Blackduck
The differance of the 18 vs the 8 (I have a 8SLT) is the 18 can zoom in to the bottom 6′ of the water column. This lets you see fish that are right on the bottom – that might otherwise be lost in the clutter on the bottom.
The 18 can also lock-in on the water – espec if you use it in the summer from a boat – your “picture” of the water column is stable – even if the boat is moving due to wave
action.
I only use my FL8 on the ice, so from that perspective….sometimes you will see what appears to be the bottom flickering – those are fish. The FL8 can’t pick them up – if I recall – it can show 2-2.5″ target seperation. The FL18 can “blow up” the bottom 6′ so that you can see those fish.
Had this happen last winter – fishing perch. They were on the bottom – you had to coax them up before the FL8 could pick them up. You would litterally see a red line (fish) detach itself from the thicker red line (bottom).
Hope this helps….
UG