depth finder

[echo]

I don't know a whole lot about depth/fish finders, but I do cardiac ultrasound for a living so know a little bit about ultrasound physics. If your transducer is mounted anywhere where some air can flow around it, it will not work. The ultrasound used (at least what we use in medical imaging) is so high frequency that it cannot get through air-that's why the "gel" is used for ultrasound tests, to act as a couplant between the transducer and the patients skin. I would guess that if your unit works at rest/moving slowly and then stops working when moving faster, air is getting around the transducer somehow and you need to reposition it. Let me know, I'm interested if that's the case.