Re: [Paddlewise] FW: Speed and short boats

From: John Winters <735769_at_ican.net>
Date: Tue, 13 Oct 1998 15:22:12 -0400
Kevin wrote;



>>
>So why exactly do whitewater kayaks require more effort?

Reasons why a white water boat might be slower than a sea kayak would be
(in no particular order since the degree of each will vary between boats)

1. Shorter waterline length.
2. Even shorter effective waterline length,
3. Blunt angle of entry.
4. Generally low prismatic coeffcients.
5. Steep buttocks (some boats) that can cause separation drag.
6. Longitudinal Center of buoyancy forward of 50% coupled with fine sterns
which can cause large trim changes that alter form coefficients .
7. Large waterplane coefficients that lead to significant lift which is a
waste of energy unless one can plane.
8. Full forward sections can cause premature (relative to sea kayaks)
pounding and pitching.
9. Lack of directional stability can require greater effort expended on
control. In addition, when the boat travels with significant leeway through
the water its drag can be greater than when traveling true.

There may be other less significant reasons such as higher wetted surface
but that too varies with the boat.  All of the above presupposes speeds
similar to sea kayak cruising speeds.

Those of you with old issues of Sea Kayaker can read the resistance figures
for a whitewater kayak in their first boat test report. I don't recall that
they identified the boat.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/







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Received on Tue Oct 13 1998 - 12:26:01 PDT

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