There is a definite learning curve to overcome when using a mechanical self-steering windvane for the first time. A vane can’t follow a compass heading and a boat’s sails must be balanced for it to work well. Because of this, many sailors new to vanes get discouraged and abandon them. This is a shame, as a windvane is an ingenious bit of engineering. Simple and robust, it is often described by proponents as the single most useful piece of gear on a bluewater boat. It works well on its own and can be an invaluable backup to an electronic autopilot.

Arcturus, our 1966 Allied Seabreeze yawl, has a Cape Horn servo-pendulum windvane, which operates on the same principle pioneered by Blondie Hasler back in the 1960s. A vertical tube supports the air vane, which pivots on a horizontal axis at its base. The leading edge of the vane is set facing into the wind, and when the boat veers off course, the wind catches one of the vane’s flat sides, causing it to topple over. A linkage inside the vertical tube transfers that force to the steering oar, rotating it like a rudder on a vertical axis. The oar, which is also hinged at the top to pivot on a horizontal axis, is consequently deflected sideways by the water flowing past it. This force–which is considerable, especially at speed–is transferred via a steel stock in a horizontal tube mounted through the boat’s transom to a small steering quadrant mounted inside the boat. Control lines run from this quadrant to the boat’s main steering quadrant or can run directly to a wheel or tiller.

All modern servo-pendulum units work on this principle, though most have steering control lines running directly from the steering oar to a boat’s wheel or tiller. In some cases, the steering oar is connected to an independent rudder. The genius of the system is that it harnesses the power of the wind and sea to steer a boat. The harder the wind blows and the faster the boat sails, the more force there is to bring the boat back on course when it starts to wander.

Balancing act

My wife, Mia Karlsson, and I (and our good friend Clint Wells) got our own taste of the windvane learning curve during a transatlantic passage last summer. We soon realized that maximizing a vane’s efficiency requires a slightly different understanding of sail trim. On a fully crewed racing boat, sail trim is optimized for very specific wind angles to maximize boatspeed, requiring constant trim adjustments and precise hand-steering. On a shorthanded cruising boat, maintaining that kind of efficiency is not sustainable. To get our windvane working well, we sacrificed boatspeed and sought a “median” sail trim that allowed the vane to more easily compensate for minor changes in wind speed or direction.

In practice, this means a boat should often be slightly under-canvassed. During our passage, I found Arcturus could maintain reasonable speed off the wind with surprisingly little sail area. Upwind, the genoa and mizzen were usually enough to make 5 knots, and weather helm was nonexistent. Downwind, we experimented with the large drifter set on the spinnaker pole and the full mainsail vanged out on the other side, sailing wing-and-wing. The boat was fast for sure, but to my delight, we found we could sail almost as fast with only the 100 percent jib and two reefs in the main. We slept much better at night knowing Arcturus would remain stable if the wind got up, and the windvane required far less attention.

When setting the vane, our first check was always sail trim. “When in doubt, let it out.” It is amazing how far a mainsail can be eased before it starts to luff, and the influence an over-trimmed main has on helm balance and vane performance is substantial. If easing the main right out to the shrouds did not ease the helm and help the vane settle down, we knew it was time to reef—our second mental check. No self-steering device can overcome a poorly balanced boat.

Hand-steering while trimming sails quickly reveals the influence of sail trim on helm balance. Experiment. The goal should be to steer with your fingertips. The easier it is for you, the easier it will be for your vane to steer. Fundamentally, setting up your boat for windvane steering involves nothing more than learning your boat. Most experienced ocean sailors will agree that learning to use a windvane actually makes you a better sailor.

When a boat is perfectly balanced, a windvane’s steering control lines should be tensioned equally. We put whippings on each of our lines to measure this, and control-line tension was the third point on our mental checklist.

It is good practice to initially set the control lines equally. Adjusting the tension affects weather helm. Slightly over-tensioning the windward control line relative to the leeward line, for example, will hold the helm down in order to counter a boat’s natural tendency to round up. In practice, we found this was often necessary, but you have to be careful. If you have to put too much “English” on the control lines to maintain course, you’re only masking an imbalance somewhere else. The control lines should remain within an inch or two of a neutral setting. Any more than that, and it is time to make other adjustments. Usually, you’ll need to reef.

Once a boat is properly balanced, a vane should steer a straight course at least as well as most human helmsmen. Arcturus stayed within 10 degrees either side of our intended course when we had our vane working well.

This may sound obvious, but if our boat is balanced, the sails are reefed down, the control lines are set correctly, and the vane is still not steering where you want, you need to check its alignment. The vane steers to the apparent wind, so slightly adjusting its angle relative to the wind will immediately affect the course.

Refinements

The action of air vanes on most mechanical self-steering units is dampened by a counterweight set below the vane’s pivot point. This helps keep the boat from yawing excessively, as the air vane is never truly edge-to-the-wind for more than an instant. In effect, it is the equivalent of the damping control found on most electronic autopilots.

On the Cape Horn unit, an adjustable bungee cord supplements the inertial force of the counterweight and allows you to fine-tune its effect. Experienced users often add such cords to the counterweights on other types of windvanes. In lighter airs, we tightened our bungee cord to prevent the vane from over-correcting. The less sensitive the vane is to the wind, the less force it exerts on the steering oar and helm–and vice versa. Conversely, when the wind picked up, we eased the cord to increase the vane’s power. On a true beam reach, generally the most challenging point of sail for a windvane, the control lines should be set very close to equal. We often found that minor adjustments to the bungee damping control were most effective when dialing in a course on this point of sail.

Another way we could fine-tune the performance of our unit was to change air vanes. In light air, we used a lightweight vane made of nylon fabric stretched over a thin steel frame. In stronger winds, we used a heavier solid aluminum vane. Other manufacturers also offer air vanes of different weights, or you can fabricate your own.

The biggest drawback to a windvane, once you’ve mastered it, is that it only steers to the wind. You can, however, fit a small electronic tiller pilot to “steer” the air vane in place of the wind. In this way, the vane can steer a compass course and keep you off the helm when conditions are calm. The tiller pilot, as it controls only the air vane, uses a fraction of the power consumed by a conventional electronic autopilot.

Conclusions

During our 2,000-mile voyage, Mia, Clint and I only hand-steered for fun. So long as there was wind to keep the sails full, the vane had no problem maintaining a course upwind or down. It even steered running under bare poles while we did foredeck work. During the crossing from Canada to Ireland, about 1,000 miles offshore, we sailed for a couple days downwind under a symmetric spinnaker with the vane doing all the work with barely a tickle of apparent wind noticeable at the stern.

Most sailors name their windvanes. On Arcturus, it took time to get acquainted with ours. Mia and I got married in Sweden only two weeks before our departure from Canada, and the voyage was to be our honeymoon, a delivery cruise to Scandinavia. We finally christened our vane “Sune-the-Driver” (pronounced SOO-neh), after the white-haired gentlemen who drove us away from the church in his vintage Volvo. Offshore, it was Sune-the-Driver who steered us home.