All About Fly Lines
How they work
First let’s take a look at how lines work during a cast. This will help to understand why lines are designed as they are.
As the rod moves during a casting stroke it pulls the line in, hopefully, a straight line path. When the loop is formed the leading edge momentum pulls on the upper and lower legs of the loop. As the line unrolls the energy is dissipated by air resistance to the diameter of the line at the leading edge of the loop. This dissipated energy is passed off into the air in the form of a small amount of heat energy. When the line rounds the corner of the leading edge it becomes more or less static assuming the line is not shot.
E=V2*1/2M – Energy is equal to Velocity of the line squared, times half the Mass of the line.
Given a floating line, the smaller the diameter (mass) in the line, the greater effect air resistance has upon its leading edge. This creates less capacity for carrying the energy and therefore energy gets dissipated.
The greater the loop surface the line presents to the air (large loops) the greater the dissipation of energy. When less line surface is presented (small or tight loops), less dissipation takes place. This allows the line to travel farther for a given amount of applied energy.
This above illustration shows an open loop. Because of the amount of surface the leading edge (loop) presents to the air as it travels forward, the line will slow quickly and may not turn over or lay the fly out straight. This is an inefficient loop when attempting to maintain distance or accuracy.
This illustration shows a tight loop. Notice that the leading edge presents much less surface to the air. This efficient loop shape will be more accurate and will travel farther than the one above, especially into a wind.
This last illustration shows the effects of poor line or leader design. If the energy is not efficiently dissipated there will be too much energy remaining in the line as it turns over. The line will continue to travel in the same direction that it was sent as it turned over, so it continues in a downward direction. The line then drags the leader along with it. On a long cast, the last few feet of the line and the entire leader will end up in a heap as much as 10-15 feet short of its intended target.
For a more detailed look at fly lines, check out the other pages in this section.
