agruss,with di or si you need boat moving to get good pic,however with di it only need to barely move.if you see fish under dock while big motor is on,you can tell where they are so why would you need to see them while sitting still? however I do have a di up front on a pole that when I move a lever I can see the fish under the dock but I find that I don't need it,so I use it to see brushpile in front of boat,still testing it .