Builders' Forum Archives
Re: OK Wood Experts
Posted by Laszlo on Oct 18, 2004
Hardness has nothing to do with weight. It's a function of how tightly the fibers are connected and cross-connected. If a piece of wood has fewer fibers that are all connected vs. another piece that has many more fibers which are very loosely connected, the lighter piece will be harder.
As far as the original question, if marine okoume was available, I'd never use fir, especially exterior. Marine okoume is lighter, more flexible and much easier to work than fir, all of which results in better performance and faster assembly.
For the rot issue, once the wood is encapsulated and glassed, rot is not a problem.
For comparative strength, a high performance composite boat will use the plywood (either type) as a core and get the strength from the glass laminations. If the sandwich needs more strength, it's better to add another layer of glass, instead of going for a heavier wood. Heavy only adds mass, fuel consumption and slowness when what is actually needed is stiffness, puncture and abrasion resistance.
All of this assumes that the boat is a high-performance, glass/wood composite design. If it's a slow, plywood on frame boat, different rules apply. But I wouldn't be building one of those so my opinion wouldn't count :-)
Hope this helps,
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