The faster you troll and the lighter your ball, the more your downrigger cable angles back behind the boat instead of running straight down — which means the number on your line counter overstates your actual lure depth. This calculator estimates that gap so you're not fishing 5-10 feet shallower than you think.
Downrigger Letback
Your ball doesn't go straight down — trolling speed pushes it back behind the boat. Cable-out always has to be more than your target depth.
BLOWBACK ANGLE
Inputs
Model is an approximation calibrated to typical published letback charts (8 lb ball, ~2 mph ≈ 17–20° blowback). Real blowback also depends on ball shape, cable diameter, and current — treat this as a starting point and fine-tune with your temp gauge or a known-depth marker.
Set Your Counter To
27
ft of cable to let out
Estimated blowback angle18°
Actual depth at that cable-out25 ft
Under 20° of blowback — you're in good shape for keeping the ball where you expect it.