Subject: Re: [baidarka] Greenland gunwale angle
From: Peter Chopelas (pac@premier1.net)
Date: Tue Oct 16 2001 - 23:07:39 EDT
Brian wrote about gunwales:
>I also can't see the point in using rot-prone natural fibers (jute, etc.) for
lashing, when synthetic equivalents that are impervious to water are readily
available.
I agree, but book for polyester imitation sinue, the nylon type will loosen
when wet. Nylon absorbs water and relaxes since it gets longer when wet, and
it makes the lashings loose. Most marie supply stores sell he polyester type
for sail repairs, also George Dyson Baidarka and Co. in Bellingham has a good
price on a huge roll that is enough to make 5 or more kayaks.
>It gaps along the bottom edge for the full length. I guess the philosophy is
that if you cannot seal the water, sand, etc. out of the area between the
gunwales and skin, you may as well provide for good drainage and air flow. It
will still seal where the skin wraps over the top of the gunwale. This makes
sense, but you notice that he ended up with so much sheer curvature that he
had to weight the frame to take some of it out. This has the effect of putting
the keel in tension, which may make for a stronger boat, but I'm not sure it
really makes any difference.
Putting the keel in tension will make the hull stiffer, but NOT stronger. In
fact it will have a lot of internal stress and could fail at a much lower
loading. Given that it is stiffer too, it means impact loads transmitted to
the frame would results in much higher stress as well. A more flexible frame
will "give", absorbing the impact and reducing the transmitted loads.
The 17 degree gunwales are also supposed to result in more of a muliti-chined
hull (at least in the center of the boat), which it does. The 28 degree
gunwales should produce a classic, four panel, hard-chine hull. It's a matter
of personal preference.
I would suspect that the 28 degree gunwales would have to be larger and
heavier to provide the same amount of strength as the 17 degree gunwales. the
more vertical the wide dimension of the gunwale, the more strength you get
from the same size piece of wood. So it should be possible to make the kayak
lighter, assuming you are going for the same strength, with smaller gunwales,
using 17 degree gunwales. Perhaps even lighter if they were only at say 10
degrees. I would also suspect that you will get all kinds of strange second
order internal stresses in the 28 degree gunwale when it flexes, causing it to
buckle sand fail sooner, than with a more vertical one. Also meaning that you
would need a much heavier gunwale to make similar strength hulls.
Peter
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