Re: [Paddlewise] Rudder profile

> Depending on speed and the power needed, the optimum width of the rudder
> varies, as power is a function of the area and speed squared, but the
> narrower it is the easier it will be to stall, especially if it is long,
as
> the sharpness of the stall is a function of the rudder's AR, aspect ratio
> (the length divided by its width). You see very few thin plate rudders of
> high aspect ratio, as they are very prone to flutter (pouch's leeboards
are
> made of thin plate and while short a tubby buzz (flutter) a lot!

I suspect air-foil blade (or is it hydro-foil?) not only improves speed (can
be deflected less due to additional lift), but also eliminates flutter.   My
Feathercraft aluminum foil double rudder (AR of wetted surface approx. 4) is
3/16" foil, and I never had any flutter.  No flutter too on small flat 1/8"
single blade of another kayak (AR about the same), but it has small area for
such a thickness.  I heard a flutter when increased area 4 times with the
same 1/8" flat aluminum, and also increased AR to, may be, 5.  The third
one, 1/8" flat aluminum by Folbot, has AR no more than 2, and of course has
no flutter, but one needs a post-and-yoke lever system of Folbot to turn
such a blade.  (or to modify it to make it balanced).

> So at low speed a wide rudder is a real boost, while at high speed a
> long, narrow rudder is good enough - US tugs have multiple rudders that
are
> far wider than long (AR < 1!)

Those tugs use hydraulics and/or motors to turn their rudders; but you
don't.  That's why narrow high-aspect blade is preferable if you want to
apply less efforts on pedals.  Or heavily balanced blade, with 30-35% of
area fore of the pivoting axis.
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