Downriggers
How to set up a downrigger, and why the counter is measuring cable, not depth
Quick answer
A downrigger's counter measures cable paid out, not the ball's actual depth, and the gap is blowback: true depth equals cable out times the cosine of the blowback angle. At 30 degrees of blowback, 100 feet of cable puts the ball at about 87 feet, not 100, so read the angle at trolling speed.
A downrigger's depth counter is one of the most commonly misread numbers in trolling, because it is not actually measuring depth. It is measuring how much cable has spooled out from the reel, which would be the same thing as depth only if the cable hung perfectly straight down. It never does. Boat speed and current push the cable and the weighted ball backward as the boat moves forward, and that backward angle, called blowback, means the ball sits both shallower and further behind the boat than the counter number alone suggests.
The correction is published trigonometry rather than a rule of thumb: true depth equals cable out multiplied by the cosine of the blowback angle. This guide covers reading that angle correctly, setting up the rigger itself, choosing a weight shape that minimizes the problem in the first place, and running the actual numbers so the counter reading and the ball's real position stop being two different things in your head.
On this page
What blowback actually is, and why it happens
A downrigger ball hangs from a cable that runs from a spool on the boat, over a boom, down into the water. If the boat were sitting still with no current, that cable would hang close to straight down and the counter reading would closely match the ball's actual depth. The moment the boat moves forward through the water, drag on both the cable and the ball itself pushes them backward relative to straight down, and the faster the boat trolls or the stronger the current, the more that backward angle grows. That angle, measured from vertical, is blowback, and it is the reason a counter reading of 100 feet almost never means the ball is actually sitting 100 feet down once the boat is underway.
The trigonometry that corrects for it
True depth from cable out and blowback angle
Published figuretrue depth = cable out x cos( blowback angle ) Example: 100 ft of cable out, 30 degrees of blowback true depth = 100 x cos(30) = 100 x 0.866 = 86.6 ft, not 100 ft
This is published trigonometry, not an estimate specific to this site. The angle has to be read off the rigger with the boat actually under way at trolling speed, since blowback at rest is close to zero and tells you nothing useful about the angle you will actually be fishing at.
True depth at common blowback angles
Every row below assumes the same 100 feet of cable out, with only the blowback angle changing, so the effect of angle alone is easy to see against a fixed cable length.
At just 30 degrees of blowback, 100 feet of cable out puts the ball at 86.6 feet, and that gap only grows as trolling speed or current increases the angle further.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Blowback angle | True depth | Depth lost to blowback |
|---|---|---|
| 0 degrees | 100.0 ft | 0.0 ft |
| 10 degrees | 98.5 ft | 1.5 ft |
| 20 degrees | 94.0 ft | 6.0 ft |
| 30 degrees | 86.6 ft | 13.4 ft |
| 40 degrees | 76.6 ft | 23.4 ft |
| 50 degrees | 64.3 ft | 35.7 ft |
Calculated directly from the published formula above. Read the actual blowback angle off your own rigger at your own trolling speed rather than assuming any single angle applies to your setup.
Weight shape changes how much blowback you get in the first place
Not every downrigger weight produces the same blowback at the same trolling speed. A round cannonball style weight such as Cannon downrigger weight, 10 lb presents a fairly blunt shape to the water moving past it, which generates more drag and therefore more blowback at a given speed and cable length than a shape designed to track more cleanly. A pancake style weight of the same 10 pound rating, such as Extreme Max coated pancake downrigger weight, 10 lb, is built specifically to reduce that drag and track with noticeably less blowback at the same speed, which effectively means holding a lure closer to the depth the counter actually reads without slowing down to compensate. The weight itself does not eliminate blowback, since the cable and the terminal tackle still generate some drag of their own, but the shape genuinely matters.
Choosing and setting up the rigger itself
A manual downrigger such as Scotty 1050 Depthmaster manual downrigger with rod holder with a built in rod holder covers most single or double rod trolling setups at a modest price, while an electric unit such as Cannon Magnum 5 electric downrigger removes the physical work of cranking a ball back up from real depth once a fish strikes, which matters more the more riggers a boat runs at once. Whichever base is chosen, mount it where the boom can swing clear of the gunwale and the transom without the cable fouling on anything as the ball is lowered and raised, and spool genuine stainless downrigger cable, such as Scotty 1002 stainless downrigger cable, 150 lb test, 400 ft, rather than substituting a lighter line that was not built for the load and the abrasion a downrigger cable sees.
Set up and run a downrigger in order
- Mount the rigger where the boom swings clear. Position the base so the boom can extend fully without the cable or the ball contacting the gunwale, a rod holder, or the transom on either the drop or the retrieve.
- Spool genuine downrigger cable and attach the weight. Use stainless downrigger cable rated for the weight being run, and attach the ball or pancake weight securely to the terminal end.
- Attach a line release at the correct distance up the cable. A release such as a Power Grip style clip holds the fishing line under tension against the cable until a strike pulls it free, and its position along the cable, not just the ball depth, decides how the lure tracks.
- Lower the ball to the target counter reading at trolling speed. Run the boat at the actual trolling speed you intend to fish before lowering the ball, since blowback barely exists at rest and only shows up once the boat is moving.
- Read the blowback angle directly off the rigger. Most riggers include an angle indicator on the boom itself; read it while under way rather than assuming a fixed angle from a previous trip.
- Calculate true depth and adjust the counter reading if the target depth matters precisely. Apply the true depth formula with the angle just read to know where the ball actually sits, then pay out additional cable if the fish are holding at a depth the current counter reading is not actually reaching.
Frequently asked questions
Why does my downrigger counter never match where the fish actually are
The counter measures cable paid out from the spool, not the ball's actual depth, and the two only match when the cable hangs perfectly straight down. Boat speed and current push the ball backward as the boat moves, an effect called blowback, which means the ball sits shallower than the counter reading suggests by an amount that grows with speed, current and the weight's own shape.
How much difference does blowback actually make
At a modest 30 degrees of blowback, 100 feet of cable out puts the ball at about 86.6 feet rather than 100, a difference of over 13 feet. At steeper angles from faster trolling speeds or stronger current, the gap grows considerably larger, which is why reading the actual angle off the rigger at your trolling speed matters more than trusting the counter number alone.
Does a pancake weight really produce less blowback than a round ball
Yes, for a given weight and trolling speed. A pancake shape presents less drag to the water moving past it than a round ball of the same weight, which means less backward force pushing it off vertical at the same speed. This does not eliminate blowback entirely, since the cable itself still generates drag, but it noticeably reduces the angle compared to a round ball at the same trolling speed.
Can I just add more cable to compensate for blowback instead of doing the math
You can pay out additional cable once you know the true depth gap at your current angle, and that is exactly what the formula is for: calculate true depth at the current angle, compare it to the target depth, and let out the additional cable that closes the gap. Guessing at extra cable without reading the actual blowback angle first risks overcorrecting just as easily as undercorrecting.
Why does the blowback angle need to be read while trolling rather than at rest
Blowback is caused by drag from the boat's forward motion through the water acting on the cable and the ball. At rest, with the boat not moving, there is essentially no forward drag and the cable hangs close to vertical regardless of what it will do once trolling starts. Reading the angle at rest tells you almost nothing about the angle you will actually be fishing at once underway.
Is an electric downrigger worth it over a manual one
An electric downrigger removes the physical effort of cranking a heavy ball back up from real depth by hand, which matters most when running multiple riggers or fishing deep water where a manual retrieve takes real time and effort during a strike. A single manual rigger on a smaller boat running one or two lines is a perfectly capable and considerably cheaper way to do the same fishing.
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Researched, not professional advice. This page is compiled from published engineering and regulatory figures, manufacturer specifications and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are boating convention rather than published standards, and they are labelled that way wherever they appear. Marine electrical work is not house wiring. Use tinned, finely stranded marine cable, size it for voltage drop and for the ABYC E-11 ampacity table rather than one or the other, and put overcurrent protection within seven inches of the battery positive terminal, because everything between the post and the fuse is unprotected. A lithium battery needs a charger with a lithium profile. Never load a boat past its capacity plate, and remember that canoes and kayaks carry no federal capacity plate at all, so their stated capacity is the manufacturer own figure. Wear the life jacket, and treat early season water as the hazard it is: cold water immersion takes your breath and then your hands long before it takes your core.