“You don’t cast any harder at 20 feet than you do at 50 feet. You just start faster over a longer stroke.“
Lefty Kreh
Lefty probably wasn’t very keen on Physics —in fact, that “start faster” above isn’t right—, but his experience served him well to understand the importance of casting stroke length, as shown by this other quote from him
onemorelastcast.net 
Shouldn’t Lefty have said you don’t cast any harder at 50 feet than you do at 20 feet? It seems to me that since 50 feet is further than 20 feet, one would naturally think 50 feet would require a “harder cast” = more effort. So 20 feet would require less effort.
Has Lefty butchered the English language protocol or am I wrong?
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The energy we need to propel our line in order to present our fly fifteen meters away is higher than the energy required to put our fly only six meters away. Common sense.
However, energy and force aren’t the same thing. The amount of energy is fixed, but the force needed is variable.
Think of a road that goes through a mountain pass. The engineers could design a road climbing up in a straight line, however that is never the case: they build a road that climbs up very progressively by means of curve, after curve, after curve. In that way they increase the distance a vehicle have to cover, so the energy needed to reach the pass is the same in any case, but wit a longer road the amount of force is much less.
The same principle applies to gears in a car transmission or a bicycle. When you are riding your bike and reach a steep slope you change gears to the biggest sprocket. What you feel is that you need to pedal more times per minute, but with much less force.
The Physics explanation is based in the concept of Work, which is the same as energy, that, in fly casting, translates into velocity. More work = more energy = more line velocity = more distance.
The formula for work is: W = F.d (force times distance).
What this means is that you can increase work (i.e. line velocity) by means of increasing distance and keeping force constant.
That is the reason for translation within the casting stroke being more than a stylistic choice.
So Lefty was right. He probably didn’t know the Physics but his intuition and experience served him well.
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Lefty had it half right, there’s no need for a faster start
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Right. But he understood the importance of translation, and that is remarkable.
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Difficulty in explaining casting always stems from a lack of common language.
If we replace harder with more Force.
And start faster , with start sooner ..(time)
We now have the correct scientific terms for explaining using Physics.
And it makes sense.
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Yes, a common and clear language is key. The question is that we all had that common language taught to us when we were kids. If we get rid of “effort”, “harder” or “power” and start using “force”, “distance”, “time”, acceleration”, “velocity”, “work”… things would fall into place pretty easily.
Another example that comes to mind is the use of “arc” when what we are describing is an angle.
By the way, as Mark pointed out above, you don’t need to start faster to get more line speed if you increase your casting stroke length.
For the same reason you don’t need to start sooner, as that would be a timing fault. We always should pull on the whole line from the start.
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Another question: assuming you cast with the same “force” regardless of distance and the only thing you change is stroke length. if I want to cast 3 times the distance, how much longer is my stroke theoretically? Ie what does the mathematical relationship look like?
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The maths are very easy. The formula for work is: W = F.d.
We cast with —let’s say— two units of “F” and one unit of “d”:
W = 2 x 1 = 2
If we want to triple the work:
W = 2 x 3 = 6
Of course there are other variables at play. For instance, air drag increases in relation to the square of the velocity, so doubling the line velocity results in a value of air drag four times bigger.
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Projectile mechanics suggests it is closer to a square law.
Distance is related to launch velocity. N times distance requires square root n times launch velocity.
N times the distance gives n times the weight to cast as well. More or less. It requires more work to achieve this higher velocity
So more work is required due to distance and extra mass..
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More distance requires more launch velocity, i.e. more energy, i.e. more Work.
But that increase in Work doesn’t necessarily mean an increase in Force, it can be achieved by a longer casting stroke.
That is Lefty’s point.
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Aitor, I think you missed the point of my post.
I didnt suggest more force.
I think to cast twice as far with the same force requires more like 4 times the stroke length to achieve the required velocity to achieve the disance not 2 times .
3 times the distance requires 9 times the stroke length.
You’re increased work needs to deal with both the increased mass and increased velocity.
Check the maths and let me know .
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Yes, right.
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Ps I may have miscalculated, so let me know where I might have gone wrong..
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