Re: [Paddlewise] FW: Toksook Paddle

>By "lenticular shape" do you mean the "willow leaf" shape as Derek calls
>it? The shape as seen when looking at the power face has little to do with
>how easy it is to use. It is the thick cross sectional shape of both the
>Toksook and the standard Greenland style paddle which makes it very
>forgiving while sculling and rolling. A relatively thick blade relative to
>will be less likely to dive or stall if you have the angle of attack off a
>little.
>
One of the problems we face in discussing paddles has to do with
nomenclature as Nick touches upon.

It seems that aeronautical terms work nicely for paddles. For example;

Profile - The shape of the paddle when you look at its face.
Section - The shape of the blade when you cut it at right angles to the
shaft centerline. Typically the section varies from one end of the blade to
the other.
Aspect ratio - Length of the blade divided by the width of the blade. For
blades that vary in width along their length the aspect the method used by
Abbott and Doenheoff in "Theory of Wing Sections" works just fine  (b^2/S
where b equals the length of the blade and S equals the area).
Thickness or camber - the percentage of thickness to width works nicely for
most paddles. It has, like the aspect ratio, the advantage of
non-dimensionality.
Edge radius - generally a radius as a percentage of thickness.

One thing that confuses the issue of how paddles handle has to do with the
edge radius. A sharp edge on a thicker paddle can produce problems when
sculling. Conversely a rounded edge can reduce sculling problems on a thin
blade. In some rather casual trials I found that a 1/4" bead all around the
edge of a thin bladed paddle had a positive effect on the handling. This
suggests that the edge radius may have more importance than thickness with
regards to handling of paddles. This seems particularly true in conditions
where lift gets generated since the sharper edges tend to stall more
quickly than rounded edges. Experiments on some types of ship rudders
support this.

My experience with various blades supports Nick's assessment of the
handling characteristics of thicker wide blades versus thinner wide blades.

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



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