North Australian FISH FINDER forums

Put the thinking caps on as we've now opened pandora's box in respect of lures.

But we already knew how and why lures vibrate in water didn't we? Perhaps some fishos not as experienced may not so a little refresher won't hurt.

Europe in the late 1800s was in the tail end of the industrial revolution. Manufacturing businesses all needed steam for their manufacturing processes. That meant furnaces for heat and tall chimneys to get rid of smoke and particles up into the atmosphere.

The biggest problem they faced was the collapse of these chimneys by wind-induced vibration so engineers all over Europe started work on finding out how these vibrations came about.

Enter engineer Vincence Strouhal from Czechoslovakia who set about determining how the wind and the chimney interacted. He successfully did that eventually and devised a solution to reduce the interaction.

However, it was a mathematician from Hungary by the name of Theodore Von Karman who (in the early 1900s) figured out the mathematics behind Strouhal’s practical solution.

Von Karman was no dill. He later migrated to the USA, joined the US space program and became one of the top scientists working on the 1969 US moon landing.

What on earth (no pun) has that got to do with fishing lures?

Everything, although neither Strouhal nor Von Karman was a fisherman nor did they realise the effect of their work on modern day fishing 100 years later.

Von Karman would have been satisfied with his contribution to the US space race I guess.

Nature had been producing vibrations due to the effects of water currents and wind currents for hundreds of thousands of years. Strouhal has also looked at the effects of vibrations induced by water currents on wharves and bridges. Apart from chimneys, bridges and wharves suffered collapse as well from the same effect.

Water currents causing objects to vibrate? Now where have I seen that happen?

Firstly in the Nogoa R at Emerald Q as a kid growing up when the river was in flood. To me at that age, it was just one of those things that trees and running floodwaters do.

I again saw it happening in the Fitzroy R along with the Daly and Roper rivers.
Hey, I’ve seen that in the Nogoa R before.

Now (with a engineering enquiring mind which I didn’t have as a kid), I thought why is the branch vibrating sideways across
the run and not up and downstream with the run?

That led me to the work of Vincence and Theodore and onward from there.

I looked at how the sideways movement came about, was simply happy to know why and left it at that.

However, that sideways vibration still niggled away at me until I suddenly thought “Surely that chimney/tree branch principle could translate into a fishing lure moving through the water”. The lure would vibrate according to the research done by those guys.

Just in water instead of air.

I’d previously looked at how lateral line vibration detectors worked in fish and had a good handle on that but the question in my mind was what had to be done to design/make a lure that would vibrate at a rate that could be detected by a lateral line. Back to front lure design.

Scientists had already determined that fish lateral lines worked across a range of vibration rates so I knew what that was. That locked one end of the mystery.

All I needed now was to apply the vibration research that these guys had done to lures to arrive at the lateral line vibration rates.

With Von Karman being a mathematician, surely he had worked out a maths formula.

Yes, he did and I found it after a month's searching. [/b]

So how do we get from tree branches vibrating in water to chimneys vibrating in the wind to wires "singing" in the wind to lures vibrating in the water?

Very easily and the transition from tree branches to lures is the easiest of them all.

To a scientist, the tree branch becomes a "bluff body" (a flat plate) sitting vertically in the water with a width the same as the diameter of the tree branch with a passing current flow.

How different is the resulting vortex turbulence being shed by the vertical plate to the vortex shedding of the tree branch?
Answer: No difference whatsoever.

Lets lean the top of the flat plate towards the back. Any difference now?
Answer: Still no difference.

Now we attach the flat plate to the front of a wooden or plastic body. That make a difference?
Answer: Still no difference but the image looks familar.

Hey, its a lure. Stop the current flowing around the lure and instead attach a line and pull the lure through the water. Any difference now?

No. Water is still flowing across the plate (bib) and is still shedding vortices just like before.

And that my friends is how we transition from a vibrating tree branch in a current to a hardbody lure with a bib being retrieved/towed through the water.[/b][