Re: [Paddlewise] Skin friction and Kayak speed vs length

From: Shawn Baker <shawnkayak_at_yahoo.com>
Date: Tue, 15 May 2001 08:07:57 -0700 (PDT)
Nick Schade said:
>> Shorter boats typically have less wetted surface...

Scott said:
>  I always though the wetted area of a boat was the result of the 
>weight of the boat and how much water it displaced -- not the length. 
>Is that not correct?

This is an extreme oversimplification, but I think I can explain it:  a
sphere has the smallest surface area for the maximum volume of any 3-D
solid. At the other end of the spectrum, a long, narrow tube has a lot
of surface area, but hardly any volume. 

If we assume they're made of the same material with the same wall
thickness, a tube and a ball having the same weight and surface area, 
would displace different amounts of water.  

Now, if the tube and the ball had the same displacement, the tube would
have a much greater surface area.

A long kayak is a little closer on the spectrum to the tube, and the
short kayak is closer on the spectrum to the sphere (although the
kayaks are closer to the middle and to each other than to the ends!)
but you get the idea. 

A 150-lb paddler in a 50-lb long kayak will displace as much as a
150-lb
paddler in a 50-lb short kayak, but the long kayak will have a greater
wetted surface area.

This oversimplification is only for explaining the wetted surface
area--don't try to think about the shapes moving through the
water--then you start feeling the effects of wavemaking and fluid
dynamics.

Shawn

Yahoo! Auctions - buy the things you want at great prices
http://auctions.yahoo.com/

***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************
Received on Tue May 15 2001 - 11:54:26 PDT

This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:30:42 PDT