Fundamentals of Fly Casting – Air Resistance
Friday, December 28th, 2007by Mark Waldin www.flycatcherinc.com A significant influence in casting distance for fly fishermen is wind resistance. Since casting a fly line is like unfurling a rolled up carpet, the resistance presented by air is primarily on the front edge of the curl or what fly fishermen call the loop. The fatter the loop the more surface area that has to cut through the air.
The amount of resistance presented by the fly line is represented in the equation 1/2CpAv^2 where C is the drag coefficient, A is the frontal area, p is the density of air and v is the velocity of the fly line. Let’s look at each component separately.
The velocity of the line is a major factor and the faster you cast the more resistance. Even worse the drag increases as the square of the velocity. On the other hand the velocity is what gives you distance. The only way to counteract this is to cast a heavier line at a slower speed. The heavier line will have more forward momentum than the lighter line giving it more reserve for fighting the air drag and the slower speed will reduce the air drag. This is why heavier fly lines cast further than lighter ones.
The drag cofficient for a fly line is in the range of 1 to about 1.3 at sea level. At higher elevations the drag coefficient goes down. The drag coefficient is dependent on how slick the surface of your fly line is. Therefore, the first thing to do is keep you fly line clean and free of debris or other particles. They will increase the drag significantly. Second thing is to find out from the fly line manufacturer what the drag coefficient of their particular line is. Some manufacturers promote their lines as having low drag. Selecting the best fly line can have an impact on this and it can make a difference, especially in lighter lines.
The frontal area of the line can be reduced by picking a fly line that has a thinner diameter than a competing fly line. Find out from the manufacturer what the diameter of the line is before you buy it and get one with a narrow diameter (but watch out that you maintain fly line bouyancy when making this comparison). The biggest thing to watch out for with surface area is fly casting technique.
Fishing with a tight loop significantly reduces the surface area of the cast compared to an open loop. There are many books on casting tight loops so I am not going to go into it in detail. The main things are to keep the tip of your rod traveling in a straight line and not in an arc. It is the arc that puts the open loop into the line. To cast a straight line, keep your wrist stationary and cast using primarily your forearm. Keep your hand high up around ear level. If you try to cast with your hand lower it becomes near impossible to maintain the straight line and you are more likely to put a hook through your eye than if you keep the rod tip higher.
In summary, get a heavier line if you want to cast further, get a narrow diameter line that has a superior (lower) drag coefficient, and cast in a straight line with a tight loop.








