Depth guage problems

Here’s an interesting one – any ideas much appreciated. Have a Navman Dept 2100 fitted with a through hull transducer that is epoxy-ed to the inside of the hull about a meter from the transom. When first installed at start of the season (May) it was fine. It now reads fine when going along at speed but gives no readings at slow speed and when moored. Cable is all fine and power to unit is fine.

The manual suggests weed growth might be to blame.

Anyone with similar experiences? I’m curious why it works at high speed. Surely weed is weed, but I cant’ think of anything else!

Thanks…

Just had a thought(dangerous)!!!

Could it be water in the hull or else the oil around the transducer moving backwards when she's on the plane???

Yes that idea on water in the hull did occur to me. There was a bit of water in the bilge that I though might be having an effect. However I thoroughly dried it out at the weekend and still had no reading. But I’ve still not ruled it out.

Remember the transducer is often sitting in an oil bath - maybe some has leaked out and you have air in there.

Has it come unstuck?

No it has not come unstuck, gave it a good wiggle at the weekend to make sure. The oil idea is interesting. Could not see any evidence of oil leakage into the bilge, but I guess it’s hard to test without trying another transducer.

Thanks for all the inputs and ideas, all much appreciated!

Just a bit of closure to this thread. The problem did seem to be weed/slime growth on the bottom of the hull. The transducer was placed on a quite thick park of the keel. After a bit of experimenting we have decided that the signal that is making it through the hull is probably reasonably weak so any weed or slime can interfere with the signal. A little scrub of the outside hull around where the transducer is solved the problem.