Re: [Paddlewise] (un)Feathered paddles in surf

Matt wrote;

-(SNIP)


>Paddling across a very strong wind a feathered paddler needs to be careful
>not to raise the blade too high or the wind can catch under it. This is
easy
>to compensate for and once the danger was recognized I never had to let go
>of the upper blade (or twist it to spill the wind) again even in exteme
side
>winds. I will speculate that if one had to do a quick brace as a side wind
>gust pushed you of balance, reactions rather than reason would take over
and
>you might well find yourself doing a sudden high brace. Now the
unfeathered
>blade would be inadvertently exposed to the high wind. This would tend to
>counteract the brace, pushing you further over to the side you from which
>you are already trying to recover.

Possible I suppose but I never had that experience. I have had problems
with twisted blades in beam winds. Perhaps one just learns to live with the
problem which ever one you have.

>Letting go of the paddle with one hand
>(or twisting the shaft to spill the wind) won't be able to help you here.
>Blade speed is roughly 2.5 times boat speed. A paddler paddling 4 knots
into
>a 10 knot wind would have (4 x 2.5) ten knots of additional paddle blade
>speed to add to the wind speed (and doubling the relative wind creates 4
>times the resistance).

I think this may have an element of exageration. Parallel flow (to the
water and hence normal to the blade) rarely occurs. Surface turbulence and
the altered flow around the paddler can cause the flow around the blade to
approach being parallel to the blade. Obviously this varies with the
altitude of the blade etc. but in any case one cannot simply assume that
the flow strikes the blade at anything near normnal to the surface.  Such
and approximation needs more study before applying it without reservations.
Of course,  one must also factor in the height of the stroke. The
traditional paddle users generally use lower strikes where the wind has
much less effect anyway.

Sailors will have some familiarity with the altered air flow around a body
(safe leeward effect) etc.

>Turning around and ignoring that you would be moving
>faster downwind for the same effort (which is working even more in my
>arguments favor) a blade moving at 10 knots downwind in a ten knot
following
>wind would gain no benefit from the wind. At best the penalty for
>unfeathered into the wind is far greater than any benefit garnered going
>downwind.

The pressure against the blade varies with relative velocities. Since the
blade doesn't always travel parallel with the air flow (the blade travels
in a roughly elliptical path or sometimes egg shaped path depending upon
stroke mechanics) and much of the time its relative velocity is much lower
than the approximation Matt used.


Having developed rather painful wrist problems from using feathered blades
and having "cured" them using an unfeathered blade I suspect that the
benefits of one over the other may have more to do with treating the paddle
and paddler in a holistic manner rather than as isolated benefits and
drawbacks.

The feathered paddle (in my case) has much less efficiency than the
unfeathered paddle. No doubt some one will say, "You just didn't use the
right stroke mechanics" and no doubt that would have an element of truth
but maybe it works both ways.


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

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