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Posted 30 October 2007 - 11:47 AM
I am going to ask another question here as well. I like this thread and I hope yall don't get tired of me asking the questions. Vodkman you said one of the solutions was to cut the back end of the lure down. This made me think about the amount of dive angle or pitch on a lure. Does more pitch/dive would cause more of the body to be exposed to the water forces, creating more pressure ,more weight on the end of the lever. Reducing the length of the body would reduce the weight/force.
When the lure body is piched down at a steep angle, does the vorticies produced by the lip have less effect on the lure. I am picturing the tail of the lure being above the horozonal line and the vorticies have less surface area to hit.
By the way in my attachment F1 is the force on the lip before the line tie . F2 is the lip force behind the line tie and the combine weight of the lure plus water pressure..
I have checked several deep diving lures and they seem to have about a 10 degree lip angle. Is this about right?
Posted 30 October 2007 - 03:46 PM
A lip is essentially a flat plate. It has little drag at level or zero degrees. As dive angle increases, so does the angle of the flat plate, so drag (and thus vortex shedding) is increased until the max of 90 degrees. I believe the attitude of the bait body may or may not take advantage of the von Karman street of vortex shedding based on design. But do not forget that the body (and everything else connected, including the line) imparts it's own effects in terms of drag and vortices.
Did you no that a tuna cannot physically swim as fast as it does? It was a mystery until researchers showed that they are using the vortices created by their bodies, detected by their lateral lines, as springboards for their tail to push off of....
Posted 30 October 2007 - 08:07 PM
Skeeter Jones. No wonder this thread is confusing, I keep making mistakes. I should, of course, said that the body should be lengthened and NOT shortened, well spotted.
First off, I welcome any and all questions. Sometimes the query makes me re-examine what is in my mind and in some cases improve the theory.
Regarding your diagram, it is more or less correct, but I cannot see any point in getting picky as it would be off the subject. I feel the need to discuss the line of instability more, as a result of your PM to me. It is a question of static and dynamic (moving) forces. The dynamic forces at the lip and the body override the effect of the ballast on the angle that the bait swims as the forces are much greater than the ballast.
However, when a deep diver at the surface is set in motion, the lure quickly reaches a balance and adopts its dive angle, of say 40 degrees. At this angle, the ballast is raised up and becomes top heavy. There comes a point at which this top heavy weight becomes too much and the lure will become unstable and roll over. This is where I draw the line of instability. The line is drawn parallel to the tow line because it is the perpendicular distance that is important.
When the ballast is sitting on this line, the bait is on the edge of instability and erratic swim actions are more likely to occur. I think that if the motion started at depth, the problem would probably not occur, as the bait would be swimming more horizontally and the raised ballast problem would go away. Unfortunately, the movement starts at the surface.
We cannot at this time calculate the position of this line, but as long as we know that it is there, we can explain what has gone wrong when the bait corkscrews and scares all the fish. Trim the lip or move the ballast forward.
Regarding your question about the lip forces having less effect as the lure swims deep and horizontal. I struggled with this one and still do. The lure is being towed in the line direction. It is this direction that the forces are acting, not the direction that the lure is traveling. The lure takes all that is given to it, ie lip forces, vortices, turbulence, ballast, buoyancy etc and then takes the path of least resistance, a basic law of nature. So the forces on the lip remain constant regardless of depth.
Clemmy. Only now are people starting to understand the true purpose of the lateral line. It had nothing to do with sensing the presence of other fish by pressure differences. I think that scales evolved for the same purpose, to re-capture the vortex energy that the fish expends and get a free rive when lurking behind a rock in moving water.
Experienced lure designers instinctively know what is wrong and know what to do to fix it, in fact they probably haven’t made a lure that suffers this problem for years. To them, this post may well represent a waste of time and effort. I am new to this game and getting on in years, I simply haven’t got the time to gain the years of experience required to make a perfect lure every time. I feel that an understanding of how it works could shorten this learning curve, it certainly has worked for me. Hopefully as I learn more, I will find a way of explaining this stuff more clearly.
Posted 31 October 2007 - 10:16 AM
You guys are great in my book. I have learned quite a bit about the science involved in making a lure. In my line of work its hard to fix something if I don't understand why it work and what each part does to make it work. I like to tournament fish and I want the lure that will knock em out and bring them to the boat . I want some erattic action. Why are there different ratios of reels? Because the slower retrive allows the lure to wiggle ,waggle,wobble more. A lure may death roll with a 7:1 ratio but be stable with a 5:1 based on the velocity of travel. I'm taking notes and have a lot of searching to do to try and find the answers I need. Thanks a bunch.