Dziadzia

Centers Of Hardbait

14 posts in this topic

Dziadzia    12

Interesting, if you know where mass centre is. I have done search and decided to present information for your judgment. At the light of this day, various materials are used to build a hardbait – foam, wood, casting resin, plastic, and silicon and so on… So, everyone knows what solid body (hardbait) has a geometrical centre and a mass centre. These two centers are different and mean different things. The geometrical centre (here and after – GC) means the centre of hardbait without any hardware (meaning only naked blank) and the position of geometrical centre is shown as ‘cross’ sign in pictures. The centre of mass (here and after – MC) means the mass centre of hardbait with hardware and indication is shown as ‘crossed circle’. I guess, the conclusion is – if these two magical centers are known, hence the prediction of behavior of hard bait could be done keeping in mind distance and location of GC and MC to each other… If someone has experienced or dealt with these centers, would be nice to know your know-how. Best, Ed

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mark poulson    1,702

Any pictorials of weight distribution on walk-the-dog top-water lures? Musky lures. Thank you.

Walk the dog lures are slightly tail heavy, with the center of gravity just past the center point of the lure. The bigger ones sit almost horizontal, with 1/3 of the head section out of the water. At least, that's how I weight my 6-8" walking baits. And my Pupfish knockoffs, which are 8-10" (which is, I think, Musy size) are weighted the same.

The smaller the walking bait, the deeper the tail can sit in the water, since there is less lure inertia to overcome to get a small lure up and walking. A smaller lure that sits in the more horizontal attitude will glide like a punker or a Pupfish, as well as walking like a spook or sammie. But it won't be as easy to walk.

Having the center of gravity past the center of the lure toward the tail helps the back of the lure want to keep moving on the pause more than the front, which gets the lure turning sideways. Then each successive stroke move the head forward and swings the tail around to the other side.

I float test my walking lures in a bucket of water, and look for the tail down as an indicater of proper ballasting. If the lure floats that way, and I've shaped it properly, I know it will walk without test driving it on the lake, and I can go on and paint and finish it.

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BobP    834

Ed, I find that ballasting at the MC tends to make a lure with an "X-ing" swim style with rotation at the MC and little if any roll.

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Vodkaman    890

This post is not a ‘how to’, but rather a picture of what is happening in relation to how the lure sits in the water.

The issue of weighting a lure in practice is fairly simple, you trim and move the weight around until it floats and swims how you want it to. Even the first estimate of position is usually fairly close with experience. However, from a theory point of view the subject is quite complex. You have to ask yourself the question, “do I need to concern myself about this”? The answer is quite simply, NO.

From here on into this post, content is technical.

Every single component that you add to the lure, changes the centre of gravity or centre of weight. This includes the paint and top coat. Some components affect the centre very little, such as the paint and top coat, because they are uniformly covering the body. The through wire harness has very little effect also, again, the harness is fairly central, but even so, I was surprised how little effect it had on the centre of gravity. The components that really affect things are the ballast weight, hook assemblies and the lip.

In the pictures, I have numbered and color coded the centre of gravities accordingly. The first picture shows the lure. It is 4” long and based on the ‘bigbandit’ lure (see post No1). I set the wood density at 0.35gm/cm3 (18.7Lb/cu ft), which is the wood that I use. The section view shows the construction of the lure. The second picture shows the movement of the centre of gravity at each stage of the build, showing how each component in turn affects the centre of gravity. I have included a 0.5” square box for scale.

Color codes

1 – Body - red

2 - Harness - orange

3 - First seal coat - brown

4 - Ballast - light green

5 - Second seal coat - dark green

6 - Lip - light blue

7 - Epoxy coat - dark blue

8 - Hook assemblies size 4 – violet

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The final centre of gravity position is only 0.07” forward and 0.15” lower than the original wood centre of gravity, as the effect of the lip and the hooks tended to cancel each other out. But still, the line through the final centre of gravity and the buoyancy centre, indicates that the lure will rest nose down by 26 degrees. The reason for this, is that the buoyancy of the wood is pulling the lure upward from its centre and the weight of the lure is pulling down from a different centre. The lure will rotate until they are directly inline with each other vertically. By moving the rear weight aft by 7mm (0.27”), I was able to reduce this to 10 degrees slightly nose down. This is quite a large movement to achieve a small adjustment in the centre of gravity position.

This is all well and good and could be used as a guide, I could even write a spread sheet, but it would be a total waste of time, because once the lure hits the water, everything changes. All the densities of all the components are subtracted by the value of the density of water. For example, the density of the lip reduces from 1.2gm/cm3 to 0.2gm/cm3, lead from 11.385gm/cm3 to 10.385gm/cm3 and the wood from 0.35gm/cm3 to -0.65gm/cm3 (buoyancy). It is just like someone just moved the goal posts.

Once the lure starts moving, everything changes again. The water forces on the lip and the body are far stronger than the effects of the ballast. These water forces, with a minor input from the ballast, will determine at what angle the lure swims. The swim angle is controlled by the tow eye position. This enters a completely different discussion and so I will stop there. However, the ballast takes on a new function once the lure is moving, by determining how the movement or action behaves. The wiggle or ‘X’ing action is a rotation about the final centre of gravity of the lure. If the weights are clumped together, you get a wide action, if the weights are fitted nose and tail, the action is reduced, but in both cases, the centre of gravity is in the same place and not necessarily where the lead is.

In reality, nothing can beat practice, experience, common sense and lots of testing to determine where to place the ballast. JPEG pictures are not very clear for this exercise. If anyone wants PDF files of the pictures for a closer look, pm me your email address.

Dave

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mark poulson    1,702

Dave,

Thanks for that explanation. I actually understood it! Not the math, but the concept.

As you know, I'm more of a "do it and see if it works" builder, with a heavy dose of "copy what already works".

But I am trying to make my cranks hunt, and I'm hoping you can help me.

In my experience, raising the ballast in a crank can make a crank "hunt" because it's right on the edge of instability.

I've toyed with using a threaded set screw to use as an adjustable weight, moving it up and down with an allen wrench, but the screws rust and sieze up too quickly.

Have you found a formula or method of achieving the instability point, so I can back off from it just a hair and have a hunting lure?

Mark

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RiverMan    10

This is all well and good and could be used as a guide, I could even write a spread sheet, but it would be a total waste of time, because once the lure hits the water, everything changes. Once the lure starts moving, everything changes again. The water forces on the lip and the body are far stronger than the effects of the ballast.

In reality, nothing can beat practice, experience, common sense and lots of testing to determine where to place the ballast.

Dave

Yep......................from my experience trying to put math to wood lures does not work............there are far too many variables. Add weight, hooks, and clearcoat and test. Take notes, repeat. Sometimes you will get lucky and the first couple of tests will work out great, other times you run a dozen tests and the lure still doesn't work very well. I have entire notebooks filled with notes, trace the lure, note the lure thickness, wood type, hook placement, weight placement, test, then write down results. After running dozens of tests you will start to see patterns that will level the learning curve.

RM

Edited by RiverMan

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dtrs5kprs    8

Dave,

Thanks for that explanation. I actually understood it! Not the math, but the concept.

As you know, I'm more of a "do it and see if it works" builder, with a heavy dose of "copy what already works".

But I am trying to make my cranks hunt, and I'm hoping you can help me.

In my experience, raising the ballast in a crank can make a crank "hunt" because it's right on the edge of instability.

I've toyed with using a threaded set screw to use as an adjustable weight, moving it up and down with an allen wrench, but the screws rust and sieze up too quickly.

Have you found a formula or method of achieving the instability point, so I can back off from it just a hair and have a hunting lure?

Mark

Try powder painting the set screw, or on an extreme level, coating it with something like a spray on firearm finish (Duracoat or one of the bake on sprays). Might solve your rust problem.

Have always thought hunting just sort of happened, very hard to reproduce bait to bait.

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mark poulson    1,702

Try powder painting the set screw, or on an extreme level, coating it with something like a spray on firearm finish (Duracoat or one of the bake on sprays). Might solve your rust problem.

Have always thought hunting just sort of happened, very hard to reproduce bait to bait.

Good ideas. I'll keep my eye out for something like that.

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rofish    2

In my experience, raising the ballast in a crank can make a crank "hunt" because it's right on the edge of instability.

I've toyed with using a threaded set screw to use as an adjustable weight, moving it up and down with an allen wrench, but the screws rust and sieze up too quickly.

Have you found a formula or method of achieving the instability point, so I can back off from it just a hair and have a hunting lure?

Mark

Mark, I think you are a genius, but have not realized it yet.

I do not fully understand what your problems were when you used your "threaded set screw", (don't know what this actually means), but perhaps this is for the better.

In order to make a device which you could use to see how the raising/lowering the weight in a crankbait would affect it's action, one could use a metal tube, threaded on the interior, and a screw without a head, that has a groove at one end, and you could move the screw upwards/downwards inside the tube by just using a small flat head screwdriver. If needed, a cylinder piece of lead could be glued on top of the screw, to add more weight to it. This way you could finely adjust the height of the weight to see the results on the lure's action.

No need to think that this will be the only weight in the lure. You could put a smaller than needed weight in a fixed place, as usual, and the rest of the weight (metal tube + screw) is something to pay with, to see the changes in the lure's action.

To prevent water to enter the wood (if wood is the material of choice) you could seal the inside of the hole, or you could use a metal tube that is somehow sealed at the upper end. So even if water would find its way up between the threads, it will inflict no damage to the lure.

The rust problem could be easily solved by using non rust metals.

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hazmail    140

Loverly bit of work there Dave - I was surprised to see how much the epoxy and lip influenced the "MC" of the lure, although on close exam the % surface area is quite large on the front /base compared to the top/rear. As you say, all bets are off once we get in the water.

Welll done - Pete

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mark poulson    1,702

Mark, I think you are a genius, but have not realized it yet.

I do not fully understand what your problems were when you used your "threaded set screw", (don't know what this actually means), but perhaps this is for the better.

In order to make a device which you could use to see how the raising/lowering the weight in a crankbait would affect it's action, one could use a metal tube, threaded on the interior, and a screw without a head, that has a groove at one end, and you could move the screw upwards/downwards inside the tube by just using a small flat head screwdriver. If needed, a cylinder piece of lead could be glued on top of the screw, to add more weight to it. This way you could finely adjust the height of the weight to see the results on the lure's action.

No need to think that this will be the only weight in the lure. You could put a smaller than needed weight in a fixed place, as usual, and the rest of the weight (metal tube + screw) is something to pay with, to see the changes in the lure's action.

To prevent water to enter the wood (if wood is the material of choice) you could seal the inside of the hole, or you could use a metal tube that is somehow sealed at the upper end. So even if water would find its way up between the threads, it will inflict no damage to the lure.

The rust problem could be easily solved by using non rust metals.

Hahaha....genius. My kids say I'm half way to being a genieass....you pick the half. ;)

Seriously, that's very nice of you to say.

I've just lived long enough, and worked with my hands long enough, to have seen a lot of stuff, and so I have a big library to choose from.

And I learn something new here every day.

The allen head set screws I use are readily available at my lumber yard. If the rust issue becomes a real problem, I'll get some sst threaded stock, and cut a slot in one end, as you suggested. Good idea.

I use PVC, so water intrusion isn't an issue, and the set screw cuts it's own threads in my pilot hole.

I probably exaggerated the rust issue. Once I find the right position for the set screw, I'll just bondo the hole closed, and it will seal the set screw in permanently.

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I think that powder coating might work if you just powder coat the head of the set screw but if you get the powder coat in the threads its not going to work, So i suggest using a STAINLESS STEEL set screw and you will have no rust at all. I know that they are made because i use to be a Knitting Machine Technician ( Lonati's) and they had stainless steel set screws every where on them. Hope this helps.

Ronnie

Good ideas. I'll keep my eye out for something like that.

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mark poulson    1,702

I think that powder coating might work if you just powder coat the head of the set screw but if you get the powder coat in the threads its not going to work, So i suggest using a STAINLESS STEEL set screw and you will have no rust at all. I know that they are made because i use to be a Knitting Machine Technician ( Lonati's) and they had stainless steel set screws every where on them. Hope this helps.

Ronnie

Ronnie,

That makes perfect sense. There have to be sst set screws. I just never ran across them before.

I really think the regular set screws will work. I think I exaggerated the rust problem. The lures and screws won't be soaking long enough to rust while I'm playing around with the ballasting, and, once I figure out what works, the screws will be sealed in the lure permanently.

Sorry to spin everone's wheels about this.

Mark

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