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