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  1. #1
    Join Date
    Sep 2007
    Location
    East Med...
    Posts
    1,676

    Default Odd problem with Raymarine plotter vs instruments

    I have this strange problem that cannot understand how it is even possible to happen.
    On my boat I have a raymarine plotter (Axiom 7) and two i-70 raymarine displays. Occasionally, the two i-70 show a much different SOG than the plotter.
    For instance let's say the boat moves at a relatively constant speed of say 7 knots. The plotter will show something like 6.8-7.2. The two i-70 displays may show the same but suddenly they start showing a SOG that fluctuates between 4-10 knots!! Or sometimes the boat is stopped in the marina, the SOG on the plotter is zero whereas the SOG on the instruments may fluctuate from 0 to 1 knots. How is this possible? I am referring to SOG which has only one source of getting this data (the plotter I guess).
    Keep sailing

  2. #2
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    8,003

    Default Re: Odd problem with Raymarine plotter vs instruments

    The plotter and instruments are connected via STNG/N2K and SOG is calculated by the plotter, as you suspected. If both i70s show an incorrect SOG it's must be that they are receiving incorrect data from the plotter. I'd check all of the connections that you can find, give them a blast with some electrical contact cleaner. Might also be worth updating the software on all devices, if you haven't already.
    Rainbow Marine.
    www.rainbowmarine.co.uk

  3. #3
    Join Date
    Sep 2007
    Location
    East Med...
    Posts
    1,676

    Default Re: Odd problem with Raymarine plotter vs instruments

    Quote Originally Posted by PaulRainbow View Post
    r. Might also be worth updating the software on all devices, if you haven't already.
    No, I haven’t. I should try this, thanks.

  4. #4
    Join Date
    Mar 2005
    Location
    Hants/Lozère
    Posts
    4,700

    Default Re: Odd problem with Raymarine plotter vs instruments

    I have a similar problem but no plotter. I have correct SOG on my P70 but incorrect but steady on two i70. Not sure ( yet) where SOG comes from as I have a Vesper marine XB8000 and a connected PC running OpenCPN. It seems the instruments are using different NMEA2000 PGNs. Maybe an update will help!

  5. #5
    Join Date
    Feb 2007
    Location
    Essex
    Posts
    22,860

    Default Re: Odd problem with Raymarine plotter vs instruments

    I had an SOG problem when my e7 was new. It was on its own, but displayed figures as bad as the pre-selective-availability days, for those old enough to remember. I whinged to Raymarine about it and they gave bland meaningless replies about errors in GPS signals etc. I knew this was rubbish because my Garmin GPS gave sensible readings. At some time there was a recall for e7s because of faulty screens and I was given a new set, when surprise surprise, the SOG problem disappeared.
    Far away is near at hand in images of elsewhere

  6. #6
    Join Date
    Oct 2014
    Location
    Australia
    Posts
    246

    Default Re: Odd problem with Raymarine plotter vs instruments

    Speed by definition is an average over a period of time. Every GPS averages it different way before displaying the result. Sometimes the averaging period is fixed, sometimes is adjustable. If your instrument has short averaging and the GPS antenna is located at a place where rocking/rolling causes a lot of movement, the instrument goes bananas. Check where the antenna is and if possible, relocate it somewhere lower and close to the centre of the boat.
    By this post I am not dismissing the other alternatives mentioned in previous posts. Just another possibility.

  7. #7
    Join Date
    Mar 2005
    Location
    Hants/Lozère
    Posts
    4,700

    Default Re: Odd problem with Raymarine plotter vs instruments

    Not the cause of my problem as the differing speed readings are steady. I have a suspicion my i70 displays are showing STW not SOG as I have an uncalibrated log sensor that reads about the same. I plan to check it out next week.

  8. #8
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    8,003

    Default Re: Odd problem with Raymarine plotter vs instruments

    Quote Originally Posted by jiris View Post
    Speed by definition is an average over a period of time. Every GPS averages it different way before displaying the result. Sometimes the averaging period is fixed, sometimes is adjustable. If your instrument has short averaging and the GPS antenna is located at a place where rocking/rolling causes a lot of movement, the instrument goes bananas. Check where the antenna is and if possible, relocate it somewhere lower and close to the centre of the boat.
    By this post I am not dismissing the other alternatives mentioned in previous posts. Just another possibility.
    His plotter calculates SOG and passes that data across the network to two other devices. The two other devices both display the same incorrect SOG. It doesn't matter how accurate or otherwise the SOG displayed by the plotter is, it should match perfectly on all displays.
    Rainbow Marine.
    www.rainbowmarine.co.uk

  9. #9
    Join Date
    Nov 2016
    Location
    Lincoln
    Posts
    886

    Default Re: Odd problem with Raymarine plotter vs instruments

    Is the problem due an offset in the calibration of the SOG on the plotter and the raw data SOG being read over the network?

  10. #10
    Join Date
    Sep 2007
    Location
    East Med...
    Posts
    1,676

    Default Re: Odd problem with Raymarine plotter vs instruments

    I will be more certain after I test it again but it seems that after the update I made on Saturday (was quite big; 770 MB!) both plotter and i-70s show exactly the same now.
    Keep sailing

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