Caitlin, I've no experience with the Hydrovane,but lots with an auxiliary rudder/trim tab vane that I designed and built for our previous boat. That experience really has little bearing on your request, so I'll only say that it steered our retired IOR one-tonner for many tens of thousands of oceanic and coastal miles. That boat had far less inherent course stability than most traditional, long keeled vessels.
But, I think you can get some idea of how your boat will react to a Hydrovane by doing a little thought experiment
: First, how big is the HV rudder compared to your boat's rudder? Second, in the conditions that you want the HV to work
, how much steering input does manual helming require? That is, do you need to add or subtract several degrees of rudder frequently, or can you mostly just tweak it a little now and then to stay on course?
If the latter, I believe the HV will do a great job. If the former, then the smaller rudder on the HV will be working pretty hard to input as much turning force as your larger ship's rudder does, and response may well be pretty slow.
My observation is that all aux rudder vanes wander a bit more than servo-pendulum types, especially downwind with quartering seas. The servo reacts immediately when the stern of the boat slews (as when it lifts to a quartering swell), well before the apparent wind shift can drive the air blade and its associated gear
. This provides a rapid steering correction. The aux rudder types must wait until the apparent wind shift drives the trim tab, and then there is a significant delay while the trim tab drives the rudder in the appropriate direction. This delay allows the boat's course to wander a bit. It will do a fine job of averaging the correct coursse... just more embarrassing woggles in the wake! This effect is more noticeable in boats with less inherent course stability of course. Could be a non-event if your long keel keeps you straight most of the time.
I really miss our old vane! The various electronic auto pilots we've used on our current
boat do a good job of course-keeping, but they burn lots of electricity, they're noisy in the aft cabins, and there is always the specter of electrical
failure or electronic gremlins in the back of our minds when on passage!
Good luck with your decision,