Neutral buoyancy rig question (someone help me with the math please)

[clock115]

First, My rig weights about 3.25 lb but I am going to say 3 lb for a slightly negatively buoyant rig. I plan on either using PVC pipe, DivinyCell, or that Stix brand stuff to add buoyancy. I'm interested to hear your opinions of all of these as well.

3lb = 1.36 kg

Neutral buoyancy is when Normal force (Mass x Gravity) = Buoyancy force (Gravity x Density of fluid x Volume displaced)

1.36 kg x 9.8 m/s^2 = 13.36 N
So, I need to create about 13.36 N of lift to get this rig neutrally buoyant.

13.36 N = 9.8 m/s^2 x 1029 kg/m^3 (density of saltwater) x V
If this is correct, I should need a volume of 0.00132 M^3 which I don't believe is right..
I'm a biologist so not much physics experience. Hopefully, there is an engineer or someone around to kick my ass with these calculations lol.

Thanks for the help and happy diving everyone.

 

[dumpsterDiver]

you need to displace 1.36 liters of water, plus a volume of water equal to whatever the weight is of your buoyancy device. water is 1 gram/ cc

 

[Storker]

Are those 3.25# the weight in water? If so, DD has it right. 3# = 1.36kg, 1 liter of fresh water masses 1kg, and for that kind of numbers you don't worry about the 3% density difference between salt and fresh water. So you need ~1.36L of air, or foam, or whatever. Which is about 2.9 US pints or 0.05 cu.ft.
Don't make it more complicated than necessary.

 

[clock115]

Makes sense. Thanks for the help guys

 

[clock115]

Any inputs on using Stix brand or just buying some foam such as divinycell? Im using Loc Line on my arms which is where I would attach it.

 

[tursiops]

How deep do you want to go? Some foam will crush pretty shallow. Make sure your Divinylcell is Marine Grade.

 

[clock115]

I don't plan on going deeper than 130 feet for now. Can you recommend a divinycell for me? I understand there are different densities such as H45 (3 lb/cubic ft), H80 (5 lb/cubic ft), and H100 (6 lb/cubic ft). I was planning on ordering some from aircraftspruce.com as it seems like the best deal.

http://www.aircraftspruce.com/catalog/cmpages/divinycellfoam.php?clickkey=116961

 

[tursiops]

Some resources:
http://wetpixel.com/forums/index.php?showtopic=18999
http://www.scuba007.com/camera-floats/index.html
http://interceptor121.com/2014/03/15/floats-and-float-arms/
http://www.uwphotographyguide.com/forums/viewtopic.php?f=3&t=304
http://www.scubaboard.com/community...ight-floating-arm-without-getting-wet.444446/

 

[clock115]

Thank you very much those are some good posts. I am going to go with divinycell H100 since it seems to be what most people are using. Have a great day!!

 

[diversteve]

I would since Stix floats are for ULCS and similar ball/clamp arm systems not loc-line.
ex: http://www.divervision.com/stix-lar...t-inon-seaandsea-arms-UFL-2.html?keyword=stix