# Help needed 1000 dollar valued award

1. May 18, 2005

### dedoo

Help needed 1000 dollar valued reward!!

Hello all,

I make fly-fishing rods from bamboo (the traditional way) and because I want to bring this to another level I would like to get some help from those who can help me. I’ll be willing to make you a rod for free (they normally sell for around US\$ 1000/1200) If you are willing to help me with this quest.

I want to be able to calculate my rod design from another angle.

I would like to graph the rods bending ( how it looks like at its greatest moment of bending)
And together with some other variables calculate the rods crossectional dimensions.

The idea is to make a whole new kind of fishing rod. I’m thinking about making rectangular shaped rods. Wider than deep in the plane of bending.

Of course it would be great if we too would be able to calculate the ideal bend form.
i.e. how should the rod be build to accelerate the fly line with minimum force.

If these few lines got you interested and if you are willing to help me out please send me an email to dannyheus@hotmail.com. I’m sure we will have a lot of fun finding the right answers.

Kind regards,
Danny

Last edited: May 18, 2005
2. May 18, 2005

### exequor

This sounds like a job for someone who is good with mathlab.

3. May 18, 2005

### willib

why not use graphite , it is super strong ,super light , and su... real stiff...

4. May 19, 2005

### PerennialII

I suck what comes to fishing but those things do bend quite a bit ... would be an interesting application to see what could be done applying optimization routines to the cross-section ... both to a local section and then the shape transition over the length of the rod and maximize tip acceleration etc.

5. May 19, 2005

### dedoo

I do not use graphite because I think we are not really done yet with bamboo. And besides that there are still (including me) a lot of people who appreciate a handmade fishingrod. I would like to show graphite and all other "plastic" users that very good fishingrods can be made from this natural material. Rectangular is not experimented much with and I would like to prove that this actually has BIG advantages in order to improve stiffness and casting abillities. In order to achive this I would like to design my rods from a diffrent point of view and start with finding the ideal bendform first. Find out about how a rod should bend and behave during a casting cycle and start with that bendform to calculate the crossectional dimensions.

6. May 19, 2005

### CarlB

The force on a fishing pole is largely perpendicular to the pole. If your pole ends up in some more complicated form, you will have to adjust this with the appropriate cosine or sine. But if your pole is only bending slightly, and the force is applied at the tip (i.e. ignoring the momentum of the pole), then the bending force that is applied to the pole at any given point is in the form of a "torque".

A torque is a force times a distance, like ft-lbs. For the case of this ideal fishing pole, the bending force is largest closest to the hand of the fisherman, and drops to zero at the tip in a linear fashion. Thus, to get the same (small) curve along the length of the pole, you want the strength of the pole to linearly decrease to zero.

And what is the strength of a rectangular bar as a function of its thickness? The resistance to bending of a rectangular cross section bar is proportional to its thickness cubed. So to get a pole that (for small bends with the fishing line perpendicular to the tip) bends evenly (i.e. as if it were an arc of a circle), you solve the equation:

Bending Moment = $$F * x = \tau^3(x)$$,

where $$\tau$$ is the thickness of the rod, x is the distance away from the tip, and F is just there to make the units work out. The solution for $$\tau$$ is:

$$\tau = \eta x^{1/3}$$

where $$\eta$$ is just a constant. In other words, you would make your rod thickness follow the cube root of the distance from the end.

I hope this gives you enough help that you can solve the more complicated problem yourself. I don't have time to give any more help (or to fish), so please save the fishing pole for someone else.

Carl