If it didn't sink into the lake bottom, you should be able to see it as a "rock". You'll just see the round part of the cowl I'd guess, maybe it would look like two rocks if the prop is sticking up also. But the resin covered fiberglass shell should give a decent return, just like a boat sitting on the bottom. I'd back the sensitivity down and use the sharpness to highlight hard returns. Blue color palette should work well, the hard returns will have a white dot with them. Green/red pallet should work real well too, it was designed to show bottom type transitions.. soft marks are green and hard are red, should light up like a red light bulb if it fell off on a soft bottom area.