Re: [Paddlewise] A Rudder Experience

John Winters wrote:
> 
> 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.  
> 
> 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.

You also may want to look into what is termed a "balanced" rudder. 
However, its primary use is in sailing kayaks, so I have no idea how
well it will work for a paddled kayak.  Basically it is one in which 20%
of the blade is forward of the pivot point of the rudder.  On most
rudders the pivot is at the lead edge of the blade so that zero percent
is forward of this.  The balanced rudder swings out differently when
being used and seems to need less radical thrusting sideways to achieve
the same amount of turn.

I know it has been used to replace the standard rudder that comes with
Kleppers, which are not all that deep in the water and have a rather
horizonal thrust to them, i.e. they are big and shallow rather than
being small and deep.  Mark Ekchart at the Klepper Service Center makes
one as part of his after market business, Long Haul Products Inc.  It
can be replicated cheaply using the standard Klepper rudder.  One knocks
out the rivet that holds the blade in its bracket, then reverses the
blade and re-attaches it to the bracket.  The result is a rudder that
looks acts like a balanced rudder (with about 15% of its blade forward
of the pivot point) and runs deeper in the water than the blade in its
factory setup.  I had a description of it in my newsletter which I would
be glad to fax or mail to anyone who asks.

Again, what I say may not apply to paddling but it works wonders in
sailing a kayak.  The original idea of using a balanced rudder comes
from Mark Balogh of Balogh Sail Designs.  The idea of reversing the
standard Klepper rudder comes from Dieter Stiller who was the North
American distributor for Klepper.  It was something he would hesitate to
tell people since he felt everything about Kleppers was pretty perfect. 
But I managed to wrangle it out of him one day in a friendly teasing
exchange.  The solution is so simple with the standard Klepper rudder
that it should be picked up by just about any Klepper owner to get less
stall out of their rudder.

ralph diaz


-- 
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Ralph Diaz . . . Folding Kayaker newsletter
PO Box 0754, New York, NY 10024
Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com
"Where's your sea kayak?"----"It's in the bag."
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