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## Rod deflection and acceleration

Moderators: Paul Arden, stesiik

Torsten
Posts: 174
Joined: Tue Jan 22, 2013 7:34 pm

### Re: Rod deflection and acceleration

Hi, you guys are again very off-topic, maybe these very detailed discussions about models are something for fly casting physics?

Lasse:
Personally, I believe it to be a huge, big, red herring
If you mean your video, yes .. I don't know what I should look for, I've found a blog entry:
https://thelimpcobra.com/2012/11/20/ben ... mechanics/

The author writes there:
as we’ll see below, Lasse Karlsson has taped two very different rods together to cast them at the same time with two identical lines of the same weight rating. simultaneous loop formation, loop shape and loop speed are very-very similar with both rods.
Well, I can see both differences of loop shapes and velocities, in that video sometimes a loop leads - I'm guessing "very similar" is a subjective term. One problem of such experiments is to replicate same initial conditions, in this case the rods have a different length and I'm sure that the rod grip has already an influence on the cast.

I suppose the statement should be that the rod action does not have the greatest effect on distance, there is a study about this subject:
http://www.sexyloops.com/articles/8rod.shtml

As you can see, the average distance is very similar, although there is a great variance of the stiffness.
It would be very interesting to compare though, if these observations are still valid today, e.g. I've seen most guys have used 8wt rods and above in Tallinn.

Graeme:
The Casting competitions suggest a light stiff rod is the best option for maximum line speed. Regardless of the mathematical models.
I don't know if we can say that always, AFAIK Grand's record with a greenheard rod stood for a long time and I know same happened with salmon distance T120 in casting sport, one German had the world record for some time with a GDR Kuckuck salmon rod (very heavy weighting over 1kg).

Merlin
Posts: 1363
Joined: Wed Jan 09, 2013 8:12 pm
Location: France

### Re: Rod deflection and acceleration

Hi Torsten

Being off topic is the rule on SL board!

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

Lasse Karlsson
Posts: 3919
Joined: Wed Jan 09, 2013 9:40 pm
Location: There, and back again
Contact:

### Re: Rod deflection and acceleration

Torsten, need a hug?

Yeah, difference can be seen, and as I have written over and over and over again, I do it in my demos and have used a wide array of rods now adays equal lengths and bigger difference in stiffness and all, and repeat the outcome.. Other people try and experience it too, but yeah, not applicable right?

About the 8 rods, have been done, I even did a fun experiment when told just picking a stiffer rod wielded 2 more meters... Didn't really happen though, do you think it should?

What's a 8 wt rod?

Grant's record, did anyone try to beat it before with the same line?

Cheers
Lasse

http://www.karlssonflyfishing.com

***Bring Mark back!!!!!! ***

Graeme H
Posts: 1740
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Rod deflection and acceleration

Hi Merlin,

Lasse's video is great and certainly does help us shoot a few misconceptions down. If he gets the chance (and inclination), I'd love to see it repeated going for maximum line speed (distance) with the CF rod, and again going for minimal loop size with the 'glass rod. It looks like the cast we're seeing is well optimised for the CF rod but the loop might be larger than we want on the 'glass rod.

What I take from the video is that the longer stroke length of the 'glass rod is adding line speed for a little longer than the CF rod provides. But what would happen if the stroke length of the CF rod was taken to the extreme, as in a distance cast? In that case, the 'glass rod would no longer show a longer casting stroke than the CF rod and the only remaining factors would be the rods' inertias and moduli.

Cheers,
Graeme
FFi CCI

Merlin
Posts: 1363
Joined: Wed Jan 09, 2013 8:12 pm
Location: France

### Re: Rod deflection and acceleration

Hi Graeme

I mostly agree with your analysis, however the relevant rod parameter is not rod stiffness, it is loaded frequency (and inertial effect to a lesser extend for comparison of rods all made of graphite). The 8 rods study mentionned by Torsten did not take into account the right technical parameters for rods, that's likely why it is inconclusive on that point. Such parameters include the equivalent mass at tip, which is easily measurable.

On the paper, the best rod is the fastest, not the stiffest. Now the performance will vary with the actual cast parameters. Skilled casters are repeateable, but up to a certain point. IMHO rod and cast variations blur each other. I once did a small contest with Jim Bartschi for designing a competition rod (for a MED 5). He won by little with his design. That context took place some 10 years ago, today we would design such rods differently for sure. I know the technical goal for parameters (inspired from casting model) but achieving such parameters needs HM material which may not withstand the stress of a powerful cast for a long time. There are means to improve the situation at the expend of MOI: you cannot get everything right if adequate materials are not available.

I would suggest to look after a saltwater rod today, the one you can push to the limit, so its stiffness or line number will vary with the caster. The trend in design is faster loaded frequency for a stiffer rod, but idealy I would chose the softer rod among rods of similar loaded frequency (with the carry used for the cast). For a higher speed I would change the rings for the lightest possible ones. The ideal frequency range is pretty high.

The fishing domain is different, in that case people often adapt their cast to the rod they use on various rivers, if not there are reluctant to change their tackle (a friend of mine is just like that). In competition, there is just one rule: max power, and the rod has to follow.

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

Bianchetti Ivan
Posts: 111
Joined: Wed Sep 30, 2015 8:25 am

### Re: Rod deflection and acceleration

It could be my stupidity, a soft rod when it straightens up, it accumulates more waves inside the passers-by! Can the reasoning be correct?

Paul Arden
Posts: 13053
Joined: Thu Jan 03, 2013 11:20 am
Location: Belum Rainforest
Contact:

### Re: Rod deflection and acceleration

Hi Ivan,

Not necessarily but certainly more likely I think. However damping I don’t think we understand fully. In fact I sometimes (quite often actually) see less damping with a lighter line on the same rod. I am sure (In fact I know!) that the weight of the line that is in the rod rings also plays a part, and you can really see this when watching the rod vibrate after the stop when casting a shooting head with overhang. Even one line number plays a huge difference in rod damping - i once won a TFO rod in a competition (booby prize - only joking ) that was a 6WT. I only had a five line and the rod had terrible damping. However later when I cast a 6 line on the rod it was actually fine. So in this case relative stiffness did not help, quite the opposite in fact.

I also think that damping has more to do with how the stiffness and mass is distributed throughout the blank, than overall stiffness. Rings are also very important too. Even a small variation in mass such as between recoil and single leg H&H rings shows up in waves in the rod leg of the loop. However more mass in the lower sections - perhaps more mass but with the same stiffness - would possibly counter this and damp the rod with the heavier rings. I have had rod prototypes that have had noticeable tip damping improvements with adjustments to the lower sections.

Cheers, Paul
It's an exploration; bring a flyrod.

Flycasting Definitions

Bianchetti Ivan
Posts: 111
Joined: Wed Sep 30, 2015 8:25 am

### Re: Rod deflection and acceleration

Hi Paul, I refer to the fact that if the softer barrel bends, when it bends it shortens, while the line inside it remains the same length, neglecting what we do to compensate, when the barrel straightens, where pick up the missing part? From the line out or from the line that enters the rings? (Does this disturb the line?) I hope there is something understandable

Paul Arden