cores: foam vs wood?

[bmcald]

Just wondering if anyone knows why most boats seem to have plywood or balsa wood cores between fiberglass instead of foam? The Airex closed cell foam used in my 1971 Stone Horse seems like a great choice of material compared to everything I hear about wood. Is it considered too expensive for most production boats? Or is there something about it that is worse than plywood or balsa that I should know about?

[Jeff_H]

Balsa cores offer the best combination of structural properties per pound and was originally considered to be most durable of the coring choices.

The newer medium density closed cell foam cores (since 1985 or so) are a really wonderful solution but come at a weight penalty to Balsa.

Plywood cores are strictly a cost cutting measure normally in areas where labor is cheap. It gets widespread use on teak decked boats because it holds screws better than other cores.

Jeff

[tsenator]

Haven''t they come up with anything beyond the foam and the balsa ?

I would think a moderately tight "closed cell" honeycomb pattern would be the most structually stiff with a combination lightness. I would think its less likely to absorb or wick any water that might ingress if the hull is breached

[Jeff_H]

Honey comb is used in very high performance yachts and in non-structural panels. The new closed cell foams are an excellent building material with tremendous durability. Balsa core when properly installed and used with materials like vinylester resin is about as good as it gets on most counts. Think of end grain balsa as being a miniature honey comb made of an incredibly light and stiff composite.


Jeff

[Magic_Moments]

I have seen a few boats with an Airex foam cored hull. One was a 1979 North American 40 built by Morgan, and two others were C&C''s, a 1980 34, and a 1985 33 which had the foam core in the forward part of the hull. All three I think are or were performance oriented boats at the time.

Ken