On Mon, 29 Mar 2010 13:44:02 -0700, Gordon wrote:


One of the big problems with wind vane steering is that they don't
work well below 3 knots or so because the foil in the water doesn't/
can't generate enough lift to move the steering device, be it tiller or
wheel.
So, I'm wondering how one would design and build a foil to maximize
power through water at low speeds. Would longer or wider or fatter be
better? Would a wing on the bottom help at such low speeds?
Impossible dream?
Gordon

You can make a wind vane steer at practically any speed by changing
the area of either the wind-vane or the rudder (the part in the water)
the problem is that if you increase the area in either areas it
becomes overly sensitive when the wind gets up.

I had a Hydro-vane installed on my last boat, see
http://www.hydrovane.com/OurProduct.html

It directly steers the boat and the rudder was effective nearly to a
stop (although it turned pretty slow at that speed :-)

You will note that the rudder is a foil.

In general aerodynamics and hydrodynamics are much the same, taking
into consideration viscosity and speed, etc. The wings you mentioned
work by generating lift albeit downward rather then upward :-)