Chuck Gould wrote:

I often see
situations where somebody is running a sounder on a flybridge and then
goes to the lower helm and turn on another sounder without turning the
first sounder off. In cases where there are separate transducers
rather than slave units I suspect they get confused about which echoes
to recognize.


That certainly seems plausible but I haven't had any
interference while running a Garmin transducer at the
starboard stern and a Humminbird at the port stern separated
by about 6 feet. Two identical units probably would be more
troublesome.