All fly casters have experienced a fly line “kick.” So, what is this kick? The fly line kicks when the tip part suddenly accelerates at the end of a cast and careens about (like a whip does). The reason behind the kick is that there is undissipated energy left in the loop when it straightens. That energy must go somewhere and the end of the fly line kicks thus dissipating energy. When casting floating lines, the kick is mostly a casting error (too much power), but it can also be used to the caster’s advantage (more later). Lines, where the mass of its head is pushed forward, are prone to kicking whether it is a sinking tip or a floating tip. The mass upfront is the issue, not the line’s density per se. When casting a line with a heavy sinking tip it will kick to a varying degree. Let’s break it down into various components.
Any line, cast without a leader, will kick no matter how gentle the cast. Just go ahead and try for yourself. There should be, by necessity, a little bit of energy left in the fly line to turn over the leader and the fly. (Now it is also obvious why you need more force to turn over a fly as it gets heavier). The leader is designed to dissipate the rest of the energy and still have enough to turn over the fly. Now you immediately realize that the leader must be constructed in such a way as to be able to do this. Imagine a scenario where you put a 6X 3.7lbs tippet on a 15# flyline (Diameter 0.005’’, 0.13mm). You intuitively realize that’s never going to work. Mass moves mass is the mantra (see blogs below). And the reason is that the mass of the leader’s butt is just too small to accept the excess energy. The mass of the leader’s butt is predicated by the diameter of the butt (not the break strength).
When I cast a floating line, I like to spend just enough energy to turn the ensemble over and lay it out straight in front of me. However, I can make any line kick by just using more force. Now, this is a casting flaw unless you want the line to curve at the cast’s end. There are two named casts where we use excessive force to curve the line. First, we have the Tuck cast where we cast in the vertical plane and overpower the cast, and the line and leader tuck down, and we can make the fly land first on the surface. This is used for instance when you want the fly to sink fast as in nymphing.
The other is the Curve cast where we cast in the horizontal plane and curve the line around an obstacle for instance a stone in the water. This is possible to do when casting in the horizontal plane. The trick is to overpower the cast and the line curves either to the right with a horizontal left-sided cast or left using a horizontal right-sided cast.
It is the same principle and the same cast. The tuck cast is in the vertical plane and the curve cast is in the horizontal plane.
The line’s design
Now undissipated energy can be there because of the line’s construction. All lines where the mass is pushed forward will certainly kick more than most other line designs. Sinking tips will kick more because of their mass (not density), but floating lines like the one above will also kick. But that’s OK, these lines are designed to cast bigger flies AND for the sinkers, the tip must sink fast so there is lots of mass in the front. But we don’t care, we’re not throwing dry flies. Good for big/heavy flies. If the tip casts smoothly it does not sink well and thus fishes badly. If the tip sinks well and fishes well it is harder to cast. You must pick your poison!
Sinking lines and sink tips are made by incorporating small pieces of tungsten (from Swedish – literally heavy stone) into the PVC coating. This increases the density of that part of the line. The tips are furthermore thinner than the floating head part and that fact is responsible for the decreased drag and the speed-up of a line thus constructed.
For the savants
The line kick can be much more subtle. One of my friends when rigging a new 2-3 wt. line cuts off the factory welded loop and attaches the leader with a 2-turn needle knot. He feels the welded loop “kick” just a bit and doesn’t like that. Line/leader attachments often result in a little lump of mass right where we don’t want it. But with the right leader butt and attachment method, the transition from line to leader can be made very smooth.
Technical consultant: Bruce Richards