The Truth About Fluorocarbon, Part II

In this next segment, we'll look at another of the egregious claims bestowed upon fluorocarbon line by anglers and manufacturers alike, and that is one of less stretch or low stretch. First though, we need to learn a little more about just what stretch is, and to do that means we need to know stress-strain curves. Keep in mind I'm not a materials engineer, but I'll try and do justice to the terminology as best I can while still getting the point across.

Many of you have probably heard the term tensile strength when talking about fishing line. Advertisers frequently reference it when trying to convince you how tough their fishing line is, often in relation to it's breaking strenth. Tensile strength is actually a measurement of ultimate breaking strength (a strain) divided by the cross-sectional area of the line in question. But material testers also use what is termed a tensile test, also commonly called a stress-strain test. Basically, a material has a strain placed upon it and a measure of that materials stretch or elongation relative to its original length for that given strain is documented. When plotted out you end up with what is known as a stress-strain curve. In the above picture, a typical curve generated for monofilament is on the left, while on the right, a similar type curve representative of what you might see for a thermoplastic such as fluorocarbon. You'll notice the differences (forget the specific units for now), and that brings us to another needed explanation.

Stretch actually involves two different components; elasticity and plasticity. Elasticity is typically at the intial loading of the curve and encompasses the ability of a material to immediately return to it's original state (length when referring to stretching a fishing line) upon release of that load or strain. Elasticity is usually a linear relationship whereby as strain increases, % elongation increases proportionately. But many materials after reaching a certain level of strain start to deform to the point of not being able to return to original length once the load or strain is released. That part of the stretch equation is referred to as the plastic phase.

In the fluorocarbon curve above, that is represented by the curve flattening out across the graph after the initial peak. At this point, a small increase in strain creates a disproportionate increase in elongation. With brittle materials, little or no plastic deformation occurs and the material fractures near the end of the linear-elastic portion of the curve. But with various thermoplastics such as fishing line there is a gradual transition from elastic to plastic behavior, and the exact point at which plastic deformation begins to occur is hard to determine.

All that brings us around to what is starting to finally be disseminated to the angling public, and that is that fluorocarbon has as much total stretch as a percentage of starting length (elongation) as monofilament when tested off the shelf. It's just that after all the stretching is done, fluorocarbon will be left at a longer length than original due to permanent deformation, while most monofilaments will be close to their original length as measured prior to testing. And since most bulk spools of fluorocarbon have some type of "trade formulation" to achieve specific attributes such as suppleness or decreased memory, it becomes very difficult to translate the strain curves in "real life".

Rick's test was probably the first I saw that documented this permanent deformation of fluorocarbon after stretching using as little as 3 to 5 pounds of stress, and more recently TackleTour's published study documented this phenomenon at only 3 pounds of stress. Which made me wonder about even lighter amounts of pressure, and whether a simple stretch test could capture this limit where the elastic turns to plastic in fluorocarbon. Could this difference in the stress-strain curves account for the supposed increase in sensitivity people claim fluorocarbon has?

So I carried out my own little stretch test using two different pound tests of line, and comparing fluorocarbon to monofilament. To try and help detect this lower stress curve, I increased the length of my test lines to approximately 15' from the typical shorter lengths used by others. The thought being that during the elastic phase with fluorocarbon, it might stretch less than monofilament as theorized by anglers based upon sensitivity and the like. My results are below.

In the first diagram are the results for the 6 pound test. As you can see the mono stretched further at all load levels, though they were all within 2-4% of each other all the way up to the 14-16% range under the 4 pound load. They probably would have stretched more before breaking, but that wasn't the point of the test. The loads started at just 0.5 pound, but there is no difference in the overall stretch pattern of the two.

In the second diagram was a test between .016" fluorocarbon and .015" monofilament. In this case, the same patterns emerged at all levels again, with the exception of the fluorocarbon stretching slightly more than the mono. The reason for the two fluorocarbon results was due to a slip in the knot at the 4.5 pound load range on the first test. I retied and ran again successfully up to the 5 pound load using the same piece of line that had already been stretched once. The same overall pattern emerged, but it is interesting to note that the second time around the line stretched slightly more initially before being identical at the 2 pound load, and then being a little less elongated after that at the higher levels. Might just be an anomaly, but is interesting none the less.

The final test, which I don't have data to show, was at just a single load of less than 2 ounces (50g) on the two 6 pound lines. The thought was that perhaps only under very light loads would the difference be apparent, but again, the fluoro and the mono stretched almost identical distances (1" over a 120" length).

So the take home message is that fluorocarbon is not low stretch, and is really no better than regular monofilament in this category. As such, another claim busted. So what are it's positive attributes, its correct claims, and why does it seem to be more sensitive? More details to follow in Part III.

Comments

[RS]

There has to be some reason I like fluoro! Maybe it is a matter of using the wrong terms to interpret what I think it is I like about it, e.g., thinking higher sensitivity is due to low stretch? But then again, no-stretch line, braid, is only sensitive if it is tight, where mono or even better, fluoro, transmits tics and thumps even when limp. Maybe we are measuring the wrong things? In any case, there are techniques, such as Senko fishing, where I wouldn't be without it. All in my head???

[Jeremy S]

My guess on the sensitivity would be that it is a denser material than monofilament so it transmits vibration better, much the same way that liquids and solids transmit sound waves more efficiently than air does (e.g., you can put your ear to the railroad tracks and hear a train long before you can hear it through the air).

[Paul Roberts]

Good stuff Brian, I've only recently begun to fish fluoro and only for the one obvious difference it offers -it sinks. I use it for deeper presentations which can provide a straighter line connection with the lure -my guess is this is your sensitivity difference right there. But so far I haven't noticed a sensitivity difference fishing shallow. I think a test for this would be easy, although tough to quantify.

Take a two spare spools with X# mono and fluoro to a shallow flat (or even your driveway) and drag a sinker with you eyes closed. Is there a difference? I'm going to make a prediction: No. There is no appreciable difference.

[Big Indiana Bass]

You guys are stealing my thunder :) Answers and theories to all the above (sensitivity, density, sinking, etc.) to come in Part III.

[Rich Ziert]

Sensitivity:

Another view on "Stealing Thunder". You won't believe this but that phrase went through my head with what we wrote yesterday.

Should we get all wrapped up in "stretch" pants and sensitivity ? ;>)

Sensitivity is far more important than stretch. Quantifiably different, one does not necessarily promote the other. . . and sensitivity is in the fiber of the beholder. That last part has all kinds of useful – thought provoking - double meanings.

Sensitivity: Care and understanding of needs and requirements. Capacity of physical sensation or response. The ability of the receiver to respond to transmitted signals. And lastly, Sensitivity is/are feelings that might be offended.

All of these definitions are important.

Incomplete ramblings follow: You figure the correlations out for yourselves.

Does 8# mono have the same sensitivity as 20 # flouro ? Does the thickness of the line make a difference ? Does a thicker diameter piece of material have the same vibration refractive quality as a thinner one. Does that thicker material have a greater water slicing vortex and sound signature ? Do you have more sensitivity than I do, than the fish have ? Does water temperature and water pressure have a say ? Does the Sun have an effect on how you feel ? Does the amount of line is out effect the outcome ? Does a greater length of line decrease vibrations of a tin can Walkie-Talkie ? Does the depth at which we fish, or the amount of line cast, coupled with interference in the water do the same ? Would you rather horse fish in or play them out ? Does the fish feel various lines the same, or differently one to another ? Would you rather get them on the hook first or worry about bringing them to net ?

More often than not, sensitivity is simply paying more attention to detail; putting aside the confusion of outside static – are you “thin skinned“ ? In some situations being so is not such a bad thing after all.

[Rich Ziert]

One other comment comes from my now retired career as a Risk Manager about Marketing Men, Underwriters, and Actuaries.

A Marketing Man, an Underwriter, and an Actuary went for a ride together one day in the countryside. When passing a farmers field along the way, the Marketing Man said, "My, my, look at that cow standing in that field; an excellent example of a very fine cow if I ever saw one." The underwriter then said, "Yeah, from this side". The actuary, not to be outdone or remain silent exclaimed, " both your views are well and good, but how would you like them to look ?"

The Marketing Man takes the best possible position at face value.

The Underwriter takes the best possible position upon thorough investigation.

The Actuary has it within his power to make the outcome appear to be anything the viewer wants.

The farmer (and maybe the cow) is/are the only one(s) who really knows what’s what.