Cleaning the Heading Sensor: Compass and Gyro

What the heading sensor does

The heading sensor is the part of an autopilot that measures the boat's direction. Raymarine describes its Evolution sensor as the autopilot's central processor and 3D heading sensor at the heart of every Evolution autopilot system. Some systems build the sensor into the central unit; others use a separate heading source that supplies data over the network. Furuno, for example, lists the PG700, SC33 and SCX20 as compatible NMEA 2000 vessel heading sources for the NavPilot 300.

The sensor may be a magnetic compass, a gyro, or a combination of both. The name on a listing tells you only that a heading sensor is required, not how it works inside. The NMEA 2000 standard describes a CAN-based network that lets marine electronics share data, so a sensor on that network can serve the autopilot and other instruments. Learn more about the types of heading sensors.

Cleaning versus calibration

Cleaning and calibration are different actions. Cleaning removes dust, salt, moisture and loose dirt from the outside of the sensor and its housing. Calibration sets the sensor's offset and its relationship to the boat's centerline, and it is described in the maker's manual or performed by a qualified installer. This article covers cleaning only; the autopilot's calibration is a separate procedure that cleaning must not change. See the calibration procedure and compass calibration for context.

A complete autopilot pack contains the parts needed for the system, and the manual that comes with it explains what you may clean and what you must leave alone. If the sensor is bumped or moved during cleaning, the autopilot may need a fresh setup, which is a job for the manual or an installer.

What can be cleaned without touching the sensor

The safe cleaning area is the outside of the sensor, its mounting bracket, the cable entry, and the compartment or console around it. Wipe these surfaces with a clean, dry cloth. If salt spray has left a crust, use a cloth barely dampened with fresh water, then dry the surface. Do not open the sensor case, do not loosen the mounting, and leave every cable connected. The sensor mount and sensor requirements guides explain what the sensor needs.

The heading sensor is usually mounted on a flat surface with the cable routed through a gland or clip. The area should stay free of loose gear that could knock the unit or shift its position. Keeping the space tidy is part of protecting the sensor.

• Opening the sensor housing
• Unplugging the network cable unless the maker's manual says so
• Moving the mounting bracket
• Spraying chemicals or water under pressure

What to use and what to avoid

Use a clean, dry, lint-free cloth for routine cleaning. For salt residue, use a cloth slightly dampened with fresh water, then dry the area. Avoid solvent sprays, alcohol, abrasive pads, compressed air, and any tool that could strike the sensor. Cleaning should never involve a magnet. A magnet near a magnetic heading sensor can change the local field and confuse the sensor. Read more about magnetic interference and compass offset.

The heading sensor is an electronic part, not a mechanical one. No oil, grease or spray belongs on the sensor or its connectors. If the maker's manual lists a maintenance product, follow that manual.

Why orientation and mounting matter

A heading sensor reports the boat's direction relative to its own alignment. If the sensor is rotated, tilted or moved even slightly, the autopilot may show an offset that is no longer correct. That is why cleaning must not change the sensor's position. The maker's manual shows the intended mounting and cable route. For a general look at autopilot choices, see the marine autopilot buying guide.

If the sensor is disturbed during cleaning, stop, leave the unit in place, and ask the maker or a qualified autopilot dealer whether a fresh setup is needed. This article gives no installation or calibration steps because that work belongs to the manual and the installer.

Magnetic interference and the space around the sensor

A magnetic compass or a magnetometer-based sensor is sensitive to nearby magnetic fields. Metal tools, speaker magnets, current-carrying wires, and ferrous deck fittings can create interference if placed close to the sensor. Cleaning the area also means keeping these items away from the unit.

The NMEA 2000 network does not change the sensor's magnetic reading, but the cables on that network should still follow the maker's recommended routing. Keep the compartment clean and organized so that wiring and gear do not press against the sensor.

When to ask the maker or a qualified installer

Cleaning is a small task, but some questions belong to the maker or a dealer. Ask what the manual says about cleaning the sensor, whether the sensor is sealed, and what you should do if you suspect moisture inside the housing. If the sensor must be removed for service, ask who should do it and how the setup is checked afterward. See the complete pack guide and the control head guide for how packs are described.

No autopilot replaces the watch. The U.S. Coast Guard's Boating Safety division reminds boaters to stay alert, and that alertness applies when working around nav gear. If something looks wrong with the setup, call a qualified installer rather than guessing.

What a listing tells you about the sensor

On this site, listings describe the parts in the box. Some autopilot packs include the sensor; others expect you to keep an existing sensor or add one. Raymarine's Evolution packs are described as system packs, and Furuno's NavPilot 300 requires a compatible NMEA 2000 heading source such as the PG700, SC33 or SCX20. Those names appear on the maker's pages.

When you compare packs, look for the word "sensor" in the listing, or check the maker's page to see whether the sensor is in the box. A core pack may leave out the drive and the control head, so check what is included before you order. Read the core pack guide and the core pack versus complete pack article to see how the two differ.

What to pick for your situation

Questions

Will cleaning the heading sensor erase its calibration?

No. Cleaning the outside of the sensor and its housing does not change the stored settings. Moving the unit or loosening its mounting can affect the setup, so cleaning should leave the sensor exactly where it is.

Can I use a magnet to check the compass?

No. A magnet near a magnetic heading sensor can alter the local field, and the autopilot may read the wrong heading. Keep magnets, speakers and tools away from the sensor.

Is the heading sensor in the pack or sold separately?

It depends on the product. Some sensors are part of the central unit, like Raymarine's EV sensor, and others are separate heading sources, like Furuno's PG700 or SC33. Check the listing and the maker's page.

What should I do if salt spray gets into the sensor housing?

Do not open the housing. Wipe the outside with a barely damp cloth and dry it. If you suspect moisture inside, contact the maker or a qualified autopilot dealer.

Can I unplug the sensor to clean behind it?

Usually not. Leave the cables connected. If the maker's manual calls for disconnecting the unit, follow that manual and the guidance of a qualified installer.