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Does anyone really know what time it is?

2K views 13 replies 7 participants last post by  gbgreen59 
#1 ·
#2 ·
I saw your post and immediately thought of the song by Chicago. However in all seriousness is can be a dangerous situation in a hurry. I have no idea how to fix it however the rest of us should pay more attention to the details on the chartplotte and laptop AND at the same time look outside and trust the old MK1 eyeball. You caught a gross error on the date, probably most of us would have missed that initially. Good job.
 
#4 ·
Interesting and useful observation. When it came time to replace our old Autohelm below deck autopilot, which we do use all that much since we have a Monitor vane we considered our options. A replacement below deck unit for a 20 ton boat was more than a little costly. We went with a CPT unit that interfaces only with the finger that turns it on/off and adjusts the course. I think that marine electronics manufacturers want to network everything because a) they can, b) it makes their products look 'sexy', and c) they can justify charging more.

BTW, our Raymarine chart plotter will sometimes show the date out by one day. It eventually corrects itself.
 
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#5 ·
How old is the unit that has the GPS in it? Did the correct date come up after a power cycle? I'm sure Raymarine just reads a data interface from the GPS unit that they procure from another source. So, either Raymarine's SW didn't interpret the year correctly for display or the GPS unit output the wrong value. It would be useful to know if this issue is repeatable or if it is a one time anomaly. Could you let us know more characteristics of this issue?
 
#7 ·
The GPS Mushroom and the control head are both circa 1995. I am guessing but Reboot had ST50 instruments when I purchased her. Yes, it happens every time now that I know where to look. An no, I have not gotten an answer back from the Raymarine folks yet. Will keep you all posted.
 
#9 ·
Have you posted your issue on the Raymarine forum. I received an answer to a question there. It took about a week though. Probably a phone call would be better though.

Here is my guess on your issue. This is just a guess for fun. I'm guessing that the date is provided in the form of an integer. The integer was not large enough to count further than whatever the start time was (maybe in 1983) and it has now started rolling over. Next year you will see 1996 if I'm correct. GPS derives the year by counting weeks since 1983. I'll bet the week is rolling over. This may yet be a GPS receiver issue and not a Raymarine SW issue (but still a Raymarine issue). Just my guess for fun. Can't wait to hear what Raymarine says.
 
#8 ·
My Raytheon C90W had a brain freeze a few years back. It was only a few years old. The result was loss of electronic charting, including the feed to my autopilot. So it was back to the handheld GPS chartplotter and hand steering for the next 35 miles.

When I contacted Raytheon via phone, they suggested a "factory reset", which is easy enough if you had the instructions. That worked, but I didn't read "the fine print" and didn't realize that the time defaulted to Greenwich Mean Time--a 5 hour difference from our area. As a result, my tide and current data were significantly off. My wife knew better: she had checked the printed tide chart and told me my impression of the tide was way off!

There were 2 lessons learned from that Raytheon brain freeze. (1) You need to maintain and crosscheck paper data with your electronic data when in doubt. (2) You need to consider failure modes when you network your electronics.

Regarding point #2, my primary chartplotter (the one that froze) was the pass through for my GPS data (which comes from a "mushroom" unit via the autopilot computer.) When it froze, I lost position and instrument data to my secondary chartplotter, so it was generally useless until the master unit was reset.

Having learned my lesson, when I changed my VHF, I opted for a unit that had a built-in GPS antenna. My intention was to always have a GPS input for the DSC function, but I also have lat/lon displayed, even on the RAM unit in the cockpit. The only downside is that the VHF base unit down below can take 5 minutes or more to get a fix.
 
#10 ·
Here is an interesting fact. 2015 - 1983 = 32. So, it has been 32 years since time began for GPS. 32 is a 5 bit integer. If the GPS receiver used a 5 bit integer to provide the year to Raymarine, then it just started rolling over this year. Hence, no reset will fix this issue. Sort of a built in "end of life" feature.
 
#11 ·
Sort of a built in "end of life" feature.
Interesting concept. Of course I despise Raymarine equipment. They have gone bankrupt more times then I have been married + the number of my children (a 3 bit integer!) I don't understand why builders like Catalina still put their crap on boats.

I did some playing around and discovered that:

1) This particular "mushroom" came in both a Seatalk (tm) and NMEA version.

2) When I disconnected the Seatalk (tm) lead from the autopilot computer the control head at the helm started reading out the correct date and other data. So Raymarine at least bridged the Seatalk (tm) and NMEA data in the autopilot computer for GPS data. They have a habit of dropping NMEA sentences between NMEA "In" and "Out", one of the reasons I hate them.

3) The autopilot control display immediately started displaying the same information that appeared on the Garmin Multifunction displays (5212 & 5012.) They had always been slightly out of sync. I had just written it off to a network interfacing issue. Now I know that the autopilot computer was getting the wrong data from the GPS mushroom. Obviously it was using that data as the "preferred" data. Since the Seatalk (tm) bus was powered by the autopilot computer I never saw the condition without the GPS mushroom until I actually disconnected ti electrically.

4) I have posted this on the Raymarine web site. We will see what they say.

Fair winds and following seas :)
 
#12 ·
Wow, how interesting is that? Pretty cool experiment, and gave insightful results.

If I'm right about the roll-over issue, then you will probably just have to toss the mushroom GPS. The issue isn't uncommon for really old GPS. Always seemed short sighted from a SW design point of view. On the other hand, memory and processor speed were much less capable back then. SW designers were doing all they could to save on storage and throughput. Not so tough now.
 
#13 · (Edited)
I think perhaps you have the right idea, but are missing the problem. Most likely, the GPS mushroom or the nema converter does not provide date. Virtually all 183 sentences that need it only have time. Position is dependent on time differences, not absolute time. So they didn't require date.

So more than likely, your MFD just simply used its date it had stored. Perhaps it's build date.

Any thoughts?
Bryce
 
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