Taper Research #1

Haven't posted in a while. I haven't been fishing much in this Arkansas summer heat and don't want to post redundant rod making stuff. I thought I'd share the results of the taper research I've done the past couple years. I'm an accountant/financial analyst by trade so I enjoy analyzing numbers...and tapers are all about numbers.

This will be the first of several taper research posts. There's a method to my madness, so if you're interested in this stuff read through all the posts in order. They will build on each other as I lay this stuff out. I called this taper "research" for a reason. This is not going to be about designing tapers or learning to read stress curves. I'm assuming anyone loony enough to read this already has a basic working knowledge of taper design. I'll be walking you through my analysis of the tapers in the RodDNA database. RodDNA is a free web based taper design tool that includes a massive archive of tapers...almost 500 of them. I didn't use RodDNA to do the analysis, just the tapers.

The table included with this post is a summary of 444 hex fly rod tapers by line weight. The vast majority of the tapers are 3 to 6wt...and most of those are 4 and 5wt tapers. The average rod length increases incrementally by line weight from 2wt at 5.9ft to 8wt at 8.9ft. The 4 & 5wt tapers average 7.1 and 7.7ft respectively. The average tip diameter starts at 57 thousandths for a 2wt and increases incrementally to 94 thousandths for an 8wt. The 4 and 5wt averages are 68 and 70 thousandths respectively. The taper slope (per 5 inch station) starts at 9 thousandths for at 2wt and increases incrementally for each line weight to 16 thousandths for an 8wt. The average diagonal value (difference between the actual taper and the trend line for that taper) is about the same for most of the tapers at -1% to 2%. However, it would be incorrect to assume that most tapers fall in that range. In fact, there's a wide variety of diagonal values in the database that represent diametrically opposed taper designs. It's just that there are about an equal number of tapers that fall on either side of the average. More on that later.

So...does any of that really matter? Here's what I got out of all that...most bamboo tapers are 4 or 5wt, 7 or 7.5 foot tapers with a wide range of diagonal values that average very close to a straight line taper in total. In other words, they are all about the same line weight and length but the action varies dramatically from one taper to the next. I'll pick up with that point in the next post.

But before I move on the the next post...you may have noticed the deflection data in the table. That's some really cool stuff that hasn't really been talked about much in the rod making community. I only know of three deflection programs that have been written, and very few makers have used them. So most of the deflection analysis in my research will not look familiar, but it should make sense. Tip deflection in this table is the distance the tip is bent from a straight position when loaded with the given line weight and length of line in a simulated casting stroke. Midpoint deflection is the same measurement at the midpoint of the rod. Midpoint percent of tip deflection just illustrates how much of the overall deflection is accounted for by the butt half of the rod. Effective length is a big deal, but that won't make a lot of sense until you see the charts in later posts. It's the straight line distance from the tip to the butt of the rod in a bent (loaded) phase of the casting stroke. For example, an average 7.7ft 5wt rod has an effective length of 6.4ft (including the grip and reel seat). That will all make more sense when you see the deflection charts in later posts.

I'm using a deflection program called FlexRod that was written by Jim Utzerath in the late 90s. Jim presented the Excel program at one of the rod makers gatherings in 2000. I read about FlexRod a couple years later in the list archives. I E-mailed Jim and he sent me the original program, samples and documentation that he presented at that gathering. It's a complex program that works through the Garrison stress calculations and then bends the rod based on several variables and calculates bent stress and deflection values with a series of Excel macros and visual basic routines. I'm using FlexRod as the engine for the calculations in this research, but I've modified the input method to work from a list of tapers rather than one taper at a time. Using a few slightly modified Excel macros, I can run hundreds of tapers through Jim's program in just a few minutes while storing stress and deflecting data for each taper for comparison and analysis. Max Satoh published a program similar to FlexRod earlier this year called DynaRod. I haven't worked with DynaRod yet, but it appears to be based on the same principals as FlexRod. The nice thing about DynaRod is that Max designed it and is supporting it. FlexRod was not packaged for mass distribution and is not currently supported. If you're interested in deflection analysis, I'd recommend giving DynaRod a try. That's enough technical chatter. The deflection stuff will make sense when you see the slides in later posts.

By the way, Jim has moved on to making violins but still lurks out there on the bamboo rod making sites. I hope he runs across this blog some day and sees that his program has been put to good use. As far as I know, I'm the only maker using it. Thanks Jim!

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