Fish Finders & Speed

[Super]

I've had a two fish finders, a Lowrance X51 and a Lowrance Elite 4X. I've been happy with both, however...

Neither one can identify passing over fish when the boat is moving faster than 6-7mph. I get a good depth reading but that's about it.

Is this because of the wash produced by the boat? Or is it just because these aren't high end fish finders? Or is this just typical of all fish finders?

[Capt. Lou]

Can read @"hi speeds if mounted thru hull or inside of hull if done correctly ! Never used the models u mentioned so can't swear to those working but all Imowned mounted thru hull or inside worked fine , Furuno , King , Simrad