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Fly line weights and stress curves


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#1 Carlin

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Posted 14 June 2006 - 01:05 PM

There has been an interesting discussion taking place on the bamboo rodmaker's listserv over the past week regarding the actual weights of fly lines. Basically the issue revolves around the problem of computing the various weights of line cast by averaging out the first 30' of fly line and using those averages to calculate Garrison-style stress curves.

For DT lines this is close to an accurate estimation of the actual line weight. The estimates do fall a bit on the low side as the first 30' of fly line includes a taper, which means the weight of the non-tapered running line after the initial front taper is calculated to be lighter than it actually is. The difference is much greater when looking at WF lines, as the running line is usually considerably smaller in diameter than the belly, so the farther out the line you go, the less accurate the estimated line weight.

user posted image

Below is a chart that shows the calculated weights of 6 different fly lines that takes into account the taper and dimensions of the different lines, not the average. Line weights are in grains, with the AFTMA weight measured at 30' (after removing the non-tapered tip).

Cortland 444 lines were used as Cortland is cool enough to post taper data on their website: http://www.cortlandl.../444_specs.html

user posted image

Notice that 80' of WF6 line weighs the same as 80' of DT4 line, and at 48' a DT4 and WF5 weigh the same!

Of course all of us who have used various lines know the effect of longer casts with WF line, yet for me it is very revealing to see the scope of the difference. Using data like this it'll be interesting to experiment with different lines and rods such as 'overlining' a 6wt with a WF7 or even WF8, and casting the rod at varying ranges.

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As far as how this information affects rod design, below are 3 stress curve charts that use the averaged DT line weight, the calculated DT line weight and the calculated WF line weight. The Z-axis on the stress charts is the line cast in feet from 3' to 60' in 3' increments. The reason for using this type of 3D chart is to more easily show the effects of the line weights and where those effects start to reveal themselves.

As a reference point, the running line (body) of a 444 DT 4 line is .043". The diameter of the body (of the WF head) of a 444 WF 4 line is also .043", but the running line after the front taper ends at 32' is .035".

This chart is calculated using the standard averaged DT line weights. Basically taking the weight of the first 30' of line, averaging that out to find the weight per foot, then using that number to calculate the stresses at the various line cast lengths.
user posted image

This chart uses the actual calculated DT line weights taking into account the front taper (and back taper if applicable). The only real difference is the stresses are slightly higher overall as the actual weight of the various lengths of line cast are slightly more than the averaged weights above.
user posted image

This chart is created using the calculated weight of WF line, including the front taper, body, back taper and running line. You can see that once the end of the front taper is reached at around 30', the stress curve grows at a slower rate which illustrates the effects of the lighter running line on the stresses.
user posted image

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#2 DHayashida

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Posted 14 June 2006 - 02:51 PM

This should be pinned at the top of the list. Good reference information.

Darryl

#3 LeeO

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Posted 15 June 2006 - 07:19 AM

Good gravy! You all are scary. wink.gif
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#4 mer

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Posted 27 June 2006 - 05:33 AM

We had a discussion kind of similar to this over on Clark's a while back. Someone had asked "what's the best line for a XXX taper?", it got to "try a bunch to see what you like best" quickly, with the resultant "Why?". So I started looking at the different profiles available on the web (Cortland, SA, Wulff, Rio) and it was eye opening. The most interesting was the front taper length. Someone had said a Wulff TT felt light until they had a bunch of line out (I think they said a 4 wt and about 25 feet), looking at the taper, you could say "yep, try a 5". The only real conclusion I was able to draw was "If it doesn't feel right, try a different line".

#5 Carlin

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Posted 27 June 2006 - 12:44 PM

That is exactly the conclusion that I've come to realize mer. Your TT example is a perfect illustration of how knowing the line taper can help determine if you are using the proper line weight, and if a different taper or weight would work better. thumbsup.gif

To get a good look at some differences, check out this chart from Rio:

user posted image

The Selective Trout DT looks like a cross between a WF and standard DT line, and the WF version of the Selective trout is as well due to the 2 sizes of running line. Nice ideas for tapers IMO.

The Selective trout is somewhat opposite of the Wulff TT taper.

The Bonefish taper and some of the spey lines are similar to a Wulff TT in shape.

The Long Cast is basically a DT line (~70') with the addition of some extra running line.


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#6 mer

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Posted 07 July 2006 - 08:48 AM

I stuck a RioSelective trout WF on a 7613 taper for this year. Even for the distances I normally fish at (nominally 30ft, 50 feet is a long way), it feels much better than the SA XPS DT 5 I had before. Rio's chart definitely made me think on what lines look like.




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