Windvane self steering

By its very nature long distance sailing can entail many tedious hours at the helm. So why not  let the wind do the work and bring you welcome relief?


Let’s face it, of the many delights of sailing, steering is one task that palls the fastest. Yes, it can be exhilarating at times, even satisfying when, say, edging a sailboat to windward in light airs or overhauling a larger boat. But, as most sailors soon learn, it becomes pure torture to be stuck at the helm on anything more than a short passage. Liberation from such drudgery allows you to engage in other more constructive or entertaining activities – clearly a huge boon to offshore sailors, usually with much to attend to in the way of other duties. Of course, you could fit an electric automatic pilot. You simply switch them on and, by virtue of sophisticated computational algorithms, they will more or less do their duty. Unfortunately, such convenience is not without its downside. They are also quite noisy, can be unreliable, and are greedily extravagant with your meagre reserves of electricity.

On the other hand, wind driven self-steering gears are silent, indomitable in their reliability, and consume no electricity whatsoever. Hardly surprisingly, they are the first choice for ocean voyagers who must conserve their resources, but would also serve coastal sailors more than most fully appreciate. In the debit column we must acknowledge their higher initial costs and the greater responsibility required of the crew to have their sails set and trimmed properly. But… hey!...that’s nothing more than a call for good seamanship, isn’t it?
Anyway, this isn’t a head-to-head contest between electronics and mechanics. There’s no competition. Windvane gears won’t work in the absence of wind and there should be no shortage of electricity when your engine is running. In common with many offshore yachts, my 40-footer Shindig carries both: the tiller pilot doing duty in the very dreariest of steering conditions – a flat calm – and the windvane minding the helm when under sail. Electronic autopilots are usually controlled by compasses (these days almost invariably fluxgate compasses) whereas windvane gears sense the wind direction and keep the boat’s head at an angle relative to it. More correctly, they sense the apparent wind, which is the wind as experienced aboard the boat – a combination of the true wind and the forward progress of the boat itself.

Between the actions of the two types lies an important distinction, each with inherent merits and traps. The compass-controlled gear will deliver the kind of straight line course you can mark on your chart. This makes the navigator’s job a breeze. Not so the windvane which will duck and weave with every variation in wind direction and strength. On the face of it, the latter might appear a serious flaw until you remember that we trim our sails according to the wind so there are very real benefits in reacting to its minute-by-minute inconsistencies. Indeed, because it never relaxes its concentration, a windvane will often take a boat to windward more surely than a human hand.

How windvanes work

Much of the development of windvane steering for yachts arose from singlehanded sailing. Way back in 1936 the French painter, Marin-Marie used a windvane to cross the Atlantic in his motor yacht Arielle. History doesn’t relate how well it worked. The first recorded use on a sailing boat was in 1955 when Ian Major also crossed the Atlantic in his yacht Buttercup. Again, not a lot is known about its efficiency.

Perhaps the true dawn of windvane technology arose in the late 1950s with preparations for the first Observer Singlehanded Transatlantic Race (OSTAR) in 1960. Among the five competitors were Colonel H.G. (Blondie) Hasler – war hero, instigator of the race and later credited with being one of the inventors of ‘modern’ self steering gears – and Francis Chichester with his 39 footer Gypsy Moth III, then thought to be about the largest yacht a man could handle alone. How wrong they were!

Direct action gears

To steer Gypsy Moth III while he rested, Chichester had fitted a rotating mizzen, fashioned like a gigantic weathercock and connected directly to the steering. It was operated by putting the boat on course, allowing the vane to feather into the wind, then tying off the tiller lines to the tiller as shown below. With uncharacteristic whimsy, he called it Miranda – no doubt with deliberate irony since Miranda is the heroine in Shakespeare’s play ‘The Tempest’.
Despite her size and theatrical associations, Miranda (see below) was said to be a poor performer, lacking both power and sensitivity. The friction in the whole system can only be imagined, but that wasn’t the only problem, as we shall touch on soon. For now, let’s accept that the output from any direct action gear is unlikely to be enough to overcome the loads found in most primary steering systems.

The search for sensitivity

The main problem Francis Chichester encountered with Miranda is inherent in all vanes rotating about a vertical axis. And it’s easy to understand why. Let’s say the boat’s head falls to leeward just 5°. Will the vane sense such a small variation in course? Well an efficient aerofoil might but not a sheet of plywood and certainly not Miranda’s flapping trappings. Given the heaving world in which boats exist, and remembering how any output might be lost to friction – not to mention the inevitable slack in steering lines and other linkages – such a vane stands no chance. The reality is that a boat must stray grossly off course before a vertical axis vane even recognises that anything is amiss.

So it was clear that some means of obtaining a greater vane output was needed. The first answer to emerge was to pivot the vane horizontally. Now, if the wind pressed even slightly on one side, the vane will be pushed over. With this arrangement, the vane’s rotational output is no longer limited by the yaw angle. It becomes both stronger and more emphatic.
Indeed, in practice, horizontal axis vanes proved too powerful and twitchy. In strong winds the vane would slam from side to side, inducing horrendous over-steer. To overcome this, a modern gear has its axis inclined away from the wind at about 15-20°. This has the effect of progressively feathering the vane as it is pressed over (see below). This dampens the output at the extremes of vane rotation, thereby reducing the associated course oscillations. With an inclined axis of 20° the vane’s angle of attack becomes zero at 30° of deflection. Incidentally, heel angle must be added to the axis angle, so an inclined axis vane becomes significantly less powerful if the boat is hard pressed. One design by Dutchman Jan Alkema counters this by having the vane pivoting at the top.

With horizontal vanes, the power output is constant over the whole deflection range. This makes them powerful but rather too violent in their actions.

Indirect action

Steering calls for a power source, whether from man or machine. There’s no arguing with that. Boats live on the interface between two turbulent fluids – air and water – which continuously buffet and toss them about. Even on the best trimmed boat, the steering loads can be high – certainly more than could be consistently overcome by the puny output from a windvane acting alone. To achieve efficient self-steering, a source of greater power is needed. Fortunately, there’s one to hand: the flow of water past the hull.

Let’s go back to that 1960 OSTAR. While Francis Chichester was wrestling with the lacklustre Miranda, Blondie Hasler on his turtle-decked Folkboat Jester had adopted a trick from aircraft design. On the trailing edge of Jester’s transom-hung rudder was a small trim tab, controlled by a windvane that Hasler could adjust from the midships hatch. Whenever the boat strayed off course, the vane turned the tab and the waterflow acting upon it pushed the rudder blade over to make the appropriate correction (see below). This could be described as having a small auxiliary rudder that steers the larger main rudder which in turn steers the boat. In this context, it’s the simplest form of servo assistance. The relatively meagre output from the windvane – which in no way could turn the rudder itself – harnesses the much greater energy of the waterflow to do the work on its behalf. This process of amplification means that the windvane can be much smaller. Oddly, Hasler never went the horizontal vane route, clinging to vertical axis vanes in all his later, and considerably more sophisticated, designs.


Still more power

The story remains with Blondie Hasler. In about 1964 he was responsible for the development of a new and immensely powerful type of self-steering gear that was to form the basis of all but a few designs that survive today.

And it was an inspired bit of thinking. Recognising the limitations of the trim tab, he looked for a new way of harnessing the hydrodynamic energy locked into the waterflow. He noted that when he held an oar over the stern with the blade aligned with the flow, it produced a little drag but no hydrodynamic force. But if he twisted it slightly to give it even a small angle of attack, a powerful force developed, tending to lift the blade towards the surface – a pendulum action, from which the term ‘pendulum servo’ was born.

Surely, he concluded, by taking pendulum lines up to the tiller or wheel this robust action could be used to steer the boat. And he was right, as history testifies, but there were problems to be surmounted first. His early experiments produced alarming results. The servo blade slammed from side to side, hard over one way then the other, with the boat yawing wildly in response. To be useful, this essentially brutal principle had to be turned into something better mannered, that allowed a more controlled ramping up of power.
Hasler had been there before with his trim tab gears. He had learned that it’s all too easy to build a mechanical helmsman that knows only two commands – hard-a-port and hard-a-starboard – and now with the awesome power his newly developed pendulum servo blade bestowed, it did so all the more savagely. By contrast, a human crew will take a proportionate view of any course corrections – applying just enough helm to counteract any yaw, gradually reducing it as the boat approaches its correct heading. This is too much to expect from a machine. Yet, he knew that somewhere in the control geometry there had to be a way of introducing a damping effect that would work entirely automatically. He was thinking about mechanical feedback – a very important element in windvane self-steering gear design. There are various ways of gaining feedback. A simple example is commonly used in trim tab gears, and is shown below in the somewhat exaggerated series of illustrations depicting a transom-hung rudder.

Basically, the push rod from the windvane acts on the trim tab’s tiller at a point astern of the main rudder’s axis. The tab’s action on the main rudder causes it to swing towards the push rod, first reducing, then reversing, its angle of attack. In sequence, it goes like this:

NOTE: Although not usually obvious, all modern vane gears use some form of feedback mechanism to tame excessive responses to course changes. Otherwise called ‘yaw dampening’ – a phrase that explains the objective perfectly.

Types of gear – themes and variations

So, we’ve covered the essential principles that lie behind windvane self-steering gears. There might be a few oddball types that lie unheralded somewhere, but the vast majority fall into three basic categories with variations that we’ll touch on later. For now, let’s look at...

Direct action

This concept involves linking the deflection of the vane directly to the steering. Chichester’s Miranda fell into this group but there are no commercial equivalents today. And with good reason, since the efficiency potential of such a crude concept is woeful – greatly surpassed in efficiency terms by other more sophisticated devices.

Direct action on auxiliary rudder

Forget the inevitable friction burdens of direct action on the main rubber. There are gears (or at least one I know of) which ignore the primary steering and instead link the vane output directly to a much smaller auxiliary rudder. The best known of these is the Hydrovane which over the years has earned an enviable reputation among sailors. Here, meticulous engineering has minimised friction and backlash while the auxiliary rudder has been optimised to be both hydro-dynamically efficient and relatively easy to turn.


• Because these are integrated stand-alone units there’s no necessity for steering lines or other linkages to the boat’s primary steering – just a single line to adjust the vanes’ orientation is led forward to the cockpit. This makes such gears an attractive proposition for centre-cockpit boats.
• Very compact
• The main steering can be locked, perhaps so as to remove any weather helm.
• The auxiliary rudder can double as emergency steering if the main rudder is damaged or lost.

• Good engineering doesn’t come cheap.
• Since, the wind is the only source of input power, by necessity vanes are generally larger than on other types of gear.
• Often requires modification to the rudder

Pendulum servo

This category makes up the majority of modern self-steering gears, with a number of excellent examples on the market. The power generated by the pendulum blade is truly awesome. How pendulum servos work is shown right and is easily understood. The sequence goes like this...
When the boat strays off course the change in the apparent wind is sensed by the vane (A) which is pressed to one side or the other. If for example, the boat turns to port, the vane wlll incline in the same direction.
The vane’s action is transmitted by the pushrod (B) to the gears (C) which converts the action from vertical to rotary – thereby turning the pendulum blade (D)
This turns the blade which is swept to one side (again to port in our example) by the waterflow.
The steering lines (E) are led to the boat’s primary steering control – either a tiller, as shown here, or a drum and clutch arrangement on a wheel,


Very powerful. On a delivery trip to the Mediterranean, I nearly lost a finger when I got it trapped by a steering line. Others have been injured by wheels and tillers suddenly swinging or spinning in response to a swerve in course
Suitable for just about any type of sailboat. Their power makes them particularly suitable for larger vessels
Unlike trim-tab gears, the pendulum blade always steers the right way. Indeed, in light airs and on a well-balanced boat, the blade will steer the boat without troubling the primary steering at all!


Steering lines can be intrusive
Expensive ... but worth it

And now to the variations...

The first part of this chapter defines the three core concepts: direct action, trim tab, and pendulum servo. However, there are gears which combine at least two of these concepts – in at least one case all three. For example, the Fleming Auxiliary Rudder and the Windpilot Pacific have pendulum servo blades operating integral rudders. The VectaVane has a trim tab actuating a pendulum servo blade.

Modern windvane self-steering gears rely on a number of separate elements:

• Vanes to sense the apparent wind direction. Vertical axis vanes are still to be found but by far the majority of manufacturers have opted for the more sensitive and powerful inclined axis type. The vane’s inclination is adjustable on some models.

• Linkages. These are usually pushrods, sometimes rotating shafts, and can occasionally be cables. Where the geometry allows it, pushrods or shafts are the preferred choice because there’s usually less friction and backlash – the latter being the slop in any system which can rob it of its sensitivity. Although the linkages might appear to be rather insignificant parts of the whole mechanism, it’s here that the positive damping occurs, so their importance shouldn’t be underestimated.

• Control surfaces. These are acted upon, via the linkages, by the windvane. On a trim tab gear the control surface is the tab itself; on a pendulum servo it’s the servo blade.

• Power output. Trim tabs usually work directly on the rudder blade – whether primary or auxiliary. Pendulum servo gears acting on the main rudder almost invariably use control lines led back to the tiller or a drum on a wheel. This can be a problem on centrecockpit boats where the routeing can be tortuous.

• Other makes also make use of auxiliary rudders. For example, the Windpilot Pacific also makes use a pendulum servo blade controlling its own auxiliary rudder and Scanmar’s Auto-helm makes use of a trim tab to do the same job. As with the Hydrovane, the only connections to the boat are the mounting brackets and the adjustments to set the course. This is undoubtedly convenient but below is something you should bear in mind...

Worth noting...

In heavy weather a ‘standard’ trim-tab or pendulum windvane gear will be steering the boat via the main rudder, and the effect will be proportional to the conditions at that time. An auxiliary rudder gear, on the other hand, has only its own rudder to exert control, and this may not be large enough to keep the boat on track on some points of sailing. To help at least partially mitigate this, it’s usually possible to lash the main rudder to, say, counteract any tendency to round up or bear away, leaving the smaller auxiliary rudder to make minor course adjustments.


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