9th February 2023
Servo Pendulum and other Self-Steering Gear
I suppose it must have been the 1995 Earls Court London Boat Show when I bought my Windpilot Self-Steering gear. Those were the days when you could browse amongst the various suppliers and compare and contrast, before getting completely slaughtered at the Guinness stand. Did you know they sold 57,000 pints of Guinness at the 2003 London Boat Show!
Probably the most elegant solution for Sumara would have been the trim-tab as detailed by Peter Woolass and used by Tui of Opua, but I really didn’t what to take a saw to my rudder and probably didn’t feel confident to construct my own system, so needed to buy a ready-made bit of kit.
Having already stuck my neck out and stated that I didn’t feel spade rudders were suitable for ocean crossings, it seemed pretty pointless buying a Hydrovane type system.
The Hydrovane needs a large windvane to operate an auxiliary rudder. One of the selling points is that it can theoretically be used as an emergency rudder. When the Hydrovane is in normal use, it is only tweaking the course because the actual course is still set by the yacht’s main rudder which has been locked off.
If the yacht’s main spade rudder has been knocked off then the Hydrovane is theoretically supposed to take over and act as an emergency rudder. Well you might well need an auxiliary rudder if your main rudder looks like the one in the diagram above, but why would you suppose that a structure bolted to your transom with another, presumably weaker, spade rudder will be there to help if your main rudder has failed?
Without the main rudder holding the boat on its course, you can only imagine the forces exerted on the Hydrovane rudder from a fin keel yacht, like the one above, wanting to pivot around its keel having no longer any lateral resistance from its main rudder.
The Hydrovane rudders do fail, although they have now beefed up the grade of steel used for the shaft.
So I quickly ruled out those vanes and I homed in on the chronically clever servo pendulum system.
It was invented by Blondie Hasler of the Cockleshell Heroes fame. It is so clever that even after 28 years, I still stare at the mechanism on my Windpilot in amazement. Unlike the Hydrovane, it doesn’t require a large wind vane as the lightest breeze will operate the ingenious “Hasler” gear.
For those not familiar with the concept, this is how it works. You set your boat sailing on your course and trim the sails as best you can. You rotate the pivoting wind vane so that is is directly in line with the wind. It will then be upright. If the boat starts to move off course, the wind will push onto one side of the vane and it will tilt. A connecting mechanism will twist a small servo pendulum rudder which is trailing in the water. When this twists, the huge force of the water passing it amplifies the force and two lines led to the yachts tiller will move the main rudder to correct the course. To connect to a proper tiller, and I’ve made my thoughts clear about wheels, you just drop on a chain between to small lugs. If you need to adjust for weather helm, just move it along a link. Easy peasy.
I know what you are thinking, that little wooden rudder also looks very prone to damage, but I am still using the original servo-rudder and after 28 years it still works perfectly. The servo pendulum rudders aren’t subjected to the massive forces needed to steer the boat, so they don’t need to be butch. Furthermore, even if it hit some flotsam, it will just tilt up. Look closely at the picture and you can just see a bolt and Nylok on the waterline. This bolt is just tweaked enough to hold the rudder in place. Should it whack anything, it will just tilt aft. When you are not using it, the servo rudder swings up sidewards and nestles near the upright shaft out of the way. As the arm swings up, replacing a broken pendulum rudder would be a very simple task. On long ocean crossings it would be a sensible spare part.
So out of all the “Hasler” type mechanisms, why did I choose the Windpilot Pacific. At the time, the Pacific Light was not an option but if your yacht weighs less than 2,500 kg it may be worth exploring. The Aries gear looked like a beautiful work of art but Sumara is a small boat and I really didn’t want that weight on her stern. So the Aries was quickly ruled off the list.
I can’t fully remember all the other choices at the time.
Cap Horn springs to mind but it looked a bit too lightweight for my mind.
I think the Monitor was too expensive at the time, but I also wasn’t keen on all the light gauge stainless steel tubes which are designed as overload protection. That said, many of my sailing friends have fitted the Monitor System and are very pleased with it. I think with changing exchange rates the pricing is more competitive now.
So in the end, the Windpilot got my vote. It has served me well for 28 years and handled Force 10 storms with no problem.
Peter Foerthmann, who makes the Windpilot, has this to say about self steering gear on the recent Golden Globe Race which is an excellent testing ground for the equipment. It is interesting to see how many fail.
I carry a small autopilot for when I am motoring. I also sometimes use the autopilot even if I am sailing when I am relatively close to the shore. With coastal sailing, the winds can fluctuate in force and the the self-steering will react to an increase in force by pointing up, resulting in a slightly zig zag course. Mid-ocean, the winds are steadier, and you are less likely to notice when the boat heads up or down a bit.
I have never tried connecting the autopilot to the wind vane. As the engine would be running, it hardly seems worth it to save a bit of battery power.