I have a Furuno 582 with a through-hole transducer. I have used the same machine with a transom mount transducer and it does not perform as well. When I had my boat built I had the builder make a flat spot on the hull for the transducer.

The machine is a little spendy, but by reading the marks I can differentiate between bass, King, and Coho.

After spending a lot of time with the machine I can tell what the salmon are doing as well. If they are feeding agressively in bait, (Red slashes ripping through bait) hunting aggressively for bait (angled red bananas at various depths in the same area), or just swimming; not interested in feeding (horizontal bananas yellow or green in color). The horizontal bananas will still bite put it takes a little more persistamce.