Re: [Paddlewise] 2ndry stability (and more)

I don't disagree that there might be some minor benefits to a capsizing
paddler to have a large backside of the curve (or a even a flatter top of
the curve that might provide a slight warning). What I'm saying is with
regards to what an expert considers "secondary stability" in a kayak these
things are irrelevant, not that they are irrelevant all the time and for all
reasons.
Further, I think an expert would prefer to keep the curve increasing at a
constant or increasing rate up to a point out beyond where he wants to lean
a kayak (without having to rely on a brace) rather than have the curve be
steeper and then break at an angle less than the angle he wants to be able
lean it (the steeper curve would have to break earlier--at the "risk"
point--in order to flatten out the top of the curve and keep the same
maximum righting moment).
The designer's task is to find the shape that will give the most security
for the paddler (the kayak is aimed at) and still keep the drag of that
kayak as low as possible given that level of security.

-----------original message--------
>>>>>>.Date: Tue, 21 Nov 2000 16:04:19 -0500
From: Nick Schade <schade_at_guillemot-kayaks.com>
Subject: Re: [Paddlewise] 2ndry stability (and more)

Just to fill in with some of the back channel response to Matt's comments:

  I am not ready to eliminate the backside of the curve yet. Even if
you go over the hump with some momentum, the backside of the curve is
absorbing energy and offers at least the theoretical potential of
slowing you down. Also if you do stop your momentum by bracing, the
stability shown on the backside of the curve will be enough to right
you without additional help from a brace. It may be a slow recovery,
but it will happen as long as no other forces come to push you back
down.

  The area under the curve from zero to the angle of heel is the
potential energy built up that is ready to push the boat back
upright. If boat reaches the point but is still moving, it still has
kinetic energy left to absorb. If the area remaining on the curve is
less than the kinetic energy of the rotating boat, it will go over,
otherwise it will stop. A boat with a lot of area under the backside
of the curve will be able to absorb a tipping hit better and will
require less bracing energy to stop the tendency to capsize.

This points to the backside of the curve being more important in
dynamic situations where some capsizing impulse has to be absorbed.

Nick<<<<<<<

Matt Broze
http://www.marinerkayaks.com



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