Vodkaman

How do lips/bills work

14 posts in this topic

With small lures, members discovered that very thin fiber/circuit board lips were more effective than thicker Lexan lips in creating waggle action. The thinner the lip, the better the action. The reason for this has not been discussed much, if at all. It is all about the sharp edge.

Water can flow around a round object with minimum 'peeling off' of the flow, thus minimum disturbance of the water. Conversely, flow cannot negotiate a sharp corner; it cannot change direction that quickly. This causes a low pressure area behind the edge of the lip. Water gets sucked back into this low pressure area and thus the vortex is born.

At very slow speeds, the shape of the water flow is symmetrical, the same both sides of the lure. But, as the lure speed increases, a certain speed is reached were the vortices start to interact. There is not enough room for the vortices to exist independently so they take turns.

The vortices start to alternate, forming one side then the other. This effect is called ‘vortex shedding’, a ‘vortex street’ or ‘Kármán vortex street’. This alternating vortex is the engine that drives the lure, causing the desirable ‘waggle’ or action of the lure. This also explains why a lure has a minimum speed before the action starts.

The sharper the edge is, the stronger the low pressure area, the stronger the vortex and therefore the stronger the action.

Larger lures in the range of 8” and larger will require a thicker lip in order to survive bouncing off rocks with all that body weight behind. But the thicker lip is not going to produce as much action as the knife edge lip of the 3” lure.

The solution is to cut a chamfer behind the lip face. This reintroduces the knife edge and improves the vortex strength and thus the action.

Another way to improve action is to make the face of the lip concave. This causes pressure to build up in front of the lip which further increases the strength of the vortex.

Here is a video that shows vortex shedding, and the start transition explaining the minimum speed.

 

Dave
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Wow Dave.  A great explanation, and an interesting video.

I always chamfer  the edges of my thicker lure bills, because I thought it made them dive faster, but I didn't realize it made them waggle harder, too.

Thanks.

 

Edited by mark poulson

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Mark - This is the theory behind it all. I don't know how significant the chamfer is, but the same goes for diving lures.

If you take a perfectly balanced and tuned diver and then add the chamfer, you will likely find that the lure is now out of wack. Because the vortices are stronger, the lip pulls down to a slightly deeper angle. If the tow eye was positioned for maximum depth then the lure will no longer hit that depth.

As for the lure getting down faster; yes, the slightly lower pressure behind the lip will pull down harder, making the lure dive faster.

Dave

Edited by Vodkaman
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Bass Shack - actually yes, but not for any of the reasons in my previous posts. In fact, I don't think this effect has been previously discussed.

I discovered the effect in my very early days of experiments but I cannot remember whether I posted it or not, I may have thought it too rudimentary to mention. Let's call it the 'lip/body funnel effect' as it describes what is going on.

As I only had a few hand tools, working on the draining board of my apartment in Sweden, I thought it unnecessary to cut a lip slot when you can just chamfer the nose at the required angle and simply glue the lip onto the face. Admittedly not a secure attachment, but perfect for prototyping. However, I discovered that the action of front mounted lip was significantly less than a slot mounted lip.

It did not take long to figure out that flow is trapped at the junction of the lip and the body, causing the flow to accelerate just like flow through a funnel. This increase in speed increases the action.

So, getting back to your point; I would say yes, a wider nose would increase the flow and generate a stronger vortex.

I believe there is a lure out there waiting to be invented by taking this effect to the next level. If you fancy some extrovert prototyping to explore the idea, be my guest. Just give me a mention when you crack it wide open :)

Dave

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5 hours ago, Vodkaman said:

Bass Shack - actually yes, but not for any of the reasons in my previous posts. In fact, I don't think this effect has been previously discussed.

I discovered the effect in my very early days of experiments but I cannot remember whether I posted it or not, I may have thought it too rudimentary to mention. Let's call it the 'lip/body funnel effect' as it describes what is going on.

As I only had a few hand tools, working on the draining board of my apartment in Sweden, I thought it unnecessary to cut a lip slot when you can just chamfer the nose at the required angle and simply glue the lip onto the face. Admittedly not a secure attachment, but perfect for prototyping. However, I discovered that the action of front mounted lip was significantly less than a slot mounted lip.

It did not take long to figure out that flow is trapped at the junction of the lip and the body, causing the flow to accelerate just like flow through a funnel. This increase in speed increases the action.

So, getting back to your point; I would say yes, a wider nose would increase the flow and generate a stronger vortex.

I believe there is a lure out there waiting to be invented by taking this effect to the next level. If you fancy some extrovert prototyping to explore the idea, be my guest. Just give me a mention when you crack it wide open :)

Dave

Dave,

The Yozuri rattle traps I used to fish had a "scooped" forehead, so I did the same thing when I made some shallow cranks, using a rat tail file to carve a channel up from the line tie to the back.

I did it because I thought it would make the bait more stable, and give it a tighter wiggle.

Is this right, or did I get it all wrong?

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Mark - a concave face, which is what you are talking about, is going to increase the vortex strength, a convex will reduce the action. As for '.....to the back', I am not sure what a concave cut into the back of the lure would have.

I think it may have an effect on roll. I have just checked a few of my under water videos, and I think that a hollow feature down the back might reduce roll. I am thinking that it would have a similar but lesser effect of having a dorsal fin down the center of the lure.

To kill the roll would only require a short dorsal fin, say 5mm (3/16"). But again, as with all my stuff, this is theoretical, but it does fit.

Often it is difficult to see what effect, if any, such features have. I am thinking back to my 'various lips' video, were I compared round, square, coffin and shaped lips. It was very difficult to see any difference between round and square, also coffin and shaped. Likewise, your concave back will be a subtle effect.

In order to confirm an effect, you have to exaggerate the feature; a wide shaped body with an exaggerated concave back, directly comparing with the exact shaped body with a rounded back. And then, you may need close video, preferably submerged, head on, to observe the difference if it is too subtle, but if the effect is too subtle when exaggerated then then there is hardly any point in taking it further. Who knows, there may be another new idea waiting to be discovered.

Whether roll is a good or a bad thing, I do not know. What I do know; is that fish do not roll when they swim. Personally; I do not like roll, but I know other very experienced builders do.

So, after pouring my thoughts out, getting back to your point; I think more action due to the concave front end, and a more stable swim (less roll) due to the concave back. Boy I wish I had my workshop and a test tank, I would be out there right now. carving up a bunch of test lures, to test this idea and the lip/body funnel effect.

I hope someone takes on these ideas and comes back with a report. BUT, they re only ideas, they not pan out.

Of course, rattle traps swim back first, and so the whole of the back length is effectively the lip.

Dave

Edited by Vodkaman
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On 1/27/2019 at 6:21 AM, Vodkaman said:

Mark - a concave face, which is what you are talking about, is going to increase the vortex strength, a convex will reduce the action. As for '.....to the back', I am not sure what a concave cut into the back of the lure would have.

I think it may have an effect on roll. I have just checked a few of my under water videos, and I think that a hollow feature down the back might reduce roll. I am thinking that it would have a similar but lesser effect of having a dorsal fin down the center of the lure.

To kill the roll would only require a short dorsal fin, say 5mm (3/16"). But again, as with all my stuff, this is theoretical, but it does fit.

Often it is difficult to see what effect, if any, such features have. I am thinking back to my 'various lips' video, were I compared round, square, coffin and shaped lips. It was very difficult to see any difference between round and square, also coffin and shaped. Likewise, your concave back will be a subtle effect.

In order to confirm an effect, you have to exaggerate the feature; a wide shaped body with an exaggerated concave back, directly comparing with the exact shaped body with a rounded back. And then, you may need close video, preferably submerged, head on, to observe the difference if it is too subtle, but if the effect is too subtle when exaggerated then then there is hardly any point in taking it further. Who knows, there may be another new idea waiting to be discovered.

Whether roll is a good or a bad thing, I do not know. What I do know; is that fish do not roll when they swim. Personally; I do not like roll, but I know other very experienced builders do.

So, after pouring my thoughts out, getting back to your point; I think more action due to the concave front end, and a more stable swim (less roll) due to the concave back. Boy I wish I had my workshop and a test tank, I would be out there right now. carving up a bunch of test lures, to test this idea and the lip/body funnel effect.

I hope someone takes on these ideas and comes back with a report. BUT, they re only ideas, they not pan out.

Of course, rattle traps swim back first, and so the whole of the back length is effectively the lip.

Dave

 

Great post Dave, as always they suck me in, especially anything related to your favorite, "Street Vortices".

If anyone wants to play with this (I do often), after dinner get your black fry pan (the bigger the better), 2/3 fill it with a mixture of water and some detergent and heat it to just below boiling and the detergent will make a thin white foam on top of the water.

Now get your square edged (or round, or coffin shaped) lips and slowly drag them slowly across the pan and see, wonder of wonders ''Street Vertices'' or whatever you want to create, an egg flip works good.

Mark-  I have been playing with concave/convex lips for years and rarely use a flat lip, also have been using rear bibs (horizontal). In the past year or so I have graduated to a concave top on a lot of my lures, I have  had some success and some failures but I am thinking this is probably a weight issue.

It's all worth pursuing, I will try and scrounge up some lure pictures and post them in the next few days.

 Thanks again Dave.

Pete

 

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Good comments Pete. I was thinking of you when I wrote about the concave lips thing. If anyone wants to experiment with curved lips, Pete wrote a super article on the manufacture of a tool for bending polycarbonate sheet.

One of my tricks for visualizing vortices; a mirror placed on the bottom of the water container.

Dave

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Very interesting read! I missed when this was originally posted.   I have a large musky crankbait that I designed for shallow use but when I tried it out, the action was minimal.  Note to self, when prototyping a lure, make the lip oversize so it can be paired down to optimal size.  The lip was too small in my case (and thick) to produce the action I was hoping.  But after reading this I think I can cut a chamfer in the backside of the lip to see if this will increase the action.  And if that is not enough, I could even sand away the face of the lip producing a concave shape.  I will experiment with it and see if I can get it useable! As always Dave, excellent research and information on a very complex topic.

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Back when I was playing around with moving ballast I made three "identical" crankbaits, using an already successful design.  All of those had a concave forehead, leading to the back (I misspoke when I said concave back) .  They had a tight Xing (wiggle) and ran down to 6'+-.  Without the concave the same bait would only run down 4'+-.  The moveable ballast was at the kill spot.  The higher the ballast, the more erratic the bait would act on the retrieve (hunting).

 

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Mark - very interesting bait.

The vortex from the lip and the forehead will combine to make a more powerful force. Clever design.

Dave

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I saw a bait in the competition baits; with a similar cut but under the chin. I was very impressed, and if I had a workshop, I would be out there now, carving away a test piece.

Dave

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