Simon Gawesworth's Guide to Fly Lines for Single-Handed RodsChoosing the correct fly line to balance your fly rod and to best serve the intended purpose of the line is critical to fly fishing success.
Choosing a Single-Handed Fly LineYour rod and line must work together to make casting and fishing a pleasure and the wrong choice of fly line can make even the best fly rod cumbersome and uncooperative.
Fly Line Construction and Jargon ExplainedFly lines have two components, the inner core and the outer coating:
The CoreEvery fly line has a core that runs through the centre of the line. The core provides the strength of the line and is a major factor in how stiff (or supple) the line is. The core also controls how much stretch there is in a line, with ultra-low stretch cores providing greater feel and control in casting and fishing techniques and more stretchy cores providing greater shock absorption with super light tippets. Core strengths vary from 15lb to 70lb depending on design criteria and line size and it makes sense not to use a leader that is stronger than the core of your fly line.
Some fly lines are manufactured to be much stiffer than others – usually lines that are designed for hot, tropical conditions. Using a regular ‘cold water’ coating, fly lines subject to high temperatures will result in a very limp, soft line that doesn’t shoot and has great problems holding a loop. If used in cool/normal UK conditions these lines are usually stiff and wiry and need to be stretched before they can be used.
The CoatingThe core of a line is surrounded by a plastic coating that is bonded to the core. The coating influences the line’s shape, weight and density.
Fly Line ShapeLine manufacturers vary the shape of a fly line to make it perform in different ways. This shape is called the ‘profile’ of the line and features a variety of different taper and diameter changes along the line’s length. These taper changes determine the line’s casting behavior. For example, a line with a long front taper and a light front end lands softly on the water and is great for presentation but would be useless with a heavy fly or in a tough wind. A line with a lot of weight at the front end, and a short front taper, would be far better suited for these more challenging conditions.
Within the fly line world, there are two generally used line shapes: a ‘weight forward’ and a ‘double taper’. As the name suggests, weight forward lines have most of the weight at the front end, and a very thin ‘running line’ behind this weight. The thin running line has less friction and drag than the head, which makes it easy to shoot line and get distance. A much lesser used line shape these days is the ‘double taper’, which is a fat line for most its length but with a taper to a thin tip at each end.
Fly Line WeightFly lines are generally made to an industry standard weight called the AFTM standard. The purpose of this standard is to help anglers match a fly line to a rod they have bought. The standard is a number given to both line and rod (usually between 1 and 12) that ensures matching numbered fly lines and fly rods balance and load perfectly. For example, put a 6wt line on a 6wt rod and a 2wt line on a 2wt rod, and so on. The standard is actually based on the weight of the first 30 feet of line, not the entire line.
Fly Line DensityThe density of the coating determines whether the line floats or sinks. Floating lines have tiny ‘microspheres’ to make them float and may also incorporate a hydrophobic chemical to repel water. Sinking lines have tungsten added to the coating to make them sink, the amount of tungsten in the coating influencing the sink rate of the line. Lines can sink at any speed between 1 and 8 inches per second.
A fly line is usually designated by a code on the front of the box, something like ‘WF6F’. Usually the first two letters of this code tell you the shape (profile) of the line, the number tells you the size (weight) of the line, and the last letter tells you if it floats or sinks. In this example ‘WF’ means it is a ‘weight forward’ line, ‘6’ means it is for a 6wt rod, and ‘F’ means that it floats. If it had an ‘S’ at the end, it would mean that the line would sink, and a number after the S tells you how fast it sinks. For example, a ‘WF7S6’ is a weight forward, 7wt sinking line that sinks at 7 inches per second.
Anatomy of a Typical ‘Weight Forward’ Fly Line
Tip – This section attaches to the leader and may feature a loop for this purpose. It is short, usually 6-12”, to allow for the trimming necessary to fit new braided loops etc. without depleting the tapered section.
Front taper – This section, typically 4’-8’, increases in diameter as it recedes from the tip. The longer, finer and more gently it tapers the more delicately the fly will be delivered, although such lines will perform poorly with large flies and when casting into the wind.
Body – This thicker section is its engine room, the longest part of the taper that transmits the full energy of the cast.
Rear taper – Here the line reduces in diameter again and can vary in length from 1 foot to as much as 25 feet depending on what the line is designed to do.
Head – The ‘head’ of a fly line incorporates the front taper, the body and the rear taper and it is usually the weight of this head that gives the line its size.
Running line – This level section attaches to the backing on the fly reel. Its thin diameter and light weight means there is little drag when making the final cast, allowing anglers to make longer casts.
I hope that's helped you!