When trolling with downriggers, compared to long-line trolling, you may think you understand how deep your lure is, but you may be wrong. The rigger has a line counter, and the line is somewhat vertical. The trolling rigs behind the cannonball may be short enough or neutral enough that one does not need to take a lure diving depth into account much. However, you must take into account the “blowback” of the cannonball and cable.
It’s easy to assume that the lure is being presented at about the depth shown by the downrigger reel. This is a very inaccurate assumption. Or, if you do understand “blowback”, you can estimate the difference, but this is very hard to do accurately.
Here is a Trolling Angles calibration for a run with a 12 pound cannonball, a flasher and a cut herring, at an indicated GPS speed of about 2.1 mph, near Ketchikan Alaska. We took only 4 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. This is a significant difference.
The app accounts for the height of the release at which the reel is zeroed (the “rod tip height”) and the angle of the unsubmerged cable at each measurement, and it accounts for the shape of the total curve of the line below the surface.
The graph shows the profile of the submerged cable.
More analysis of this situation is in This Post.
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One response to “Trolling Angles with Downriggers”
On the photo, the snow covered mountain looks like the clouds in the background. Zoom in just over the engine to see it.