© Tapani Salmi 4/2011

**Motto: "The Nature Is Full of Brilliant Mathematicians"
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Papyrus reeds are triangular in cross section!
It is always a good idea to follow the trials practically tested by the nature.
THEORETICALLY in engineering science the stiffness of an object (rod) is calculated using the formula of "moment of inertia", MOI.
These mathematical formulas for MOI and stiffness are different for e.g. hexagonal, pentagonal, quad and triangular shapes and cross sections
(see eg.
en.wikipedia.org/wiki/List_of_area_moments_of_inertia#cite_note-tri-4
and
www.efunda.com/math/areas/triangle.cfm
.
The formulas are useful typically useful when comparing different bamboo fly rods - e.g. if wi would like to compare two or more rods which are made of
six (HEX) / five (PENTA) / or four (QUAD) strips and are of equal length and built equally in weight (their cross section areas are equal at every point). When we use these rods for casting and fishing we notice some differences in their action like in their stiffness. We describe the rods "faster" or "slower". An optimal rod would be light in weight and cast the short and long line as easily as possible.
We bamboo rodmakers think that bamboo as the natural material is the best material to achieve this goal. In addition, we like to make these delicate rods using our hand tools!
The mathematical formulas tell that if we have the cross section area (or weight) of value 1.00 and the rod is hex (six strips) the MOI value is 0.80. The rod with equal weight built as quad (four strips) has MOI of 0.83 - it is about 3-4% stiffer. For the penta (five strips) the difference is about the same. If we construct the rod as hollow built the mathematical calculation gets more complicated.
If we make an equal TRI rod in triangular cross section with the area of 1.0 the MOI is 0.95 which is 20% greater than HEX rod. The difference in stiffness between TRI and HEX rods is thus FIVE TIMES the difference between QUAD and HEX. You really notice the difference at once in casting - TRI rod is much stronger and faster compared to HEX or QUAD rod of equal weight.
IN PRACTICE the stiffness and power is of great advantage when constructing long rods. Typically, rods with length of 8,5-9-10' tends to be either very slow and/or very heavy. The long two-hand salmon rods are a very special problem. Bamboo is a good material to build a spey rod but the long spey rod tapers result in very heavy rods.
Triangle rods seems to give really superior properties for long two hand rods due to the extra stiffness of the triangle construction.
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Triangle rod using three strips
I started the experiments by constructing a triangular (TRI) rod with three strips. Such rods consist of three strips with corners of 30-120-30 degrees. These kinds of strips are not very easy to make using hand tools.
I started the construction by making Excel spreadsheet to convert the “hex tapers” into equal triangular area and the dimensions of the strips.
The 30-120-30 degree strips are difficult to construct manually. I made first 60-60-60 degree (HEX) strips with equal width of the final 30-120-30 strips. The rod taper dimensions could be converted by multiplying the dimensions by 1.41 (=sqrt(2)).
Thereafter I plane the upper 60 degree corner into 120 degree corner. For that purpose I made a simple hand mill of my own. The hand mill consists of two blades with a 120 degrees angle. The proper taper is achieved by mounting the strip on a wooden support. This support is elevated gradually to achieve the exact dimensions for the taper. This all took several months to finish.
Finally I had a construction system to make the strips with 30-120-30 degree corners and glued my first triangular rod.
I choose my first triangular taper to be PH Young's Driggs River Special (line weight #4-5). It was an obvious choice because I have previously made several
Driggs River rods using different constructions like hex, penta, quad, inside-out, hollow-build with different kind of ferrules (bamboo, scarf joint) etc.
When the first rod blank was complete I made the scarf joint ferrules and fixed the line guides onto the rod. To my surprise the triangular Driggs was not casting #4-5 line but #7 line - it was extremely stiff and much stronger than the original hex rod of similar weight.
As the difference was so huge I wanted to try with longer rods and I constructed some straight tapers for #5-7 9-10' rods and 14' #7-9 two-hand salmon rods. I even have made 10' #4 rods They all are surprisingly light and especially good in streamer and salmon-fishing. The stiffness and strength of the TRI rod is caused by the very wide strips and they are really as good as calculated mathematically.
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TriStar – a triangle rod using six hex strips
As mentioned the TRI rod using the 30-120-30 degrees of strips was difficult and slow to manufacture using hand tools and therefore I decided to try another triangular construction.
The idea is to use six strips with normal 60-60-60 degree corners (strips 52. in Figure).
In this construction the strips are first turned 60 degrees inside-out and then glued together - the strips are thus glued with the power fiber surfaces together (60.).
This results a inside-out hex rod. This hex rod is then modified into triangular TriStar rod.
To change to rod into a triangular TriStar rod I plane the three corners with no power fibres away. The corners with power fibres are left untouched.
The weight of the blank is thus diminished up to 50% while most of the strong power fibres are included into the rod.
This reduction of the weight by 50% is equal to make a hollow build rod with a 29% final thickness of the wall (reduction of 71% of the thickness of the strip)!
This extreme reduction is achieved simply by planing the blank.
If you want to modify the taper you may simply plane the rod more.
In addition the benefits of wide strips in the triangular shape and the high MOI value is remained.
If you are building a very thick rod the power fibre part or the cane material may not be thick enough and part of the strips are actually composed of the soft pith material.
This is not a problem for TriStar construction as you simply plane the soft part of the strips away - just like in hollow building.
I call the rod TriStar because the shape is triangular (TRI) and the cross section with the powerfibres is arranged as a STAR shape.
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TriStar Tapers
Theoretically any HEX rod taper is very simply converted into TRI taper - you just multiply all the HEX dimensions with value of 1.40 (sqrt(2.0)).
The resulting inside-out TRI rod is two times heavier than the original HEX taper.
Then you plane 50% of the mass of the blank away as described. This results in a triangular rod of equal weight as the original taper.
The stiffness of the new TRI rod is however much much higher and the rod is suitable for much heavier line than the original taper, the difference may be 2-3 AFTM line weights.
My present formula to modify a HEX rod to TRI rod is to multiply the HEX strip dimensions by value of 1.25 - 1.35. This has resulted quite good results (see below).
The more accurate tapers could be developed using the formula of MOI as the mathematical base.
I include below some tapers which I already have build and tested in fishing.
Because the rod is glued as inside-out it is possible to modify the
resulted glued blank by planing it thinner - see the idea here
http://personal.inet.fi/private/tapani.salmi/Salmi_PowerFibers_Issue_24.pdf>
There are some obvious disadvantages in the TRI construction. The shape and outlook is certainly not usual and even strange!
The construction of the ferrules may be difficult and you have to change the HEX shape of the ferrules into triangular shape.
I have used mainly scarf joints which are very light. In scarf spliced joint the two sections are typically taped together.
I build a ferrule to the joint using shrink tube support - see
http://personal.inet.fi/private/tapani.salmi/SCARFFERRULE.HTML">
Even the cork handle is more difficult to manufacture with triangular hole for the blank. I have used compressed cork plate material (thickness of 5 mm), cut pieces to proper dimensions and simply glued them on the wide surfaces e.g. using PU glue.
The compressed cork plates are used on the floor beneath the parquet material. It is cheap and available from parquet shops.
As the surface is not very hard I wipe a very thin layer of PU glue on the cork. This results a stronger and still pleasant surface.
The triangular rod is not bending symmetrically during the cast – it is stiffer when the rod is hold the sharp edge towards the casting direction.
Therefore the rod is faster and stronger if you fix the line guides on the sharp edge of the rod and not on the flat surface.
For that purpose you have first to twist the feet of the snake guides a little to adjust the guides to the sharp corner.
TAPERS
If you want to convert a HEX taper into TRI taper you could use HexToTriCalculator EXCEL program - download it here.
When you give the HEX taper values, constant swelling factor for soaking (1,0 for no soaking) and CONVERSION factor 1,25-1,35 you may get the dimensions of TRI rod strips in MMs (Sheet1) or in INCHES (Sheet2)
Go to HexToTriCalculator.xlsx EXCEL program
List of some tapers:
The tapers are given as the height of the single strip. In the figures the values are the height of the final TRI rod.
The values are in MILLIMETERS with 5" stations.
I use very light reel seats (sliding bands) and scarf joint ferrules to keep the rod as light as possible. The weight is for the finished rod.
For the scarf joints of double hand salmon rods I recommend e.g. one millimeter of extra thickness for the lower joint area to make it stronger!
I have build and fished these rods and hope to hear comments.
8'4" #6 119g : really nice and light rod
1,63 - 1,88 - 2,17 - 2,49 - 2,77 - 3.21 - 3,57 - 3,81 - 4,11 - 4,33 - 4,68 - 4,98 - 5,22 - 5,48 - 5,95 - 6,30 - 6,54 - 6,84 - 7,00 - 7,25
9'6" #6 134g : still very pleasant to use
1,35 - 1,73 - 2,00 - 2,30 - 2,61 - 2,97 - 3,26 - 3,55 - 3.79 - 4,03 - 4,22 - 4,46 - 4.68 - 4,84 - 5,00 - 5,21 - 5,44 - 5,71 - 5,91 - 6,09 - 6,22 - 6,26 - 6,26
10' #6-7 159 g : a little too heavy for my wrist but perhaps could be used for salmon / steelhead fishing.
1,51 - 1,73 - 2,01 - 2,30 - 2,61 - 2.97 - 3,26 - 3,55 - 3,79 - 4,06 - 4,32 - 4,60 - 4,80 - 5,02 - 5,20 - 5,20 - 5,37 - 5,57 - 5,80 - 6,00 - 6,28 - 6,52 - 6,69 - 6,86 - 6,94 - 6,94
14' #8 SPEY rod 480g : for salmon fishing. For scarf joints I recommend 1mm of extra thickness for the joint area!
1,92 - 2,16 - 2,57 - 3,00 - 3,29 - 3,58 - 3,84 - 4,22 - 4,47 - 4,78 - 5,05 - 5,40 - 5,60 - 5,85 - 5,97 - 6,21 - 6,34 - 6.52 - 6,69 - 6,82 - 7,03 - 7,29 - 7,56 - 7,90 - 8,04 - 8,23 - 8,40 - 8.56 - 8.66 - 8.74 - 8.83 - 8.83 - 8,83 - 8,83
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TriStar rods - triangular cork handles and reel seats with gliding bands
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Scarf joint ferrules with shrink tube.
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TriStar rods
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My special thanks to Juha Jokinen, Carsten Jörgensen, Ray Gould and Christian Meinke for their help!
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NOTE: some aspects of the triangular cane rod building are patented technology. If you are an amateur rodmaker you are welcome to build any rods for yourself and I hope that you could inform other builders (and me) about your experiences, new tapers and results.
If you have commercial interests please contact me - tapanisalmiAThotmail.com
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Kola river - TriStar rod is bending
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Kola river 2009 - salmon 8 kg and TriStar rod
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