Subject: RE: baidarka Comparison of types of wood
From: Peter A. Chopelas (pac@premier1.net)
Date: Tue Dec 05 2000 - 16:16:34 EST
Ash is about 40 percent heavier than Sitka Spruce and 33 percent heavier
than most other common spruces by volume. There are a number of species of
both Ash and Spruce and their properties vary so if you want specifics you
will need to state what species of each you want to compare.
On average the various species have similar strength to weight ratios,
though again it depends what properties you are comparing: bending
strength, stiffness (modulus of elasticity, or MOE), compression parallel
to the grain or perpendicular to the grain, shear, tension, etc. all vary
quite a lot. For example American Ash is about twice as strong in all of
these properties as Sitka Spruce except it is only 32 percent stronger in
compression parallel to the grain and 22 percent stiffer (MOE), yet it
weighs 40 percent more.
Assuming you size the members accordingly so as not to take too much of a
weight penalty for using ash, the ash would resist dents on the keel and
gunwales better than spruce because it's cross grain compression strength
is so much higher.
The only disadvantage of the using ash is the weight, even with adjusting
for the size you will likely take about an 4 LB weight penalty. If you
make no adjustments to the member size you are looking at about a seven
pound weight penalty (though with a much stronger frame, assuming you
connections are also stronger).
Neither of these woods have much rot resistance, that is why they should be
"well oiled".
I would add the mold and fungus additives available in most paint supply
stores to your wood finish. The additive only cost a few dollars to treat
a gallon of finish and it helps prevent rot. If you are using paint as the
sealant on the skin you can add this to the first few layers of paint to
preserve the canvas, it appears to make a noticeable difference.
Peter
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