A look in the archives shows that we have discussed fly lines in the past but it has been some time so I think it is a good starting place as I consider the fly line to be the distinguishing factor between fly fishing and other forms of fishing.
Fly fishers use a weighted line to propel a nearly weightless bait to the target. Because we are casting a line rather than throwing a weight it takes a degree of skill and practice to learn how to cast a fly in an efficient manner with reasonable accuracy. Attempting to throw heavier baits, such as nymphs and weighted streamers, can be made easier by understanding how to choose the right fly line for the job.
A bit of history
Fly lines were originally made of woven horsehair that was tapered to a few strands of hair. A description of the process can be found Horsehair Fly Lines (Extracted from A Treatyse of Fysshynge with an Angle by Dr. Andrew N. Herd) – http://www.flyfishinghistory.com/horshair.htm . Fly line technology did not change much until the 1800s when silk was added to the horsehair and eventually replaced horsehair completely. Silk had the advantage that it could be woven into various tapers and treated with oil coatings to make them float (horsehair lines did not float) although the floatability tended to last only a couple of hours and then a dry line had to be substituted if floating was desired. Wet silk lines had to be carefully dried, treated, and stored in order to prevent them from rotting. Creating woven silk line was also a labour intensive process and a skilled worker could produce about 8 lines per day.
During World War II silk became scarce and nylon was introduced. Nylon fly line manufacture was still done by weaving the desired taper even after the introduction of a PVC coating in 1949. The idea of creating fly lines by using a uniform core and adding a tapered PVC coating was introduced in 1952 and for the first time it was possible to mass produce fly lines.
Prior to 1959 fly line sizes were identified by letter designations that related to diameter. An “H” line measured .025″ in diameter; a “G” was .030″; a “D” was .045″; a “C” was .050″, etc. An “HDH” double tapered line was made to taper from a tip diameter of .025″ (H) to a body diameter of .045″ (D) then back down to .025″ (H) again to complete the line. A “GBF” was a three diameter weight-forward taper design measuring .030″ to .055″ to .035″ for the running line. The letter designations served the purpose very well – as long as all line manufacturers produced lines with braided silk with an oil impregnated finish coating. The weight factors were much the same – and an HDH silk line made by one manufacturer would weigh very close to that of an HDH produced by another maker using the same process. (Evolution of the Modern Fly Line (J. Leon Chandler) – http://www.flyanglersonline.com/features/readerscast/rc150.php)
After plastic coatings were added to fly lines the diameter rating system was no longer adequate because it was no longer possible to accurately determine the weight of a section of line from its diameter. This lead to the AFTMA rating system developed in 1959 and still in use today.
Technical Terms
Mass and weight Mass is used to describe how an object reacts to an applied force (Force = mass x acceleration) and weight is a measure of how much force gravity exerts on an object. Although they are not always the same they are often used interchangeably and on earth an object with 1 kilogram of mass will weigh 1 kilogram.
Grains The units that the mass of a fly line is typically measured in. A fly lines mass may also be measured in grams. There are 7000 grains in a pound or 15.4 grains in a gram.
Density Mass per unit volume, e.g. pounds per cubic foot or grams per cc. If something has a higher density than water it will sink. If it has a lower density than water then it floats.
Linear density The mass of an object such as line or string per unit length. eg. 30 feet of 6 weight fly line weighs 160 grains so its linear density is 160/30 = 5.33 grains per foot.
Mass profile This is also linear density although with fly lines we may also talk about how the linear density varies from one end of the line to the other end (see taper)
Taper (line profile) the change in diameter of the line as you travel from the tip of the line to the rear is referred to as the line taper. A typical fly line has a tip, front taper, belly, rear taper and running line although this is not always the case.
Drag or air resistance The resistance that an object feels as it moves through the air. Drag increases as speed of the object increases. It also increases as the surface area of the object increases which is why we try to keep our loops small. Drag has less affect as the mass of an object increases which explains why wind has less affect when casting heavier weight lines. This video gives you an idea of how mass and size are related to air drag https://www.youtube.com/watch?v=Z4gK5Kuy1bE&feature=youtu.be
T-rating The linear density of a fly line. For example a T-8 line has a linear density of 8 grains per foot.
Sink Rate How fast a sinking line sinks. This can be descriptive (slow, fast, very fast) or type (type 1 being slow, type 7 being very fast) or in inches per second. Be careful not to confuse T rating or linear density with sink rate. A 15 wt floating line has a linear density of over 18 grains per foot while a 6 weight sinking line has a linear density of just over 5 grains per foot. Remember that it is the density of the line, not the linear density, that determines if it will sink or float and how fast it will sink.
Overhang A measure of how far the head of your line is out past the tip of your rod, or how much running line you have past your rod tip. Attempting to cast with too much overhang is difficult to do.
Head The tip, front taper, belly and rear taper of a fly line.
Running Line vs Shooting Line Running line refers to the rear portion of a weight forward line. Typically it is a fully integrated part of the line. Shooting line is attached to the rear of a shooting head. It is often made of a different type of material than the shooting head it is attached to and is typically thinner than a running line. http://globalflyfisher.com/fishbetter/shooting-lines/
Specific Gravity The ratio of an objects density to the density of water. Floating line has a specific gravity of less than 1. Sinking line has a specific gravity greater than 1.
Information Sources
A Treatyse of Fysshynge with an Angle, Dame Juliana Berners, 1496 Available on-line at http://www.flyfishinghistory.com/treatyse.htm
Horsehair Fly Lines (Extracted from A Treatyse of Fysshynge with an Angle by Dr. Andrew N. Herd) – http://www.flyfishinghistory.com/horshair.htm
Modern Fly Lines, Bruce Richards, 1994 Considered by many to be the standard reference for fly line technology, unfortunately it is out of print and is difficult to find.
How to Design Fly Lines, Al Buhr
Beginners Corner: Choose the right line size from our handy chart – http://www.orvis.com/intro.aspx?subject=2107
How to Choose the Right Fly Line Weight, by Lefty Kreh – http://www.scientificanglers.com/plan-your-trip/fly-fishing-tips/how-choose-right-fly-line-weight-lefty-kreh
Fly Lines Explained (Peter Hayes) – http://www.tasfish.com/index.php?option=com_content&view=article&id=551:fly-lines-explained&catid=87:issue-63-august-2006&Itemid=137
Evolution of the Modern Fly Line (J. Leon Chandler) – http://www.flyanglersonline.com/features/readerscast/rc150.php
History (Scientific Anglers) – http://www.scientificanglers.com/about-sa/history
AFFTA Approved Fly Line Weight Specification (AFTMA) – http://www.affta.com/wp-content/uploads/2012/01/fly_line_weight_specs.pdf
Cores and Coatings (Scientific Anglers) – http://www.scientificanglers.com/plan-your-trip/fly-fishing-tips/cores-and-coatings
Choosing the Right Fly Line (flyfishusa) – http://www.flyfishusa.com/lines/choose-line-home.html#Coating
Okay – that’s it for now. I’ve given you a bit of history, some technical terms, and some references that you may find interesting. In the next post we will look at the characteristics of fly lines and how to select and set up fly lines.