Windvane steering off centre

[Deltaromeopapa]

First post so hope I have this in the right area.
Classical thinking is that a servo pendulum vindvane should be mounted on the boat centre line with unobstructed airflow. Looking at videos of vindvanes in operation there is plenty of gear cluttering the pushpit of boats with windvane and they seem to work so the unobstructed airflow theory is a bit weak.
Capehorn, Windpilot and Sailomat all suggest that off centre mounting of the vane is acceptable, Capehorn to the extent of 300mm. When questioned they say that there is no discernible difference between port & starboard tack performance and that less rudder in the water on one heeled tack is not significant because output force is proportional to boat speed squared and the boat should be moving quickly if heeled (assuming balanced sails).
I want to fit a vane to y Halmatic 30, I'm leaning towards Neptune because of cost but they are adamant about on centre line mounting which with a transom hung rudder requires additional metalwork. Putting a vane in the wrong place to see if it works and getting it wrong leaves holes which I don't want to do.
Anybody any experience to offer, would be greatful to hear from you.

 

[Normalfornorfolk]

PM sent.

 

[john_morris_uk]

PM sent.

Why reply by pm when lots of people might be interested in the information?

 

[James Marinero]

I opted for a Hydrovane because I wanted to mount off centre - 50 cm from the centreline in fact. OK, not pendulum servo like the ones you mention, and a bit more than I wanted to pay. BUT after 3k miles downwind (much of it F6-8) in a 29 ton steel schooner, I'm very happy with my Boy George. Our main rudder had a fishing net around it for 800 miles - SWMBO and I alone and seas too big to attempt net clearance. So, I was mightily glad of the second rudder the Hydrovane provides. The net eventually dropped off during a slow gybe. I've no connection to Hydrovane company.

 

[Babylon]

Why reply by pm when lots of people might be interested in the information?

I agree.

Re the question, I have a Monitor servo pendulum system which (like all systems) is infinitely adjustable, so it has always seemed to me that any effects of wind interference (in my case by a transom mounted radar pole on starboard quarter, wind-gen on port quarter) is simply adjusted for implicitly when settling the boat on its desired course.

Then, all the auxiliary rudder is doing is providing power to the tiller (or wheel) through being rotated (by the vane flopping one way or the other) and thus being forced over in a flow of water that is linear to the water-track of the boat - which doesn't change even if the rudder is offset. So, assuming the rudder is deep enough to bite on both sides at normal levels of heeling, I cannot see what difference a minor offset of the whole gear is going to make.

 

[JVL]

Have a look at Auto steer by Hydra. I have it on a long keel Petrel 32 its set up off centre and works fine. Friend of mine had the same system on his Nic 31 the same boat as yours? Has the added advantage that it easy to fit a tiller pilot driving the trim tab

John

 

[capnsensible]

Hydrovane will certainly do the job. Mine is mounted central and has happily steered across the Atlantic and back. Earlier on this year I used an off set one on a Bavaria 46 I was delivering across the Pacific, no problem.

Tops.

 

[Deltaromeopapa]

Guys thanks for your updates, sounds like I thought, there isn't much evidence to support the 'on the centre line theory'. JVL yes please he Nic 31 and the Halmatic are very similar, just a foot apart.
Peter

 

[vyv_cox]

I suspect that the oar of my Windpilot would be half out of the water on a hard beat if there was any significant offset to the mounting. This would inevitably have an effect on its performance.

 

[Deltaromeopapa]

Vyv hi
Just what I thought but the manufacturers say either: to have a slightly longer ar OR that it makes no difference because the force is proportional to the square of the speed and if you are well heeled then you are shifting enough to move the oar!!