I have a 581i HD which I use on a inflatable boat. The transducer is located on the stern, near the motor.
The depth readings shows correct depth for at least an hour, then suddenly it goes to show incorrect depth.
It does not matter if you are sailing or stationary. I have tried to turn the unit off but it still showes wrong depth. The depth readings are all kind, anything from 60 to 100 meters. The correct depth is not that much around 30 to 40 meters. I usually use it with 200 Khz, but I have not tried it with 455 Khz.
Does anybody else have that kind of experience. Is there any way to test the unit and the transducer on land ?