I ran across this on a walleye forum. It was in response to someone asking about FFS-
"I'm not trying to tell you what brand to buy. this is FYI only! I watched a film on trolling using a Garmin with some kind of side scan transducer set up sideways on the transom that would show fish in front and back that would also show the fish moving and the depth of the lures to the fish. it was amazing to watch the screen. I set and almost cried. I had bought a used HDS9 GEN 3 with a 3D structure scan box and transducer for our GPS, and I had just bought a used HDS12 LIVE with the 3 in 1 transducer. if I hadn't just spent my life savings I might have went a different route".
Have you ever heard of this?
I would wonder if it would work since the transducer is sideways, and not drawing a normal picture due to the boat moving forward.