What is the formula to calculate depth if all you have is angle below horizontal and length of line? Trying figure out how to determine how deep my lures are running when I troll.

One of the crucial considerations in trolling is presenting the bait at the proper depth. Many lures come with a depth rating, but knowing the precise depth your baits are actually running can be challenging. Calculators and protractors may not be standard gear on an offshore fishing trip, but...

What is the formula to calculate depth if all you have is angle below horizontal and length of line? Trying figure out how to determine how deep my lures are running when I troll.

I wasn’t aware there was a formula. I just searched for my lure depth chart. “Bandit 300 depth chart” and this is what came up. Based on 10 lb test and going 1.6 mph.

I remember watching a documentary on the towed sonar used to find shipwrecks. They had to include the water temperature at the surface and at depth in their calculations because both affected the drag on the line and the probe enough to make a difference. Their calculations could be way off from the sensor measured depth of the probe at depth (which was also affected by temperature).

I would think you would need to know trolling speed, line test or diameter, length of line out and model of lure you’re using. My Bandit 300’s with 50 feet of line out dive much deeper than my Bandit 200’s or 100’s with everything being the same by design.