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Full Version: [TG11] ST40 Depth flashing "Last" in 15 ft of water
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Hi all,

I am having some problems with my ST60 depth transducer, and maybe with some other ST60 Seatalk devices.

My depth transducer will report the accurate depth for about 10 seconds, then will flash "Last" for about 10 seconds, then report depth again. This was in my slip with boat sitting still. When sailing, we had some more severe behavior, such as the "Last" value suddenly jumping to 3.5 feet (in an area that we knew to be 15 feet), and all the alarms going off. This seems to be a random occurrence, but can last 10 or 15 minutes, with the alarm repeatedly coming back a minute after I silence it. It's not totally random, since it seems to especially occur when we abruptly change direction, as when we tack.

There are other "gremlins" in our system that might or might not be related to this. I have the ST100 wireless autopilot remote. It's worked perfectly for 4 years on two different boats, but this year its reception has suddenly dropped to about 3 feet. It used to work over 30' away from the transmitter. New AAA batteries in the handheld device did not solve the problem.

Also, my ST60 wind transducer suddenly was 30 degrees out of alignment. I tried to fix this through calibration, but after turning the boat through circles the acknowledge beeps never happened. I had to give up after 3 full circles due to too much boat traffic in the area.

All of these problems cropped up suddenly after launching after being on the hard over the winter. In past years we never had any problem like this - everything was rock-solid. We've made no hardware changes to our setup. Since the manual suggests that the flashing "Last" message indicates a poor connection, I opened up the Navpod today and inspected and re-seated all the Seatalk connectors as well as the 3 depth transducer wires. No signs of any corrosion or other problems.

I'd appreciate any suggestions, especially if there is a way to diagnose whether the depth problem is control head or transducer. Obviously I hope it's not the latter, as that may require a haul-out.
Hello B-A,

I'll go through the problems one by one.

Depth data: the display will show the last depth when it's unable to detect a decent signal strength from the bottom. The fact that this is most common after a tack etc. is evidence of this: the disturbances in the water across the transducer in the turn have the effect of dropping the signal level further.
If the echo from the real bottom is weak then occasionally a depth transducer can pick up a signal from the keel with the outer fringe of the beam (particularly common with bulb keels); the display will always report the shallowest strong return as the depth. I suspect that this is why you're seeing a consistent shallow depth number.
As to why this problem has occurred now: my guess is that the transducer element has been damaged, e.g. by a strap resting on it or by hull cleaning done during the lift.
Another alternative is that something in your boat is now giving interference at around the transducer's 200kHz frequency; this could me almost any electronics, even if not new or not apparently faulty.
A good technical dealer can test the transducer with an Airmar transducer test set, test the display with a sounder test set, test for interference with an oscilloscope or test any of the above by isolation and substitution.

S100 range: this could be that either the S100 or base station is failing, or that you have an RF interference problem. A good technical dealer or one of our service centres would be able to test it for you.

ST60 Wind angle alignment: the Linearisation process is only required at first power-up or if changing the masthead sensor or display. It will only occur on first power-up (out of the box), or after a Factory Reset. It's not required to adjust the alignment, though: you can do that in User Calibration without doing circles.


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.
Often a combination of factors will cause problems: perhaps what sounds like a little corrosion on the terminals, plus the extra coating on the transducer face, might have been enough to prevent proper performance. If the signal levels are marginal then it's easier for the system to maintain a 'lock' on a known depth (even if its wrong) than to pick up a new depth value from scratch, which is why you saw dashes after the power-cycle.

If the visible external surface of the crimps were a bit tarnished then I think it very likely that you also have corrosion surrounding the wire itself, so yes, it would be a good idea to cut back and re-terminate.

If you still have no luck after that then I'd get the display and/or transducer tested by a Raymarine technical dealer.

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