Choosing and Understanding Self-Steering Gear

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A guide to equipping your boat with an electronic autopilot or windvane: Part I  (published October 2013)

Since the earliest days of long-distance solo or shorthanded sailing, a variety of devices have been invented for holding a boat on her course without the need of a constant helmsman. One of the early—and for many boats, still useful—methods was called “sheet-to-tiller” steering, which balanced the forces on a mainsail’s sheet against a spring or shock cord to steer the tiller in the appropriate direction when the boat would heel and reverse the direction when she would start to round up. This is obviously a delicate balance that required careful and often time-consuming readjustment when a course change or wind shift occurred.

Along with sheet-to-tiller steering came windvanes, which use a variety of methods to transfer a course change into a rudder angle using various paddles or vanes attached at the stern of the boat. Then, with the dawning of reliable electronics came motor-driven electric “autopilots” with a variety of methods for operation and all with the requirement for electric power and various instrumentation sources.

Today, a dizzying array of self-steering gear exists and it’s often difficult to know where to start. Some kits costs more than a small boat, and others can be made or cobbled together from spare parts in a garage. But by understanding the principles, major options, advantages and caveats of the various gear on the market, a prudent skipper can choose the right self-steering gear for his or her boat with confidence, knowing it will suit the boat in all conditions.

MAJOR CONSIDERATIONS
The major questions and choices when faced with the purchase of new self-steering gear are: What conditions the unit is expected to perform in; what are the possible failure modes, how to recover from them, and how to detect or prevent them when underway; whether to get an electronic unit, windvane or both; where to mount the components and how to attach them to the boat; and last but not least, how much should ongoing maintenance and the expected service life of the gear be considered?

I’ve listed the options in this order because the most important thing about self-steering gear is whether or not it suits the conditions it is expected to operate in, including whether or not it is a good match for the vessel. The decision between an electronic autopilot and a windvane can only be made when a skipper decides these other issues first. After that, the decision becomes a technical one between models and options.

In order to help the skipper understand which equipment makes a good match for what conditions and vessel, it’s helpful to go into some detail on the various components and options available. So in this first of two articles on the topic, let’s dive more deeply into the realm of the electronic autopilot.

WHY CHOOSE AN ELECTRONIC AUTOPILOT?
Since ships started installing electrical equipment onboard, the electronic autopilot has become a go-to self-steering device for both sailors and powerboaters alike. Combined with an electric or optical compass, all an autopilot needs to keep a boat on a constant magnetic heading is electric power. With the advent of data networks aboard, wind and GPS instrumentation can be combined with the autopilot to steer to waypoints, maintain a constant wind angle like a wind vane, steer specific patterns in the sea (e.g. circles, grids, or holding position for fishing or search-and-rescue), and perform many other clever tricks that a simple wind vane cannot do. And, of course, the electronic autopilot can do all of this whether or not the wind is blowing. As a result, electronic autopilots are nearly ubiquitous on most modern sailboats.

Electronic autopilots require three main components: a drive unit, a compass—usually called a “fluxgate compass” or for short, “fluxgate”—and a processing module, or “brain”.  The processing module may or may not require a separate display and control interface, or it may incorporate it directly, and any or all of these components may be included in the same physical device. Make sure your autopilot package includes all of them though, or you may have to spend significantly more money later.

There are two major categories of electronic autopilots and quite a variety of options within those categories. The differences are crucial to your boat and to the system’s reliability, so it pays to at least take a cursory glance at some of these important details.

TILLER AND WHEEL PILOTS
The most common category on small boats, a tiller or wheel pilot is an electronic motor attached to either a sliding lever or a spinning gear that is connected to the ship’s own tiller or wheel to physically move the boat’s rudder. Simple to install and easy to understand, these are typically the least expensive devices and are usually only reliable up to a certain amount of rough sea conditions, after which they often don’t have the power to keep handling the helm. In addition, they are constantly exposed to salt spray, and attachment and dismounting results in a certain amount of wear and tear over time. However, they are simple to understand and use and for smaller boats are often perfectly sufficient as long as the expectations on the system are reasonable. There are a few wheel units these days that have been used with success in heavy seas offshore, but they are rare and require a well balanced or easily helmed boat and are subject to limitations on rudder size and force.

Tiller and wheel pilots often, but not always, integrate the processing module and the drive unit in the same housing, simplifying use even further. They do not, however, offer anything in the way of redundancy over and above a ship’s own steering system, as they are dependent on that very system to perform their job.

Often, a skipper will fit a tiller or wheel pilot as a backup to a windvane when they decide that a wind vane is most suitable for their vessel.

BELOWDECKS PILOTS
The common “upgrade” on a tiller or wheel pilot is to affix a control system belowdecks, often directly to the rudderstock itself as a backup to the ship’s main steering cables or tiller. This provides a degree of redundancy as well as protecting the main drive unit from the elements. In addition, because the system is permanently mounted, a larger and more durable motor and connection system can be fitted if desired, further increasing the reliability of the installation.

There are a variety of methods to attach these pilots to the rudderstock. The one you choose will likely be dictated by the type of steering your vessel already has, although you may have some choices between a few similar options.

For sailboats, the most common drive types are either rotary gear drive or linear drive. As the name suggests, rotary gear drive mechanisms have a motor with a reduction gear that, through a heavy chain, spins another gear affixed to the rudder shaft, similar to how a bicycle’s pedals spin the rear wheel through a pair of gears and a chain. Linear drive units work like a tiller pilot in that they extend or retract an arm that is affixed to a steering quadrant belowdecks. These can either use the existing quadrant on a rudderstock, or a special quadrant or lever arm can be bolted to the rudderstock specifically for the autopilot, like a miniature tiller belowdecks. Rotary gear systems are typically used with ships that have worm gear steering or similar solid-shaft coupling between a wheel and the rudderstock. Linear drives are more commonly used with cable steering.

There is usually only one option for boats with hydraulic steering, and that is an electronic hydraulic pump controlled by your autopilot. These can require special care during installation depending on if the existing system has proper backflow valves to allow for secondary control or not, and may require interlocks to be installed to prevent simultaneous operation of both hydraulic drivers at once. This is beyond the scope of this article though, so consult a knowledgeable steering gear installer for assistance with your particular hydraulic setup.

INSTALLATION CONSIDERATIONS
Autopilots require careful mounting consideration, as the forces involved can be tremendous. Since modern belowdecks electronic pilots turn the main rudder directly they are subjected to the full force of the rudder, which, on a downwind run in heavy seas, can be severe. The mounting and rudder attachment for the drive unit is therefore critical and can involve construction of new structural framing, modification of the rudderstock to handle the additional loads or other significant rearrangements of existing equipment.

Mounting the processing module is less critical, but the display units definitely need to be accessible from the helm, and often, to maximize use of the self-steering gear, a belowdecks display and control station can duplicate what is at the helm.

Something to keep in mind with electronic autopilots is that, given the forces involved, they can require a substantial amount of energy to operate. As the seas get heavier, the unit has to work harder, which means the energy used by an autopilot increases. It is important then to pay close attention to your energy supply early and to monitor it more often as the seas build.

COMMON FAILURE MODES
Electronic autopilots, while often quite reliable, are still mechanical and electrical devices and as such, have failures. Apart from the obvious need for a continuous and copious electrical power supply, they work with very delicate compass sensors and many types of drive units can be subjected to the wear and tear of every rudder movement whether they are in use or not. A failure in any one of these components can render the autopilot unable to operate, and failures in fluxgate compasses tend to be more common than manufacturers would like to admit. Also, wiring itself is subject to corrosion, accidental disconnection and chafe. All it takes is for a single control or power wire to become disconnected at the wrong time, say in heavy wind and a following sea, or when close to and passing a large vessel in a narrow channel, and the boat can be put in a dangerous situation very quickly. Thus, a prudent sailor treats the electronic autopilot like any other piece of gear and plans for failure while maintaining the equipment to the fullest.

One surprising failure mode I have had the misfortune to observe firsthand is with a hydraulic autopilot that was a separate system from a hydraulically steered boat. The systems worked perfectly when used independently and offered 100 percent redundancy in control—at least, as long as the boat had power and the rudder remained intact. But when the autopilot was engaged and the helm was touched by someone, the two immensely powerful hydraulic rams fought each other and the resulting back and forth vibration and side loading destroyed a rudder bearing in very short order. So it pays to have interlocks installed when other hydraulic steering systems may be in place simultaneously with a hydraulic autopilot.

Look for Part II in the November issue of BWS where we will cover windvane self-steering in detail, and consider how to best determine what you should be equipping on your own vessel.

Daniel Collins, an ASA certified sailing and navigation instructor, amateur extra class radio operator and small boat racer, enjoys experimenting with marine electronics. He is also actively involved in community-driven social change. Email him at daniel@oddasea.com, or read his blog at www.oddasea.com.

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Author: Daniel Collins

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