insulation if you choose the right stuff.

The biggest problem with honeycomb is that it has the lowest impact
resistance of any core material and it is difficult to get a good
bond.

There are probably others, but less significant in terms of commonality.


Chopper gun and matt are core material in an old-fashioned "solid
glass hand lay-up." They are very heavy but cheap and generally have
high shear strength.

Another "core" material is strip planks of light wood such as spruce.
A lot of traditional boats are built this way but the builders don't
like to think of what they do as "core" material.

Fresh Breezes- Doug King

Bart wrote:
On Jun 14, 11:02 pm, "Maxprop" wrote:

"Bart" wrote in message

roups.com...


Boat and yacht decks and hulls are commonly cored to
save weight.

What are the various types of core material?

Airex foam
End-grain balsa
Plywood
Metal honeycomb




What are the characteristics of each?

Airex: a near-perfect core material, won't absorb water, quite rigid,
fairly lightweight, far cheaper than balsa or honeycomb, provides insulation
factor.

End-grain balsa: very lightweight, expensive, labor-intensive, low-tech,
will absorb water, quite rigid, some insulative properties.

Plywood: cheap, heavy, absorbs water like a sponge, very rigid, good
backing for major hardware like winches, cleats, did I mention cheap?

Honeycomb: rigid, very expensive, won't absorb water, but if damaged during
construction water can flow into the cells, no insulative properties, high
tech and the lightest in weight of the bunch.

There are probably others, but less significant in terms of commonality.

Max


Hey Max! Good answer--worth 2 points, athough not as
funny as Joe's who get's 1/4 pt for his humor. A dozen
lashes to the Swab for being such a lame swab.

Bart


Oh, no fair, Bart. I played nice and didn't say "apple" cause I didn't
want to be lashed so I think you owe Joe at least 6 stripes!

OzOne wrote:
Biggest problem with foam cores is that they will break down and
granulate.
Seen this on many Syd-Hobart racers after the really big races
pounding to windward.


Heck, anything will break if you pound it hard enough, long enough.

Sounds to me like the problem might be a difference between the
fiberglass fatigue properties and the foam fatigue. Even if the bond
doesn't break down, tiny bits within the foam get excessive fatigue
and break up. Maybe?? Or is it from small areas of skin bond failure?

Would denser foam hold up better?

I have a couple of ideas how foam cored structures could be build to
accept higher load cycles, but am occupied with other things at the
moment

Fresh Breezes- Doug King

Would denser foam hold up better?

OzOne wrote:
Apparentl caused by flex in the skin.
It just destroys the foam till the skin fractures and peels back in
the worst cases.


Hmm. sounds like localized fatigue all right. As the foam goes, the
skins gain more & more freedom of movement until the bond fails or
they exceed their fatigue limit.


Denser foam appears to make no difference, it's just a foam thing.

Do you know if anybody has tried using (say for example) 20# foam? All
the ones I see are using 8# and 6# for "heavy structural
applications." One fairly savvy builder says it makes more sense to
use spruce stringers than heavy foam... seen some pretty impressive
boats built with laminated wood skins over foam too.


IIRC, the bigguns have gone to balsa where cores need to be super
strong.


Balsa has it's problems too. Good stuff in the right application. Part
of the situation is that the buyers of these boats need to recognize
that a boat intended to sail hard can only be built so light. But they
go with the design/build team that promises the best numbers.... go
figure...

Hey Bart, if you're still reading this, I would recommend building in
some uncored stringers under your deck rather than replacing core.
Kind of like the C-beams I put under the super-dinghy's thwarts, if
you remember that pic.

DSK

"Bart" wrote in message

My understanding is balsa has far superior adhesion because
the end grain is rougher. Foam can suffer from extensive
delamination due to freezing--as water continues to propagate
in the layer between the laminates. Does anyone have
any experience with this?

My experience: There are four C&Cs in our marina, all of which have
end-grain balsa above the waterline and in the decks. And all are quite
wet. As for structural integrity, all the owners have remarked that they
aren't going to do anything about it, as the hull and deck stiffness is
still pretty good. I do worry about the freeze/thaw issue, however. And
weight.

My sloop has Airex foam. No delamination anywhere, and I can't find any
water in the hull or deck at all. I've been over the entire boat with a
moisture meter several times in subsequent years. Of course that is just
one man's experience, but I'm happy.

Max