Furuno WAAS GPS alarms cause failure? - The Hull Truth

sblunden · 08-19-2005, 05:16 PM

I have a GP1710C NavNet GPS with a 320B WAAS antenna attached. Last Sunday I lost all position data on every device on the NavNet. When I went down to the lower station where the Chartplotter is installed and found that the GPS Status screen was displaying an alarm saying "WAAS Signal Lost". I had to power the plotter/GPS off and everything came back up. This seems a little extreme..I thought the unit would just keep going in degraded mode.

I've submitted this to Furuno support, by the way. Has anyone else seen this? I could turn off the "WAAS Alarm" setting if this is a known problem or if it's working as designed.

Somethin-Fishey · 08-19-2005, 07:09 PM

I get the waas alarm when going under bridges slowly or when I power up under a covered awning, but it has never caused any problems other than the beeping.

08-19-2005, 08:05 PM

Its happend to me one or two times with my Northstar 952.

Kerry · 08-19-2005, 09:28 PM

The whole purpose of systems like WAAS is for position integrity so it could be argued that if set to WAAS and WAAS positions are expected then when it looses WAAS you really don't want it automatically changing back to normal GPS, which has no position integrity and running amuck. Furuno appears to drop the position fix after 90 seconds of invalid data, which in some cases 90 seconds is even a dam long time before starting alarms etc as one can go a long way in 90 seconds especially in confined waters.

So really it could be considered inappropiate to simply carry on in normal GPS mode as no fix can in some instances be more appropiate than a dud fix or fix of unknown quality? Furuno are quite vague in just what is supposed to occur when there is "NO WAAS SIGNAL" but I could understand that if WAAS was "specifically configured" (by alarm setting or whatever?) and signal was lost then it could go into a no navigation (no position) type mode?

Cheers, Kerry.

Somethin-Fishey · 08-19-2005, 09:57 PM

I don't think so. I get an alarm within seconds of going under a low bridge. I have also used my unit beside my house blocking the WAAS signal for hours with no ill effects either short term or long term. WAAS is a luxury and if it goes away and you get an alarm, consider yourself warned that you have a reduced fix position, but GPS with SA off is still very accurate.

sblunden · 08-20-2005, 07:53 AM

Quote:

Somethin-Fishey - 8/19/2005 9:57 PM

I don't think so. I get an alarm within seconds of going under a low bridge. I have also used my unit beside my house blocking the WAAS signal for hours with no ill effects either short term or long term. WAAS is a luxury and if it goes away and you get an alarm, consider yourself warned that you have a reduced fix position, but GPS with SA off is still very accurate.

William...when you get the WAAS alarm...do you have other NavNet devices attached? I didn't state in the original question that on the GPS plotter itself I DID still get position data, but it stopped being sent over the NavNet when the alarm went off, which I think is a bug.

Somethin-Fishey · 08-20-2005, 08:58 PM

Yes, I have other devices (Nema radio and NavNet Autopilot) Next time I go under a bridge I will check for that anomally.

sblunden · 08-21-2005, 02:49 PM

Also, please check to see if you have WAAS Alarm turned on or off in your GPS sensor setup. WAAS Alarm Off apparently means to sound the alarm 3 times and then continue operating, On seems to say to continuously alarm until it's reset. I just turned the alarm off and will see what happens!

Thanks