Crankbait lip source

29 posts in this topic

I am just really curious..... How do you guys know that polycarbonate has more flex than circuit board? How do you really know that you are getting an extra foot of depth? And how do you really know that circuit board has better reflecting properties? How in the world does a trailing edge cut through the water???? And how does this trailing edge create a vortex? I just can't see how this trailing edge creates a stronger pull down force.


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Q1. How in the world does a trailing edge cut through the water?

Q2. How does this trailing edge create a vortex?

Q3. How this trailing edge creates a stronger pull down force?

Skeeter. I get the distinct impression that you are not buying into the application of vortex theory on the action of the lipped lure. But that is acceptable as I have never really explained the theory in words, I have only provided links to web articles on the subject as they explain it better and there is less chance of me attaching my own interpretations which may or may not be correct. This thread is not the place to deal with the subject comprehensibly, so I will limit the discussion to addressing your questions.

Q1 and Q3 are essentially the same, my statement of ‘cut through the water’ was a bad choice of words. However, a lip with sharp edges front AND sides will exert more down force than a lip with just the leading edge sharpened.

Explanation. Consider the requirement to move a body one inch wide through the water with the least effort. Like a wing, bullet, rocket or a submarine, the shape that you would select would be a torpedo type shape. The water (or air) parts at the front, slips by the object one inch wide and re-joins at the rear, causing a minimum of turbulence. Turbulence is a chaotic mess of vortices also known as drag.

As the body is shortened in length, the effort required to move the body through the fluid increases. The fluid finds it more difficult to cleanly re-connect at the rear, due to the severity of the change of direction. As the object shape is shortened further to a sphere, the chaotic vortices increase further. As the shape flattens further and approaches a flat plate, the point at which the vortices are formed is at a single line around the edge of the plate. At this point, the force required to move the object is at a maximum and under the right conditions of speed, fluid density and size of plate, which are all present in the fishing lure application, the vortices join and act as one.

Throughout the changing shape, from torpedo to flat plate, the area presented to the fluid is the same, i.e. one inch. The only difference is the trailing vortices. The vortices or eddies are low pressure swirls of fluid formed behind the edge of the plate or lip. They apply an additional negative force on the rear/edge of the lip. One could form an argument that the only force on the lip is due to vortices sucking the lip back and the supposed pressure on the front is less significant, but I am not confident enough to make such a sweeping statement that is so difficult to visualize and therefore be accepted.

So, in answer to Q1 and Q3, if the lip edge was sharpened, the negative (sucking) force on the rear face of the lip would increase, thus applying more down force to the lip.

As for Q2, as the water flows past the edge of the flat plate, it tries to fill the vacuum or void behind the lip. This change in direction causes the vortex to form. An example. On the next windy day, stand with your back to the lee (down wind) wall, right in the corner. Notice how calm the air is. You are now standing in the void or low pressure area. Now move slightly away from the corner. The wind increases, but the direction of the wind is toward the corner. The wind is rotating, a vortex is present. Throw some leaves into the wind and observe the movement of the wind.

If a lure is already built on the edge of instability, then the maximum depth condition is already present. Any sharpening of the lip under these conditions will merely push the lure balance over the edge and the lip will spiral or death roll. However, if the lip is not on the edge and it is required to gain more depth, there are several solutions available. A. - move the tow eye rearwards. B – increase the area of the lip. C – shorten the body at the rear. These are all very invasive changes. Simply sharpening a thick lip to an edge will achieve the same result. It will increase the down force at the front and ‘cut’ more water.

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Regarding the resilience or ‘rock bouncing’ properties of the different lip materials. The idea that some materials rock bounce better than others has been discussed many times over the years. A simple experiment can be set up to test the resilience of various lip materials and put this one to bed.

Cut a round disk of each material to be tested, say 2 inch dia. Drop it from a set height onto a hard surface, stone floor tiles work well. Measure how high the disk bounces. Repeat many times to get a good average. It would be a good idea to record the thickness that you tested also. The one that bounces the highest wins the resilience contest.

I cannot do the test for you as I have neither of the materials in question. I’m hoping one of you out there will do the quick test for us all and solve the mystery and remove the suspense.

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