Wind vane on a 50' catamaran - will it work

[IanClarke]

Hello, I would like to hear from anyone who has experience of using a wind vane on a 50' foot or similar sized catamaran. I am interested in the Hydo Vane in particular, but any sort of wind vane on a cat would be relevant.Can this work, or am I crazy.
The logical benefits of this system for ocean crossing is clear.
No power requirements, backup rudder in case main steering system fails.
The system would be mounted at he end of one hull. It could get plenty of clear air on on tack but my concern is that it may not get enough air when on the other tack.


Would appreciate it if skeptics and theorists hold their itching fingers, I would like to hear from those who have done this or spoken to those who have. All three of you. They are out there, I have seem pics of at least one.


Regards Ian

[Cotemar]

Maybe these will help.

http://www.cruisersforum.com/forums/...arans-320.html

http://www.cruisersforum.com/forums/...ork-17511.html

http://www.cruisersforum.com/forums/...ats-98449.html

[colemj]

But none on a St. Francis 50. Since all boats will be different - particularly catamarans - it seems like the experiences of any of the 3 people who have put a windvane on a catamaran would be as irrelevant as anyone's who has not.

Just what kind of relevant experience from a 31' Wharram with a vane do you expect to translate to your boat?

Mark

[Meandercp]

I have a Autohelm self steering unit (from Scanmar marine) on my 37 foot cat. I originally had it on one hull, it worked, but I could not support the rudder structurally. I ended up putting the rudder in the center and it works fine although a bit more exposed.

One of the nice things about the Autohelm is that the vane portion is separate from the rudder. They are attached only with cables that can be routed via blocks. That way the rudder can be wherever you can mount it while the wind vane remains on the centerline (or vice versa). It is, of course, better to minimize the number of turns to reduce friction.

Another thing I like about the Autohelm is that it is very simple. There is nothing on it that you can't repair or replace in a pinch with hardware store stuff.

I see no reason it would not work on a larger boat, but the Scanmar people will tell you if they have a rudder large enough for you.

[Reiziger]

I believe in the HydroVane, they have proven to work way off center very well.

But get in contact with John and Karen Curry.

[barnakiel]

Talk to Windpilot. The big model Pacific Plus (pendulum + independent rudder). Talk to the guy behind the company. He may help you sort out some of your concerns.

b.

[IanClarke]

Thanks for all of your responses. Mark ( Colemj) I do take your point :-) I was only joking about the number of three out there. But you are correct, if the number out there is low, it should be telling me something, and the relevance of a 30 foot cat to how a 50 foot cat will work could be limited. The size of the hydra vane rudder compared to the current rudders on the boat is a concern, especially in heavier seas.
Regards Ian

[Jim Cate]

One of the secrets to use of a wind vane on a cat or planing monohull is to realize that there are some situations where you can't use it. For instance, in surfing conditions, where the boat accelerates rapidly down the face of a wave, the apparent wind rapidly goes forward. The vane, attempting to maintain a constant apparent wind angle, steers further down, which can bring the boat beam to the sea and lead to a broach... or then the boat reaches the bottom of the wave and slows suddenly and the apparent wind goes aft and the vane steers into a gybe. Neither is a good outcome!

But in more stable conditions, the vane can work well. And remember, with the Hydrovane or the Autohelm, the main rudder(s) take out any fixed helm, and all the vane rudder must do is make small course corrections, and thus needs not be so large.

I think if one heeds these issues the vane could be a big help, but one should have a good auto pilot as well.

Cheers,

Jim

[robert sailor]

I agree with Jim, in the past vanes and cats didn't go together because as Jim explained the cat accelerated so quickly during puffs of wind and surfing. These new cats are much slower and are much closer to mono hulls in many characteristics so windvanes could be a good addition to an already good autopilot.

[colemj]

Originally Posted by IanClarke

Thanks for all of your responses. Mark ( Colemj) I do take your point :-) I was only joking about the number of three out there. But you are correct, if the number out there is low, it should be telling me something, and the relevance of a 30 foot cat to how a 50 foot cat will work could be limited. The size of the hydra vane rudder compared to the current rudders on the boat is a concern, especially in heavier seas.
Regards Ian

I think the actual number of cats who have windvanes really is three.

The points about acceleration being an issue are true, but not the real problem. The real problem is getting steady airflow to the vane on a St. Francis 50 (or most other cruising catamarans).

Even out on a hull on a beam reach, the airflow is swirling in direction and continuously changing strength. The big cabin and bimini is the problem - even with steady winds not coming over them, they create venturies and eddies that disturb the air quite a ways behind and outboard.

I suspect you would only have a reasonable chance of one working if you were on a beam to broad reach in strong winds - and only from the side you have it mounted.

And then you have the whole issue of running control lines and losing the access of one of your sterns.

You can talk to the manufacturers and they will tell you how successful their products will be on your boat. But I don't see a St. Francis 50 being steered successfully by a wind vane.

You already have a backup rudder, so I don't see why you are concerned about that. Main steering failure shouldn't be a problem because the AP is connected directly to one rudder. For <$2,000USD you could install a drive unit on the other rudder and the AP could drive either one in the event of a rudder failure of either side. This would only cost ~$500 if you have hydraulic steering. Or just install the mounts and move the drive unit in the rare event of a rudder failure.

For those unfamiliar with this boat, this is the challenge:

Mark

[IanClarke]

Thanks Mark,
good point you make. Buying a backup auto pilot and control hardware may be cheaper and easier than installing a Hydrovane.
The St Francis 50 has hydraulic steering. I will look carefully at the hydraulic lines. It may be possible to isolate one rudder if it was lost/damaged. The other benefit that a hydrovane provides is a completely independent alternative steering system should one of the parts of the autopilot fail. Eg. the course computer goes up in smoke, or the hyrdrauilc pump fails, or any one of the critical parts of a modern autopilot. The other benefit is there is no power drain. Under sail at night I am loosing about 15-20 amps. But I think a Watt and Sea will take care of a lot of that even 6-7Kn sailing speed. I think the high risk component is the autopilot course computer. The hydraulic pump should be reliable if oil is keep up to it. The spare course computer would be a lot less expensive than fitting a hydrovane. I guess it is a compromise and a bit of luck that we carry the correct spare. Murphys law states that the bit that fails is not the bit we carry as a spare.
Thanks again for all the comments guys, really appreciate them all.
Maybe a Hydravane with a tall pole to extend the wind vane above the top of the hardtop over the cockpit is the answer.
Regards Ian