Selecting an Autopilot

How They Work
Autopilots consist of three main components: a heading sensor, logic and power circuits, and a drive mechanism. Advances in electronics have enabled very inexpensive autopilots to have similar sensors and logic to the most expensive autopilots we sell. The drive mechanisms vary most among autopilots.

Operation is simple: you put the vessel on the desired heading, hold the course for a few seconds, press AUTO, and release the helm. The autopilot will lock the course in memory, and will respond with helm corrections to keep your boat on this course. Modern autopilots have various methods of maintaining a more accurate course than their predecessors: auto-trim, auto sea-state, and integration with GPS or Loran. See Glossary for details on these functions.

What autopilots do best:
Autopilots are outstanding at holding a steady course in light to moderate conditions with minimal helm movements. They do not get tired like their human counterparts, and have an infinite attention span. They will open up opportunities to use your boat that would otherwise be missed due to lack of crew, lack of interest, or lack of time. And because they steer so accurately, they will save fuel and get you to your destination faster, especially when interfaced with a GPS.

What autopilots have difficulty with:
When it is difficult for you to steer, an autopilot will generally have similar problems. This is true when a sailboat's helm is not balanced due to the wrong sails, when the boat is yawing in following seas, or when the spinnaker is making the boat round up.

Showtime, our company powerboat, is a traditional Northeast bass boat design and she really yaws when going down seas. The autopilot seems to magnify this yawing, since it cannot anticipate the waves like a helmsperson can. We find that by changing our speed, we can get Showtime to work with the autopilot in waves, but we generally resort to hand steering.

Autopilots cannot see, so they cannot avoid obstacles or other vessels. You must, as always, maintain a watch so that you do not end up on the beach.

Autopilots cannot hear the cry of "Man Overboard!" and cannot return to pick up a victim. If you are single-handed, you cannot afford to go over the side-when using an autopilot or at any other time!

Autopilot Reliability and Longevity-Read this!
Because we operate our own repair center for electronics, and because we repair a lot of our customers' autopilots, we've learned quite a bit about what works, and why things fail. By sharing this information with you, we hope you can avoid the inconvenience of having to have your autopilot repaired.

Probably the biggest problem with autopilot reliability is that long-distance sailors frequently buy small, cockpit-mounted autopilots, then expect them to operate flawlessly during a multi-year cruise. When their autopilots need repair, and they will need repair eventually, our customers find themselves in a location where it is difficult or impossible to get the pilot serviced. Since it is common to sail short-handed, and to depend on the autopilot for much of the steering, it can ruin a cruise when the pilot fails.

How to Select an Autopilot

In addition to boat length and displacement, there are three aspects of boat performance to consider when selecting an autopilot. One is the heaviness of the helm. How much force does it take to hold the helm when going upwind in a blow? Remember that a tiller-mounted pilot is trying to steer about 12" away from the axis of the rudder. The second aspect is how fast the helm needs to be adjusted. Downwind, autopilots have to throw the helm over to counteract overtaking seas. A sailboat with a spinnaker up really needs to have fast response, since delay can lead to round-ups, or worse yet, round-downs! Powerboats need responsive pilots downwind as well, since they tend to slew and yaw as they run down seas. Slow pilots get out of synch with the waves, and oversteer as a result. The best way to measure the speed of an autopilot is the number of degrees per second of helm correction, not hardover time, which may include more or less throw for different models. We suspect that a 25' boat may require 15° per second; a 40' boat may require 10° per second; and a 70' boat may require 5° per second. The third factor is how far the helm has to be turned. Some sailboats hardly notice a 10° helm correction, due to their inefficient or undersized rudders, which means that their pilots have to have a long throw.

So how do I buy the correct size autopilot?

1. Start with manufacturer's recommendations and don't exceed them. Yes, we told you they don't always work, but begin by finding out which autopilot is recommended for your type of boat.
2. If you are near the upper limit of the manufacturer's recommendations, especially in displacement, go up a size. Remember that your boat's displacement may increase by 20% when loaded for cruising.
3. Are you going to race your boat? Are you going to fly a spinnaker? Select a fast pilot, and don't undersize or you'll end up sideways.
4. Are you sailing across oceans? Buy a below-deck pilot. Period.
   

Sailboats with Tillers
Use linear push-pull models like those from Autohelm and Raytheon. Some models have a separate compass/control unit which can be mounted where convenient. Note: Don't extend the push rod length more than 8" with extensions.

Sailboats to 40' with Mechanical Wheel Steering
Use either the Autohelm or Raytheon cockpit wheel pilots. They are easy to install, and have adequate performance for most conditions. Again, for trans-ocean use, we'd upgrade to a below-decks pilot.

Sailboats 35-70' with Mechanical Wheel Steering
There are many great choices in this category from B&G, Navico, and Raytheon using a drive unit mounted below decks and connected via an Edson tiller arm to the rudder shaft. There are two styles of drive mechanisms: electrical/mechanical and electrical/hydraulic. The electrical models use an electric motor to drive a series of reduction gears, which push and pull on an actuating arm. This system is inherently more efficient. The electric/hydraulic models use an electrically-driven pump, which actuates a hydraulic cylinder which pushes and pulls on an actuating arm. Both systems work well.

Small Powerboats with Mechanical Steering
Use the Raytheon SportPilot or SportPilot Plus. Each unit connects between your steering wheel and helm. It uses a special clutch at the wheel which allows you to steer around obstacles by simply grabbing the wheel. Installation is very simple in both cases.

Medium Powerboats and Sailboats with Hydraulic Steering
Use a small to medium hydraulic autopilot like the Raytheon ST5000 Plus.  The pump motor simply connects to the hydraulic steering lines and starts pumping when the Auto button is pressed. A rudder sensor provides information to the autopilot's brain so that it knows where the rudder is aiming at all times. The smaller pump motors require smaller power switching circuitry due to the low power requirements.

Larger Powerboats with Hydraulic Steering
Large power boats have larger steering rams, requiring larger hydraulic pumps mounted in the engine or machinery compartment. They are selected by the size of the boat, and the volume(s) of the hydraulic cylinder(s) that is used to actuate the rudder(s). These units are almost always installed by professional installers, although you might want to discuss your situation with us. Autopilots in this range include the Raytheon 6000 Plus and 7000 Plus, B&G Network, and Raytheon RayPilot 650.

Recommended Additions

1. For sailboats, autopilots can be interfaced with the boat's instruments, and use the wind angle information from the masthead sensor. This allows the pilot to follow a course relative to the wind direction, yet use the compass to smooth out heading changes.
2. Both powerboat and sailboat owners can benefit by interfacing their pilots to a GPS which provides corrections to the pilot so that heads directly for a waypoint. This is especially helpful when wind or current would otherwise cause the boat to go off-course. Interfacing to a GPS may require a separate interface box, or might be built into the pilot.
3. Most autopilots have optional remote hand controls for controlling the pilot from a distance. Some provide remote compass or instrument readouts, man overboard functions, course dodging and the ability to change the steering characteristics of the pilot.

Glossary
Auto Sea State reduces the amount of unnecessary helm movement in choppy seas. Most boats will wander to port and starboard when moving at an angle against head seas. These movements are cyclical, and the autopilot will not appreciably improve the course accuracy by moving the rudder. Auto Sea State tells the autopilot to ignore repeated course deflections, which reduces power consumption and increases drive mechanism life.

Auto Trim corrects the center location of the helm for consistent heading errors. For example, if a sailboat experiences an increase in wind speed, it will require more rudder deflection to hold a course. Rather than return the rudder to straight ahead, the autopilot will induce a steady port or starboard correction. Powerboats that are in a crosswind will also benefit from this.

Auto Wind is the ability of an autopilot to steer to an apparent wind course, tempered by the stability of the compass course. Since apparent wind sensors tend to be buffeted by erratic wind flow, modern autopilots use a long averaging period of wind data, and alter the compass course slowly to correct for wind direction changes.