On 6 April the GPS week number will roll over for a second time. 

This has the potential to cause inaccuracies in GPS position and time as stand-alone GPS receivers and systems using GPS chips may produce data that is 19.7 years either in the past or future.

Newer equipment and units which have had regular manufacturer firmware updates are at less risk than units which are older than 10 years and equipment that has had no firmware updates.

The week number is stored as a 10-bit binary number which can accommodate up to 1024 weeks (19.7 years) after which it resets to zero. As this is the second time that the week number will have rolled over, most manufacturers are prepared.

The Maritime and Coastguard Agency (MCA) has issued a safety bulletin which suggests actions to take.

  • Ensure all recent firmware updates are completed;
  • Check with your GPS manufacturer for further information and identify what action, if any, is required by the user;
  • Identify what effect this could have on your current plans and potential issues if failure occurred; and
  • Users should monitor and, wherever possible, verify their equipment for any errors.

Read MCA Safety Bulletin 13 – GPS Week Number Rollover.

The RYA provides safety information for boaters on its safety hub – visit www.rya.org.uk/go/safety.