Contribution rod bend/spring makes to cast

[Paul Arden]

Hi Gordy,

I think we all know the 20% spring 80% lever result that Grunde and Torsten compute. However I believe you also made the observation that the bend allows us to put more energy in? Was the figure double?

Many thanks,
Paul

[Merlin]

Hi Paul

Some comments before Gordy can answer:

There are four sources of energy in the line for a cast: leverage, spring, inertia and haul. The three last can be estimated with my 2D model (one can cancel the haul or cancel the inertial effect or both). Leverage is taken as the difference of the sum of these three contributions with 100%, there is no way to get it directly.

First example with a trout rod for a fishing cast: spring 19%; inertia 14%, no haul, so leverage is 67%.
For a leader cast and the same rod: spring 33%, inertia 18%, no haul, and leverage 49% (note: figures are small).

Second example with a competition cast and a 906: spring 20%, inertia 11%, haul 33%, so leverage is 36% in that case.
Same cast without the haul: spring 30%, inertia 9%, no haul, and leverage 61% (of course the performance is reduced).

There is no such 20/80 general rule. If there was one, it should have four percentages included, not two.

Merlin

[Lasse Karlsson]

How far did the competition cast go Daniel?

Cheers
Lasse

[Stoatstail50]

Being a little dim here....how does inertia provide a source of energy to the line ?

[Merlin]

Hi Lasse

I cannot tell, I have no model for the roll out of the line. In this example the 24 grams carry is launched at 66 m/s with a 1.5 m wide loop.

Merlin

[Merlin]

Being a little dim here....how does inertia provide a source of energy to the line ?

The inertial effect can be called the momentum effect. I re invented warm water when I identified it, this phenomenon have been known for a long time. The rod maker Edwin Powell (Powell rods, California, now closed) published a paper in 1937 where he explained that casting energy could come from leverage, spring, and momentum. The haul was not something well known at that time. The momentum effect is not easy to describe but let’s try a simplification. It is nearly as if the momentum of the rod was varying sufficiently slowly and that a momentum input (a rotation of the rod) would be compensated by a change in rod speed (an opposite momentum) at another place (the other end). If I put forward momentum in the butt, the tip wants to go the other way, backwards, just as if momentum was nearly conserved. When I decelerate the rod butt, the tip wants to go the other way around and goes forward faster. The heavier the rod (e.g. cane) is, the greater the momentum effect is. It is thus less easy to detect with a synthetic rod.

Merlin

[Stoatstail50]

However I believe you also made the observation that the bend allows us to put more energy in? Was the figure double?

I believe it was Grunde who made that observation way way back, I don't think an actual figure was suggested. I also don't believe that the distribution of energy in the line via spring, lever or inertial effects has much to do with it either.

The main reason that you can put more energy in is because the bend in the rod mediates between the tip path and the hand path. With a completely rigid rod, to get an SLP for example, the hand path has to compensate for the convexity of the tip path as the rod rotates...ie its severely concave. As rods get bendier the hand paths become less extreme and so it becomes physiologically easier for the caster to apply force and thus input energy. How much is up to the caster. There is a goldilocks zone, largely depending on the casters preference, after which increased bendiness also begins to demand weird hand paths and the capacity of the caster to apply force is reduced as a consequence.

I re invented warm water when I identified it

Yes, probably...

[Paul Arden]

Thanks guys. What I was actually referring to is that the bendy spring characteristics of the rod enable us to put more effort in (I believe).

So comparing spring to lever (and haul/inertia?) isn't an accurate representiaon of the effect of the spring if this is not taken into account. It's all very well to say that the lever is 70% but if the spring enables the caster to (say) put twice as much force into the cast, then I would think that the spring has a considerable advantage compared to a rigid rod. I'm sure Gordy studied this

Cheers, Paul

[Stoatstail50]

A bendy rod has many advantages over a rigid one, this is just one of them. Don't know where it would sit in my top ten advantages of bend list though...have you ever played a fish on a rigid rod ?

[Paul Arden]

The way I play fish here Mark, it may as well be! Talking of which when are you coming to visit?