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What's the best procedure for changing the line weight of a taper using Hexrod?

What I did was input the original line weight and dimensions of a rod (say a 6' #4) to get the stresses.  Then I changed the line weight (to #2) and started tweaking the dimensions until the stresses were roughly the same as the original rod.  Could I reasonably expect the new taper to have a similar action got with the lighter line?  (Bill Benham)

    Use the Online Interface to Hexrod that is under the Software section of the Rodmakers home page, it will do all that for you, just input the changes you want to make and, presto, new taper. It also has a great taper archives and lots of other features, not to mention a search engine to search the List archives.  (John Channer)

    If you enter the original as you said and then hit the button that says something like "change rod fundamentals," change the line weight and make sure it says "keep stress curve same" at the bottom, it will recalculate the dimensions and the stresses should be identical to the original.

    When it says that the stresses are identical, if you go down in line or longer in length - expect the action to be slower than the original.  At least, that's what I have observed.  (Jerry Madigan)


I am intrigued with using Hexrod to determine line weight as you describe. However, when I check certain rods, like Gary Lohkamp's Dickerson 8014 posted to the online archives, I have to bump the line weight up to 9 or 10 to get that upper range at or near 200,000. When do you know when to stop?

Like in the above 8014 example, the 6 wt stresses are this:

Point    Dimension    Stress 

0          0.076        - 
5          0.095        109037 
10        0.114        130638 
15        0.133        128384 
20        0.151        122340 
25        0.167        118840 
30        0.181        118272 
35        0.192        122498 
40        0.200        131570 
45        0.208        139963 
50        0.223        136299 
55        0.243        127013 
60        0.264        117618 
65        0.284        110951 
70        0.295        115279 
75        0.315        109483 
80        0.336        103721 
85        0.359        97337 
86        0.359        99791 

As a 9 weight the stresses are this:

Point    Dimension    Stress 

0          0.076        - 
5          0.095        149130 
10        0.114        177327 
15        0.133        172757 
20        0.151        163014 
25        0.167        156648 
30        0.181        154122 
35        0.192        157745 
40        0.200        167422 
45        0.208        176032 
50        0.223        169010 
55        0.243        154983 
60        0.264        141550 
65        0.284        131898 
70        0.295        135521 
75        0.315        127397 
80        0.336        119556 
85        0.359        111208 
86        0.359        114008 

Are there some rods it works better on? Am I completely misreading what you are posting? Hexrod is a useful tool in many ways, but I am stuck on this one and would like your expertise.  (Bob Maulucci)

    Amount of line fished is an important part of the calculations. You can keep the same line weight and increase the amount of line fished to increase the stress values. The stress curve for a 4 weight at 55’ is about the same as a 5 weight at 45’ with the same dimensions.  (David Dziadosz)

    The other factor to take into account is the length of the line that you feel is a normal cast. I generally put in 40 feet, but if you know you are going to be casting 65 feet most of the time, then there is a lot more weight involved. Also take into account the weight forward lines go into a thin running line at about 40 feet, so the weight increase will not be that much past 40 feet for WF lines. DT lines will have an increase in weight all the way to the backing.

    Some rods are just stiff, and the were designed that way. The Lee Wulff 6 footer - I forget what it was called - is another one that has a very low stress curve. Didn't he make it to catch salmon?  (Darryl Hayashida)

      I am assuming the online Hexrod is using DT as the default line type since I get no choice, but I guess it doesn't matter because in testing it is not changeable....

      So I earlier determined that the Lohkamp taper of the Dickerson 8014 is more of a 9/10 weight than a 6 weight at 40' using the default line type, but it is a good 6 weight when using 70' of line because then my high point maxes out at around 200,000?  (Bob Maulucci)

        It's a matter of your preference. If you like the way it casts at 70' with a 6 wt. and the stress curve is saying the peak is at 200,000, then for future reference use that value. I've found that for dry fly fishing a maximum point closer to 250,000 is better for me. If I make a nymphing tip for a rod I make it with a more rounded peak on the stress curve and closer to 220,000 (usually a little below). A stress curve by itself is meaningless. You have to relate it to the way the rod casts for you, and what you like. Graph up all the rods you can, go out and actually cast the rods, look at the stress curve. Soon you will be able to relate the stress curve to the way the rod casts. You will find that similar rod actions have similar stress curves. Then you will be able to design a rod by using just a stress curve.  (Darryl Hayashida)

          Okay, let me ask this again. You don't need to explain any other facet of Hexrod to me, just explain the way you use it for to determine line weight to me. This is my understanding of your method...

          You have said on the List that when Hexrod finds the stress curve for a given taper  that  ranges  within  the 120,000 to 200,000 range that is the approximate line weight for that rod. For example, when a lister asks what line weight the rod should cast, you have answered that they can run it through Hexrod and see a stress curve that peaks out near 200,000 and that means that would be a good starting point.

          I just want to know if that is what you are saying to do? Yes or No?   (Bob Maulucci)

            Yes.  (Darryl Hayashida)

              If you are using the Garrison stress curves to compare rods then I think you must fix the length of line or the comparisons will not have a common basis, i.e. if you want to compare the shape of the stress curve for a 7' 2/2 4 wt to that of a 8'-6" 3/2 6 wt then you must keep the  length of line the same... JMO.  (Kyle Druey)

                The overall shape of the stress curve doesn't change much with different line lengths, or even different line weights. You will have proportionally higher peaks  with greater weight, and of course the stress values are higher, but the over look or general shape of the stress curve doesn't change much.  (Darryl Hayashida)

                  The shape and location of the curve are relevant... i.e. I can have a straight lined stress "curve" at 200,000 and it feels like  a real noodle or have the same straight line at 100,000 and it is much stiffer...  so I think shape and stress levels are important for comparisons.  (Kyle Druey)

                    Okay. What I am saying is in trying to determine the line weight of a rod that you do not know the line weight, plug in a line weight in Hexrod and look at the stress curve. Use a line weight with the length of line that you feel is reasonable. With a weight forward line I use 40 feet. Most WF lines turn into a thin running line around 40 feet and will not add a lot of  weight past 40 feet. adjust the line weight until the top of the curve reaches around 200,000. Go out and cast the rod using that line weight and  your length  (whatever it is - 40 feet for a WF) as a starting point.  Determine if you like the way the rod casts. If not, use a heavier or lighter line. Find the weight of line that feels best to you. Go back and plug that line weight into Hexrod. Note where the curve is - lowest point, and highest point. Use those values in the future to estimate a line weight for a rod that you are trying to find the line weight for.  (Darryl Hayashida)

      It is my understanding that the stress curve can do about 3 things for you.

      1. Give you a "fingerprint" of the taper which gives you a clue to what Wayne calls the rod's character.

      2. Allows you to estimate the position and magnitude of the maximum bending stress.

      3. Allows you to duplicate the stress curve (general character of a rod) using different fundamentals (action length, line weight).

      None of these is exact. Function 1 requires that you know what casting characteristics correspond to which stress curves. This requires that you cast rods with various stress curves and remember how they cast. Function 3 allows you to re calculate the stresses using different lengths and line weights (what you see is not always what you get, particularly when you make radical changes in rod fundamentals).

      Function 2 (the one being discussed here) is estimation of maximum bending stress which Garrison only used to determine the load limit for a rod- Not the appropriate line weight and length cast. Bottom line: The rod does not cast best with the maximum stress in a particular range of magnitudes. The rod casts best with the line weight you determine  as best by casting it.  (Doug Easton)

        I agree with what you are saying. I just posted a message, and I have said it before, that a stress curve is meaningless unless you relate it to the way a rod casts for you. By "you" I mean you personally. Not the way it casts for me, not the way it casts for your buddy, the way it casts for YOU. Cast a rod yourself, look at the stress curve. After you have done this many times for many different rods you can start designing rods by using a stress curve by itself. As a function of a lot of experience with a stress curve you can get a real close approximation on the line size. Not exact, but close - personal preference again.  (Darryl Hayashida)

    Regarding your question. I would be very careful trying to determine the line size just using Hex Rod. You do not know what the maker had in mind when he was making the rod. As for the 200 thousands point, I have made many fast rods that, using the right line size and line length, peak at over 250 and they are fine rods.

    From what I can see, the 8014 is a very stiff rod having an average taper difference of 15.3 thousands between  stations, (13.4 is a good average for most rods.)

    It is very stiff from 5 to 30 inches, then will flex some to 50 inches although the ferrule will stiffen it up at 48 inches. The butt is also very stiff except for one point at 70 inches where it will flex a little. Over all it is a stiff rod that will handle a 6 to a 8 or maybe 9 wt line. It is not one I would like. Have you tried it or built it, would be interested in  your comments.   (Bob Norwood)


If I want to modify a taper to make a 4 wt a 5 wt, should I simply bump each station up .006 or should I tweak the rod until the stress curve for the 5 wt is exactly the same as the stress curve for the 4 wt?

It seems to me that I'd want the stress curves to be the same but I've been told it's the other way around,  simply bump it up by .006. I've done both and the design with the identical stress curve gets up to .014 larger than the original rod in the butt and .011 in the tip. Presumably this would make it a 6 wt?  (Jim Lowe)

    If you use Hexrod to change the line weight, it increases the diameter to keep the stress curve the same, in other words, it increases by a proportion, rather than a fixed dimension. If you just add .006 to all dimensions, you have made the tip drastically larger and hardly changed the butt diameter at all. I believe in the Hexrod method, even though stress curves leave me cold and I never look at them, I look at the actual taper graphs.  (John Channer)

      Good point John, thanks.  I think I'll go with the stress curve approach.  (Jim Lowe)

      Surprisingly, Mr. Milward suggested adding a fixed amount to each taper to increase or decrease it by a line size.  To be fair he only suggested it for one line size, but such technical sloppiness is worrying in a architect! As you say,you should modify rods by using the "Stretch stress curve" option, not the other one, which I don't understand.  I do understand stress curves, and do go along with Milward's suggestion that they might be misleading.  However, since they are not especially useful for taper designing, proving as they do that  all tips are too thick but not much else, we may safely consign them to history.  What IS useful, as a once only exercise, is to equalize all the stresses using the Hexrod "modify stresses" option, and see what shape you get........

      I might add that we suffer the same problem with hollow building, the wall thickness should be a constant proportion of the overall diameter.  (Robin Haywood)

        I think Ray Gould in his first book also suggested adding a constant to change line size?  (Steve Dugmore)


If I take the numbers for a 4 wt rod and feed them through Hexrod and change them to a 5 wt, is there any tweaking I need to do to get the action as close as possible? Both would be the same length and its not a complex taper.  (Bill Walters)

    I think that Hexrod gives a much better conversion than the old "change by .006" every station". I've made about 2 dozen rods with the original tapers changed by using Hexrod and I have liked the results every time.  (John Channer)


I want to convert a taper from a 4 weight to a 5.  I did this with Hexrod by increasing the line size to a 5 and holding the stresses constant.  What's the rule of thumb regarding the length of line cast in Hexrod?  Should I increase it from the 40 ft. for the 4 weight to 45 or 50 for the 5?  Do I have to leave it the same as the 4 weight version for the 5 weight rod to have the same feel?  How about if I wanted to take it from a 4 to a 6?  I think I've read that, in Hexrod, as the line weight goes up the line cast should too, but I couldn't find anything in the archives that says by how much.  (Bill Benham)

    The line size of a rod is all about weight of the line in the cast, so it's the length of your average cast with a DT line or level line if you use a level line. But consider this - if you use a WF line once you get into the running line very little weight is added no matter how long the cast. Most people shoot the line once they get past the belly anyway. So, the basic questions are: What type of line are you going to use, and what is the average length of your cast?

    I have a short rod that where I usually use it I don't cast more than 15 feet. The average cast is under ten feet. To load the rod in that short a distance I use a 5 weight line. If I think I'm going to cast more than 20 feet I use a 4 weight line. I sometimes use a 3 wt DT on it, but I usually don't go lighter than a 4 wt if I use a WF line.  (Darryl Hayashida)


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