“I always use 20-pound-test line when fishing for..” It doesn’t matter what, catfish, salmon, carp; the point is, the person making that claim always uses line 20 with a breaking strength — often called “test.”
So what’s the test for “test?” That seems a simple question. Tie a piece of 20-pound-rated fishing line to a 19-pound rock and lift. The rock should come off the ground. Tie the line to a 21 pound rock and lift until, snap, the line breaks.
Simple? Sure. But that’s not going to happen in the real world — and it’s not even a fair test. For one, most fishing line makers “under-sell” their line when it comes to how large a rock it will lift. It probably dates back to when the first fishing line was marketed.
No fishing line maker wanted to get the reputation for selling weak line. So if they made a line that would hold up a 20-pound rock but wouldn’t hold a 21-pounder, they labeled it 15 or perhaps 17-pound strength. Word of mouth was the social media of the day, and the line company didn’t want word to spread their 20-pound line wouldn’t lift a 19-pound rock. They suspected, however, fishermen would actually brag if their new 15-pound line would lift an 18 or 20-pound rock. Few fishermen bothered to actually see how large of rock they could actually lift with their line, they just trusted the line maker’s label.
There are other strengths to consider, as well. Chances are, if you are trying to lift a 20-pound rock with 20-pound line and the line breaks, the break will occur at the knot used to tie the line to the rock. Depending on the knot, the 20-pound line (if it really does break at 20 pounds of pull) when knotted with a good, “fisherman’s” knot will lift an 18- or even 19-pound rock. If it’s tied with a “granny” knot, it probably won’t lift a 12-pound rock. It’s called knot strength and though line makers will advertise their line has terrific “knot strength,” they won’t list any numbers with it since they aren’t the ones tying the knots.
Once you have that 20-pound rock suspended using 20-pound line, try bouncing the rock up and down. You may get away with a little bounce, but much more and the string will break. Actually, you can probably break the line with a 15-pound rock, just bounce it a bit more.
Due to the laws of physics and gravity, it’s likely the 15-pound rock or even a 10-pound rock, bounced hard, is putting more than 20-pounds of force and breaking the line. The line could be broken, however, without exceeding the 20-pounds of force, if the force is applied quickly.
I’m not going to do the math, but it’s possible to calculate just how far you have to drop even a 1-pound rock to have it hit the end of the length of line at a force between 15 and 19 pounds. The line should hold, right? That would depend on the line’s tensile strength, basically the ability of the line to withstand a sharp jerk — like when a fish strikes hard or when you set the hook. A line with low tensile strength won’t stand up to a sharp jerk, whether it’s a fish, a fisherman, or a falling rock.
The point is, the person who made the “I always” statement at the beginning of this column must usually have success with 20-pound line he’s chosen. Good for him.
Be aware, however, there’s much more to choosing a fishing line than just its strength rating. Breaking strength, knot strength, tensile strength should all be considered as well as the material from which the line is made, the color of the line, the amount of stretch — in some cases, even the cost of the line can be a factor. All line is not created equally and there’s no such thing as one line that’s good for every type of fishing or rock lifting.