I think what kosmo is saying is that would help you determine if the cover is under the boat. HB 2d sonar cone at 200khz is only 1/3 depth of water at the bottom or only a 6.67 ft circle in 20 feet of water (3.335' each side of transducer). So if you where using 2d/DI you would at least know the cover is under the transducer or to one side. Is your FF a SI unit or a DI only unit?