Quote Originally Posted by bazakwardz View Post
I'm not an engineer, either. I got the method from Claude Freaner's article on furled leaders. Basically, you don't get the correct diameter for the twisted leader by multiplying the size of the mono by 4. This has to do with the circular cross section of the mono. You have to calculate the area of the circle, multiply it by 4, and then reverse calculate the diameter. Maybe an engineer will come along and explain it better.

I just figured out another interesting result from this method. When the leader goes from 4 strands to 2, the step down in diameter is only around 30% instead of the expected 50%. The same goes for the transition from 2 strands to 1.
Quote Originally Posted by Steven View Post
Got it. Fascinating. Interestingly, the 30% step-down is within the range as detailed by Gary Borger.
Yep.

Actually what is happening is that by reducing the number of threads, you are reducing the mass of the leader. Without getting into formulas for energy and momentum, mass is what turns over the leader. So with a tapered leader single strand or furled, greater mass is always turning over a lesser mass. Mass of a tubular object is directly related to cross-sectional area of that object so that with a leader, the cross sectional area ratio of a proximal to a distal segment of the leader is directly related to how efficiently the energy of the proximal segment can be transferred into the distal segment.

We want a smooth transition. Gary has experimentally determined that linear mass ratio of the proximal segment to the distal segment of a mono leader can be no more than 2:1. This correlates to about a 30% decrease in diameter. 7 squared is 49, and 10 squared is 100 and the mass ratio of 7/10 diameter ratio is then 49/100.

Notice that this goes against the old rule of thumb that says never step down more than 2 X sizes between leader segments. This makes no sense when one considers this rule allows you to only step down from 0.020" to 0.018" (10% step-down) but a step down from 0.004 to 0.002 (50% step-down) is OK.

If this mass related methodology works for furled/twisted leaders, then the calculation for furled/twisted leaders is simple. There is no need to back calculate the total areas of the combined threads, and from this get the theoretical diameter of the combined threads in that segment. What makes the calculation easy with furled leaders is to never drop the step-down ratio of the number of threads from one segment to another below than 1/2. So for 9 threads, you can go no lower than 5 for the next segment to theoretically stay above the 50% mass step-down.