Thanks for this info. I contacted them.

They build Schilling design rudders for their own river barges and are
very impressed by the performance.

The will custom build for smaller river or canal craft to order.

You will need hydraulic or geared mechanical steering which is capable
of moving the rudder through 70 degrees, port or starboard to take
full advantage of the rudder 'side shifting' capabilities when you
have the engine at maximum power. The kind of power you will not be
able to control with a manual tiller bar on a narrow boat or wide
beam canal boat.

R W DAVIS boat builders http://www.rwdavis.co.uk/

Tel: 01452 740233
Fax: 01452 741307
e-mail:

Junction Dry Dock
Saul, Gloucester GL2 7LA
UK

A cheap a cheerful solution is just to weld an equal angle, say 11/2
inch on the the trailing edge of a flat plate rudder, as done by many
fishing boats. Try it with a tiller and gauge effect. Schilling
rudders are not good at making sternway. On my own vessel, I got
heavily into schilling rudders but eventually, after lengthy
discusions with the vessels designer of many beers, went for a
conventional NACA profile, which still has 70 - 0 - 70 rudder arcs.
Turning performance hard over at rest is pretty good, but would be
better had I had top and bottom plates added to direct/contain the
propwash.