If you troll, especially with downriggers, you need Trolling Angles.
You know that a cannonball rig is “blown back” behind the boat by the force of the water’s drag on the rig and the cable. This causes a curve in the cable, so that the actual depth of the cannonball is significantly less than the length of the cable that is deployed.
Determining blowback is really difficult, because it is dependent on so many factors, such as the weight and shape of the ball, the diameter of the cable, the speed of the boat, the drag of the lures, flashers, and dodgers. The curve is complicated and it’s different for every situation.
The Trolling Angles app uses a patented method which lets you measure the angle of the cable at multiple line lengths, it calculates an accurate approximation of the line’s curve, and then can show you the actual depth of the rig for any line length. The app runs on your Apple or Android smartphone with no additional hardware, and is currently only $30 for a permanent license or $10 for a year.
This screenshot is based on on an actual run with a 12 pound cannonball, a flasher and a fly with a cut herring, at an indicated GPS speed of about 2.1 mph, near Ketchikan Alaska. We took only 4 quick measurements as we deployed the rig while fishing.
With 70 feet of cable, the bait is only about 51 feet down, and with 90 feet of cable, the bait is only about 63 feet down. Without this knowledge, you could be trolling almost 30 feet above the fish echoes. Your cable counter won’t do this, and neither will your 2-D sonar. If your 2-D sonar shows an echo from your cannonballs, it is displayed at a very misleading depth. The best blowback chart will not match your exact rig and speed, and is harder to use. An underwater probe might get close, but is expensive and creates its own drag.
See the Trolling Angles web site for a lot more information and a video, the FAQ for some short discussions, and the Blog for some longer articles.
