The Truth About Fluorocarbon, Part I

Of all the hype and advertisement lingo generated by bass fishing tackle, perhaps some of the most misunderstood relates to fluorocarbon line. We're going to take a look at some of the claims, and set the record straight on much of what you hear or read, "Big Indiana Bass" style. That means they'll be lots of science and/or math involved, or actual experiments used to make the points. We wouldn't have it any other way on this site.

In this first part, we'll tackle one of the two worst abused properties of fluorocarbon, that being the claims of "invisible", "nearly invisible" or "virtually invisible". This is widely touted based upon a term called refractive index. You can read about it at the link above, but the numbers you hear thrown about are the following:

• Water has a refractive index of 1.3330
• fluorocarbon has an index of 1.42
• and nylon monofilaments tend to range from 1.53-1.62

All this means is that fluorocarbon's number is closer to that of waters, but it doesn't necessarily translate into any form of "invisibility" because of it, simply because there are so many other variables involved. Back in 2001, Jeff Thomson posted a great piece that refuted scientifically any claims as to whether fluorocarbon line was "invisible". That piece has since disappeared from the Net, but being the science junkie I am, I immediately saved a copy when I first came across it. I've tried to contact Jeff to get permission to use the piece on this site, so far unsuccessfully, so this may or may not stay up depending, as my intent isn't to in any way risk copyright infringement. It has been 5 or 6 years since I've seen Jeff post on any of the message forums, but I've added his presentation to the reports section of this site, just because such nice pieces of fishing related science shouldn't be lost to the world :)

So, to once and for all crush this idea of fluorocarbon invisibility, see Jeff's piece entitled "Mathematical Theory of Fishing Line Visibility" at this link, or in the reports section of the site, lower left sidebar.

Comments

[Paul Roberts]

I see...Scattering will occur through any translucent cylinder -regardless of refractive index.

But...how much?

I didn't see a comparison between mono and fluoro. Not that there needs to be one.

I've always said that the biggest innovation the angling world could see would be being able to get rid of that line tethered to our baits. And visibility is just not the key issue.

[Rich Ziert]

I see that this is only part #1. of "The Truth"

Does "Part 2" talk about the medium in which the line is viewed and the time variant of where and how it is viewed. . . by fish ?

Actually, the medium is very important, as is the viewing position. There is no such thing as natural pure water. All natural water has "stuff" in it to one degree or another and that stuff is viewed at various times of the day or night and from various positions in the water column.

All this, of course, will make "any" line #1. more, or #2. less visible depending on the color, and thickness of the line, quality, quantity, of that "stuff" in the water, and at what intensity and angle the light hits same, as well as the viewing position.

So, it can very well be that there are times and places when/where line is invisible. Or at the very least the refractive index is reduced to a point of micron near invisible.

The thing of it is that if we pick our targets with a little more thought as to how our line and lure appear under what conditions, in what direction they move, and how they move, we’d catch more than a little more fish.

[Jeremy S]

To me the biggest problem I see with people using fluoro is that in a situation where they would downsize mono or copoly due to finicky fish, say throwing 6 or 8 pound versus the 12 they normally throw, they will use the 12 pound fluoro or sometimes even heavier because they think its "invisible". I would think the disturbance in the water caused by the heavier line would be more likely to be picked up by the fish's lateral line than the fish seeing the line and getting spooked by it.

Fluoro has certain beneficial attributes that are nice in certain situations: it sinks, its highly abrasion resistant, it tends to be more sensitive than mono. However, it deforms when it stretches (yes it most definitely stretches) which would likely leave it weaker than mono which tends to spring back to its original dimensions when stretched. It's also downright expensive. I can buy a spool of braid for the same as a spool of decent fluoro, and the braid will last as long as there is enough left on the reel to cast properly while the fluoro will have to be changed nearly as often as plain old mono.

I see fluoro as being useful as leader material in certain situations, but as a main line I think there are much better options.

[Rich Ziert]

Then there is whether or not fish give a hoot on a recognition scale. Unless a fish is caught repeatedly over a short period of time and recognizes something (fishing line) as being the thing that caused his pain/stress, the operant conditioning factor wouldn't amount to a hill of beans. Certainly the line looks unnatural, but should not be an overwhelming deterrent to aggressive younger fish with little or no association with being caught.

All creatures learn from day one of birth and learning does not work its way into DNA. We should never confuse:

The ability to learn and learning - acquiring knowledge or skills, with

Instincts/traits - an impulse behavior shaped by biological needs and survival.

Learning enhances instincts, not the other way around. All fish even of the same hatch or school are different; learn differently and have a different position on the learning curve.

[Big Indiana Bass]

Paul, it appears he only calculated for FC, but since FC with a RI of 1.4 results in a final number of 1.05, mono with a RI of 1.5-1.6 would result in a higher number (>1.05) yet. I tried to solve for mono but I'm not certain of the units used as mine aren't canceling out correctly :) and I don't have the time necessary at the moment to figure out the error/conversion needed. That said, I'm in agreement that when/where you want to "hide" your line, use the smallest diameter possible.

Rich, all good points. Part 2 will deal with other claimed properties, many that Jeremy mentions in his comment, especially stretch/density. Especially like your next to last paragraph. Certain times and conditions, yes, but that would apply for all lines, not just fluoro.

A lot also depends on your state (or condition) of observation. For example, a Stealth bomber can return a radar signature equivalent to a bird, making it appear nearly invisible, yet it would certainly not be nearly invisible to someone seeing the plane fly overhead.

Jeremy, another good point. The larger the diameter line, the greater the pressure wave it will create from displacement in water, to a degree. Interestingly, the largest pressure waves (disturbances) appear to be created by braids even though they are thinner. This is due to their uneven (woven) texture which unlike the smooth, rounded surface of either mono or FC, creates more vortices due to its uneveness.

[Rich Ziert]

You definately have a basis for an advanced BIB blog article here. Carry on captain.

[Paul Roberts]

From what I've seen over the years -lots of UL fishing and FF -it's the diameter affecting the presentation that counts most.

The easiest way to quickly describe in short it (sans my anecdotal examples) is a lure tethered to a line can be registered (seen/heard/felt) by fish as much larger than the lure (not to mention it's intended action) itself.