above water self steering

[Rhosyn Mor]

This is a picture of of a self steering unit that has come into my hands. Although it has Hydrovane stamped all over it , it appears not to be a hydro vane, or if it is it is a very early one, '70's perhaps?
any way it look like it was meant to act directly on the wheel/ tiller, an above water self steering with no seperate rudder. Has anyone used a system like this? how effective are they.
Also attached is a picture of Rhosyn Mor, currently at the dock awaiting a haulout.

As soon as this weather in the Chesapeake turns and I can get a haul out we are on the way down to Latin America, so a wind vane would be nice ( We did 2400 miles hand steering, not a pretty sight

Nick
SY Rhosyn Mor
Ipswich