The Offshore Voyaging Reference Site

Servo-pendulum is Not Bullet Proof Either

A few weeks ago I pondered the very high loads that auxiliary-rudder self-steering gears put on themselves and the parts of the boat they are bolted to, based on the failure of Simon Curwen’s Hydrovane gear while leading the GGR.

Now we are getting reports that Abhilash Tomy is having a hell of a time keeping his Windpilot servo-pendulum gear operational.

As I understand it, both Abhilash and Simon started having big time trouble with their gears when they got in really nasty weather west of Cape Horn and got broached repeatedly.

Obviously, this is a small sample, but I think the takeaway might be that no vane gear is going to consistently stand up to broaches in big seas, no matter how well made. Seems logical.

And, further, that the idea that a servo-pendulum gear will kick out of the water and unload before damage is done might not be true, at least in really big seas.

And this in turn makes it even more important to have storm survival gear aboard, a strategy in place to prevent broaches, and the ability to get through really nasty storms without steering and with the vane gear safely out of the water.

Of course, as I understand it, that last requirement is easy to execute with the Windpilot and Cape Horn, and very difficult with gears like the Hydrovane.

On the other hand, the Hydrovanes seem to have done better than the Windpilot in this and the last GGR, aside from Curwen’s unfortunate experience.

Again, nothing definitive here, but worth thinking about when we are selecting a vane gear.

I think, on balance, I would select one that I could easily pivot out of the water.

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Emile Cantin

I don’t know much about other types of windvanes, but the Cape Horn specifically is designed so that the rope acts as a fuse and break when the loads are too high. This strikes me as a pretty good design as it’s easy to carry some spare line (in the GGR, for example), and if you don’t have it on board it’s easy to find anywhere in the world.

And yeah, as you mention, it’s very easy to get out of the water.

Edward Pearson

A problem we experienced deploying a series drogue in big seas was the risk of the bridle lines hooking under the vane mechanism and applying enormous forces even when the unit was swung up. Eventually we evolved rope deflectors from the corners of the transom to the lowest protruberance of our Fleming unit which functioned well.

James Chase

My understanding was that the locking pins in a Hydrovane are designed to shear under extreme rotational loads like you might expect in a broach (though this is only in rotation of the rudder, and not in the direction needed for the rudder to swing up if it struck something). As previously mentioned, under those conditions, there’s no way the rudder could be intentionally removed, unless it was done while hove-to well before experiencing the extreme conditions,… but that would defeat the purpose of using it in the first place! Pretty much everything else would come down to reinforcing the mounting location, to the extreme. If the transom/vane mounts “can’t” fail, then the only other realistic failure points that I can think of would be the rudder snapping?!, the shear pins breaking, or the main shaft bending- but that’s hard to imagine!… A massive amount of force, no doubt.

Bill Attwood

A couple of points on the Windpilot Pacific:

  1. The vane twists as you raise it out of the water, and the recommendation from Peter is that it should be done at under 2 – 3 knots of boat speed (the speed from memory).
  2. Being hit by a big following sea (somewhat mild description for a S Ocean monster) will be like going fast astern, not good for any rudder or vane.