I also have my transducer mounted to the bracket on the back of my pontoon. My port side has the pump for the livewell on it and the starboard has the transducer on it. I used it all last year with absolutely no problems. I have to agree with John though, mine doesn't work well at high speed either but is perfect at trolling speed up to about 10 mph. I think the water turbulance(??) coming off the back of the 'toon that screws it up.
