It's aeration in the flow of water over the transducer, the only
solution is to get the transducer into clear water. Get your boat up to
speed and look over the back of the baot where the transducer is, if it
is all chrrned up then that is your problem. Lok across the transon
and see if there is an area where the water is clean(ish), this is
where the transducer is most likely to work. If there are no clean
sections, then you can try going lower into the water with the
transducer, but then you run the risk of knocking it off! .