Choosing and designing fly casting and fly fishing leaders.
Fly fishermen I’m sure want to ensure that their leader is correct but judging by the number of questions I receive there are misunderstandings. This will help! A fairly high proportion of anglers that I see use a length of level monofilament as a leader and struggle to get it to straighten when cast, so there is obviously some lack of understanding as to the functions of the leader. There are lots of different materials available and aspirations to cast long distances, present accurately and fish with many different techniques, with a vastly increased range of fly sizes and weights necessitating a range of leaders suited to each method. In addition to the traditional leaders we now have many types of proprietary leaders of different densities available and I will also take a look at those and their uses.
Trout casting, good turnover is important.
Most obvious purpose of the leader is to provide an “invisible link” between fly and fly line. It must be strong enough to cope with the strain of fighting fish of the expected species and size. Presentation must be good so the leader should “turn over” or “present” the fly as desired and fish it properly. It is the last of these qualities that is by far the most important and is usually understood or regarded less than the others. To convince yourself of the importance of correct leader design try casting the fly line without a leader and you will see the end of the line and the leader whip over too quickly with a splash rather than landing gently Without the leader or indeed if you use a leader that is too light or too short for purpose you will get a similar effect (Fig 1).
Fly fishing leader is too short or too light for the line and fly combination
If you aim higher to avoid the splash the excess energy will cause the leader to extend then recoil due to the elasticity in the rod, line and leader. Not a favourable outcome! Then attach a straight length of monofilament to the line, make it your usual leader length and breaking strain and try casting into the wind for the most undesirable effect. Note how tricky it is to get the leader to extend nicely because it is difficult to transmit the necessary energy down to the tippet and fly with a level leader.
Fly fishing leader is too long for the line and fly combination
If the leader is very long (Fig 2), the drag that it imposes on the fly line will make it difficult to lift line from the water in an orderly fashion and much harder to get the line and leader to turn over at any time. Underhand casting techniques actually exploit leader drag on the water surface to enable the casting of shooting heads without the fly line itself being in contact with the water surface. This specialised technique requires perhaps more than anywhere a well balanced combination of fly and leader is essential for good performance.
Fly fishing leader is correct for the line and fly combination
Therefore in order to achieve good presentation the leader must be able to absorb and transmit energy from the fly line to the fly. The shorter the leader the more energy will be transmitted to the fly, hence the general relationship between fly size and leader length, bigger (or heavier) fly, shorter leader. Conversely of course small, light flies can be cast on longer leaders. Ideally the fly should be propelled just far enough for the leader to extend predictably and as desired and cause the fly to drop quietly into the water (Fig 3). I have used the words “as desired” rather than straight because it is sometimes preferable (e.g. in conventional dry fly fishing) for the leader to fall slack so that the occurrence of “drag” is less likely.