ST40 & C80 both showing fixed incorrect depth?

[danstanford]

Yesterday, in the middle of a trip the depth on the ST 40 suddenly showed 3.5 feet and would not change despite the actual depth. Later, I added depth to the data bar on the C80 and it came up correct and the ST 40 Bidata changed to correct. It was ok for the day and now something I did when using the C80 seems to have out both back to 3.5 feet. Any ideas where to start?

Dan

[dfelsent]

I have seen this when there is either very deep water or a thermocline that is reflecting the sound at a shallow depth. In my case it's common to many brands not just raymarine.

[rwidman]

My boat came to me with two depth sounders, one for each help. If both were turned on at the same time either display could read anything at random. They interfered with each other. Maybe that's what is happening in your case.

[danstanford]

6 days of sailing through lots of depths from 8 feet to well over 200 feet showed a tendency to read what I think were accurate depths with reasonably frequent periods of time that she read 3.5 feet. While there is only one transducer the Bi-data and the C-80 would show values close but not identical unless it was 3.5 feet. I do wonder if perhaps 3.5 feet might be the minimum it would show and that weeds may have caused the issue but certainly far from certain.
I had lots of other strange things including an autopilot that would not hold a heading and frequently would show "no data" then shut off and the gps position on the C-80 showing us jumping all over the place when sitting tied to the dock or moving in a straight line. Starting to think they are all related to a bad connection or part. I did have to replace the circuit board of the ST40 wind instrument as it would lock the system up when connected and this was only solved when I replaced it.

Sigh,

Dan