Autopilot Sensors: What You Really Need

What sensors does an autopilot use?

An autopilot system needs to know two things: which way the boat is heading, and where the rudder is. The heading sensor, often called a compass, provides the first. The rudder reference, sometimes called a rudder feedback unit, provides the second. A GPS receiver is a third input that many autopilots use for route following and for modes that steer to a waypoint.

The heading sensor is the core of the system. Raymarine describes its Evolution sensors as "the autopilot central processor and 3D heading sensor at the heart of every Evolution autopilot system." That means the sensor does more than just report a heading: it also runs the autopilot's logic. In some packs, the sensor is built into the control head or the drive; in others, it is a separate unit that you mount and connect. When comparing packs, see our complete autopilot packs guide to see which include the sensor.

The rudder reference tells the autopilot how far the rudder has moved. This is important for the autopilot to make smooth corrections. Without it, the autopilot would not know if the rudder is centered or hard over. Some autopilots, like Furuno's NavPilot with Fantum Feedback, can work without a physical rudder feedback unit on certain outboard installations. The Furuno page says Fantum Feedback "no longer require[s] use of a physical rudder feedback unit" and uses a "time-based rudder gain process" instead. For a deeper look at how rudder feedback works, read autopilot rudder feedback sensor.

GPS is used for navigation. When you engage route following, the autopilot uses GPS position to steer toward the next waypoint. Some autopilots also use GPS speed to adjust steering response. GPS is usually shared over a network like NMEA 2000, which the NMEA describes as a standard for interconnecting marine electronics. You do not need a separate GPS for the autopilot if your boat already has a GPS receiver that can share data.

Heading sensor options

The heading sensor can be a separate unit or built into another component. Raymarine's Evolution line uses a dedicated sensor that is both the "central processor and 3D heading sensor." This sensor is included in some packs, but not all. For example, the EV-100 Tiller Autopilot pack includes the sensor, while some core packs may not. If you are considering a core pack, check whether you need to add a sensor; our autopilot core packs guide explains what is typically included.

Furuno's NavPilot 300 requires a heading source. The product page notes: "A Furuno PG700, SC33, SCX20, or other compatible NMEA2000 vessel heading source is required." That means the autopilot does not come with a heading sensor; you must have one already or buy one separately. This is a common situation with autopilots that are designed to work with an existing network.

When you read a listing, look for what is in the box. If the pack includes a heading sensor, the listing will usually say so. If it does not, the listing may say "sensor not included" or "requires heading source." The maker's page is the final authority on what is required and what is included. You can also compare the different heading sensor types in our autopilot heading sensor types article.

Rudder reference: when is it needed?

A rudder reference unit (RRU) measures the rudder angle and sends that information to the autopilot. It is a separate component that is often included in complete packs, but not always. Some autopilots can operate without an RRU, using other methods to estimate rudder position.

Furuno's Fantum Feedback is one example. The Furuno page says that with Fantum Feedback, "NAVpilot outboard/sterndrive installations no longer require use of a physical rudder feedback unit." This is available on the NavPilot 300 and 711C/OB models. However, some features still require an RRU. The NavPilot 300 page states: "Point Lock feature requires a Rudder Reference Unit (RRU) or Dometic Steering with built-in RRU." Similarly, "RRU (Rudder Reference Unit) required to enable Fish Hunter mode on NavPilot 711C/OB models."

For most autopilots, especially those for sailboats with mechanical steering or powerboats with hydraulic steering, an RRU is part of the standard system. If you are buying a core pack, you may need to add an RRU separately. Check the listing for "rudder reference" or "feedback unit" to see if it is included.

GPS and the network

GPS is not a sensor that comes with the autopilot; it is usually already on your boat. The autopilot receives GPS data over a network like NMEA 2000. The NMEA 2000 standard is a CAN-based network that allows marine electronics to share data. The NMEA page describes it as a "low-cost moderate capacity bi-directional, multi-transmitter/multi-receiver instrument network."

To use GPS with your autopilot, you need a GPS receiver that is NMEA 2000 certified and connected to the same network. Many chartplotters have a built-in GPS and can share that data over NMEA 2000. If your boat does not have a GPS, you may need to add one, but that is a separate purchase. For more information, see autopilot NMEA 2000 connectivity.

Some autopilots also use GPS for features like route following and speed-based steering. For example, Furuno's NavPilot 300 has a "Route Smoothing" feature that uses GPS to anticipate turns. These features require a GPS input, so if you want them, make sure your boat has GPS available on the network.

What to check in a listing

When you compare autopilot listings, look for these details: whether a heading sensor is included, whether a rudder reference is included, and whether a GPS is required. The listing may say "sensor included" or "requires heading source." If the listing does not mention a sensor, it may be missing from the pack.

Also check the model line. For example, Raymarine's EV-100, EV-200, and EV-300 lines have different sensor requirements. The EV-100 Tiller Autopilot includes the EV-1 sensor, while the EV-200 Power Pilot may include a different sensor. Furuno's NavPilot 300 requires a separate heading source, as noted on its page. To see how control heads and sensors are packaged, review our autopilots with control head guide.

If you are unsure, the maker's page is the best source. The Raymarine autopilot page says to "contact our knowledgeable team of autopilot experts" if you need help choosing. The Furuno page lists the required heading source. Use those pages to confirm what you need.

Common questions about sensors

Do I need a separate compass? Not always. Some autopilots have a built-in heading sensor. For example, Raymarine's Evolution sensors are part of the system. But if the pack does not include one, you will need to buy a compatible heading sensor.

Can I use my existing GPS? Yes, if it is NMEA 2000 certified and on the same network. The autopilot will receive GPS data from the network. You do not need a dedicated GPS for the autopilot.

What if I do not have a rudder reference? Some autopilots can work without one, but you may lose features. For example, Furuno's Fantum Feedback eliminates the need for an RRU on certain outboard installations, but some modes still require it. Check the maker's page for details.

What to pick for your situation

Questions

Does every autopilot need a separate compass?

No. Some autopilots include a heading sensor in the pack. For example, Raymarine's Evolution packs include the EV sensor. Others, like Furuno's NavPilot 300, require a separate heading source, such as a PG700 or SC33. For a full comparison of sensor types, see our article on heading sensor types.

Can I use my boat's GPS with the autopilot?

Yes, if your GPS is NMEA 2000 certified and connected to the same network. The autopilot can receive GPS data over the network for route following and other features. Read about NMEA 2000 connectivity for the details.

Is a rudder reference always required?

No. Some autopilots, like Furuno's with Fantum Feedback, can work without a physical rudder feedback unit on certain outboard installations. However, some features may still require an RRU, so check the maker's page. More info is in the rudder feedback sensor article.

What if the listing does not mention a sensor?

If the listing does not mention a heading sensor or rudder reference, it may not be included. Check the maker's page for the pack contents, or ask the seller for details. You can also review our autopilot core packs guide to see what is typically left out.