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Depth finder not matching charts.

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  • Depth finder not matching charts.

    Had this issue last year but forgot. I have two Garmin chart potters networked to one transducer and a separate Lowrance with it's own transducer. The GPS I do not believe is off as I can place my boat right in the slip on the chart and leaving the harbor I am exactly where it says I am. Driving by landmarks on the chart I am spot on.

    But when I fish, the corresponding depth indicated on the chart and the depth finder sonar depths are different on the plotter network and the Lowrance depth matches the chart plotters sonar depth. As much as 100' off at times. Disconcerting because the reading is telling me I am deeper than the chart. So I could run into a 100' wall and the plotter would be telling me I am at 0 feet.

    I checked the transduces in the spring and everything looked good. Angle, locked in the bracket and nothing looking off. I know that the angle of the transducer can throw you off and the deeper the water, even further off. But both transduces give the same numbers. Both mounted wrong?? One thing is the keel offset, it is only 2' so that isn't it.

    The chart was updated last year. Should be good to go.

    Kind of a stumper. I looked thru everything on the plotters program that I thought might be giving me an error but can't find anything. Any ideas???


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  • #2
    I have the same problem with the charts on my Garmin. Definitely causes concern when your charts are so far off of the depth finder. I'm confident my depth finder is accurate and the chart id off.

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    • #3
      I have all Garmin equipment with the premier coastal navigation charts as well as g3 bluewater--one plotter with its own internal sonar with PS30 panoptix transducer, and the other with a sonar black box connected to a GT51-TM transducer. And I've noticed the same thing--chart depth does not match up with sonar depth. However, both sonars read within less than a foot of each other.... I suspect giten is correct.

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      • #4
        It is probably caused by the lack of current and/or in-accurate NOAA data used in making the electronic charts. I thought that NOAA was updating their bathymetric data a couple of years ago but not sure if they are finished.
        2007 24ft NorthRiver OS
        Twin 175 Suzuki's
        "Thunderbird"
        MMSI #338033856

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        • #5
          I've noticed the same on Garmin units and now rely on Navionics on my phone or Lowrance.
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          Heavy Hitter Fishing
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          • #6
            Garmin acquired Navionics in 2017. Supposedly they are sharing and combining content (not playing corporate strategy games).
            I've been researching makes/models to replace my ancient sounder.

            The amount of private sonar activity, if recorded and uploaded, would provide insane bathymetric data to NOAA and others.
            Then again, that special underwater pinnacle that you found, would be on everyone's iPhone.

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