Field Notes / October 2026
How deep does your lure really run? (It's not what the box says)
At a glance
| main variables | line out, diameter, speed |
| braid vs mono | +20-40 % depth |
| max depth | reached at 75-150 ft line |
| verdict | measure it |
Quick answer
A lure's running depth depends on how much line is out, how thick that line is and how fast it moves. The depth printed on the box assumes one combination. Change any of them and the lure runs somewhere else, often by metres.
The problem
You can't see your lure. You can only trust the box, and the box was tested with somebody else's line, speed and line length. Most anglers never find out that their favourite lure runs a metre or two shallower than they think.
01
The people who measured it properly
In the early 1990s, two walleye anglers set out to measure trolled crankbait depths for real. Their Precision Trolling data was collected with a scuba diver underwater, recording where each lure passed while a boat trolled it at different speeds and line lengths [1][2]. The premise is simple: lead length, line diameter and trolling speed control diving depth [3]. Their casting study later found that a lure on 8 lb mono ran about 20 % deeper than on 14 lb, and about 10 % shallower again on 20 lb [4].
02
What changes the depth
- Line out. More line means more depth, up to a point. Most crankbaits reach maximum depth somewhere between 75 and 150 ft of line; beyond that, extra line mostly flattens the angle [5].
- Line diameter. Thinner line has less drag, so the lure digs deeper [4].
- Line type. Braid is thin and doesn't stretch, and can add 20-40 % depth compared with mono [5] (see Braid vs mono: how your line changes lure depth).
- Speed. When trolling, faster usually pushes lures up and slower lets them run deeper, and every lure has a speed range where its action works [5].
- Casting distance. On a cast, a longer cast gives the lure more time to dive: a 100 ft cast went about 15 % deeper than a 70 ft cast in the same study [4].
With PROBE →
With PROBE on the line, each variable stops being theory. Let out 30 m, then 50 m. Speed up by half a knot. Change to thinner line. The app shows the real running depth after each change, so you learn how your lure responds with your gear.
03
Why it matters
If fish are holding at 5 metres and your lure is running at 3.5, you are fishing above them all day. One of the most common trolling mistakes is changing lure or colour when the real problem is depth [6].
Know where your lure really runs.
See trolling mode →04
How to check your own lures
Dive charts are a good starting point, but they are measured with specific lines and speeds. Your reel, your line and your boat are not in the chart. The only way to know is to measure.
PROBE
How PROBE helps
PROBE records the actual depth of your lure on every cast and every trolling pass. Run each lure in your box once at your normal speed and line, and you have your own dive chart, made with your gear. In trolling mode, the app shows lure depth in relation to boat speed, so you can see exactly which speed puts your lure where you want it.
Field log /
Testing one crankbait, box depth 4–5 m
| Line | 0.35 mm mono |
| Line out | 40 m |
| Speed | 2.5 knots |
| Box says | 4–5 m |
| PROBE measured | 3.1 m |
| After switching to 0.15 mm braid | 4.4 m |
On mono, the lure ran well above the depth printed on the box. Braid got it into the range.
Field rule
The box tells you what is possible. PROBE tells you what happened.
FAQ
Frequently asked questions
Why doesn't my lure run as deep as the box says?
The box depth is measured with one specific line, line length and speed. Thicker line, less line out or a different speed all change the real running depth.
Does more line always mean more depth?
Up to a point. Most crankbaits reach their maximum depth somewhere between 75 and 150 ft of line; after that, extra line mostly flattens the angle.
How can I check my lure's real depth?
Measure it. A sensor on the line records the actual depth on every cast or trolling pass.
Build your own dive chart, with your own gear.
Get PROBE →Sources
- The Next Bite, "Precision Trolling Testing Never Gets Old"
- US Patent 11473893, "Method to achieve a trolling depth by analyzing line angles"
- Fishing411, "Precision Trolling Testing Never Gets Old"
- Bassmaster, "A guide to precision cranking"
- HuntFishSport, "Trolling Depth Calculator"
- Fiskesajten, "Trollingfiske - en komplett guide"