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what about working depth?
10 replies to this topic
Posted 08 October 2007 - 09:47 PM
Hi there, I'm working on my first lure, a carved minow, it will be about 5 in x 3/8 in x 5/8 in, the lip 1/2 in long, and at a 10 deg. angle to achieve a faster 5 ft depth, if you see someting wrong pleas tell me.
The problem here is i need a heavy 1 - 1.5 oz to compensate wind and casting distance, I use a 6 ft casting rod, and usualy I fish in sea waters.
How does weight afect working depth? is there a rule of tumb to calculate the weigth- working depth relation?, how can I apply this "rule" to lipless lures?
I'll apreciate your coments and response.
Posted 09 October 2007 - 12:05 AM
On a lure, it is safe to say that everything has an effect, it is just a question of degree. The following is just my take on what is happening and because I am constantly changing my opinion on certain aspects of the lures mechanics, what I have to say cannot be counted on as the absolute truth.
The main influence on how deep a lure will fish is mainly down to the position of the eye. As the water acts on the portion of the lure in front of the eye (mostly lip), the lure rotates nose down. As it does this, the body rear of the eye rotates up and into the flow of water. A point is reached when the forces in front and behind the eye are equal. This fixes the angle at which the lure swims. The lure then takes the path of least resistance, this means that, although the line is pulling the lure upwards at say an angle of 10 degrees, the lure could be swimming downwards at an angle of say 15 degrees. As the lip/body ratio increases, the dive angle increases.
However, there is a limit. My current thinking is that once the lip swims perpendicular to the tow line and still has not found equilibrium or a balance with the body, then the lure will flip over or roll sideways in a ‘corkscrew’ fashion. This is what I understand to be death roll.
The maximum diving capability of the lure is when the eye is positioned to balance with the lip close to perpendicular to the line. The position of the ballast weight relative to the tow line is quite critical also. When the lure is in its dive attitude, the ballast will raise above the tow line. There is a critical point, beyond which the ballast will cause death roll. Also, if the weight is in line with the tow line, the lure will become very reactive and can suffer death roll.
In order to achieve the most action, it is necessary to flirt with these instabilities as it is the edge of stability that reveals the most action. This is the advantage that the hand made ‘lure-man’ has the edge over mass production. The hand made lure can be tuned for the best performance right up to the edge, production lures have to be manufactured within a window and this window cannot be allowed to stray too close to the edge.
As for the weight of the ballasts effect on depth, I believe it has very little. Yes, tie a horse shoe to a three inch popper and it will scrape the bottom of the Mariana trench, but keeping the ballast to realistic values, the balance between the lip and body is far stronger than the ballast effect. So, most lures, even deep divers, are actually floaters. This allows the fisherman extra ammunition, in that when the lure stops moving forward, it rises. Try this simple experiment. Cast half an ounce of lead weight and reel it in as fast as possible, remembering the resistance feel. Repeat with a small lure of your choice. The resistance is many times greater.
Another very important influence on depth is line. If the lure swims downwards at say 30 degrees to the line then the lure would reach a maximum depth during the retrieve when the line points down at 30 degrees to the waters surface. Unfortunately, the line exerts considerable resistance to the water and ‘bows’ in the water. The lure, swimming at 30 degrees to the line therefore reaches horizontal much sooner, never reaching its theoretical depth. The thicker the line the more water resistance, the less depth achieved. The most depth that people are reaching from normal cast and retrieve is 18 to 23 feet.
As for the possibility to calculate the lure geometry, I love this question, because it was the first question that I asked. Unfortunately, the lipped lure utilizes vortex geometry for its action (did I hear a groan!), this is a very complex area of engineering involving frightening mathematics. I still believe that a simplified analogous calculation is possible, I searched for it and will again, but no progress so far. I recommend that you read up on ‘vortex shedding’ on the web, this will give you a good understanding of how the lipped lure moves and it is not complicated to understand.
It pains me to say that experience cannot be beaten as far as lure design is concerned, but if you can understand the theory of what is happening then the experience learning curve is greatly reduced and can be counted in months rather than years. Best advice is to experiment and keep accurate measurements and records. Do not discard the failures as they are your best opportunity to learn. I suggest that you post the failures and we will all learn a bit more.
Posted 09 October 2007 - 02:33 AM
Very well stated Volkaman! The seasoned builder or beginner can garner information from that statement. A primer for a deeper understanding of crankbait action.
Posted 09 October 2007 - 04:51 AM
Great stuff Dave, I'm going to check out 'vortex shedding' - wish I could think that deep (No pun intended) . pete
Posted 09 October 2007 - 05:04 AM
Here is an interesting paradox. A lure balanced and setup to dive at say 30 degrees. Reduce the ballast slightly and the dive angle will increase. Conversely, increase the ballast and the lure will swim shallower!
Posted 09 October 2007 - 10:58 AM
Well thought out as usual Dave. I agree that weight amount is less important to depth as many would think, with 2 caveats: 1) Weight needs to be propelly positioned for dive angle and balance in order to achieve max depth inherent in a given design. and 2) Weight is important due to increasing casting distance (due to the parabollic nature of a crankbait retrieve).
Of course, this is not a reflection of weight's effect on a crankbait's action during retrieve or pause.
Posted 09 October 2007 - 05:34 PM
thanks Vodkaman, that realy clared it down for me, and I'll read about vortex shedding.
and for the paradox you posted :
A lure balanced and setup to dive at say 30 degrees. Reduce the ballast slightly and the dive angle will increase. Conversely, increase the ballast and the lure will swim shallower!
the explenation is that's because the change in ballast (up or down), changes the angle of the lip? ( it's a bit confusing trying to think and translate at the same time in two language lol)
And for lipless baits? I asume that the neutral bouyancy principle wold enter here to achieve the working depth is that wright?.
I´ve been thinking maybe too much at this, some times I need to go to that cientific poin in things to understand, heck I've even diged mi phiysics books out lol.
as you mentioned : but if you can understand the theory of what is happening then the experience learning curve is greatly reduced and can be counted in months rather than years.
Posted 09 October 2007 - 05:59 PM
I know depth is not the end all of lure making (certainly not for me anyway). I was astounded 2 days ago when fishing and trying some new colors on my 3" lures to find that they were regularly hitting bottom at 15' and this is a 10gm lure (unweighted)- the only thing that I have altered recently is about 2 degrees on the lip which is 1mm Poly instead of 1mm Al. This minor alteration has increased depth by about 5'-6'. Like you all are saying weight is not everything. I have put this extra depth mainly down to the difference in weight which is quite minor (influence lure balance) between Al and poly lips (caught 1 x 4.5lb Brown) Pete
Posted 10 October 2007 - 12:20 AM
The explanation for the ballast weight paradox mentioned in my reply above is fairly simple, but by the time I have finished explaining it may not seem so.
It’s all about moments. I don’t mean those special moments in life, rather an engineering moment. A moment is a force times a distance. A simple example of moments is a lever. The force is your effort to lift the heavy weight with a lever, the distance is the length between the lever fulcrum and the force you apply. This is the clockwise moment. The anticlockwise moment is the weight to be lifted times the distance of the weight from the fulcrum. When the clockwise moments equals the anticlockwise moments, the lever is in equilibrium. One ounce of extra force and the weight lifts.
Do not concern yourself with the actual forces or distances as we are not going to calculate anything.
Consider the forces acting on the lure. Assume that the fulcrum is the eye position for now. Visualize the lure on the table in front of you, pointing to the left. The first moment is the lip. It is trying to rotate the lure anticlockwise. the force is the water acting on the lip, the distance is the centre of the lip to the eye.
A second moment is the body behind the eye. This moment is trying to rotate the lure clockwise. The force is the water acting on the body, the distance is from the eye to the middle of the body surface.
A third moment is the ballast. This is trying to rotate the lure clockwise. The force is the weight of the ballast acted on by gravity, the distance is from the centre of the ballast to the eye.
You can continue this process to the n’th degree, depending on how accurate you want the results (if you were in a calculating mood). The buoyancy of the body material has an anticlockwise moment, each hook and eye has a clockwise moment, even the paint and finish has a clockwise moment.
When all of these moments are calculated out, the lure finds a balance position or it reaches a state of equilibrium (in engineering speak).
So the paradox stated that if the weight of the ballast is reduced then the lure dives deeper. When the weight of the ballast is reduced, its moment is reduced (force x distance). The ballast had a clockwise moment, so in the overall balance, the clockwise moment has been reduced, the result is the anticlockwise becomes stronger and the lure rotates nose down until the balance is restored.
If the weight of the ballast was kept the same and the distance to the eye was shortened (weight moved forward), this would have the same effect. The moment of the ballast is reduced because the distance is reduced even though the weight is the same (moment = force x distance).
In my original reply above, I stated that everything has an effect. The above is an explanation of that fact. Move the belly hook rearwards and its clockwise moment increases, resulting in an anticlockwise rotation of the lure (it now swims shallower).
If a lure has death roll, the chances are that it is diving too steep, the clockwise moment needs to increase of the anticlockwise moments have to be reduced. To increase clockwise moment you can, a) increase the ballast, move the ballast to the rear (generally not a good idea), c) move the hooks rear and increase size, d) add a coat or two of epoxy.
To decrease the anticlockwise moment you can, a) trim the lip length or width.
Alternatively, the eye position can be moved forward to achieve the same. This is generally the preferred solution, but don’t discount the others, often the eye relocation is a destructive process if the eye is in the lip. To non-invasively establish the death roll problem, the moments of the lure can be adjusted by adding a little weight to the nose or to the rear hook. If one or other improves the situation then on the next build you can adjust the moments accordingly.
I was right, it did get a bit complicated and I apologize for that. But it is worth reading it over a few times as understanding this engineering theory will make understanding the lure, its balance and problem solving so much easier.
Posted 10 October 2007 - 08:20 PM
could not explain it better, I' am a bit familiar with vectors, moments and forces and that stuf, basicly aplied on buildings, problem is that is harder for me to translate it.
Posted 10 October 2007 - 08:26 PM
could not explain it better, I' am a bit familiar with vectors and forces and that stuf, problem is that is harder for me to translate it.