This explains the importance of the rod tip height value, and how it relates to the length of the submerged line and the unsubmerged line.
- The trolling depth of a rig depends only on the submerged line, not the unsubmerged line.
- It is not practical to directly measure either the submerged line or the unsubmerged line, but the line counter gives their sum, the total length.
- The rod tip height is used to determine the length of the unsubmerged line.
There are two separate rod tip height fields, one for the Calibration, and another for the Trolling slider panel.
In the Calibration Phase, the user measures a set of line lengths and angles. In addition, the Calibration data includes the height of the rod tip at the time the measurements are taken. For each measurement, the length is directly obtained from the line counter, and the angle at which the line enters the water is measured using the smartphone. During measurement there must be some line above the water, so that you can see and measure its angle. Since the unsubmerged line is straight, you can measure this angle at any part of the exposed line.
In the Analysis phase, the Trolling Angles app calculates Curve Data which is the relationship of the submerged line length to the depth. The Curve Data does not include the unsubmerged line. For every measurement, the unsubmerged length is calculated, using simple trigonometry, from the rod tip height and the line angle. The unsubmerged length is subtracted from the total length to obtain the submerged length.
When using the Trolling panel with the slider, you enter the rod tip height used while trolling, which might be different than the rod tip height of the Calibration. If you troll with the rod tip at the surface, or are using a planer board, this height is zero. For any given depth, the app can find the submerged length and the surface angle from the Curve Data. Then, it calculates the unsubmerged length from the angle and rod tip height, and adds it back to the submerged line to show the total line length for the line counter.
Notice in this graphic how the length of the unsubmerged line changes as more line is deployed.
