If you are trolling, use the countdown method to determine approximate depth. I recommend starting with harnesses and spoons, but stickbaits are good too.

Old School trollin
get boat to speed, let line out with closed bail until hit bottom. Then reel in to surface counting number of handle turns to get up. If you know how deep, you can interpolate like this. 40 fow and 20 reel turns equals 2 feet of depth per reel turn. 10 turns puts you about 20 feet down, 15 turns about 30 feet down.

Next time you let out lure, keep bail closed and anti reverse off. let pull on bait pull out your line out while counting reel turns. Use the interpolation you set up to judge how deep you are. In 40 fow the line curve is negligible with braid, barely more with mono. In 70 fow maybe start to think more about the curve effect.

If you are a little shallower than you think, that is usually better to keep bait above the fish eyes. Every bait will be different and every weight different. Every reel may be different. Helps to have 2 or 3 of each setup in order to minimize mental math. Jets and diving baits may be harder but can still be done this way.

Rickerd