Weighting flies

[alanb_ct]

Like others on the board (BlackLabel) I have done some work on stoneflies and their weightings. A lot of folks equate a fly's size with its mass, thinking that big flies need to be heavy. A bigger nymph fly, when tied light, tends to exhibit a side-to-side flutter that fish can't resist. Other aspects of the fly (legs) tend to affect it hydrodynamically too, but a heavy fly glued to the stream bottom can't flutter much!

I first learned about the flutter from Joe Humphreys' videos. He uses PT-style flies with prominent legs made from pheasant tail. He mentioned the flutter effect.

(I may have said this before on the forum) This year I have done a lot of experimentation with selection of anchor flies with different weightings. In one run I knew was full of fish, I experimented with three different weightings S, M and L. The small (S) weight produced two fish, the medium produced six and the large only one. I then went back to the most successful weighting (in this case M) and caught four more. I have also done this on other occasions, usually on the Farmington, since I know it so well.

Try fishing with lighter flies to reap the rewards. You will be amazed as once in a while even your light flies will still snag the bottom due to turbulent flow; this is proof that light flies still get in the feeding zones. A light fly in a laminar (even) flow, will give you the longest possible drifts with a long leader setup. My best drifts are over 50 feet.

[alanb_ct]

I was just thinking about this further and realized this may represent a convenient way of producing a system of weighted flies. The key is the volume of the fly stays the same, but only its density changes to produce a different mass. All other materials on the fly are identical.

I did a quick example based on the quoted densities of tungsten and brass beads, and lead and lead-free wire.

This table represents the relative mass of the 4 combinations:

Lead Lead-Free
Tungsten 1.00 0.85
Brass 0.66 0.51

You can see that a brass bead/lead-free combo has half the mass of the tungsten/lead version. In this way, you could produce 4 versions of your favorite fly, and carefully adjust your anchor according to stream conditions.

[alanb_ct]

Put another way...the mass of a fly used as an anchor is probably as important as it silhouette and colors. I hope this is understandable, and sorry for making fly selection sound overly technical.