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post #17 of Old 02-11-2003
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Balsa cored hulls - old boats

Bob Austin

Can you clarify your posting a bit? I understand your point about the construction technique on ''Teachers Pet III'', which is as you descibe it, especially relative to conventional cored construction. The part that I did not understand was your point about balsa cell configuration and bonding.

Balsa like most wood species absorbs far more moisture in the capilliaries between the cells than through the cell walls. In other words, if you wet the end grain of a piece of wood, vs the side of a piece of wood it will absorb more water in a given time over a given area then the side of a piece of wood. The theory behind end grain balsa is to take advantage this capilliary action to allow resin to soak into the exposed capilliaries and to form a physical bond and at the same time seal the end grain to minimize the amount of water that can enter the capilliaries and start rot. It also in theory slows the spread of rot since water cannot flow as easy through the side walls of the cells or capilliaries.

If properly wet out and bonded, this is a very good system since Balsa offers excellent sheer resistance for the weight and cost. Of course the big ''If'' is whether it has been properly wet out with resin and bonded. When the surface has not been properly wet out it is easy for delamination to take place. In theory Balsa should be easier to bond than closed cell foam which requires special treatment to create a mechanical bond similar to Balsa, and it takes a heavier higher density foam to equal Balsas sheer stength.

All of that said, I still prefer a high density foam, both above and below the waterline, for its greater durability in the case where it has been exposed to water.

I do have a box of old hull corings from my boatyard working days. I used to use them for backer blocks. I have not seen them in a while but I am sure they are here somewhere. Where are you located?

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