Introduction to Autopilots

Today's autopilots can do more than steer you straight.

October 4, 2007

Today’s autopilots do more than free your hands and steer your boat in a straight line. They have become an integral part of a ship’s navigation system, working in partnership with your GPS and heading device, either an electronic or gyrocompass, to “learn your boat’s handling characteristics as well as compensate for sea conditions.

The Five Basic Parts of Every Autopilot

Autopilots have five main components. The control head is often chosen for its looks and feel. It’s important to locate it where the helmsman can easily reach it. Larger units serve as navigation control centers, displaying a variety of performance data as well as graphics. When trying one out, make sure you feel comfortable with it. Trying to hit the right button while your boat is bouncing around in rough seas can be a challenge. Some units feature pushbutton-only controls, while others use a large rotary knob to control your boat’s direction. Most systems allow the installation of additional control units throughout your boat as well as the use of handheld units.

Next choose the type and size of the drive system, the electromechanical or hydraulic device that actually moves the boat’s rudder(s). Although it’s possible to order most autopilots with rotary or linear drives, hydraulic systems are simple and reliable, and are used by the majority of today’s vessels. When you turn the helm, you are turning a steering wheel pump that sends hydraulic fluid in one direction or another. The fluid travels under pressurized hydraulic lines from the wheel pump to a cylinder head attached to the rudder shaft. Various check valves typically prevent the rudder, when affected by wave action and the forces of turning, from moving the helm.


A hydraulic pump activated by electrical signals sent from the control head drives the system. Pumps must be matched to the overall volume capacity of the vessel’s hydraulic steering system as well as the boat’s voltage system, so know the displacement value, in cubic inches, of your boat’s system (available from your dealer, builder or system manufacturer). Most pumps for popularly sized boats are 12 volts DC, but larger ones require 24 volts. While a typical pump draws between 3 and 10 amps, power consumption is not of critical importance except in sailboat installations. Today, more and more motor vessels over 45 feet are equipped with power assist or full-blown power steering hydraulic systems. In these cases, a smaller reversible pump or a series of solenoids or servo valves turn the fluid flow off and on.

The heading device is the next key component, a compass of one type or another. Autopilots typically use the fluxgate compass, a relatively simple and reliable device which senses the direction of the earth’s magnetic field by a ring core sensor in a fluxgate coil and transforms into a digital signal. To overcome errors caused by sharp turns or rough seas as well as “dip errors, a phenomena that is more pronounced as you get closer to the earth’s magnetic poles, a number of manufacturers offer a hybrid fluxgate compass or “rate compass. Essentially, a rate sensor limits the effects of pitch and roll, providing more accurate steering. Relatively new, GPS compasses are setting standards for accuracy and dependability and are being used as the boat’s primary heading device. Because they have no moving parts and are virtually maintenance free, they offer superior reliability. More and more larger yachts and commercial vessels are adding these units as a backup to the ultimate heading device, the $20,000 to $50,000 gyrocompass.

Now come the brains. Not long ago, most autopilots could make only basic adjustments for sea state, rudder control and boat speed. But today’s advanced autopilots feature CPUs where the heading sensor and rudder feedback unit send their data and the control unit sends its commands. These mini-computers are able to make use of hundreds of steering parameters, enabling them to deliver optimum performance regardless of sea conditions or the handling characteristics of your vessel. Today’s autopilot “learns as it goes, increasing its accuracy as it becomes accustomed to your boat and senses the conditions you’re in.


Last, but not least, is the rudder feedback device, which tells the autopilot’s computer where your rudder is at all times. This is usually a rotary device attached to the rudder quadrant that transforms the position of the rudder to a digital signal read by the CPU. Unless the computer knows the exact position of your rudder, it cannot steer a straight course.

Onboard Data Networking

Steering you straight in a variety of sea conditions is just the beginning of what autopilots are capable of. Networked to your vessel’s navigation system, your autopilot will not only provide an easier, more accurate way of getting from point “A to point B, but when used properly, it will enhance the overall safety of your vessel’s operation. Consider a man overboard scenario in which your GPS can tell your autopilot to steer back to the exact spot where the incident occurred. Some autopilots are even capable of keeping you pointed straight while you’re standing still by sending signals to a bow or stern thruster.

By sharing data with your GPS and chart plotter, your autopilot will allow you to “point & click your way from waypoint to waypoint. The autopilot’s computer will make adjustments for wind and current by analyzing up-to-the-minute data from your GPS and making the necessary course changes. One must be careful, however, not to become too confident and take your eyes and mind off your immediate situation. Avoid setting your “Go To point to the exact location of a buoy or lighthouse, as this will put you on a collision course with these marks.


The ability of today’s autopilots to “talk to other instruments has been enhanced by the recent introduction of the NMEA 2000 communications and control protocol, which has replaced the old standard NMEA 0183. Its open architecture allows products of different brands to talk to each other in a very fast, precise manner. And, its single network cable provides a true “Plug & Play setup. While not all marine electronics are NMEA 2000 certified as yet, you’ll be ahead of the game if you choose an autopilot that is.

The market leaders, such as Navman, Furuno, Raymarine and Simrad, have their own proprietary network protocol. If you’re considering an all-new electronics package for your boat, there are advantages to sticking to one brand. Each of these market leaders produces high quality autopilots as well as top radars, chart plotters, radios and more. But you’ll want to do your homework and talk with a qualified electronics technician to help you make the right decision for your boat and your needs. Whatever you choose, you can be certain your new autopilot will do a lot more than steer you straight.


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