Re: [Paddlewise] skeg ups

Robert Woodard wrote:
> 
> > Rudders increase the effect by allowing an even greater angle of
> > attack and,
> > if the rudder has a suitable section shape, it can provide significant
> > increases in lift.

> I've seen you guys refer to rudders and lift before. I've seen reference to
> making rudders in a foil shape, is this what you mean by section shape? I've
> seen probably 30-40 rudders mounted on kayaks, but they've all been the flat
> blade types, although I've been told foil shaped blades exist.
> 
> > An interesting aspect of skegs comes from their location. Both skegs and
> > rudders generate lift to offset leeway.
> 
> Here is where I'm really lacking in understanding all of this: How does a
> skeg, essentially a flat piece of metal or composite, aligned with the boat,
> generate lift? I see the skeg as creating lateral resistance. Is this the
> same thing as lift?

Woody, I'm pretty sure they are talking about "lift" to the side, which can
not be generated without some resistance (an aircraft maxim:  no drag, no
lift; high lift  to drag *ratio* is good; low lift to drag ratio is bad).  In
other words, a force at right angles to the rudder/skeg surface.  So, the
rudder/skeg, when hit from the left (port) side, for example, by water as you
move through it, produces a force, due to its "airfoil" shape and its angle of
attack, to the right, analogous to the lift (in the vertical direction) which
an airplane wing generates as it moves through air.

Any airfoil which moves through any fluid, be it air or water, will generate
"lift" if it has a positive angle of attack (ignoring stalling, to simplify
things).  The discussion about the influence of rudder/skeg cross-sectional
shape ("airfoil" used in a different sense) on the *efficiency* of the
lift/drag combination seems to be drifting towards the conclusion that flat
plates are not as good as virtually any airfoil, and that some airfoils are
better than others.

Winters (and others) must have tank test and/or field test data to suggest
what is the best airfoil.  At the Reynolds numbers a yak rudder operates at, I
wonder how much difference it might make, and am really curious what data
exist to show an airfoil makes enough difference for me to notice when
paddling.

-- 
Dave Kruger
Astoria, OR
***************************************************************************
PaddleWise Paddling Mailing List - All postings copyright the author and not
to be reproduced outside PaddleWise without author's permission
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.paddlewise.net/
***************************************************************************