Re: [Paddlewise] Evolution Kayaks

From: Matt Broze <mkayaks_at_oz.net>
Date: Thu, 12 May 2005 02:00:47 -0700
PeterO asked:
>>>>>>Does solid secondary stability generally correlate with a less
comfortable
ride in choppy water? i.e with increased stability and less tendency to stay
vertical on a wave, is the ride likely to be less comfortable? I seem to
feel that in boats I've paddled.<<<<<<<

I think John and Dave did excellent jobs of answering that, and yes I think
you were confusing secondary stability with primary (initial) stability. The
only things I would like to add to what they wrote is that I like a
progressive secondary stability that doesn't peak until a large angle of
lean combined with a low initial stability. Effortless to lean at first but
much more secure feeling when leaned than a kayak with high initial
stability (or one with low initial and low secondary stability). If viewing
a stability curve (such as in Sea Kayaker magazine reviews), this looks like
a straight line of increasing stability with increased lean. If the line on
the graph is initially too much towards the vertical (high initial
stability) you won't be able too lean at much of an angle before the
stability line starts to bend and shallow out (and once it starts to shallow
out you aren't in the steadily increasing stability situation I like any
longer). If the line starts out from zero degrees nearly horizontal (little
or no initial stability) there won't be much secondary stability either
unless the curve takes a turn upward later (and then you don't get the
comfortably consistent progressive increase in stability with lean). The
greater the angle of lean before the curve starts to bend and shallow out
the more the kayak can be leaned and still have that cushion of even greater
stability helping keep you from leaning further too quickly--possibly
accidentally capsizing or at least having to throw in a quick brace.

I wrote about secondary stability much more in the FAQ's on our website.
High initial stability I likened to leaning a four legged chair, high
secondary stability seems more analogous to a rocking chair. If you made the
rockers on a rocking chair the arc of a relatively small circle that would
be more analogous to neither initial or secondary stability. Sea Kayaker
also did a good technical sidebar on this subject of how to interpret their
stability graphs in their Spring 1986 issue (reprinted at the end of the
Mariner XL review on our website for those who don't happen to have it
handy--five different kayak's stability curves are also in that review and
article).

To answer the question above more directly, it is the low initial stability
that causes the Pittarak to automatically not be tipped in side waves
(essentially by not offering the wave much lever arm with which to tip it).
The kayak with low initial and high secondary also doesn't give the wave
much of a lever but is also much more comfortable doing leaned turns and is
usually comfortable when on the face of even a steep wave or breaker (unless
the deck is too low and too wide such that the wave or breaker can get on
top of the side deck, where the falling water can essentially get a good
grip on the edge sticking into it and tip the kayak in towards the wave).

Matt Broze
www.marinerkayaks.com
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Received on Thu May 12 2005 - 01:58:54 PDT

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