Question about Garmin GPSMAP 440 Chartplotter GPS with Ocean Shoreline Info

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Sonar not working properly, intermittent

I have a Garmin 440 on my boat. It works fine as I'm going slowly through a no wake zone (5 knots) but when I accelerate past 2,000 rpm or 15 knots, the readout blinks at the last depth and it appears the thing is not tracking with the boat. Any suggestions?

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  • Dean
    Dean May 11, 2010

    Are you referring to the GPS tracking of your location or the sonar readout of water depth features under your boat?


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  • 18 Answers

Generally, that indicates air bubbles in the water under the transducer. If you have a transom-mount transducer, make sure the bottom surface is level or angled slightly down. If you have a thru-hull, make sure your bottom is fairly clean in that area.

Posted on Jun 18, 2009

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