Specific gravity of Plastics

[tubinator]

Has anyone done any tests on this? Like How many cubic inches of plastic it would take to suspend a gram of weight?

[Vodkaman]

Is there a density or specific gravity figure quoted on the plastic container?

If not, it will be possible to calculate it. Cast the plastic into a cube or a shape that can easily be measured.

First, calculate the volume, length x breadth x width measured in centimeters.

Measure the weight in grams.

density is measured in grams per centimeter cubed (g/cm3).

Divide the measured weight by the volume and that gives the density. It has to be less than one to confirm that it floats.

To calculate how many cm3 it would require to support 1 gram of weight::

Vol cm3 = 1 / ( 1 / density – 1)

Do not be put off by this formula, simply type into your calculator as follows:

1 / density – 1 = write this number down or put it in the memory.

Cancel.

1 / memory = answer in cm3.

To convert this number to cubic inches, multiply the answer by 0.061.

If this is no clearer than mud, PM me the density.

[tubinator]

Thanks for the formula Vodkaman. With this I was able to run a test on the LC 532 plastic and came up with 47.333grams of plastic will barely float 1 gram. Very close to suspending. I tested this on a hook and 6" of mono. line which weighed .3 grams, 14.2 grams of plastic nearly suspended the hook and line. So I figure a bait weighing 14.2 grams will just about suspend on a carolina rig with 12-18" of leader.

[Vodkaman]

Excellent. Glad it worked out for you.

[saint308]

Hunh? Saint.

[tubinator]

Saint,

Now if I want my bait to stay out of the rocks and crap on the bottom of the lake and suspend above it I can design some baits (based on hook weight) that will do it. Kinda Like a suspending jerkbait. But if the fish are holding around 25-30 ft deep in 50 degree water it's kinda hard to get a jerkbait down to them.

[saint308]

So you can make it sink to a certian depth then level off at that depth? Saint.

[BBC]

If you do a search I had a thread about this stuff a while ago. I did a lot of testing of materials and have created a program that calculates the density of lures taking other factors into consideration (amount of salt, amount and size of glitter, etc.). It is almost complete. Unfortunately I just changed jobs and I'm in the process of moving so I won't be able to finish until later this winter.

Eric

[tubinator]

Saint, In theory you could, but it really would depend on water temp, ie colder water is more dense, therefore the bait would slowly fall in warmer water until the density of the colder water slowed or stopped the fall. I don't think it would be practical to go to this extreme though.

I am just trying to find the weight (size) of a bait that would suspend or slightly float different size (weights)of hooks in 50-60 degree water.

BBC- your past posts on the subject are very interesting reads. Do you have the densities of the different size glitters? Although at a 47.33/1 weight ratio of plastic to steel I think that changing the plastic say to 47.5/1 would be as accurate a formula as I need to float the small amount of glitter in the bait.

[BBC]

I have the bulk and skeletal densities of del's 0.035" and 0.015" glitter as well as senkosam's 0.035" sugar flakes. You need both the bulk and skeletal density of them if you are measuring them by volume, only need skeletal density if you are measuring them by weight. Depending on how much you're adding, it will change the density of the bait. Like you said though, if you're comparing the bait to a lead or steel weight it doesn't matter as much. My analysis was mostly for stick baits.

PM me if you want more info on what I did.

Eric