HOW ALL LURES WORK

[Ronje]

Principles underpinning ALL lures including swimbaits

Thought you guys might see value in having a look at this.

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What's the principle behind a fishing lure? Surely it is to trick a fish (lure it) into believing that food is on offer.

The fish uses a very basic left/right direction-finding sensor (called a lateral line sensor) which can detect vibrations in the water even in conditions of little or no light. The lateral line "tells" the hunting fish to steer left or right until it confronts the potential meal.

So how do we generate suitable vibrations in the water to interest a fish? Pretty simply as all we do is copy what nature has been doing for hundreds of thousands of years.

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 out 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 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 in central western Queensland 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 in coastal Qld along with the Daly and Roper rivers in the Northern Territory.

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 couple of months' searching.[/b]

[Ronje]

PART 2 – (How lures work)

We’ve seen how tree branches vibrate sideways when in run or floodwaters.

What the two scientists worked out was that the effect occurred with other shapes in water.

That a vertical plate (called a “bluff body”) also vibrated sideways just like the tree branch.

Like so:

What if we used a flat plastic plate as a “bluff body” and leaned the top of plate back to the right a little? What would we have then?

No difference. The leaning plate is still shedding vortices.

Now, attach a “body” to the plate and pull the result through the water instead of having the water flow past.

What then?

I can't put the image on here so have put it in the next reply

We’ve seen these flat plastic plates before. They called bibs and the result is called a hardbody lure.

I know its not a plastic swimbait but just be a bit patient. The same principle underpins swimbaits and I'll show how they work.]

So how does the “contraption” work?

The red Xs mark where the water is shed from the plate creating a little vacuum. The bib is “sucked” into the vacuum and cancels it.

There is a vacuum on the opposite side of the bib which then pulls the bib in that direction to fill that vacuum.

That vacuum is cancelled resulting in another vacuum on the opposite side again and the cycle of sideways bib movement continues.

Off the “contraption goes on its merry way through the water nodding its head (its connected to the bib) from side to side shedding the vortices as it goes.

So lets use a real hardbody lure to demonstrate.[/b]

Vibration rate.png (41.58 KiB) Viewed 803 times

Take special note of marks A and B as these are the points on the axis about which the sideways “pull” on the bib/head rotates.

Its pretty obvious that the rate at which the vortices/vacuums are shed from the lure depends on the length of the axis A-B.

And THAT determines the vibration rate of that lure.

Its not rocket science is it, so determining vibration rate of such a device by a guy who IS a rocket scientist (Von Karman) would make putting together a calculator a “walk in the park”, don’t you think?

He did so.

So why isn’t it a “walk in the park” for the lure manufacturers/ backyarders and hordes of fishing experts and gurus?

Then they could display the vibration rate of their masterpiece on the box, couldn’t they. Yep.

DO they? No they don’t.

Instead, the use these flowery and meaningless words centred around the word “action”. Eg tight action, fast action, moderate action, snake action. The only "action" term they DON'T use is in-action.

Why do they do this?

next time.

[Ronje]

Image missing from above post

[Ronje]

PART 3 (Vibration rates of hardbody lures)

We’ve come a fair way so far.

We know how the vibrations are generated by the bib AND we know that the vibrate rate relates directly to the width of A/B axis where the bib joins the body.

So the first step is to work out what vibration rate we have to aim for.

That’s easy. It’s the vibration rate to which the fish lateral line is tuned. Do we know what that is? We sure do. The piscatorial scientists worked that out years ago for us.

It's a frequency of 1 – 10 hz (hertz/cycles).

Don’t despair we can easily convert that to an understandable beats-per-minute by multiplying by 60 (number of seconds in a minute).

So we need our lure to vibrate between 60 to 600 beats/cycles per minute.

Because the width of the bib at the junction with the body determines that AND Von Karman worked out a calculator for us, that’s easy peasy.

Translate Strouhal’s work (and Von Karman’s vibration formula) to modern day fishing and we have the vibration rate of a bibbed lure. So what’s the calculator ? Here ‘tis..

Lure vibration formula.
St = f L/U
where: St = Strouhal number; f = frequency of vortex shedding (vibration rate);
L = Diameter of cylinder/tree branch/bib width and U = velocity of water flow (lure retrieve speed).

Geez, we only want to go fishing not learn a new scientific language.

Maths wasn’t my strong suite at school either. Using fingers, toes and other things, I couldn’t get past 21.

However I did manage to rearrange Von Karman’s calculator to a much easier format.

The calculator does everything for us.

All we need to know is the width of the bib at the junction with the body.

Now where is that lure again?

Image 7.png (36.22 KiB) Viewed 770 times

Screenshot (438).png (11.75 KiB) Viewed 770 times

Oops, vibe rate is a bit above the max of 600 bpm we were looking for and if we retrieve or troll the lure any faster, the vibe rate would go even higher. It'll need a fish with an over-active lateral line to detect it.

So there is lesson number one about hardbody lures. Avoid bibs that are narrow at the body junction unless you are prepared to slow down the retrieve/troll speed quite considerably.

Lets look at the same lure with a 10mm bib.

Screenshot (439).png (11.54 KiB) Viewed 770 times

567 beats per minute. That’s better (under 600).

The calculator is not something that you have to be using or remembering.

Its for the guys who make hardbody lures so they can put the vibration rate in bpm @ 1kmh on the box.

THEN the buyer knows exactly what he’s getting.

None of this mamby-pamby action “goobledegook”.

[Ronje]

re Part 3 (vibration rate of hardbody lures)

Early In part 3, I made this assertion about the frequency that fish lateral lines are tuned to by nature.

“That’s easy. It’s the vibration rate to which the fish lateral line is tuned. Do we know what that is? We sure do. The piscatorial scientists worked that out years ago for us.

It's a frequency of 1 – 10 hz (hertz/cycles)”.

How did I know that to pass on to you guys?

From this (courtesy of The Company of Biologists).

Screenshot (441).png (77.08 KiB) Viewed 682 times

The top of the diagram (A) is how the vibration sensor of a fish works.

A picture is worth a thousand words. Look at diagram sections A and B. It also shows (on the vertical axis of part B) how the amplitude of the receive vibration drops off as the frequency of the vibration increases

C (phase) doesn’t interest us.

Section A shows how a neuromast bends backwards and forwards at the same rate as an incoming vibration.

Section B showing how much of that incoming vibration is sent on to the fish’s nerve centre.

Follow the red line. Its horizontal and then drops off.

At the green point on B marked “Cut-off frequency”, that marks the point at which the fish’s lateral line response starts to drop off. It doesn’t cut-off suddenly. The lateral line starts to become less responsive (it gets “deafer”).

Following the green line down vertically from that point , you’ll come to the bottom horizontal X axis which reads “Frequency Hz”.

That vertical line coincides a bottom reading of 10 hz.

That’s the top frequency of the range of vibrations that fish can detect best with their lateral line. The lower frequency response starts at approx. 1 hz.

So the measured response by The Company of Biologists research team is 1-10hz (60 – 600 beats per minute).

Note that we are not talking about sounds/hearing here. Fish “hearing” has a different sensor because it operates on a different frequency range (band) and via different body parts.

Iv’e put this up as a post so that you guys are aware of where my assertion came from.

Not opinion, guessing or b/s. Facts.

[Ronje]

SOFT PLASTIC SWIMBAIT VIBRATIONS

The fundamental difference between a hard body lure and a soft plastic lure is where the vibration generator resides.

With a hardbody lure, the generator is at the bib and with a soft plastic lure the vibration generator is at the tail.

With a hardbody lure the vortex stream has to roll along the body to get past.

THAT creates a problem that relates directly to the solution that Strouhal used to stop wind vibrations causing chimneys to fall down.

How does it relate?

Well, Strouhal found that to prevent chimney (or other tall structures) collapse, he had to attach a “fin” to the leeward side of the chimney that stopped the wind vibration.

Obviously the attachment of a fin worked. Those chimneys and tall structures stopped collapsing.
But the wind could come from any direction, so Strouhal had to think of a way to address wind direction. And he did with chimney strakes

If you look around, you’ll see his solution everywhere (even today).

Screenshot (445).png (72.66 KiB) Viewed 599 times

Back on subject.

With out hardbody lures, we also have a vibration-reducing fin which shifts the vortex “street” away from the vibration source which is our bib. It reduces the magnitude of the vibration but the vibration rate remains the same.

And the fin that reduces the magnitude?

Its our lure body.

So… what can we do about that?

Easy, just shift the position of the vibration generator to “downstream” of the lure body. Like so:

Screenshot (448).png (69.35 KiB) Viewed 599 times

Enter the soft plastic swimbait with vibration generator no longer impeded by a lure body.

The tail paddle becomes a trailing bib complete with vibrations (same principle as a hardbody lure) with no body downstream to impede the vibrations generated.

Easy peasy,eh!

You know, there's an irony about this. The work and research by Strouhal and Von Karman put into preventing vibrations is the very same research that we fishos use to increase vibrations. Strange bedfellows.

So how does this paddle tail lure work?

[Ronje]

How paddle tail soft plastics work

Vibrations produced by soft plastic lures are still controlled by the work of Von Karman and Strouhal which deals with the effect of vortices from water flow on objects in the water.

The fundamental difference between a hard body lure and a soft plastic lure is where the vibration generator resides. With a hardbody lure, the generator is at the bib and with a soft plastic lure the vibration generator is at the tail.

See image H/body vs soft plastic in post above

While the bibbed hard body of the lure introduces “drag” on the vibration generator because its “downstream” of the bib, that’s not the case with a soft plastic.

There is no lure body downstream of the paddle tail vibration generator to create drag and the flat paddle is drawn through the water like a trailing bib.

The vortices created where the waterflow go around the edges of the paddle cause the paddle to be pulled left and right alternately (similar to how a bib on a hard body lure pulls the head from side to side).

The significant water flow is along the sides and underneath the SP to the tail where it flows around the edges of the paddle.

Water flow over the body, tail/paddle and wrist produces vortices on the back of the paddle. A Von Karman Vortex Street flowing off the paddle.

These vortices are small rapidly rotating “whirlpools” containing high energy whipped up by the velocity of the rotating whirlpools formed in the vortex trail “downstream” of the paddle edges.

Screenshot (451).png (215.51 KiB) Viewed 508 times

Sideways forces generated by the vortices (red Xs on image above) apply a twisting action on the paddle and the lure “wrist” which connects the paddle to the lure body. First one way then the other.

If the correct balance between “wrist” material flexibility and stiffness has been used, then the paddle wrist will exert rotational force on the body and “roll” the body in timing with the paddle movement. Resulting in lure body roll.

Liken it to the tail wagging the dog.

If the tail “wrist” is too flexible/supple/thin then it will absorb rotational/twisting forces from the paddle like a twisting rubber band and none will be passed onto the lure body. There will be no body roll.

If the tail “wrist” is too stiff then the body will resist the twisting motion from the paddle and won’t “roll”.

In fact, it will resist the sideways movement of the paddle entirely. Again, there will be no body roll and (more importantly) the lure won’t “swim”.

T-Tail soft plastics

Screenshot (452).png (39.31 KiB) Viewed 508 times

Remember this: If the tail “wrist” is too flexible/supple/thin then it will absorb rotational/twisting forces from the paddle and none will be passed onto the lure body. There will be no lure body roll.

What we are doing by using a narrow wristed /thin longer tail is allowing some of the vortex energy generated by the paddle to be transferred to the thin wrist.

The thin wrist twists like a rubber band and absorbs that energy transferring none to the body. No body roll.

We’ve split the vortex energy generated by the alternating paddle vortices. Feed some energy to the lure “wrist” and only the remaining vortex energy is fed into the vortex trail.

As we’ve divided the energy, action of the paddle is reduced. It almost becomes a simple flapper. There will be a small amount of vibration which works over short distances so the moving lure will need to be close to the fish.

The wrist and tail are acting like the clutch on a manual motor vehicle feeding only some energy to the wheels (the vortex/vibration stream).

Fast flapping of the tail might look significant but it does little to generate real vibrations.

Maybe it could be said that this thin T-tail type of SP is busy being busy (flapping) rather than actually generating much in the way of meaningful vibrations.

In addition, thin T-Tails distort in shape by the energy generated and "fail to fire properly".

The job of the lure designer is to get the relationship between the “clutch” and the business side of the lure (vibrations and body roll) balanced.

How do we determine (and keep) the vibrate between 60 – 100 beats per minute?

Just like hard-body bibbed lures and vibes, the width of the paddle (which is acting like a bib) determines the vibration rate of the lure as does the retrieve rate through the water.

How is that worked out again?

That’s right. The same way that we did with the bib on our hardbody lures. Using the Strouhal/Von Karman calculator.

Three different sized s/p paddle-tails with the vibration rates quoted for the standard retrieve speed of 1 kmh. Also a table for other sized paddles.

Slow down the retrieve speed and the vibration rate slows. Speed up the retrieve speed and the vibration rate increases.

Note that the wider the paddle the bigger the lure and the slower the vibe rate so who do we think might benefit from this knowledge?

Well, sometimes we need to keep the paddle-tail off the bottom which means a faster retrieve speed to keep it higher in the water column and away from snags etc.

But a faster retrieve/troll speed means a faster vibration rate to outside the desired rate.

That being the case that we’re stuck with a faster retrieve/troll speed, we have to use a p/tail with a larger paddle to stay within the vibration rate range that we desire.

Black is within the vibration band and red is outside.

The lesson here is not to retrieve smaller width paddle-tails at speeds which will generate vibration rates in excess (the red numbers) of target vibration beat/m

Three different sized s/p paddle-tails with the vibration rates quoted for the standard retrieve speed of 1 kmh.

Slow down the retrieve speed and the vibration rate slows. Speed up the retrieve speed and the vibration rate increases.

Note that the wider the paddle the bigger the lure and the slower the vibe rate so who do we think might benefit from this knowledge?

Sometimes we need to keep the paddle-tail off the bottom which means a faster retrieve speed to keep it higher in the water column and away from snags etc.

But a faster retrieve/troll speed means a faster vibration rate to outside the desired rate.

That being the case that we’re stuck with a faster retrieve/troll speed, we have to use a p/tail with a larger paddle to stay within the vibration rate range that we desire.

Black is within the vibration band and red is outside.

The lesson here is not to retrieve smaller width paddle-tails at speeds which will generate vibration rates in excess (the red numbers) of target vibration beat/m.

[Ronje]

SOFT VIBE LURES

Remember how Strouhal got rid of the vibrations causing chimneys to collapse?

The top image shows how he did that.

Screenshot (459).png (303.45 KiB) Viewed 460 times

The bottom image shows that hardbody lures suffer from the same “fin solution” with the lure body acting like a Strouhal vortex suppressor.

The lure body acts as a vortex suppression fin just like the strakes on a chimney and there are two ways to get around this unwanted effect.

Reduce the length of the lure body to keep it under 100 mm while still retaining considerable vibration. It’s a trade-off.

The other way is to do away with the body of the lure altogether! Bit drastic?

Use a soft plastic body and put the “bib” at the back end. That gets rid of the body interference completely.

There is yet another way.

Remember the strange aircraft that looks like a flying wing? Stealth technology at work. B1 bombers or F-117 night fighter/bomber.

On the left is the flying wing (B1 stealth bomber) and on the right is the “stealth lure” with the bib being the lead weight at the bottom (in blue) and the body is above it (in red).

A “flying bib” lure is simply known as a vibe or blade lure. The whole lure is basically a bib and it gets vibration-inducing movement from the water flow over its body by being raised up and down in the water column.

The same Strouhal/Von Karman formula for vibration rate that applies to hardbody lures also applies to vibes. The vibration rate of the lure is dependent upon the thickness of the bib/lead weight and the speed of retrieval through the water.

The “bib” can be made of metal (as in a thin blade) or it can be made of “soft plastic over a lead weight” like Arnold Schwarzenegger’s cyborg terminator.

The body is also the bib.

Screenshot (2548).png (77.83 KiB) Viewed 460 times

[Ronje]

The Strouhal/Von Karman calculator.

Screenshot (439).png (11.54 KiB) Viewed 415 times

It's obviously the key to ANY angler being able to work out the vibration rate of any lure.

THEN the angler will know if a lure's vibration rate is within the "ball park" of that which fish lateral lines are tuned to (by evolution over 100s of thousands of years).

I've only been posting images/photos of the calculator so far and have asked WB Fishing staff how I can post "the real thing" which is a live xls sheet.

The live calculator itself is then available to ALL members to use as they wish.

Maybe one of you guys knows how to post an .xls file on here.
[/b]

[Ronje]

Well, it looks like WB Staff are unable to assist with info about posting .xls files.

My name is Ron Jenkins and I live in Australia on the Queensland coast on the Tropic of Capricorn.

I'm happy to give free to anybody who messages me that they'd like me to send to them a working copy of the calculator.

No strings attached. No trojans or viruses within. To do with as they like.

I've spent 10 years following up the science/facts relating to lateral lines and lure vibrations. I don't deal in opinions.

I only wish that this sort of information had been available when I started out fishing 50 years ago.

I'm doing OK in life. I don't need money or anything else. Hence its free.

I guess u might call this my legacy to recreational fishing both in Aus and the USA.

Anyway, seeing that it's probable that I can't put a working copy on a post, message me with a return e-mail a/d if u would like a working copy of the calculator.

regards

Ron J

[Ronje]

Nobody wants the calculator.

That's fine. I'll give it another forum.