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Find Volume and Neutral Bouyancy Weight of Your Plug In 30 Seconds

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TopStriperAngler

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Learned this from a lure making site today. This will give you: 1) volume of your plug 2) target weight for your plug to be neutrally buoyant

 

Need: gram scale, ideally something to within a 1/10th of a gram if making smaller freshwater stuff. 

 

This is called the suspension method of measuring volume. You are going to suspend your plug underwater. 

 

1. Weigh your plug in grams

2. Fill a container with water that is big enough to completely submerge your plug in

3. Put filled vessel on your scale and tare/zero it. 

4. Using pliers or wire submerge the plug without letting it touch the container

5. Record the weight in grams 

 

The recorded weight equals the amount of water displaced by your plug.

 

The recorded weight is also the same weight your plug would need to be in order be neutrally buoyant. Make your plug heavier than this weight if you want to sink. 

 

The recorded weight can be converted to volume by just swapping cubic centimeters for grams. Because 1 gram water=1 cubic centimeter. 

 

 

I don't understand the physics and I was hard pressed to find much about this method online but a research paper I found explained it as follows:

From a physics point of view, the analysis of the situation is quite simple. We have an object suspended in water that is stationary. If an object is stationary then we know that the forces on the object are balanced. In the case of an object suspended in water at the end of a line, the downward force due to gravity (g) is balanced by the upward buoyancy (b) and tension (t) of the line (figure 1). If the forces were not balanced then the object would move. Therefore a stationary object suspended in water is equivalent to a volume of water of exactly the same size and shape at the same position as the object. We can take any arbitrary surface within a static volume of fluid and the surface integral of the force will be zero, i.e. the forces are balanced. 

from https://www.researchgate.net/publication/27477716_Archimedes_revisited_A_faster_better_cheaper_method_of_accurately_measuring_the_volume_of_small_objects

 

 

 

 

 

Edited by TopStriperAngler
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If it works, go with it. I do several float tests during the lathe process to mark the ‘up’ side of the blank. I plug the through holes while testing. Archimedes would be proud of you. Thanks for the tip.

Tis better to remain silent and thought the fool, than to speak and remove all doubt.

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You're suspending it underwater with pliers or wire or even your fingers holding the throughwire. It's not floating. 

 

I don't understand it but somehow the forces involved--gravity, buoyant force. tension of you holding the plug--cancel out and the plug becomes equal to a volume of water. It basically becomes a virtual volume of water, is what I think the paper described it as. And the scale measures that. 

 

Try it. Frankly, it's a little bit trippy. But I'm not that great with science so I guess I'm easily blown away. 

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I'll use it to get volumes for molds so I can get a sense of how much resin to mix up. Will also use to determine how much silicone to put in a mold. 

 

Also will be able to use it for smaller 3"-4" spooks to get a sense of how heavy I can make them before they sink. I actually make them a little more dense than water and they will still walk on top. 

 

Will use for gliders.  

 

Can also use when deciding how much weight to drill out of a plug that sinks too fast. 

 

Can also use to get a sense of your epoxy cushion for a plug that you want to just barely float. Larger plugs can require several grams of epoxy. 

 

 

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I made a middle school and high school science class do this a few weeks ago. I don't think any kid should graduate high school without being able to measure (length, mass/weight, volume, buoyancy, etc.) but that's just my angry old man opinion. I also got the same classes to tell me which spheres were lead or SS based on mass, volume, and the density. In truth, they seemed to enjoy getting out of their seats, off the computer, and playing with grad cylinders, scales, and a hand-held calculator. 

 

Using a trip beam balance, I had to 'preset' the weight adjustment ahead of time to within a gram, and let them adjust it accurate.

 

I don't have an accurate scale at home, so I just hot glue weight onto a lure and throw it into a container of water 10x until I get it right. I find a little heavier is usually better to account for salt water and retrieve/current speed (which tend to, combined with fishing line tension) make the lure rise

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Goggle says 'ocean water has a 3.5% salt/water ratio' 35 parts per thousand - so weigh your full tanks, etc & a bit of math & add salt - (use up that little bit of rock salt, leftover from this winter) ... 

Morone Saxatilis... God put them in the Surf to take them, not in the freaking boat!

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Just looking around online. One cubic centimeter of seawater weighs 1.02g. One cubic centimeter freshwater weighs 1g. So conversion factor no matter what units you're measuring with would be 1.02 (maybe higher I guess varies). I guess this conversion factor is the same as specific gravity(ratio of density of water to density of seawater)?

 

 

 

 

Edited by TopStriperAngler
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