weve tried to use the SI right up at the dam but the water is too turbulent for it to function right .. all you get is alot of static like on your screen .. but if you back up about 50 yds off the red line it starts to work.. but it wont go all the way to the dam... unfortunately.. too turbulent ... hes had his for like 4 years now and is a wizard with it ... they are nice... another buddy has the hds 10 by lowrance .. now that thing is sweet also.