Re: [Paddlewise] Weatherhelm

14% is a whole lot more believable than the 40% you had mentioned in the
original post. Still with a sailing canoe we are talking about a much bigger
fin being forced through the water at an angle than anything usually found
on a kayak.
Matt Broze
http://www.marinerkayaks.com
-----Original Message-----
From: 735769 <735769_at_ican.net>
To: PaddleWise_at_lists.intelenet.net <PaddleWise_at_lists.intelenet.net>
Date: Wednesday, October 06, 1999 6:57 AM
Subject: Re: [Paddlewise] Weatherhelm


>As I mentioned earlier, I  think most rudders and skegs could use some
>improvement.
>
>Many skegs fit rather loosely in their trunks and have rough or irregular
>edges. I believe the vibration (singing skeg or rudder) that some develop
>usually results (not sure that other causes of vibration apply to kayaks
>given their low speeds) from vortices shed off the trailing edge. Sailors
>cured this problem by shaping the leading and trailing edges carefully. In
>all my years of boat building and sailing I never found a case of singing
>rudder or centerboard that reshaping the edges could not cure. In general
>one wants a leading radius of around 1.5% of the chord length for rudders.
I
>suspect the same would apply to skegs where the boat has a tendency toward
a
>lot of leeway (in excess of 7 degrees).  Sharp or squared off at an angle
>trailing edges work nicely.
>
>Of course, one should have a rigid rudder head. To me the floppy rudder
>heads cause a lot of problems including wear an tear on the system and poor
>response.
>
>Both skegs and rudders work best when they have proper section shape. The
>ubiquitous (among sailors) NACA 0006 and 0012 airfoils seem to work just
>fine. If they didn't a sailboat race would sound like a giant kazoo band
>engaging in a game of bumper cars.
>
>Improper shaping (mostly flat plates) causes most of the ventilation that
>increases drag in  a big way.  Nicely rounded leading edges and a fuller
>foil like the NACA 0012 just about eliminate it for all but the most
>aggressive turning actions. Back when I was racing 505's I experimented
with
>an NACA  a section supplied by a friend at NASA and despite all reasonable
>efforts I could not make that rudder ventilate. The section was the same as
>that used on the U-2 spy plane wing and designed for high lift. I believe
>(but won't swear to it) that the section was designated NACA 2006.
>
>I have modified flat plate rudders by gluing wood on each side and then
>shaping the blade. A little varnish and it looks rather sexy and works
>better too.
>
>I prefer rudders with stops that prohibit turning the rudder more than 20
>degrees. This reduces the possibility of ventilation considerably.
>
>If one uses the rudder more like a  trim tab and set it at an angle to hold
>a course rather than wiggling it back and forth all the time it seems to
>work quite well (someone mentioned that earlier but I cannot recall who).
>Interestingly the Inuit seemed to have used their rudders this way. They
had
>control lines running around the front of the cockpit that they must have
>adjusted and left since one can't paddle and handle lines at the same time.
>Can learn a lot from those Inuit.
>
>Managed to dig out the paper on the International sailing canoe tests. For
>those who want to get it search for Tanner, T. , Full Scale Tank Tests of
an
>International 10 Sq. Meter Class Canoe, Royal Institution of Naval
>Architects, 1960,
>
>Unfortunately they printed the graphs in such a small scale that taking
>information off results in lots of error not to mention the error due to
>normal distortions of copies etc. Doing the best I could for 5 degrees of
>leeway I got  a 1.8% increase in drag at 2 knots, 11.4% increase at 3 knots
>and 14% increase at 4 knots.
>
>Now, don't go off and quote me on those saying that John Winters said that
>Blah blah blah % blah% blah% !!!!!! First off, even Tanner admitted to some
>problems in fairing the data and my take-off certainly won't win any awards
>for precision. In any case, the graphs do suggest that leeway can result in
>considerable added resistance and that it may even pay to design boats with
>small keels or hull shapes that resist leeway.
>
>Lots of options here and fun for designers, builders, and advertising copy
>writers.
>
>Cheers,
>John Winters
>Redwing Designs
>Web site address, http://home.ican.net/~735769
>
>
>
>
>
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