The following is “asking for a friend” so my apologies for the slight lack of clarity.
I helped a friend install a new Hydrovane
on his boat
a few months back. It works well, however since the very first use he has experienced an issue where the drive unit slowly slips on the shaft. Over time, with the drive unit and tiller locked in the straight ahead position, the rudder
ends up pointing more and more to port.
We installed it a little offset to the starboard side of the boat
(A Duncanson 37 or something like it from memory) to clear the stern ladder.
We were very careful about vertical alignment in both the fore and aft and port and starboard axis.
He has contacted Hydrovane
about the problem but has had little in the way of advice
so far. I suggested I should post here as there are many users of the Hydrovane on this site who may have some advice