Walter & Group...
As we discuss forward tapers related to presentation, I thought I'd bring up a point often missed.
Discussions on tapers almost always centers on fly line and leader profile. Measurements are made of the diameters at various points.
What REALLY makes the difference in presentation is the way the fly line and leader turn over ..... the rate and completion (or not) of energy dissipation as the loop unfurls.
This, in turn, is almost fully determined by the MASS PROFILE of both the fly line forward taper and the leader.
When diameter changes as we go from one end of the taper to the other, the mass changes in direct proportion. This is because the density and therefore the specific gravity of the material doesn't really change which allows us to use the more easily measured diameter for description and depiction.
Of course, this isn't true of lines with tip segments of different specific gravity, such as the sink tip designs and the clear tip lines.
Caveat: Actually the density & specific gravity change just a tiny bit with the fly line taper only because of the fact that the core doesn't change as we traverse the taper, but the coating does. (The core has a slightly different SG than the coating.) This difference is so slight as to be unimportant.)
Now, let's discuss all this with respect to the leader:
The basic principles of leader turnover are not much different than those for the forward taper of the fly line. One can look at the leader as an extension of the fly line. There are some differences, however :-
1.) When leader segments are connected, we cannot assume that the specific gravity (density) of each segment will be identical. (Long ago, Lefty taught me that it is best to use the same brand of nylon mono for each segment for best results when tying up multisegmented tapered salt water leaders. ..... for reasons of knot strength as well as SG.)
2.) As we traverse the length of a one piece tapered leader or tied multisegmented leader made up of the same material, we do not have that tiny bit of difference in density which I described above with respect to the fly line, because we have no core covered with pvc or other coatings. (Technical point, unimportant for practical consideration).
3.) If we tie up the leader with greatly different materials ( such as interposing flurocarbon segments with nylon mono) we'll have weaker knots as well as different leader behavior because the materials differ with respect to density (SG)
AND STIFFNESS !
Lefty has demonstrated that salt water leaders turn over better when relatively soft (less stiff) materials are used. The reason is explained well in his books. (Basically, the stiff material resists bending as the leader tries to unfurl.)
Being aware of this, I used to teach that the main thing which determined the way the leader turned over was the relative stiffness to diameter of the material. I had thought that stiffness was all important.
Now, I've become aware of the studies done by Bruce Richards and Noel Perkins which show that while stiffness of material is indeed a factor, that it is secondary to the mass profile of the leader design. Bruce likes to say that a leader behaves in much the same way as the fly line.
4.) Rather than dealing directly with things that are hard to measure as we make up leaders, such as MASS and MASS PROFILE, we make assumptions such as those described above, ie. using material diameters. This works fine for most rigging for fresh water fishing. It would work for salty leaders, too..... however, custom dictates that most salt water fly fishermen use rated pound test as a rough but workable easy way of choosing their leader segments. The reason this works is that the mass per length of the material changes fairly well with the pound tensile strength of the leader material.
5.) In his book, LEFTY KREH'S ULTIMATE GUIDE TO FLY FISHING, p. 182, Lefty presents and diagrams a very simplified way of looking at fly leader turnover as a function of the length of the tippet. (This follows the time honored "Kiss Principle").
For a more detailed discussion of leader construction for trout fishing, try PRESENTATION, by Gary Borger, pp. 178 - 183. (A book which I feel should never have been allowed to go out of print.)
Gordy