was out at xmas with my dad in his little 14ft ali boat. at about 3 or 4 knots the ff screen turned to mush which i assume is engine noise as you could see it increase the faster we went.  is there anyway of clearing this up? i assume because he has an older engine with no shielding

Thanks that could it. right side of the Ob reason i thought electrical noise is that it was a very definate change from nothing to mush. I say mush but when i first saw it i thought it was the green sea lettuce that is prevalent in the tauranga harbour this time of year but when we slowed and it all disappeared. well that theory went out the door. dad was getting all excited as it was showing as hundreds of fish. lol that all of a sudden disappeared when we stopped. i will get him to look at his mount and how it sits in the water