Is the transducer externally mounted, or is it a shoot-through? This sounds like a transducer issue although it's a bit puzzling why it drops only at shallow depths.
We have an ancient Datamarine Corinthian (rebuilt once) that continues to work just fine - and the waters on the SE GA and SC coasts are about as turbid as they come - while that may (and does) cause some infrequent erratic readings, we've never lost it completely.
Bill & Lisa Ballard
S/V Jo Beth
1984 PSC Crealock 34, Hull #16
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"Twenty years from now you will be more disappointed by the things you didn't do, than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover."
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