Re: [Paddlewise] Why does rocker and carving work?

From: Nick Schade <schade_at_guillemot-kayaks.com>
Date: Tue, 4 Dec 2001 09:58:27 -0500
>Nick wrote:
><SNIP>>>Leaning the boat can have many different effects depending on the
>design of the boat, but one effect is almost universal regardless of
>the kayak. Because kayaks get narrow towards the ends, when you lean
>the boat you give it more rocker and more rocker makes it easier to
>turn (see above).<<<<<<
>
>In the paddle flutter discussion I am in near total agreement with Nick.
>Here though, I think there is a slight flaw in his explanation.
>Imagine a perfectly cylindrical "torpedo" floating on the surface with a
>draft of 1/2 its diameter (and also having narrow ends) would not change its
>shape in the water or any handling characteristics by being tilted even
>though the ends might be narrow. Therefore the easier turning isn't just due
>to pointed ends. The reason a kayak turns easier when leaned (to either
>side--into or away from a turn) is that kayaks are usually wider from the
>midline than they are deep below the water so there is more curvature on the
>sides of the kayak than on the bottom. Leaning this shape puts the wider
>middle deeper into the water and the now more curved underwater shape
>decreases the depth of the ends (and often shortens the waterline as well
>especially if keels that are now shifted to the side are involved).

I actually think we are say the same thing. I just tried to be brief 
and thus was incomplete. A typical kayak floating level has a couple 
(2 to 4) inches of rocker (at best), and a kayak on its side has 
several (8 to 12) inches of "rocker". Even if some kayaks have fairly 
straight keels, almost all are narrow at the ends and wide in the 
middle and the relative difference is greater than the height towards 
the ends vs the height at the middle. So a result of leaning the 
kayak is effectively increasing the rocker as well as shortening the 
waterline.  I think you are essentially saying the same thing, just 
more completely.

I am not trying to enter the fray about how a shape can make a design 
actually initiate a turn. I don't have a coherent theory about that. 
Although I have paddled boats that turn better when leaned one way or 
another, I haven't consciously paddled a boat that on flat water 
shows a distinct tendency to turn due entirely to leaning with no 
other input. The number of boats I have tested is far out numbered by 
those that I haven't, so I don't feel qualified to comment.

I do think that leaning to the outside of the turn will give any 
"skeginess" in the stern a more streamlined shape so that it offers 
less resistance to turning. Because it is angled away from the 
resisting water. Since the stern travels farther through the water 
than bow during a turn, this makes a relatively more significant 
difference.

Nick
-- 
Nick Schade
Guillemot Kayaks
824 Thompson St
Glastonbury, CT 06033
(860) 659-8847
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Received on Tue Dec 04 2001 - 06:58:53 PST

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