# Downrigger Ball Trolling Depth Chart



## Smart Troll

Attached is a chart you can use to help determine the depth of your downrigger ball when trolling.

The depth of the ball is determined by the angle of the cable and line-out...this chart helps you to indirectly measure the angle.

The chart assumes the DR boom is 3 feet above the surface of the water. If yours is different or if you want numbers for different amounts of line-out let me know and I will add to the chart for ya.

Please note that I rounded the numbers to avoid decimals and small fractions.

The first column represents the difference (in feet) between the point where the cable would enter the water if the boat was not moving (cable straight down) and the point where the cable enters the water when trolling.


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## Gnarf

What size ball and what speed is this based on?


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## Smart Troll

Gnarf,

The data is based on the angle of the DR cable so it will work for any ball and any speed. For any given ball...if you go faster the blow back will be greater so the point where the cable enters the water will be farther back (first column). As long as you know where the cable enters the water in reference to where it is when the cable is straight down then you can use the chart to determine the angle of the cable. If you know the angle and the line-out then you can determine the depth of the ball. 

This chart is only accurate if your DR boom is 3 feet above the surface of the water. If your DR boom is only 2 feet above the surface then the first column in the chart would be quite different.


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## Nick D.

Nice chart, thanks for posting

Sent from my SCH-I545 using Ohub Campfire mobile app


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## SWMbruiser

I will have to bring my extra large protractor out with me next time. Great, one more thing in the boat. I kid. Thanks for the info.

Sent from my DROID RAZR HD using Ohub Campfire mobile app


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## Smart Troll

Here is a better graphic I made since posting the one above. This one is more visual and user friendly.


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## 1mainiac

How did you come up with the numbers because it does not match up with numbers I have used for years.


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## Smart Troll

1mainiac,

Thanks for your reply.

Calculating the depth is a matter of math.


But I googled and found a chart with similar information made by someone else that you can compare. It looks like the numbers are pretty close but please let me know if you see a mistake and I will correct it.

http://thescientificfisherman.com/true-downrigger-depth/

I will note that technically when the DR cable is straight down it is actually at a 90 degree angle to the surface but I use that as a zero starting point. For example...when I say a 10 degree angle I mean 10 degrees from being straight down which is technically an 80 degree angle to the surface.

I will check the numbers again when I find the time but (as I said) I appreciate any feedback if mistakes are found.


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## Robert Hunt

My riggers are mounted mid ship and I mark them on my lowrance


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## Smart Troll

The attached file illustrates how a DR ball seen on sonar shows the distance to the ball...not the depth of the ball. Because of the angles associated with a mid-ship mounter DR there is an illusion that the sonar indicates depth but it does not. 

Imagine that it was possible to have a ridiculously wide cone from the transducer that went all the way to the surface. if the DR ball was 50 feet away but 1 foot deep the sonar would say 50 feet.


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## Robert Hunt

At 1-1.5 mph I estimate 1 .3 foot loss per 10 feet down and I can see them going down on my graph. Consideration also for wind speed and direction .


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## Smart Troll

It seems like you would not have that much lift at that slow of a speed unless you use a very light ball. But you can use the chart attached to post #6 above above to verify it if you want. The chart assumes your DR boom is pretty close to 3 feet above the water's surface. 

It will be easiest to use on a calm day when the surface is pretty flat. With the chart you can determine the DR cable angle by measuring where it enters the water when trolling and comparing it to where it would enter the water if the boat was not moving (true vertical). Once you know the angle it is just a matter of math to calculate the depth.The chart has the math done for you.

Just measure how far back the cable blows before it enters the water and you can use the chart to determine the depth of the ball. Compare it to what shows on your sonar and let us know how it goes.

PS - For the chart to work it is also important that the counter on the downrigger is accurate. You could measure and mark 100 feet on the cable if you want to be sure.

If you are comparing the reading on Sonar to the counter on the DR...you cannot be sure the counter is accurate.

Having said all of the above I will also say that at very slow trolling speeds (like the 1.5 MPH you mentioned) there is very little blow-back so the depth of the ball doesn't change much and the distance, depth and cable-out will all be close. But at faster trolling speeds with greater blow-back the ball will lift and they will no longer match.


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## MattBird

This is about what I figured mine were running. Appreciate it!


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