Dalton, All
What you've done is interesting, but the question isn't can you cast 5 wt line on 7 wt rod, but can you cast that line better. You raise an interesting point about line speed, and I'll get to that below. However, if you have issues with control in calm conditions, I doubt they would improve in high wind.
Anyway, I had some slow time at work so I tried to solve the problem more rigorously. To start I found the following paper "Comparison of numerical and analytical solutions for fly casting dynamics":
http://link.springer.com/article/10.1007%2FBF02859893
The paper has a simplified model for fly line dynamics that includes drag, but I had to modify it for the inclusion of wind.
I compared an 8wt line to a 7wt line in a 10 mph wind and a 15 m (~50 ft) cast in two conditions the first with the same initial velocity, and the second with the same initial kinetic energy. When the fly rod bends, it is storing energy (like a spring). The Lefty article suggests "proper loading" of the rod, which I'll assume that means the same amount of stored energy. Then assuming all of the stored energy is transferred to the line for the same cast they would have the same kinetic energy. I think this agrees with your observation of the 5 wt line on the 7 wt rod having very high line speeds.
The results of the modeling work are attached.
For the same initial velocity:
The results show, as expected, that the 8 wt line casts the full 15 m in less time and maintains its velocity throughout the cast better than the 7 wt line.
For the same initial kinetic energy:
I was surprised that the 7 wt line will completed the cast faster. This supports Lefty's claim, but as the velocity plot shows, as the cast unfolds the velocity of the 7 wt drops below that of the 8 wt. The model does not include the turning over of the fly, and I would suspect that it would make it harder to do that with the lighter line. However, I do concede that it raises the possibility that a lighter line could be more effective in some scenarios.
In conclusion:
Physics is hard. It took a lot of time to do all of this, and in the end the question was not satisfactorily answered one way or another. In no way do I think either one of those cases matches reality, and the model required many assumptions that I am less than confident in. Despite this, I still feel that the heavier line will be a better option in the wind. The factors that go into generating a "properly loaded" rod, and the ability to control the line as the speed increases, at least in my mind, are favored by the heavier line. But my highly idealized model shows some room for the lighter line to actually be the better choice. I think this idea would work better for shorter rather than longer casts, but who knows.
Anyway, if anyone is interested in the model I did it in mathematica, send me a message and I'll send it to you.
Howard
On Monday, November 2, 2015 at 10:39:22 AM UTC-5, Dalton Terrell - TPFR President wrote:
-- What you've done is interesting, but the question isn't can you cast 5 wt line on 7 wt rod, but can you cast that line better. You raise an interesting point about line speed, and I'll get to that below. However, if you have issues with control in calm conditions, I doubt they would improve in high wind.
Anyway, I had some slow time at work so I tried to solve the problem more rigorously. To start I found the following paper "Comparison of numerical and analytical solutions for fly casting dynamics":
http://link.springer.com/article/10.1007%2FBF02859893
The paper has a simplified model for fly line dynamics that includes drag, but I had to modify it for the inclusion of wind.
I compared an 8wt line to a 7wt line in a 10 mph wind and a 15 m (~50 ft) cast in two conditions the first with the same initial velocity, and the second with the same initial kinetic energy. When the fly rod bends, it is storing energy (like a spring). The Lefty article suggests "proper loading" of the rod, which I'll assume that means the same amount of stored energy. Then assuming all of the stored energy is transferred to the line for the same cast they would have the same kinetic energy. I think this agrees with your observation of the 5 wt line on the 7 wt rod having very high line speeds.
The results of the modeling work are attached.
For the same initial velocity:
The results show, as expected, that the 8 wt line casts the full 15 m in less time and maintains its velocity throughout the cast better than the 7 wt line.
For the same initial kinetic energy:
I was surprised that the 7 wt line will completed the cast faster. This supports Lefty's claim, but as the velocity plot shows, as the cast unfolds the velocity of the 7 wt drops below that of the 8 wt. The model does not include the turning over of the fly, and I would suspect that it would make it harder to do that with the lighter line. However, I do concede that it raises the possibility that a lighter line could be more effective in some scenarios.
In conclusion:
Physics is hard. It took a lot of time to do all of this, and in the end the question was not satisfactorily answered one way or another. In no way do I think either one of those cases matches reality, and the model required many assumptions that I am less than confident in. Despite this, I still feel that the heavier line will be a better option in the wind. The factors that go into generating a "properly loaded" rod, and the ability to control the line as the speed increases, at least in my mind, are favored by the heavier line. But my highly idealized model shows some room for the lighter line to actually be the better choice. I think this idea would work better for shorter rather than longer casts, but who knows.
Anyway, if anyone is interested in the model I did it in mathematica, send me a message and I'll send it to you.
Howard
On Monday, November 2, 2015 at 10:39:22 AM UTC-5, Dalton Terrell - TPFR President wrote:
Howard, Gene and others,
A few of the casting nerds did some experimentation on underlining yesterday morning at the Fletcher's clinic. Our results weren't conclusive at all but we did theorize the potential reason Lefty said to underline: higher line speed.
We threw a 7wt rod with a 7wt bass line, and then dropped down to a 5wt trout line--not exactly an ideal comparison. But what we did notice is that we could push the rod more with the lighter line. Does this additional velocity overcome the disadvantages of less mass, who knows, but it may be possible? With either set up, I could somewhat calmly hit 75 ft or totally overdo the power and end up with a 75 ft pile cast, which says a lot more about my technique than the equipment.
Dalton
http://www.tpfr.org
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