How Autopilots Work

If you've never spent quality time on autopilot, you're in for a treat. First, here's a primer on what's involved.

17th February 2012.
By Lenny Rudow

Autopilots seem like they should be so simple: you press a button or two, and the boat goes in a straight line. Big deal, right? If only life were that simple—unfortunately, there’s a whole heck of a lot more that goes into autopilots and how they work.

What’s that you said? You don’t really need an autopilot in the first place? That’s what many boaters (myself included, at one time) think until they actually get to run a boat equipped with an autopilot for a season or two. If you’ve never captained a boat that has an autopilot, you just don’t know what you’re missing. You’ll be freed from manipulating the wheel for hours at a time during long cruises, you’ll save time and fuel because in most cases the machine can hold a straighter course than any man, and your hands will be available to work the electronics or grab a drink. If, that is, the autopilot works correctly. It’ll have to fight currents, waves, and wind without losing its way. It’ll have to make friends with your steering system. And in many cases, it’ll also have to learn how to play nice with your electronics systems. That means an autopilot needs to have several different components, all working together in conjunction.

The essential elements of the Garmin GHP 12 autopilot.

Since the autopilot is taking over the steering job of a human being, it’s helpful to think of it in terms of a person’s physical make-up. The first part of the system is its muscle-power, its hands and arms—the drive unit. Naturally, just how strong your unit needs to be depends on how large and heavy your boat is, and what kind of steering system it has. In the case of a small sailboat up to 10,000 pounds or so, your unit’s muscle can be as simple as a “linear arm,” a unit that merely pushes and pulls a tiller from side to side. Sail and powerboats with mechanical steering systems will need either a mechanical linear or rotary drive, which operates the steering system with an electric motor. And if you have a boat with hydraulic steering, the brawn comes in the form of a hydraulic drive pump which mounts to the steering arm.

All of that muscle-power, of course, needs a brain to keep it in control. This brain, the second major component of an autopilot system, is commonly called the control head or control unit. It’s your interface with the steering system, which allows you to tell the boat where to go. In many cases, it also allows you to pre-program helpful directions; some units have dedicated trolling patterns for anglers, or the ability to detect (via networking) and follow specific bottom contours.

An autopilot control head from Simrad.

In some cases, the control head may be split between a black-box brain that mounts out of sight, and/or a dash-mounted unit with an LCD screen. In some other cases, a remote control gets added into the mix. One or all of these intelligent items may also be hard-wired into your main electronics system, as long as all of the gear is networkable, and is either built by the same manufacturer or is NMEA 0183/2000 compliant. Just how smart is this brain? The latest and greatest autopilot control heads are actually quite advanced, armed with adaptive software that can even “learn” how your boat reacts to different sea conditions and speeds, through time.

Think of the third main component of the autopilot system as the eyes; without being able to see where the boat is going, the brain can’t tell the muscle which way to turn. These eyes can come in the form of a heading or compass sensor, a rate compass, and/or a rate gyro. Depending on the quality (read: cost) of the unit, it may sense not only direction, but also pitch and yaw, and rate of turn. This allows for course errors to be recognized and corrected before most people would even be aware of them. In many cases these electronic “eyes” will be a separate, dedicated unit which gets mounted along the centerline of the boat away from the control head. But in a few systems, the heading sensor is built right into the brain.

Naturally, there may be a need for some other pieces and parts to the system. Many require a rudder feedback sensor, which tells the control head where the rudder (or drive unit) is at any given time. Some systems offer bits and pieces like key-fob style wireless remotes, or unbalanced valve kits. And in a few situations (small tiller-steered sailboats, in particular) the different components can all be contained in a single package, attached to the tiller arm.

The bottom line? These units aren’t nearly as simple as you might think, and there’s actually quite a bit of confusing complexity to consider when it comes to how an autopilot works. But there’s one thing that shouldn’t be confusing at all: if you think you don’t need an autopilot, the chances are you’ve never had one.

Popular marine autopilot manufacturers include:

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- Lenny Rudow



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About the author:

Lenny Rudow

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Lenny Rudow is Senior Editor for Dominion Marine Media, including Boats.com and Yachtworld.com. With over two decades of experience in marine journalism, he has contributed to publications including Boating Magazine, Marlin Magazine, Boating World, Saltwater Sportsman, Texas Fish & Game, and many others. Lenny is a graduate of the Westlawn School of Yacht Design who has won 28 BWI and OWAA writing awards.
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