If you are fishing a stream where a twelve-inch trout is a behemoth, you probably aren’t too worried about knots. It’s unlikely a fish will break you off, even with 8X tippets. But ply your fly in waters with bigger fish, especially if you are using lighter tippets and the situation can be very different. This is when knots can quite literally make or break your chances of success.
There’s a lot of information about fishing knots online and in print, such as how to tie them, how strong they are, and which ones to use for specific applications. For most folks, this is all the information they need or want. But there’s a small subset of fly fishers who have an annoying habit of continuously asking why. They might find themselves wondering what is going on when the fish and fly fisher pull on a knot from opposite directions. Perhaps they think a much closer look at knots might provide some useful insights. Apparently, I’m one of those folks.
One of the many maxims in fly fishing is “no knot breaks until it slips”. This is why we make sure to use the correct number of turns and lubricate them with saliva before cinching them down. But what if you tied a knot the right way, using brand new tippet material and it still failed? Did it slip or is there something else going on?
Anglers aren’t the only folks interested in knots. Mathematicians and scientists have been busy studying them in great detail. To get a better handle on the subject, I looked at what the academics had to say. A review of several mathematical papers was interesting, though some of the equations were pretty brutal. The scientists are doing some cool stuff, but most of it is a bit too technical to be of direct value to fly fishers. Fortunately, a paper in the New Journal of Physics did provide a useful observation. It stated, “Knots break at the point of highest curvature, which is located at the entry to the knot.” Put more simply, a knot breaks when the twist at the end of the knot gets too tight.
To see if this “tight-twist” theory held true for fishing knots and tippet material would require some serious magnification. Fortunately, like most fly fishers, I have a digital microscope that shoots videos and photos at up to 100X magnification. Setting up the microscope was relatively easy, but building a traction device that was stable enough for high-magnification videos was a real challenge. That took several hours. Once everything was sorted out, I contacted Josh Jenkins at Scientific Anglers and he kindly provided several spools of factory-fresh tippet materials.
The knots were tied onto a micro swivel to make it easier to align them with the scope. After each knot had been meticulously tied, lubricated, and cinched down, sections of the knot were color-coded with Sharpie markers. This would help show any movements as the knot was subjected to increasing tension and hopefully pinpoint the location of the actual break. The twists were left transparent, so any internal movements of the knot would be visible. Seconds before each test began, a drop of water was added to the knot to help mimic actual fishing conditions.
I wasn’t sure what to expect. Boring videos of knots doing nothing and then suddenly breaking seemed quite likely. Almost a hundred tests were run, using different knots and tippets, covering a wide range of freshwater and saltwater fishing scenarios. To avoid turning this into a long technical treatise, let’s skip over most of the details and get straight to the stuff that matters in the real world of fishing.
Slipping
The videos were far from boring. It turns out fishing knots are mesmerizing shape-shifters, which slither and squirm as the tension is increased. Twisted knots such as the Clinch and Uni exhibited the most slip, resembling a transparent anaconda squeezing toothpaste from a tube. The Trilene knot (basically a clinch knot with a double wrap through the eye) showed slightly less movement, no doubt due to increased friction from the extra wrap. Non-twisted knots such as the Orvis and Palomar knots slipped the least, though they certainly weren’t lifeless. The majority of the movement occurred as the knots came under tension and reduced as they approached the breaking point.
Sliding
One thing that stood out was how the tippet slid around the inside of the eye, much like a rope sliding over a pulley. I had no idea knots did this and can’t recall anyone ever mentioning it. Close inspection showed that this tippet section started with a normal round profile but progressively flattened as the tension increased. Just before the knot broke, it had formed a very flat oval.
Break Location
Following each test, the tippet was given a post-mortem examination to see which Sharpie color mark was at the break. In almost every case, the knot broke at (or just after) the section of tippet inside the eye. Microscopic examination revealed that this section of tippet had developed a flat surface that was one to three millimeters long and almost half its width. Being simultaneously dragged over and crushed against the metal produced a shear force that permanently deformed the tippet. While I can’t be 100% certain, it seems highly likely this is the reason why good knots ultimately break. Apparently, the physicist’s tight-twist theory doesn’t seem to hold for hook knots.
Good Eyes?
Given that the vast majority of breaks were associated with the section of tippet inside the hook eye, a closer examination of this part of the hook seemed warranted. Rough spots or defects in the metal could potentially damage the tippet, reducing knot strength. A variety of hooks from different manufacturers were placed under the microscope.
Every conventional ring-eye hook showed some anomalies, mainly at the back of the eye. There was a small nick on the outer edge, close to where the end of the wire butts up against the shank, presumably associated with the eye-forming process. In some hooks the end of the wire was slightly flared, creating a potentially sharp edge that protruded into the eye. Both of these features can be seen with a good magnifying glass.
The microscope revealed a flattened area on the inner surface of the eye, presumably formed when the hook wire was bent around a hard metal post. I searched online, but couldn’t find any reference to this flat surface. This has potential implications for knot strength.
Scientists say the reason a tight twist causes knot failure is that the molecules on the outside edge of the monofilament are stretched and torn apart. Think of snapping a freshly cut twig over your knee. At first it bends and then the fibers on the outer edge splinter, which causes the twig to break. The transitions from the curved surface to the flat area creates two small angled edges, a bit like a miniature version of the knee and twig situation. This results in the outer edge of the tippet being subject to slightly more stretching than it would if the surface of the eye had a round profile. The wider the flat area, the sharper the angle and the greater the stress on the tippet.
In most hooks, the flat area was confined to the back half of the eye, but some of the cheaper hooks showed flattening around the entire inner surface. Does this really matter? I don’t know. Some break strength testing hinted at an effect but wasn’t conclusive. Perhaps it’s best to assume that when it comes to internal flat spots, less is better and none is best.
While most hook eyes had a smooth outer surface, several hooks (from low-cost, private-label brands) had noticeable grooves and pits. Like the flat areas, these defects could weaken the tippet as it tightens and slides over the eye. Given the variability in the size and location of these defects, it seems likely they occurred during the wire-forming process. Presumably, one of the reasons the hooks cost less is because they use a lower-quality wire.
Most knots grip the front of the eye so, under normal circumstances, defects at the back are unlikely to damage the tippet material. However, loop knots are free to move around the eye, which means defects at the back may be of concern. This might explain why loop knots can sometimes fail at the end of the loop, as opposed to the knot itself. The end of the loop probably gets dragged over the defects multiple times during each cast and retrieve.
There was one type of hook that did not have any noticeable eye problems. Tapered loop eye salmon hooks appear to utilize high-quality wire and an eye-forming process that produces an almost flawless surface. Unfortunately for the nymph and dry fly folks, these hooks don’t seem to be made any smaller than size 8.
Hooks aren’t the only piece of tackle that can cause trouble with your knots. I made the mistake of buying a pack of cheap tippet rings off the internet. In preparation for an upcoming lake fishing trip, I decided to add them to some leaders. The first three attempted tippet knots didn’t even survive the cinching process. At that point, it was obvious sloppy knot-tying was not to blame. A check with the microscope revealed that the ring’s inner surface was completely flat, like an extreme example of the flat area in hook eyes.
Tests were also run on leader-to-tippet knots, all of which broke at the tightest twist located at the end of the knot, just as the physicists had stated. This is reassuring but also provides a cautionary warning. According to the academics, the knot with the tightest turn is the overhand knot, which most fly fishers know as the wind knot. A few years back, I ran a bunch of knot strength tests and found that a single wind knot reduced tippet strength by an average of 50 percent. Others have gotten similar results.
So what have we learned from these experiments?
All knots slip, regardless of type, tippet, and tying technique. You could, in theory, cinch a knot so that it only slips at the moment it breaks, but that would be close to impossible. The tension you’d need to apply would be incredibly close to the break strength of the knot. It’s unlikely that even the most skilled vascular surgeon has hands with that kind of precision. Besides, knots don’t break at exactly the same tension, there is always going to be some knot-to-knot variability. This means you can only guesstimate a knot’s break strength and will inevitably break a proportion of knots before they even get in the water. Just cinch the knot down until it looks right and fish it.
The eye of the hook may be a factor in losing fish. Any defects could damage the tippet and reduce the knot’s break strength. Given the microscopic size of these defects, it’s impractical to check every fly before tying it on. The obvious “acid test” is to discard any fly that causes the knot to break when it is fully cinched down. It also makes sense to get rid of any flies that show signs of rust.
The ring eye hooks with the best eyes were generally from premium brands. If you buy flies, check to see if the company lists the make of hooks they use. These flies may cost you an extra buck or two, but isn’t that better than losing a big fish? If you tie flies, just use the best hooks. The cost is unlikely to be more than twenty-five cents per fly.
Fly tyers could also consider covering up any irregularities at the back of the eye with thread and head cement, especially if the fly is likely to be fished with loop knots. For freshwater flies tied on hooks larger than size 8, such as hoppers, stoneflies, and streamers, it might make sense to switch to tapered loop eye hooks with their defect-free eyes.
Folks who use loop knots for streamers and Clousers should keep a close eye on the end of the loop and retie the knot every so often. If this sounds like too much trouble, just use one of the metal fly clips or snap locks from well-known companies. They may look a bit clunky, but they really do work.
If you use tippet rings, only buy from well-known companies. If you have exceptional eyesight and a good magnifying glass, you may be able to see if the inner surface of the ring is smooth or flat, but I doubt it. For folks with less than 20/10 vision, it’s probably best to test your knot carefully before pitching the fly to the fish. If the ring fails the test a couple of times, ditch it.
Last, but certainly not least, don’t ignore wind knots. Sure it’s a pain in the derriere to replace the tippet, but you’ll be glad you did when that big fish takes your fly and the fireworks begin. You really don’t want to miss that show.
Always like the precision of your studies. Well done!
Thank You!