WAAS or wasn’t

[All U Get]

Hi all,

I have ignored the clock on my Furuno chart plotter for several years and have a renewed interest in setting the date. The time of day is correct, but the date is off. I reset the GPS unit (GP-37) and wondering how long it will take for the WAAS to correct the time?

 

[Tom J]

A few years ago, GPS was updated, or modified, or something, and I had the same issue with my Garmin. I finally had to check with Garmin about how to update my unit to accept the new format. You might have to do the same with Furuno.

 

[Davidasailor26]

Tom is close - GPS had a rollover of its dates a little while back. Like Y2K but with the dates in the GPS messages. Older receivers that weren’t built with the rollover in mind should work except that the date will be wrong. If the manufacturer still supports the device and offers a software update that should fix it.

 

[senang]

If I remember correctly it has to do with the weeknumber being coded up to 999 and then starting again at 0. So at slightly less then 20 years the old system software counts dates incorrect, and only a software update can correct it.

 

[Davidasailor26]

If I remember correctly it has to do with the weeknumber being coded up to 999 and then starting again at 0. So at slightly less then 20 years the old system software counts dates incorrect, and only a software update can correct it.

Yep, actually it’s a little tricky - the official rollover happens at 1024 weeks (10 bits of binary data), not 999. More details on that at https://www.navcen.uscg.gov/pdf/lnms/LNM_Special_Notice_2019_Use_GPS_Equipment_Indefinite.pdf. But some manufacturers (Simrad in particular) must’ve also been storing the week in decimal format and had trouble at 999 weeks.

 

[All U Get]

Thanks for the replies, do you like irony?