How to Calculate the Depth of a Trolling Lure
- 1). Measure the distance from the back of the boat to the bait while the lure is on the surface. One easy way is to pre-measure and pre-mark the fishing line every ten feet with a permanent marker, then count the number of marks that pass when you let out the bait. This will give you the length (L), which will form the base of the triangle in your calculations.
- 2). Place the rod in the rod holder in the position it will be while trolling. Measure the vertical distance from the rod tip to the surface of the water. This distance will become your height variable, H.
- 3). Increase the boat's speed until you reach your desired trolling speed.
- 4). Estimate the angle (A) made by the fishing line intersecting the surface of the water. A protractor may be useful for estimating the angle but may prove difficult to use while the boat is in motion.
- 5). Locate the tangent of angle A, either by using the tangent function on a calculator or by looking up the value in a tangent table.
- 6). Multiple the tangent of the angle A by L, then subtract H. This will give you an estimate of how deep your bait is.
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