Alan Dechovitz posted a discussion

I purchased a boat with a suite of ST 60 instruments.  The ST 60 Tridata depth finder is unreliable in shallow water.  My boat draws 5.5' and I have gone thru the user calibration process to set the offset at -5 feet.  The sender is 4' 9" above the keel.  So when this setup reads zero, I should be aground.  I checked this all with a lead line.  And yet I have run aground with it indicating 18', 5.4', and 9'.  After a recent grounding a friend in a power boat found the bow in 3 ft and the stern in 11 ft ( the Tridata reported 5.4' and we were stuck in the mud).  When we got her off and into deep water, we compared readings in several places and were within one or two tenths of each other ( we corrected for him measuring total depth and my sender measuring below the keel. His instrument is brand new).  If there was some consistent pattern I could compensate.  But I am at a loss.  I have seen some other postings of people having trouble with various older raymarine depth finders.  But no solutions.  Obviously, I don't care if its accurate in deep water, but when I run aground smoking the fleet in the Club's annual Cup race for the first time, well I need a solution.  Solutions very much appreciated.See More