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Solved problems · Electronics · Crew answer

Why has my chartplotter lost its GPS fix?

A 'no fix' or 'position lost' alarm usually means the plotter can't see its GPS source: a failed antenna or cable, a network problem, a poor antenna location or interference.

Symptom

The chartplotter shows no position, a 'no fix' or 'position lost' alarm, the boat icon jumps around, or position comes and goes.

Likely cause

Most plotters use either an internal receiver or a separate GPS antenna connected by cable or by the NMEA 2000 or SeaTalk network. Raymarine lists the usual causes: an antenna without a clear view of the sky, nearby equipment or cables causing interference, a damaged or loose cable or connector, or the plotter set to the wrong data source. A network fault, such as a missing terminator or a power drop, can take GPS and other data down at once.

Stop now if

You're navigating near hazards, in fog or at night when the fix drops out. Slow down, switch to a backup such as a handheld GPS, phone or paper chart with dead reckoning, and keep a lookout before troubleshooting.

The fix, in short

  1. Switch to a backup. Use a handheld GPS, phone app or paper chart and dead reckoning while you troubleshoot.

  2. Check the data source. In the plotter's settings, check which GPS source it's using and whether it can see the antenna on the network. Pick the right source if several are listed.

  3. Check the antenna's view. An antenna needs a clear view of the sky, away from radar, the mast and other antennas. Moving it often fixes intermittent loss.

  4. Inspect cables and connectors. Look for corrosion, water in connectors and damaged sheathing, especially where cables pass through decks or rails.

  5. Check the network. If other network data drops at the same time, test the NMEA 2000 backbone, its power and its terminators.

  6. Replace a failed antenna. If the antenna has power and is connected but never gets a fix, replace it.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Navigation electronics: Chartplotter or MFD, GPS/GNSS antenna or receiver, NMEA 2000 or SeaTalkng network

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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