Hi, Group:
Just to clarify the bulk of information on the many messages regarding calculations of loop speed, and to give credit to Bruce Richards' valid simplification of the math, let's put it in a form which compares loop speed and fly speed without shooting line and then, with a line shoot.
1) Cast with no line shoot:
Fly (top leg) speed = (V1)
Rod leg (bottom leg speed = (V2)
Formula to calculate LOOP SPEED = (X) :-
1/2 (V1+V2) = X .
Bruce's example: The top leg (fly leg) is moving at 80 ft./sec. The bottom leg (rod leg) is moving at 0 ft./sec. We add the speed of the two legs and come out with 80+0=80. Dividing that in half (since the forward motion of the loop will be half that of the fly) , we come out with a loop speed of : X=40 ft./sec.
2.) Cast with line shoot:-
We use the same formula : 1/2 (V1+V2) = X
The top leg (fly leg) is moving at 80 ft./sec. The bottom leg (rod leg) is now moving at, say 40'/sec. Adding the two, we get 80+40= 120. Dividing by two, we get 60 ft./sec. as the calculated loop speed ie. X=60'/SEC.
Gordy