Self-Steering—with No Strings Attached

Part II: Our journey through the realm of windvanes wraps up with trim tabs and auxiliary rudders


Fleming’s auxilliary-rudder model uses a servo-pendulum system linked to an auxiliary rudder. Courtesy Of Fleming

Although servo-pendulum windvanes, which we covered last month (“Sorting Out Self-Steering Options,” January), remain the most popular type of windvane self-steering system, other designs fill an important niche. Some sailors prefer the direct mechanical linkages–so there are no steering lines to the cockpit–that these other systems feature, and some boats simply won’t work well with servo-pendulum designs.

The alternative designs fall into two categories: trim-tab systems, which work with the boat’s rudder, and auxiliary-rudder systems, which steer with their own built-in rudders. These windvanes feature the same three major components as the servo-pendulum designs we reviewed–sensor vane, underwater course-correction unit (servo-rudder), and linkages.

The servo-pendulum windvanes we reviewed use low-stretch lines led through blocks to connect a vane’s powerful pendulum-rudder to the boat’s tiller, wheel, or steering quadrant. In the trim-tab and auxiliary-rudder systems we’ll look at, the linkage to the boat’s rudder or auxiliary rudder is mechanical, an arrangement that avoids problems of excessive stretch, chafe, or incorrect tension but can introduce corrosion problems and linkages that have their own complications. For owners of center-cockpit boats, the direct linkage eliminates the need for long lines running across the afterdeck.


The boats that stand to gain the most from such systems are ones with hydraulic steering or with wheel steering having four or more turns between stops, ones with high freeboard, or ones that are otherwise incompatible–or less compatible–with servo-pendulum steering vanes. In most other cases, servo-pendulum vanes offer undeniable advantages.

Trim Tabs
Like the flap on an airplane wing, a trim tab is the trailing edge of a larger foil–in our case, either the ship’s primary rudder or an auxiliary rudder. When directed by the vane sensor, the trim tab turns. As long as the boat is moving fast enough, the lift provided by the change in water flow provides the force necessary to move the larger rudder.
A trim tab should be balanced (meaning that its leading edge is forward of its axis of rotation), so that it’s easily driven by the vane sensor, and appropriately sized, so it provides sufficient power to control the rudder. Friction at its pintles and gudgeons should always be minimal.

Few of the trim-tab units we’ll review can be lifted easily out of the water or quickly removed from the rudder, a common shortcoming among both trim-tab and auxiliary-rudder systems. This not only makes the underwater unit more difficult to maintain and more vulnerable to damage, corrosion, and fouling; it also can add an unexpected twist when backing a boat under power. The biggest drawback of a traditional trim tab is that it can’t produce the same amount of power as a pendulum rudder of the same size, so a boat’s sail trim and helm balance become even more important. Heavy-displacement vessels with unbalanced rudders can make the trim tab’s job particularly tough.
For emergency steering, you can use a trim-tab system that connects to the main rudder as long as the rudder to which it’s attached is intact and is still capable of turning (as in the case of a broken steering cable, for example).


Saye’s Rig: The Saye’s Rig is one of the few production windvanes that still uses a flag- type vertical-axis vane sensor, which functions like a masthead wind indicator, rotating so that its leading edge always points into the wind. A vertical-axis vane, however, can’t generate as much force as a horizontal vane of the same size. Nevertheless, the Saye’s Rig manages to provide an efficient steering impulse with a powerful wedge-shaped cloth vane. One reason the Saye’s can get away with a relatively small vertical-axis vane is that the trim tab it commands is a very small, well-balanced, servo-pendulum rudder, which provides far more power than a conventional trim tab of the same size. The linkages are simple: The pendulum rudder’s shaft passes through an extended U-shaped tiller arm attached to the boat’s rudder. The longer tiller arm, the more power it provides, so it works best on boats with inboard rudders. The simple design allows for durable construction in 316 stainless steel and cast bronze.

Auto Steer: This system, made in England, is easily adapted to boats with outboard rudders. Through a simple acetal-plastic and silicon-bronze universal linkage, the horizontal-axis sensor vane connects to a custom-sized trim tab made of wood and stainless steel attached to the boat’s rudder. The Auto Steer trim-tab vane is made of LM25 aluminum castings and 316 stainless steel, with insulation between dissimilar metals to minimize galvanic action. The manufacturer, Hydra Engineering, doesn’t recommend the system for heavy-displacement boats over 35 feet. For larger boats, the company makes a more powerful servo-pendulum unit.

Auxiliary Rudders
An auxiliary rudder, because it’s smaller and often better balanced than the boat’s main rudder, reduces the resistance to the steering impulse, which, in the models we’ll look at, is delivered by either a trim tab, the vane sensor, or a servo-pendulum rudder. Because they operate independently of the boat’s rudder, auxiliary-rudder systems are compatible with hydraulic steering. They are also capable of serving, in a limited way, as an emergency rudder.


When selecting an auxiliary-rudder system, carefully consider proper rudder size and how it’s attached to the boat. Although the boat’s main rudder will be used to compensate for weather helm, the auxiliary rudder still needs to be powerful enough to steer the boat before a high quartering sea. Attachment points at the hull should be well reinforced, and the rudder shaft should be rugged. These details are particularly important if you need your auxiliary rudder to serve in an emergency. Heavy-displacement boats that are difficult to steer can test the limits of an auxiliary rudder that’s required to steer in an emergency.
Auto-helm: This system features a large, wedge-shaped, horizontal-axis vane sensor made of 6061 T6 anodized aluminum that’s linked to a trim tab on an auxiliary rudder. The rudder mounts and underwater fittings are made of 316 stainless steel. The easily turned trim tab helps amplify the relatively weak wind impulse into a force that can drive the auxiliary rudder. The unique cable linkage (similar to a bicycle’s brake cables, but with smooth Teflon sheaths) between the sensor vane and the trim tab allows a great deal of flexibility in where you mount the vane. The vane can even be mounted on top of davits, which often interfere with other designs. These cables must be kept clean to ensure minimal friction. The sensor vane can also be used with a custom trim tab attached to an outboard rudder, in a manner similar to the Auto Steer system.

Hydrovane: This auxiliary-rudder system uses a horizontal-axis vane sensor to drive a well-balanced, solid-nylon rudder on a stainless-steel shaft. To accomplish this, the Hydrovane uses a relatively large sensor vane, a semibalanced rudder, and a variable ratio in the vane-to-rudder linkage. This adjustable linkage–with three separate positions for light, moderate, and heavy air–controls the mechanical advantage that the vane has over the rudder, or how far the auxiliary rudder will turn as the vane tilts. Another feature is an adjustable axis on the sensor vane, which allows you to further match the steering impulse to wave and wind conditions.

Construction of the Hydrovane unit is cast LM5 anodized aluminum, silicon bronze, and 316 stainless steel. An endless line to the vane allows you to position the vane relative to the wind from the safety of the cockpit. The Hydrovane’s rudder can be easily centered for maneuvering in port or completely removed by simply pulling a pin.


Fleming Global Auxiliary Rudder: For boats that aren’t suited to its standard system, Fleming links its servo-pendulum windvane directly to an auxiliary rudder. Its auxiliary-rudder system uses the same high-quality stainless steel (2205 duplex-cast castings and 316 tubing) as the standard version we reviewed last month. It also carries the same array of stainless-steel bearings in Delrin races to reduce friction. An endless line led to the cockpit permits infinite course adjustment. Of the auxiliary-rudder systems we compared, the Fleming is the only one that has a hinged auxiliary rudder with overload protection. A shear pin offers impact protection, and the hinge makes it easy to lift the rudder out of the water. The servo rudder, which also has a shear pin for impact protection, easily swings out of the water–like the standard Fleming. You can also simply remove the servo-pendulum part of the system by undoing one bolt.

The linkage between the servo-pendulum rudder and the auxiliary rudder has a variable power ratio. This allows you to adjust how much rudder deflection there is for a given course error and lets you fine-tune steering characteristics to suit a variety of wind and sea conditions. A clutch system allows you to engage or disengage the servo blade under load.

Windpilot Pacific Plus: Windpilot takes its Pacific-series servo-pendulum vanes one step further by using a servo-pendulum system to drive an auxiliary rudder. The combined unit features the same construction details as the Pacific series: infinitely adjustable course setting, bevel-gear linkage between the vane and pendulum rudder, a lift-up pendulum rudder, and low-maintenance sleeve bearings. The body construction is high-grade AlMg5 aluminum-alloy castings. The linkage between the servo-pendulum and the auxiliary rudder is a bronze bevel gear that’s easily disengaged. Although you can easily fold up the servo-rudder, the auxiliary rudder is designed to stay in the water. You can, however, quickly center the rudder when the servo-pendulum rudder is in the raised position.

Darrell Nicholson is a Cruising World associate editor.