whats the formula on sink rates when trolling standard mono and rudder weights example: 1 mph 34oz with 250ft. of line out how do you figure the depths

Posted on July 10th, 2014

Hi Stan…Not so straight forward to figure out. The amount of resistance the lure/bait produces is a critical element of the formula & the line diameter. Monofilament has the largest line diameter when it comes to fishing lines. Bigger diameter, more water resistance, slower sink-rate, & it takes more line to get to a desired depth. Also, the more line you let out, the more water resistance comes into play, so the angle of line-to-bottom becomes much smaller.

The modern braided lines like the Sufix 832 braid has very low diameter (20 lb. test Sufix has 6 lb. test monofilament diameter), and a fast sink rate requiring much less line to get to the desired depth. I can tell you that I “bottom-bounce” for walleye using a 4 oz. bottom-walking sinker (“L”-shaped wire with weight on longer arm of wire to maintain the weight as the closest thing to the bottom), large blade worm harness/worm, with Sufix 832, 20 lb. test line in 65′ of water at 1-2 mph (hard to keep consistent speed with winds/waves), and I only have about 100′ of line out. That means I have minimal “lag” in my line and a “steep”, line-angle to my rig (rather than having a slight angle and having twice as much, or more line out). I find I contact the bottom about every 5-10 sec., and because I don’t have a lot of line out, I get very good hook-sets. This is the rig I use trolling in the middle of Lake Erie this time of the year for walleye.

For your set-up with, let’s say 12 lb. mono, as you know, the more line you have out, you really increase the “stretch-factor”/3-4 oz. “keel-bead-chain sinker”, and a fluttering spoon 3-4″ long (like the Great Lakes trolling spoons used off of downriggers), which have minimal water resistance, I would think you would need about 20-30% more line out to reach the same consistent depth. Based on the above, 60′ depth/130 feet of line, 30′ depth/50′ of line, 15’/25′ of line. Remember that the shallower you troll, the less hydrographic resistance on your rig/line, so you will decrease the ration of line distance to depth to reach desired depth. Deeper water, more water resistance, more line out to reach desired depth….God bless you, Italo

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