Stiffness and Tip speed

[VGB]

Don’t worry about it Daniel, it’s easy to get lost in the complexity. I’m still confused by your answer though, what is your reference axis?

[VGB]

Sorry Daniel I have a secondary question as well, having been out casting a #6 and #10 outfit today. What rod mass do you use for calculation?

Regards

Vince

[Merlin]

Hi Vince

Here is an example of speed history showing the location of speeds given in the graphics posted before:

The mass I use corresponds to the blanks with hardware (the handle is not considered), and given the design it varies from 45 grams to 65 grams approximately. The MOI is more important for the model.

You can see the "stopless" character of the rotation and its amazing short time.

Merlin

[VGB]

Thanks Daniel, I need to ponder the graphic for a while because I am travelling to France for the week and haven't got time to study it just now. I realise that MoI is important but I don't have swingweight data. Nevertheless, I do know that the mass of 7ft #4 rod that I built last year with thin wire guides and cap and ring for seat furniture was only 65g and believe that a real life selection of #6-10 rods will be much higher. It may be that these differences may be the cause of your high tip speed prediction.

I tried casting a #6 GT125 line with a #6 Loop Cross S1 and a #10 Vision GT4SW yesterday. The air temperature was 6 degrees C, the ground was damp from morning frost and I was casting into a slight headwind of about 2-6 mph. I did 2 sets of 5 casts with each rod for each test.

In terms of absolute distance, I cast the #10 about 1.5m that the #6. However, I found the haul timing much easier with the #10 rod because I was moving it slower; this observation seems to accord with Ulriks findings:

Regarding sequential coordination, it was shown that during forward false casting, there were increased time delays between the peak speed of rod translation and rotation as well as between the peak speed of rod translation and line haul for Sea Trout compared to Trout 1-3. During the delivery cast, there was an increased time delay between the peak speed of rod translation and rod rotation, but a decreased time delay between the peak speed of rod rotation and line haul, for Sea Trout compared to Trout 1-3. The latter finding may suggest that there is a shorter time delay between the peak speed of the rod tip compared to the peak speed of the rod butt in Sea Trout compared to Trout 1-3, which seems reasonable due to the fact that stiffer rods are used in Sea Trout. However, as mentioned before, this needs to be investigated with another measurement system whereby the movement of the rod tip can be included in the measurements.

My own thoughts are that in terms of pure timing, it is much easier to hit the haul with the stiffer rod. Logic tells you that you can only increase that time delay by either travelling further or slower. The only way we could travel further is by having Inspector Gadget arms but my own observation was that my movements are slower. This again has been measured in Ulriks studies:

Post-hoc analyses showed a significantly lower peak speed in rod translation, rod rotation and line haul for Sea Trout compared to Trout 1-3

We don't see this peak speed reduction in the model, which lead me to surmise that there is a physiological limitation on speed with the increased MoI and my forearm is certainly grumbling today. To test the hypothesis that the distance increases were due to timing than leverage effects of a stiffer rod, I tried distance casts with both rods without the haul and found no discernible difference. I have asked a couple of other casters to give it a try and I'd invite anyone to provide their own obsevations.

Regards

Vince

[VGB]

For reference, the mass of my home made Cross S1 is 103g, the GT4 is 128g.

Regards

Vince

[Merlin]

Hi Vince

Although my Meridian weights some 109 grams, I consider an "effective" mass of the model 908 rod by skipping the last 20 cm from the bottom (top of grip location approximately). Same for the reel. I did some test with those parts but that brings more complexity than significant results. The lower butt section of the Meridian represents 79 grams, and if one deletes the mass of the cork, the reelseat, and the lower 20 cm, then the "effective" mass, guides included, is less than 55 grams. In fact I take into account the corresponding MOI for the "effective" rod, which needs complex calculations since it changes with rod bending.

I can tune the model by adjusting the translation speed along the rotation speed, that seems reasonable. I can also consider that the record was done with a TCR likely, and that the corresponding maximum rotation speed should be applied to the 906 rod, not the 908. That will contribute to lowering the overall speed level. If I had a record I would also tune the damping function accordingly, at this time the damping is small (this is a twisted way of taking some aerodynamics on board). Since the "virtual" caster is superman, there is no MOI he cannot withstand, there is no limit in torque (the basic reason for illustrating a mapping).

For the haul, I think it may be better to start either with something staying constant, either with some adjustment that one has to estimate for me, some kind of rule of the thumb. I shall analyze Ulrik's paper to see if I can find some guideline, but beware of the interpretation of multiple variations occuring at the same time. The current value may be overestimated (above 12 m/s for maximum haul speed), I can go down to 10 m/s which may be more realistic. I am not surprized if you find hauling easier with the stiffer rod, it is in such case that the haul best tuning covers the MCF to RSP interval completely (I explained that in the old board thread I think). The question of tuning the haul timing is open: should I keep it the same for all rods? Should I optimize haul timing for each rod?

Remember that the illustration is a kind of mapping of performance, and not a baseline only (like the back line which considers the same input for all rods). This mapping is here to put into light the possible sources of variations from caster to caster, and from rod to rod.

On top of that I am working on lowering the non linear stiffness to get a larger piece of SLP. Not an easy task again, but first attemps look promising.

Merlin

[VGB]

Hi Daniel

Although my Meridian weights some 109 grams, I consider an "effective" mass of the model 908 rod by skipping the last 20 cm from the bottom (top of grip location approximately). Same for the reel. I did some test with those parts but that brings more complexity than significant results. The lower butt section of the Meridian represents 79 grams, and if one deletes the mass of the cork, the reelseat, and the lower 20 cm, then the "effective" mass, guides included, is less than 55 grams. In fact I take into account the corresponding MOI for the "effective" rod, which needs complex calculations since it changes with rod bending.

I understand the complexity of the problem. In particular, the MoI being changed by the rod bending and the change in loaded frequency due to the rod rotation. However, it only needs the caster to remove the reel and stick it in his pocket to understand that the mass of the reel effects the casting stroke and rod response. Feel isn’t just MoI it is also linear momentum and a host of other effects, many of which are particular to the caster. As a matter of interest, I have a 7 piece rod that I can remove 18 inches of the butt section from. It doesn’t feel much different and there’s not a great difference in the distances cast in either configuration.

I recall your haul tuning piece, it was in response to a point I made that there was a huge focus on absolute haul speed and not on timing. I am not convinced that the caster focuses on rod shape for the haul, it seems that the visual cues are associated with the butt being vertical. This suggests to me that they are trying to maximise line speed in the direction of the cast and that the focus on late haul is associated with the haul occurring before loop formation to avoid pulling mass out of the fly leg.

Regards

Vince

PS. Sorry, I won’t be able to look at your new paper for a while. Having been working in France this week, I now have domestic electrical and plumbing jobs to do

[Paul Arden]

Flavio had a 4 piece 9 WT with him when he fished in the jungle. Out of interest he took his spare blank and with the lower three sections built a second rod, which I still have. I would say that doing this turned it into a ten weight. This surprised me. But it didn’t surprise Flavio and I think it cost me a beer

Cheers, Paul

[VGB]

Removing the butt section makes hauling difficult because the stripper guide is close to the grip

[Paul Arden]

It was a fresh build as an experiment would a shorter rod be better for fast shots. It’s one of the ideas behind the HT 7’6 #10. And it is but accuracy and distance suffer on the Snakehead Shot. Fighting fish is great however!