Re: [Paddlewise] A Rudder Experience

Gerald wrote;


>I then decided to lower the rudder to ease any possible strain on my
>shoulder.  As soon as the rudder was down, the stern anchored slightly and
>the bow blew off.  This was easily corrected by a bit of rudder.  However
I
>immediately began falling behind Kris.  Added drag, I guess.  I re-raised
>the rudder and caught up to her again.  I repeated the experiment with the
>same results.
>
>A bit later the wind died.  I lowered the rudder again and was able to
keep
>up again.
>
>Conclusion:  The rudder adds drag only if deflected.  Obvious, I guess, if
>you think about it.

The rudder adds drag even when not deflected (surface friction plus some
form and wave making drag)  but the dramatic difference you noticed may
have been due to stall. Stall occurs most easily in flat plate rudders that
are common on sea kayaks. You may have been getting stall even with the
rudder aligned fore and aft due to the leeway being made by the boat.

Nicely shaped commercially available rudders see to be the exception rather
than the rule here  here in North America. The "Classic" configuration for
a rudder would be the NACA 0006 airfoil. Its characteristics would be a
thickness of 6% of c (c = the airfoil chord), maximum thickness 30% of c
from the leading edge and a leading edge radius of 0.04% of the c.



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