Choosing and designing fly casting and fly fishing leaders.
Before the days of synthetic materials such as nylon and fluorocarbon, tapered leaders were tied from three pieces of gut of different diameters but usually of about the same length of around two or three feet in each. A good basic rule for tying up such leaders is the two thirds rule which says that for the same material, diameters of adjoining sections should be stepped down no more than two thirds of the diameter of the proceeding section in order to prevent hinging. Fortunately this rule also holds good as a guide for making your own simple tapered leaders with a minimum of knots but more complicated leader designs can be produced if you wish. Like most things tapers can be overcomplicated and I have seen custom designed leaders that look like a succession of knots just a few inches apart.
Double Uni Knot or Grinner Knot
It is not necessary to have so many pieces and I doubt the value of sections less than 6 inches in length. Too many knots cause drag and disturbance and look untidy anyway. Given that tapers require two pieces of dissimilar diameters or even of different characteristics to be knotted together choice of knot is important. For many years I have relied on the Grinner (or Double Uni) (same knot) for this purpose because of its good strength, reliability and ease of tying. One of its beauties is that the knot made from the heavier material can be tightened with that material rather than knots like the Double Blood Knot where the lighter and heavier materials are pulled apart to finally tighten the knot, sometimes causing stress in the weaker material.
Trout leader selection is important
Therefore all things considered the fly size and weight broadly determines the choice of rod and line rating. Large and heavy flies require higher line ratings to cast them successfully whereas small light flies can be cast on lower line sizes. The line characteristics i.e. stiffness and diameter determine the ideal leader butt qualities for a good match and smooth transition. Consideration of the fly size and weight determines the leader length and stiffness, big bulky flies require short stiff leaders and tiny flies can be cast with long and fine leaders. Fly size and intended presentation also determines the choice of tippet diameter. So for a given outfit and chosen fly we can fix the leader butt material, decide on the preferred tippet material and choose a suitable length of leader. All that remains is to figure out the tapered section between the butt and the tippet. So as an example let’s suppose that I have some 0.45mm monofilament that is a nice match to the stiffness of the tip of the fly line. I want to fish for some large trout with a size 12 fly and a tippet of 3X diameter. Using the “rule of elevens” (11 thousands of an inch is 0X), therefore 3X is 11 minus 3 thousands of an inch which is 0.008 inches. The X sizes derive from the days of drawn gut and that is why they are given in imperial dimensions which unfortunately make life a little more complicated when calculating tapers in metric countries (you can of course do the sums with inch measurements) but the X size has a fortunate relationship to fly size. If you divide the fly size by 3 and call the result the X size your leader will in most cases be suited to the fly. To make life a little easier I have included a conversion table.
Mono conversion table
3X converts to 0.20 mm so using the two-thirds rule I should be able to make a very basic tapered leader stepping down from 0.45mm to 0.30mm to 0.20mm. If however I wanted to be able to reduce the tippet size for presentation purposes, say to use a smaller fly the leader performance may not be good but I can cope with that if, say I step down 0.45mm, 0.35mm, 0.28mm. 0.22 and use a 0.20 tippet. Now I could probably change the tippet between 0.22mm and 0.015mm without much of a problem. As an example if the 60/20/20 rule was used the result would be about 5 feet of butt, 1.5 feet of taper made up of three pieces of material and 1.5 feet of tippet to make a leader of about 8 feet long. My preference is for leaders of around 9ft and I tend to use a 50/25/25 or even a 33/33/33 percentage length profile in most situations.