[carpholeo]

I made Swimbait recently from blank of unknown wood, just by luck it wound up having neutral buoyancy. Its a great bait and I would like to make more of them. However,in the future, I would like to rely on more than just luck.

So when planning A suspending wooden swimbait, what are some of the things I need to do to wind up achieving neutral buoyancy.

[fish devil]

I use a pitcher of water and put it inside a cooking pot. Make sure the pitcher is full to the top. Put the bait in the pitcher of water and submerge it. Weigh the water that spilled out of the pitcher into the pot.

[woodieb8]

yhats a tricky neat way from fish devil. i have experienced big changes in water temps to buoyancy factors.

[hazmail]

Google 'Archimedes Principle' ---------- not 'Screw'. pete

[Vodkaman]

http://www.tackleunderground.com/forum/hard-baits/13095-how-estimate-weight-needed.html

This link covers a method of calculating volume by weighing a suspended body.

http://www.tackleunderground.com/forum/hard-baits/12275-how-does-clearcoat-affect-bouyancy-lure.html

This link discusses the effect of a D2T top coat.

http://www.tackleunderground.com/forum/soft-plastics/10027-density-materials.html

This link discusses other methods of calculating volume, like the pitchers and pans or jars and tubes, basically as stated above by fish devil.

Both the above mentioned methods of calculating volume work, but the displacement method, using pitchers and pans, has accuracy problems. The smaller diameter the pitcher, the more accurate the result.

For example, if the pitcher was the size of a bucket, you could almost submerge the lure without spilling, under normal meniscus tension. If the bucket was so full as to make spilling inevitable (forced meniscus tension), once the meniscus breaks and the water flows, it will not settle until it reaches its normal tension, thus giving a false high value of the weight.

The following thoughts are not meant to put anyone off the idea of calculating ballast, in fact that is the direction I am heading myself. But it is meant to highlight the issues that effect the results. It is far more involved than the puzzle seems initially.

Knowing the volume of your lure immediately gives you a figure to work with. It tells you how much the lure must weigh to be a suspender, provided you work in metric units. If you work in imperial units, you will get bogged down with incompatible units.

Example metric. If a lure has a volume of 23 cm³ or 23 ml, its suspended weight will be 23 grams.

Example imperial. If a lure has a volume of 1 inch cube or 0.554 US fluid ozs, its suspended weight will be 0.3197 ozs.

It took me about 30 minutes, a couple of web searches, two large vodkas and a lot of number crunching to arrive at the US numbers above. Inconvenient to say the least. Conversely, using metric units, you do not need a calculator to convert volume to weight.

But none of the above, or your question tackle the real problem. That is, you want to fit the ballast before the top coat. But D2T is heavier than water and will sink the lure. D2T has a density of 1.17gm/cm³. This means that D2T is 17% heavier than water.

I fear that things are even more complicated than that. Think of it another way. Consider a lure (80mm length) of volume 23 cm³ with hardware and without top coat, requiring 1 gram of D2T.

1 gram of D2T has a volume of (1 / 1.17) 0.855 cm³.

Adding the D2T increases the lure volume by 0.855 to 23.855 cm³ and also the suspended weight to 23.855 grams.

The weight of the lure has increased by 1 gram to 24 grams.

Therefore, the D2T has added (24.0 – 23.855) 0.145 grams and the lure sinks.

But it gets worse! You drill the hole and fit the correct ballast and weigh the lure, just to check. The weight is wrong. The fact is that when you drilled the ballast hole, you removed some weight of body material. The result is light by this weight. Small but significant. My experience is that the range of tolerance for a suspender is approximately 1/100 of the weight of the lure, so for a 20 gram lure, accuracy of less than 0.2 grams is required.

I will be putting all of these thoughts to a practical test soon, with the intention of producing a comprehensive spread sheet that will greatly simplify weighting suspenders.

All this theory and calculation is well and good, but there is nothing wrong with good old trial and error. Hands on experience with suspenders can be quite pleasurable.

I believe weighted stick-on dots can be purchased for the purpose of fine tuning suspenders. Another solution to fine tuning: Approximately 20mm of Φ1.05mm solder weighs 0.1 grams. So if you can get your finished lure very close to suspension, then by gluing the solder to the rear belly of the lure, the solder can be snipped to fine tune the suspension. The trailing solder also adds a little realism to the lure!

[redg8r]

Water displacement isn't the best method for accurately measuring buoyancy.

Example: any piece of matter, lets say, 2 boxes, both measuring 1 cubic inch.
one filled with air, one filled with lead.

Both will displace the same amount of water, but the buoyancy of each is obviously much different.

What needs to be measured is the amount of force needed to hold the lure submerged.

I think Lapala touched on a technique a few years ago, but not 100% sure.
I would think you could use a string to pull the bait under & measure the force using a postal scale or similar, but to do that you need the string to re-emerge out of the surface, which could be done using a pulley mounted in the bottom of the container.

then again I'm not a physicist, so I don't know if using a pulley will lighten the load, I know using a series of pulleys does indeed lighten the force needed.

And as woodieb8, skeeter & others have noted, water temperature will affect buoyancy to a degree, how much would be another great experiment.

Good topic to get the minds gears crankin.

Originally Posted by vodkaman

You drill the hole and fit the correct ballast and weigh the lure, just to check. The weight is wrong. The fact is that when you drilled the ballast hole, you removed some weight of body material. The result is light by this weight. Small but significant. My experience is that the range of tolerance for a suspender is approximately 1/100 of the weight of the lure, so for a 20 gram lure, accuracy of less than 0.2 grams is required.

An easy fix would be to:

1. Attain the additional weight needed.
2. Drill cavity for necessary added weight.
3. Weigh the bait after drilling cavity
4. Subtract that weight from the total needed weight to achieve = buoyancy.
5. Add that sum back into the lure.

Agreed, epoxy topcoats, hardware, hooks, etc. should be included.
Paint IMO would be negligible.

Still, the biggest gorilla in the room is the fact that water temperature affects buoyancy to some yet unknown degree AND line type/weight will be a factor, and water pressure may be factor also.
All 3 may be minuscule, but might be a consideration to look at.

[Vodkaman]

Jerry, everything you state is correct of course. The best we can do is get it as close as possible and fine tune at the waters edge. Every day the same body of water will vary due to temperature.

Another thought, if you use a quick release for attaching the line, this too should be included in the lures hardware.

Regarding the buoyancy fix. True, the calculation is an iterative one. The answer has to be fed back into the question a few times to hone in to the real answer. Spreadsheets are very good for this application.

[redg8r]

Companies, make & market neutral buoyancy all the time & for most intents & purposes they are close.

Like you, I'm just trying to get all the fundamentals out there for brain candy & I'd love to see a spreadsheet to help alleviate the trial & error.
I think one (a formula/spreadsheet) could be produced to get most baits very close & acceptable to remain in the preferred strike zone.

Water displacement can be used as a primer for determining needed weight, I just didn't want people getting perturbed if they used it as a single method for determining weight.

[Spike-A-Pike]

Okay guys, take 10 minutes for a potty break and an alcohol run and we'll take up how drag impacts wiggle and wobble of a bait - Just kidding.

A great thread but it requires to much brain power for a Saturday morning when the grass needs to be mowed...

[redg8r]

@ Spike......... and Pete........ just "got" your post

I forgot the simple fact that objects don't weigh the same above & below the surface.
Some good reading:
Pressure