Backing Math? [Archive] - Fly Fishing Forum

: Backing Math?


GrantK
02-21-2006, 06:24 AM
If a reel will purportedly hold a WF9F and 240 yds of 20 lb. dacron backing, how much 30 lb. dacron backing will it hold with a WF8F? Anyone have a formula of sorts for guesstimating in instances like this?

jfbasser
02-21-2006, 07:26 AM
Some reel manufacturers publish capacity data for both 20 and 30 # backing for a subset of the reels in their product lines as well as backing data across a few flyline sizes...If you stare at it long enough:smokin: with a little simple scaling you can probably apply it to your specific problem. The alternative is to try to find line diameter info for the backing and assume that the capacity goes as the inverse of the diameter.

See post below using data from one source.

Dave17
02-21-2006, 11:02 AM
Try (240 x diameter of the 30 lb) / diameter of the 20 lb

jfbasser
02-21-2006, 12:27 PM
Using info on the Abel website and scaling, expect to use 225 yds of 30# with that 8 weight line.

juro
02-21-2006, 12:47 PM
Try (240 x diameter of the 30 lb) / diameter of the 20 lb

Clever! But I believe the formula would be (240 x diameter of the 20 lb) / diameter of the 30 lb)

GrantK
02-21-2006, 02:19 PM
Thanks for the replies. The formula provided works pretty well for converting from 20 lb. dacron to 30 lb. dacron, but of course it doesn't account for the difference in line size.

Using some numbers I found in a saltwater article that purported to list the average diameters of dacron as .018" for 20 lb. and .024" for 30 lb., I came out with a number of 180 yds of 30 lb. in the place of 240 yds. of 20 lb.

Anyone have a method for guessing the difference between line weights? And yes, I know all I have to do is spool it on there and then I'll know. That's not the point here. I'd like to come up with a way to try and fairly accurately standardize and evaluate--within reason of course--capacities from one maker to another.

juro
02-21-2006, 02:32 PM
Thats better derived from a reel co's ratings of one line wt vs the other line wt on same backing then applying the ratio. For instance reel brandX says 8wt and 240 yds of 20 or 9wt and 190 etc.

If you really care you can go wind the line first then the backing over and reverse it onto another reel at a shop, but most of the time I put on as much as I think I can get away with, wind on the line and pray.

For my bonefish reels I go with 50# gelspun and load 'er up.

Bob Pauli
02-21-2006, 02:33 PM
All backing is not the same. Some 30# dacron takes 15% more volume than others. A reel that holds 250 yards of white SA backing will hold about 213 yards of colored Micron backing [both 30#].

It is worth reading Abel's literature or web site. You will notice the specs are for SA backing only, white color only, with reductions for other material.

SA is the smallest diameter backing I have found, hence more fits on a reel. Wulff oval backing is the next smallest. Abel uses SA in order to maximize backing capacity. Micron is among the largest diameter dacron backings, and is used in Tibor advertising.

If you choose a colored backing material, you will lose capacity.

If you search prior posts on the subject you will find an angler can get major increases in the amount of backing installed by using white material from SA.

BigDave
02-21-2006, 03:00 PM
SA is the smallest diameter backing I have found, hence more fits on a reel. Wulff oval backing is the next smallest. Abel uses SA in order to maximize backing capacity. Micron is among the largest diameter dacron backings, and is used in Tibor advertising.

So True! I had a Riptide spooled up to the capacity line on the spool which is supposed to be 250 yards of 30# dacron. It took well over 300 yards of Orvis 30#dacron to reach the line. Probably the same stuff as SA.

In fact the 30# Orvis Dacron is so close in diameter to 20# Micron it's tough to tell the difference.

GrantK
02-21-2006, 03:24 PM
[QUOTE=juro]Thats better derived from a reel co's ratings of one line wt vs the other line wt on same backing then applying the ratio. For instance reel brandX says 8wt and 240 yds of 20 or 9wt and 190 etc.QUOTE]

Absolutely. Problem is that there are reel makers that don't provide that information. They have one line size listed with one size of backing for a particular model. Unless the reels you're comparing, from one manufacturer to another, are both quoted with the same weight lines and same type backing it is very difficult to compare them in terms of capacity. My question was more of whether anyone had ever come up with, or heard of, a general ratio for changes in line size, e.g., 10 percent more backing with one line size smaller and conversely 10 percent less backing with one line size greater. Obviously there are a ton of variables from brand of backing (and even color apparently) to taper of line that will all have a big impact and make such an estimate pretty inaccurate, but I would think there could be some general figure in terms of the difference that could be applied that would at least get a person into the ballpark.

And like I said before, I know I can spool backing and line on any reel and know exactly how much it took. That's not the point, though.

Also, anyone know of a listing for diameters (in thousandths) of any of the various brands of GSP? The basic catalog type listings generally make reference to an equivalent in monofilament. Curious if there's anything more accurate out there? Anyone have a formula they've used for converting dacron to GSP? I've seen a copule real simple formulas in the past, but have heard of wildly differing experiences using them.

Dave17
02-21-2006, 03:27 PM
Clever! But I believe the formula would be (240 x diameter of the 20 lb) / diameter of the 30 lb)

Here's my thinking:

20lb / 240 yds = 30lb / x yds

Cross multiply:

20lb * x yds = 30lb * 240 yds

solve for x:

x yards = (30lb * 240 yds) / 20lb

The forum gets algebraic:lildevl:

juro
02-21-2006, 04:21 PM
Yes, impressive! And the best answer of all, I am just saying it was 240 of 20 not 240 of 30 and you are solving for amount of 30lb where 20 is already known.

The logic is awesome, however if you run the diameters thru it you will see what I mean. You should get less 30# than 240yds.

Who woulda' thunk this would ever be fun! :D

jfbasser
02-21-2006, 05:06 PM
Juro, this is what your looking for..I think:confused:

More pound test (larger diameter) requires less yardage of backing. they vary inversely!

Two objects that vary inversely are also said to "vary indirectly" or to be "inversely proportional."

One quantity is inversely proportional to another when the product of the two quantities is constant. An inverse proportion can be described by an equation of the form xy = k, where k is the constant of proportionality. The equation of an inverse proportion can be written in the form .

240 * Dia20 = k= X * Dia30

X= (240 *Dia20)/Dia30

Given that the Diameter of 20 is about 4/5ths ( .8) the Diameter of 30

X=240 * 0.8/1.0

192 yards of 30#

As for fly line weight and its effect as stated above Abel's site is as good as any. Winding the line on first is good, but I like Juro put more then enough on, then wind the flyline on and figure out (guess) how much backing to clip off based on how much flyline is left sticking off the spool. On certain reels where I have been known to use intermediates one day and a sinker some other day I find that a 120 foot sinker takes up about as much space on the spool as a 105 foot Intermediate.:Eyecrazy:

Eddie
02-21-2006, 06:57 PM
Orvis lists three line weights for some of their reels. Batenkill LA comes to mind. I think that based on those differences, you could apply it to any reel.

Quentin
02-21-2006, 07:28 PM
Hmm . . .

Seems to me that it's actually an inverse-squared relationship since we're really talking about volume. This yields the same equation as Basser except that the diameter values would be squared, so using the same assumption as above (i.e., diameters have 4/5 ratio) the result would be 153.6 yds of 30#. The ratio has a huge effect on the result so it might be quite different when you plug in the real line diameters.

Q

Adrian
02-22-2006, 04:02 AM
Just to throw a proverbial "spanner" into the equation, is it valid to assume a linear relationship between the diameter of the backing and breaking strain?

i.e If diameter 'x' tests at 'y' lbs, does it follow that diameter 2x will test at 2y lbs?

Anyone got a spare Houndsfield Tensiometer we could 'borrow' for some tests?

pescaphile
02-22-2006, 04:38 AM
Quentin is correct. It varies with the reciprical of the diameter squared.

Published diameters for Micron. 20lb - .017"and 30lb @ .019"

So, using those diameters, 240 yds of 20lb works out as equivalent to 190 and change using 30#. Sounds about right to me.

Adrian, No. In simple terms,tensile load capacity = material strength (intrinsic property) x material area (geometric property). So, it varies with the square of the diameter (Area = Pi R-squared which is the same as one-quarter Pi Dia-squared) , e.g. if material at diameter x tests y, then dia 2x tests at 4y, 4x at 16y, etc.

Edit: Grant - I now see you want to also want to take into account a change from a WF9F to WF8F. We can include that too and answer your question, but also need to know the reel's stated capacity with the WF8F line for either 20 or 30lb backing. I suspect jfbasser's guesstimate of 225yds will be pretty close.

Incidently, I looked again at the micron specs again after seeing Bob's post and the hi-viz 30lb Micron's diameter is published as 0.021" vs 0.019" for the white. So, with this reel and the WF9F line, you could have 190+ yds of classy elegant white or a couple yards shy of 160yds of that garish yellow stuff that stains your flyline!

juro
02-22-2006, 06:41 AM
Well now this has gone from casual estimation to a much more exact pursuit!

Q's theory and Pescaphiles's proof assume that diameter is a meaningful variable applied to a mesh tube that compresses and stretches in response to tensioned spooling. Are the fibers thickened in one brand where more of the same fibers are weaved more densely in another?

Diameter, although it's all we got, might only be indirectly related to the actual volume of a finely weaved mesh tube on a spool that ain't round (i.e. not a diameter per se) when compressed and tensioned. Most of that is probably air. It may not necessarily be a linear relationship at that (which is at the heart of Adrian's point).

IMHO we can figure as exactly as possible, or have a useful 'rule of thumb'. So the question remains... what is that useful rule of thumb? We could easily put it into an algorithm and add it to the expertise page :smokin:

When I worked at a flyshop I found one gets pretty good at just 'eyeballing it' on the line machine. :)

jfbasser
02-22-2006, 07:04 AM
Thanks Q, my first thought was inverse square but it is inconsistent with the Abel site capacity info and data I currently have on the diameters of 20 and 30 # micron. I will have to call Cortland and check on the diameters. The end result may have to consider the packing factors of the two different diameter lines.

FredA
02-22-2006, 07:08 AM
There ain't no math in flyfishing.

juro
02-22-2006, 07:09 AM
The end result may have to consider the packing factors of the two different diameter lines.

see the mesh tube comment

juro
02-22-2006, 07:10 AM
There ain't no math in flyfishing.

:hihi: :chuckle: only during the winter

jfbasser
02-22-2006, 07:16 AM
Neglecting mesh tube & packing factor for the moment:smokin:

Using pescaphile's result on the breaking strength going as the diameter squared and Q's result on volume involving the square of the diameter.....don't we get back to a inverse linear relationship between lb. test and capacity? So 240 of 20# is equivalent to 160 of 30#? Needs more work!

Back to mesh tube...I believe there is a packing factor phenomena even though the backing were incompressible.

GrantK
02-24-2006, 12:47 PM
Edit: Grant - I now see you want to also want to take into account a change from a WF9F to WF8F. We can include that too and answer your question, but also need to know the reel's stated capacity with the WF8F line for either 20 or 30lb backing. I suspect jfbasser's guesstimate of 225yds will be pretty close.

Here in lies the rub. Many companies, and the company whose reel I was using as the example to begin with, do not publish or otherwise make available backing capacity estimates for more than one line size or backing breaking strength per reel. As a result, if you're going to compare that particular brand and model of reel to another brand and model of reel to determine the relative capacity of each then you have to have a method of doing the conversion yourself. And, if the other reel company in question doesn't publish multiple listings for the same model either, you may have to standardize both to really compare.

Some great responses, but it's pretty aparent that it's tough to come up with little more than a guesstimate. And the final answer with the reel in question? It took quite a bit less than 200 yards of 30 lb. Cortland (Orange) to fill the reel to capacity with a fairly long taper 8 wt. floater (Rio Atlantic Salmon/Steelhead).

Interestingly enough, the published references to dacron diameters that showed a 25 percent difference between 20 lb. (.018") and 30 lb. dacron (.024") appear to be pretty close. That is to say, the 240 yards of 20 lb. published for the reel in question did in fact come out pretty close to 25 percent less 30 lb. As for the differences in line weights? Hard to say, and obviously very dependent on taper design and such, but it looks like it makes a difference of between 5 and 10 percent. My research into the difference between dacron and GSP revealed that in many cases the expected increase beteween 30 lb. dacron and 50 lb. GSP is approximately 25 percent as well. That is, you can purportedly get 25 percent more backing with 50 lb. GSP than 30 lb. dacron. It will be interesting to see how that actually works out.