Autopilot Compass Offset: Where to Set

What is a compass offset

A compass offset is a correction you enter into an autopilot to align the heading sensor's reading with the boat's actual heading. The sensor, often a fluxgate or solid-state compass, may not point exactly to the boat's bow because of its mounting position, nearby metal, or magnetic interference. The offset is a single number, usually in degrees, that you add or subtract to the sensor's reading so the autopilot knows which way the boat is really pointing.

The offset is part of the autopilot's calibration. It is not a permanent fix for a misaligned sensor; it is a way to tell the autopilot how much the sensor's reading differs from the true heading. You set it once, and the autopilot applies it every time it reads the sensor.

Why the offset matters

If the offset is wrong, the autopilot will steer to a heading that is not the one you want. For example, if you set a course of 90 degrees but the sensor reads 90 degrees when the boat is actually heading 95 degrees, the autopilot will hold the boat at 95 degrees. The boat will follow a line that is consistently off by the same amount.

A correct offset is especially important when you use the autopilot with a chartplotter or follow a route. The autopilot uses the heading from its sensor to steer, and the chartplotter uses GPS to know where the boat is. If the heading is off, the boat will not follow the route as expected. The offset is one of the first things to check if the autopilot seems to steer to the wrong heading. For more on how autopilots connect to other electronics, see our guide on NMEA 2000 connectivity.

How to determine the offset

To find the offset, you need to know the boat's true heading and compare it to what the autopilot sensor reads. The true heading is the direction the boat's bow points, usually read from a compass or a chartplotter that has its own heading source. The sensor reading is what the autopilot displays as the current heading.

A common method is to point the boat at a known heading, such as a landmark or a compass bearing, and then read the autopilot's heading. The difference between the two is the offset. For example, if the boat is heading 180 degrees by your compass but the autopilot reads 175 degrees, the offset is 5 degrees. You would enter that value into the autopilot's setup menu.

The exact steps for entering the offset are in the autopilot's manual. The manual will tell you how to access the calibration menu and where to enter the offset value. Some autopilots have an automatic calibration routine that does this for you, while others require manual entry. If you are considering a new autopilot, you might want to compare complete packs that include a control head with a setup wizard.

Where to set the offset

The offset is set in the autopilot's setup or calibration menu. This is usually accessed through the control head or a connected chartplotter. The menu may be called 'Compass Offset', 'Heading Offset', or 'Calibration'. The exact name and location depend on the autopilot model.

For example, Raymarine Evolution autopilots have a setup wizard that guides you through calibration, including setting the compass offset. Furuno NavPilot autopilots have a similar setup process. The manual for your specific model will show you where to find the offset setting.

If you are not sure how to access the menu, check the manual or contact the maker's support. The offset is a simple setting, but it is part of the calibration process, so it is worth doing carefully. For guidance on choosing a control head that makes this easier, see our guide on control head options.

Common mistakes

One common mistake is setting the offset while the boat is moving or while there is magnetic interference nearby. The sensor reading can be affected by the boat's motion, so it is best to set the offset when the boat is steady, such as at a dock or at anchor.

Another mistake is entering the offset with the wrong sign. If the sensor reads higher than the true heading, you may need to subtract the difference, and if it reads lower, you may need to add it. The manual will explain the sign convention for your model.

A third mistake is forgetting to re-check the offset after changing the sensor's position or adding new equipment that could cause magnetic interference. The offset is specific to the sensor's location, so if you move the sensor, you should recalibrate. For more on sensor placement, see our article on heading sensor types.

When to ask for help

If you are not comfortable setting the offset yourself, a qualified installer or dealer can do it for you. The maker's manual and the dealer's expertise are the best resources. The offset is a small part of the overall calibration, but it is important for the autopilot to steer correctly.

If the autopilot still steers to the wrong heading after you set the offset, there may be another issue, such as a sensor problem or magnetic interference. In that case, consult the manual or a professional. You can also review our guide on autopilot calibration procedures for a broader look at the calibration process.

What to pick for your situation

Questions

What is a compass offset on an autopilot?

A compass offset is a correction you enter to align the autopilot's heading sensor with the boat's true heading. It is a number in degrees that the autopilot adds or subtracts to the sensor reading.

How do I determine the compass offset?

Point the boat at a known heading, read the autopilot's heading, and calculate the difference. Enter that difference in the autopilot's calibration menu.

Where do I set the compass offset?

In the autopilot's setup or calibration menu, which is usually accessed through the control head or a connected chartplotter. The manual for your model will show the exact location.

What happens if I set the offset wrong?

The autopilot will steer to a heading that is consistently off by the same amount. This can cause the boat to follow a line that is not the one you intended.

Can I set the offset myself?

Yes, if you are comfortable with the autopilot's menu. The manual provides the steps. If not, a qualified installer or dealer can do it.

Do I need to set the offset every time?

No, you set it once during calibration. You may need to redo it if you move the sensor or if magnetic interference changes.