Guide number question

[gordonjudd]

To make a long story short I calculated (cane) rods deflection for several rods knowing their guide spacing chart: tilted 45 degrees from horizontal,

Merlin,

Did you need to know the stiffness profile of the rod blank to make that bendform calculation or was it a measured shape? Is there any significant difference in the bending profile when the load is just attached to the tip of the rod vs the shape you get with the line going through the guides?

with static load representing 20 times the reference mass of the corresponding line

I assume that reference mass uses the AFTMA value for 30 feet of line. Thus for a 5 wt rod the load would be 20*9.1=182 grams.
Gordy

[George C]

Hi Merlin

Tonight I strung up an Sage RPLx 908-3 with dacron line, marked the line at the tip, then put it under load and the mark moved about an inch out from the tip. I then strung the rod through only 2 guides and placed it under load again. The line extended about 4". At first this seemed minor and less than I had expected. But then I reversed things a bit. I placed the rod under load and fed 3" of line into the rod. The reduction in load on the flexed blank was subjectively substantial.

So I wonder. When there are many guides the length of line stays fairly constant between loaded and unloaded states, so most of the load in the blank can be transferred back to the line as the rod unloads. Conversely, when there are few guides the line cuts the corners so the length of line in a loaded state is several inches shorter than in the unloaded state. I'd think this means as the rod unloads it can slide up the line those extra inches (or the rod can lengthen those few inches without transmitting force to the line?). This, in turn seems like slipping line into the blank as it unloads (the opposite of a haul) and slipping even a few inches seems to fairly dramatically lessen the load on the blank. Enough, I suspect to affect a cast. I will try casting the rod each way tomorrow, although line interference from the unused guides (and my erratic casting) will make a true comparison sketchy.

I'm wondering, can your model generate an estimate of line speed for an unhauled cast vs a cast where 3" of line are pushed into the rod (i.e., the opposite of a haul) as it unloads? Or are my guesses of what might be occurring misguided yet again?

Thanks
George

[gordonjudd]

Tonight I strung up an Sage RPLx 908-3 with dacron line, marked the line at the tip, then put it under load

George,
How did you put the rod under a load? Was the end of the line tied to an immovable point or was it loaded with a freely hanging mass?

If the load was free to move then I don't see why the length of line from the end of the rod to the hanging mass would make any difference in the rod bend.
Gordy

[Merlin]

Gordy

I knew all rod dimensions, they are available on databases. Also I did calculation “without guides”, the load (yes, 182 grams for a DT5 rod) being placed at tip top. That makes my life easier although it is an approximation. There is a practical difficulty for calculations if you want to go down to such a level of precision, you need using a lot of elements to describe the rod, something like half an inch for each. And that requires another file able to handle that level of discretization, on top of adding specific calculations due to the actual angles between the line and the rod shaft, including the height of guides (oh my god!). This simplification happened to be enough; you do not need an extreme level of precision to locate guides in practice.

You described all the possible parameters when considering the location of the stripping guide, and perhaps the simple rule given by Tom Kirkman is OK for fishermen. I do not think that Jim used anything but his experience to study guides position on his rods. The approach for the Excel file is “sophisticated” by comparison.

Merlin

[George C]

How did you put the rod under a load? Was the end of the line tied to an immovable point or was it loaded with a freely hanging mass?

Hi Gordon
I tied it to an immovable object then lifted it the same amount with each line threading option. All I was trying to determine initially was how much less line was contained between the tip and collector guide.

Perhaps this is what Merlin meant by "blank compression"? If so, then it would be present with any guide system (other than an inside the blank option), just more pronounced with fewer guides.

I also suspect that Scott Rods was not as much concerned about collector distance from the butt or reel (as is a major issue with spinning rods) but rather because moving the collector closer to the reel gives them room for additional guides above. When I had the rod under load it was interesting at how little effect 'corner-cutting' had on the top section of the blank. Not a surprise in retrospect since this is pulled straight under serious loads. Most of the compression occurs in the lower 2/3 of the blank when under a large load and it would not surprise me if Scott was taking this into account.

I owned a Scott Sector 8wt (alas it went swimming never to be seen again) and the collector guide on this rod is indeed placed several inches closer to the butt than the other companies rods I own. Too close and it does interfere with the backcast pickup, however.

A year ago I experimented a little with a "hauling guide".........a tall framed spinning guide whipped on just above the handle. Did it more to improve my hauling but gave up on that approach quickly.

Thanks
George

[gordonjudd]

All I was trying to determine initially was how much less line was contained between the tip and collector guide.

George,
I don't know why that would be important, but the amount of line between the stripper guide and tip top will be different in a static condition such as with your immovable point as compared to the combined effect of line sag between the guides when casting.

We had a discussion on the unusually large number of guides used in the Ultrawave rod (17 guides plus two stripper guides) on the old board. All those guides were used to reduce the amount of line belly that Fox Statler believed had more impact on shooting line than did guide friction.

line_belly_example.jpg (45.91 KiB) Viewed 1460 times

I don't think any studies were done to put that theory to the test, but those rods were apparently not the disaster I would have expected because they added so much extra mass to the rod.

If you are interested here is Fox Statler's discussion on the subject at Youtube. https://www.youtube.com/watch?v=kF3sZzR ... FoxStatler

Gordy

[Merlin]

Hi George

I can certainly tune the model for a "negative" haul, but I do not think thid would represent reality in terms of rod dynamics. Forces at guides level induced by line tension increase the bending moment of the rod (what I called compression) if guides are too far apart from each other. How does it affect rod dynamic behavior I don't know.

When it is less cold over here, I shall test a stripping guide / tip top only combination and see how the rod reacts.

Merlin

[gordonjudd]

I shall test a stripping guide / tip top only combination and see how the rod reacts.

Merlin,
That should put an upper bound on the line belly problem.

I would think that 16 guides on a 9 foot rod would be sufficient to put a lower bound on the line belly effect.

Too bad that Magnus's promised high speed videos and tests of of the UltraWave rod never became a reality.

Post by Magnus » Mon Feb 14, 2011 7:47 pm
Hi Fox
Just off the phone with Ben, we're hoping to make some slow motion video next Monday. Depends on weather, all being well that should give us something to chew over.

Gordy

[George C]

Thanks Merlin and Gordon

For the little it is worth I tried a crude experiment yesterday. I cast the RPLx 908-3 with a SA Mastery Standard 8wt (true to weight/60' head) both lined normally then with the line through none of the mid section guides (approx a 3' span). I first tried without the tip section guides threaded as well (just the tip itself) but line wrapping was an issue. I was surprised by the results. I noticed no difference in casting distance (@100' against a tape). There was, however, an interesting a subjective difference. When set up with a 3' long unthreaded mid-section the rod felt like it had a faster action.

I took the first observation to mean that, at my current skill level, there was unlikely much practical gain achieved by squeezing 1-2 extra guides into a rod.....even if intuitively I suspect there should be a benefit.

The second observation just raises a new question. Does distributing where/how force is applied (distributed) along a blank through guide placement change how a blank feels as it is cast? Seems like maybe it does.....although I understand the actual properties of the blank itself are fixed at manufacture.

And, Gordon, thanks for the link to the Ultrawave rod thread. It was a fun and informative read on a lot of levels.
George

[gordonjudd]

The second observation just raises a new question. Does distributing where/how force is applied (distributed) along a blank through guide placement change how a blank feels as it is cast?

George,
I would expect there to be little difference since the line tension at the tip is so much bigger force than the transverse bending force produced by the line tension in the guides.

You should be able to test the difference in the oscillating frequency with the line going through all the guides or just the stripper guide and the tip top to see how big of an effect that might be. Just clamp the cork grip so the rod is horizontal and use a couple of rolls of pennies (250 gr mass) tied to the end of the line to act as a tip load. Then take a video of the rod oscillation with the line going through all the guides and compare that frequency to the frequency you get with the line just going through the stripper guide and tip top.

I will be interested to see if there is much difference in the two test conditions.

Gordy