G'Day Steve,
Many hydraulic
steering systems suffer from "creep"... that is the
wheel position that results in the
rudder being straight ahead slowly changes. This confounds the typical
wind vane. I have been told that well designed hydraulic systems do not suffer from this problem, but I have no personal experience of this.
Any auxiliary rudder vane system will circumvent that problem, and there are others besides Hydrovane, including
AutoHelm (from Scanmar) and
Wind Pilot. Likely are others as well. Further, the very simple Sayes Rig (also
sold by Scanmar IIRC) which is a servo that drives the rudder directly would
work, but they only are applicable to rudders that are very close to or hung from the transom.
Cheers and good luck with your choice... a good vane is priceless!
Cheers,
JIm