Thank you for your replies.
It is true, the transducer was directly mounted at the trolling motor (electrical motor
). this was, as I said, the very first test.
I will try to mount the transducer at a rod and 1 ft. or 2 ft. deeper than the motor.
On the other hand, I was travelling sometimes over the same position with different speeds and setting - this causes additional interferences
The I am on is called "Motzener See", 20 km south of Germans capital Berlin.
Unfortunately the battery allows just one hour travel with this motor, gas engines are not allowed at all (and this is pretty good for scuba diving).
Attached you will find a kmz-file for google earth. - It is not allowed to attach kmz
therefore it has been zipped. And it is to large. I will upload it on my server and send the link here afterwards.
None of them are as good as I thought before. It was my first time.
I look forward to any tip