[TG11] ST40 Depth flashing "Last" in 15 ft of water

[Breakin Away]

Tom,

Thanks for the thoughtful, detailed explanations. I will contact a Raymarine dealer for diagnostics after I've worked through a couple of remaining hypotheses.

The front sling lift straps were a good 3-4' behind the depth and speed transducers. The boat was kept in a DIY yard where I was present to assist with strap placement, and we always place them as far aft as possible (due to clearance issues with the backstay under the lift, but also to keep them far away from the transducers). I clean, sand, and paint the bottom myself, using a plastic bristle brush to remove slime, wet scuff sand by hand, and apply solvent based ablative bottom paint on all but the transducers. The transducers get MDR brand waterbase black transducer paint, which I have used for many years on this boat and prior boats. I never sand the transducers, because I have never had adhesion problems with the transducer paint. I just wet brush off any slime.

Here's my question: This year the transducer paint looked fine from last season, but I applied two more coats before launch. Is it possible that there is too much transducer paint, and that interferes with signal? I've been tempted to dive on the boat and scrub some of it off. Do you have other suggestions?

There are some additional details from my diagnostics since posting my initial note. In a nutshell, aggressive cleaning of the three transducer wire terminals (with thin strips of sandpaper) eliminated the "Last" message, but I continued to receive readings of 3.5-3.8 feet in a slip that I know to be 8-10 feet deep. (No plant life on the bottom that I could find with a boat pole). That worked for a couple hours, so I turned off the instruments while doing other work. Before leaving the boat today, I powered up the instruments again, and this time received "---" continuously with no "Last" reading at all. Does this bring to mind any alternative diagnoses? Should I try replacing the wire terminals?

After these things, it may be time to call for professional help.