Message-Id: <199710111736.NAA29296@www.onlink.net>
From: "John Winters" <jwinters@onlink.net>
To: <baidarka@lists.intelenet.net>
Subject: Re: KAYAK DESI
Date: Sat, 11 Oct 1997 13:22:13 -0400
Paul wrote;
> The seaworthiness of those broad cutoff sterns has been questioned
> (see Marchaj, 'Seaworthiness, the forgotten factor' - or something like
> that). I think the modern style sail boats are much more prone to
> broaching. Part of the problem is that with the broad stern following
> seas can easily lift the rudder out of the water.
This is quite true and Marchaj's book is a valuable discussion of light
displacement, high beam watercraft (despite the emphasis on sail boats).
(SNIP)
>
> But the stability issues involve three planes of motion. I don't know
how
> stern design would affect role behaviour in following seas. A good
> directional stability in following seas would reduce the tendancy to turn
> you broadside to the waves. Full bows have been promoted as a way of
> keeping the bow from digging in and forming a pivot about which boat
could
> be turned broadside. I remember sometime back reading descriptions of
the
> Nauteraid Single which has a 'fish form' (max width forward) - it was
> supposed to be more 'user friendly' in following seas.
The issue is complex because it is affected by the way one paddles in a
following sea. The aggressive paddler has a much different problem from the
conservative paddler and the tactics that work best are also influenced by
the length and steepness of the waves. This is one reason why it is so
important to superimpose the critical wave length and height over the hull
to see how the volume is distributed in the critical condition.
There are a number of techniques one can use to improve control downwind.
The fish form hull is one. Also used are chines and knuckles forward,
flare, overhangs, and "U" shaped sections. Each has merit. The flattish
sections and the long overhang of many Greenland boats is quite effective
at preventing broaching. I also feel the extreme rocker aft is useful as it
makes the boat extremely responsive to corrective strokes. This is one area
where kayaks differ so greatly from sailboats etc. They must rely upon
their rudders (or in the case of the windsurfer, trim and aerodynamic
forces) for control. By comparison the paddle is a much better device for
control in that embodies power and control in one tool.
Cheers
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://www.onlink.net/~jwinters