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Satellite failure


What happens to my boat if I stop receiving satellite positioning data? In the very rare event that the satellites of the GPS global positioning system fail, are taken offline or are blocked, you’ll still be absolutely fine.


Here are five useful tips covering what to do if you lose live positional data and what to look for as the cause.

Use your other instruments


A loss of satellite signal doesn’t prevent the rest of your marine electronics from working, so focus on the things that remain operational, like depth, your speed log, compass and if you have it, radar. Plus of course the most valuable instrument of all – your eyes.


Loss of signal may also be very temporary, so the main thing is to avoid panic and work the problem.

Slow down


If you are temporarily confused by a loss of positioning data then slow down and maintain heading or even stop if you know you are heading towards restricted waters. Make a note of the course you were steering and where you are while doing so. It’s the perfect way to buy some time to figure things out.


Remember at 30 knots you are covering more than 900m (nearly 3000ft) every minute. At five knots that drops to just over 150m (500ft) a minute.

Check for local interference or power loss


What you think might be a loss of satellite signal could also be caused by equipment failure, power loss or even interference from other kit that you carry on the boat, like laptops and cheap LED light sources. If you have a standby GPS then check that out to see if it is responding.


If you experience what seem like random drop-outs of the signal ensure all electrical connections are sound.


If you lose GPS signals when the radar is operated then ensure the GPS antenna is not installed close to and at the same height as your radar antenna, which is not recommended.

Ensure your GPS can see the sky


A GPS needs a clear unobstructed view of the satellites it receives it’s signals from.


If your GPS antenna is close to where crew can reach it then check no-one has found a new purpose for it and thrown a set of heavy coats or wet towels over it. Yes, it has happened!


We benefit from a large constellation of satellites that are spread across the sky. For that reason GPS antennas can usually function okay if shielded across a narrow angle by something like a mast. If the antenna is in a location with significant obstructions then you should consider moving it.

Use alternative systems


We’re not solely reliant on the US-funded GPS system these days to keep us guided at sea. Modern position antennas like Simrad® GS25 GPS Antenna also use positioning signals from the established Russian GLONASS system and the more recent European Galileo system. If you have one of these receivers then it will typically automatically adopt the best data to produce it’s position fixes and you should not need to manually intervene.