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the truth about stretch (
elasticity), elongation under an applied force
Laboratory Manager
Dr. Steve Adams explains what line-stretch really means, and doesn't mean!


While we were doing all the wet abrasion tests on the lines for Brian's article, it reminded me that an equal amount of rubbish is talked, written and claimed about the elongation of fishing lines in-use and under an applied force, known as stretch. I mentioned this to Editor, Nick Caine, and he suggested that I might like to do some tests and then to write an article about the results, and so here it is. Firstly I should say that being a very keen angler and a textile technologist to-boot, much of the incorrect terminology used to describe fishing lines sometimes gets right up my nose, and it just goes to prove that a lot of these fishing-tackle marketing companies just don't know what they're talking-about or are deliberately trying to con us; at the very least, in ignorance, they constantly copy and regurgitate things that are incorrect and often misleading. Take the abbreviation "B.S." for example: this means Breaking Stress or Breaking Strength and not Breaking Strain — strain is not a measure of the applied force required to break a line, it is a measure of the distortion (e.g. stretch) of the test material, caused by the application of a force i.e. stress.


Many figures are bandied-around about this line having "x% stretch" and that line having less or more — now, I have no idea what this means, and I am sure, therefore, that neither do most of the people who write or talk about stretch. Do they mean elongation as measured on a dry line? Meaningless ! Do they mean elongation as measured on a unknotted line? Fairly meaningless in practical fishing terms! Do they mean elongation as measured at the Breaking Point of a properly conditioned i.e. wet line? This is a meaningful figure but not in terms of everyday fishing, when your line never normally experiences any applied force approaching its Breaking Strength. Do they mean elongation as measured on a properly conditioned line at its elastic limit? Or a half its elastic limit? Or at 10% of its elastic limit? Or what? Who knows? Most of them don't, for sure!


When you're measuring the Breaking Strength of conditioned (i.e. wet) knotted (e.g. using a Palomar knot) or unknotted line, the machines we use also automatically measure the amount of elongation that has occurred when the line breaks. And we don't just do one single test! We usually test each sample at least six times, more if the results don't look consistent. When you're trying to compare the BS and Elongation-at-the-Breaking-Point (E @ BP), obviously you have to compare like-with like although different polymers (e.g. nylon 6, nylon 66, fluorocarbon, HPPE etc) may be used in the extrusion of the monofil or braid, the comparative diameters are important. Of course, when you carry-out BS tests, you are establishing the actual BS, not the claimed BS. So, testing lines to their Breaking Point will give you the actual BS and actual elongation at the Breaking Point, with lines of known polymer composition and known (i.e. measured) diameter. To give you some idea about how ridiculous some of the marketing claims for some lines are, for Nick's website and this article, we tested (at considerable cost and time), over 20 monofilament fishing lines of comparable claimed BS and claimed diameter. There isn't space to tabulate all the data here, but here's some examples of claimed and measured 5.5 kg & 3 kg B.S. monos:-


But, as I've already said, the percentage (%) elongation of lines at their Breaking Point is pretty-much completely meaningless for practical fishing purposes. If you have to pull-to-break from a snag, you're hardly going to care a monkey's wotsit about the elongation that occurs, are you? Much more meaningful would be comparative data on the percentage stretch of lines of similar diameter and actual BS at an applied force of something like 10% or 25% of their actual BS, well within their Elastic Limit. The data above were measured at 25% of their respective Elastic Limits and at their Breaking Points.


The Elastic Limit of a line is the maximum elongation (stretch) that can occur when a force is applied to the line, after which it will return to its original length when the force is removed. If a force is applied to a line such that the line is stretched past its Elastic Limit, then, when the applied force is removed, the line will not return to its original length, and will have lost some of its original elasticity (variable stretch). Indeed some lines are sold as "pre-stretched", presumably past their Elastic Limit, and presumably so that the line stetches less in-use and is perhaps more sensitive. Of course, it's most important to re-test the BS of "pre-stretched" lines after they have been stretched! Here are some averaged data for one particular 8 kg measured wet unknotted B.S. co-polymer mono with very high abrasion resistance. You can see that it doesn't stretch anything-like some of the claims of 18 to 22% made or suggested by some people and/or companies:-


FACT: Under normal everyday conditions while you're fishing, unless you hit a big snag or specimen fish, your line never experiences any forces that come anywhere near stretching it to or past its Elastic Limit — period ! If you're casting long distances with mega-lures and hefty jerk-baits, obviously the forces on your line are greatly increased but still not enough to take the line anywhere near its limits, assuming of course that you selected a sensible BS in the first place.
Elasticity (stretch) in a line is a double-edged sword though; personally I prefer a bit of elasticity in my line when I'm lure fishing if only to provide some shock resistance to reduce any hefty transient forces that might otherwise snap my high-modulus rods — this is especially true when I'm sea-fishing with lures. Otherwise of course, like most up-to-date & switched-on lure-anglers, I use one of the many HPPE Superbraids or fusion lines that abound these days and which have very little elasticity or stretch, even at their Breaking Point — and there's the obvious downside to that too.


So, if you're still with me so far, and have understood what I've been trying to put-over, for sure you'll now know far more about stretch and elasticity than many of the fishing tackle companies who market their lines with spurious claims about stretch. Of course, all that matters at the end of the day, is the safety (of the fish and you) and the success and enjoyment of your fishing, but the point I'm trying to make here is that if you're choosing and buying lines based on their claims of N% stretch, "low stretch", "pre-stretch", "high stretch" or whatever, the chances are that they figures are meaningless, and you should be aware that you may be being fooled i.e. deceived into parting with your money for one line rather than another. Get me?!
The sad or rather, annoying, thing is that a lot of these fishing tackle marketing companies are either ignorant, arrogant, or non-receptive to suggestions for corrections to their claims, or too tight-wad or too frightened to actually have their lines tested by an independent, internationally-accredited Laboratory. When I find that lines don't meet their claims, I pass the data to my friendly local Trading Standards Office — there's no way fishing tackle companies should be allowed to get-away with charging for products that are based on false claims.
And to leave you with a typical quote from just one such company, which says it all, and made me chuckle at the time, but not any more, it just gets me angry, viz.
" .... don't try to blind us with facts!" ... I ask you?!! Grow-up!
Anyway, knowledge and facts are strengths, so enjoy your fishing & my fishing tackle facts!

click on the photos to enlarge