Bad Grounds question

[lineman49]

  Just installed a new Lowrance Elite 7 HDI  fishfinder/chart/gps. On the sonar I get alot of vertical "static lines" on the screen & was told it might be bad grounds in the boat.The faster I go the worst it gets.  It is worst when I am using the trolling motor than with the main motor .  My question is where does one start looking for bad grds. & where is the main grd found on a boat?  Any good ideas?   Thanks!

[Xxx]

Just installed a new Lowrance Elite 7 HDI  fishfinder/chart/gps. On the sonar I get alot of vertical "static lines" on the screen & was told it might be bad grounds in the boat.The faster I go the worst it gets.  It is worst when I am using the trolling motor than with the main motor .  My question is where does one start looking for bad grds. & where is the main grd found on a boat?  Any good ideas?   Thanks!

.

Is your boat I/O or outboard, all main grounds come from neg. side of battery to engine block,check the neg cable for corrosion and the terminals for the same and the the connections for tightness,are you. Using the same battery for troller and starting? Where are you getting the ground and power from, the fuse panel, or did you run new leads from a different power source?

[Lund SSS]

The only "true" ground on a boat is the neg. side of the battery as the block of the motor is isolated from the hull of the boat by mounts. The 12 volt system only functions off the return to ground.The most simple fix is running a 2 conductor straight to the battery.

[lineman49]

Thanks guys! I'll be checking all grds. & connections.