Buoyancy of aluminum, ss and lead or: How much lead does my 2# aluminum bp equal?

[JessH]

First things first, how negative is a pound of aluminum underwater? What about stainless steel? lead?
I did a little bit of math using specific gravity and came up with the following numbers, could someone please tell me if they are right? Obviously this is only for fresh water, but what really matters is the relationship to lead.

Aluminum: 0.621212121 pound
Stainless Steel: 0.87012987 pound
Lead: 0.911894273 pound

So my aluminum bp from hammerhead scuba weighs 1.8 pounds, this would mean it is 1.1 pounds negative, or equal to 1.2 pounds of lead.

I was thinking about the DSS Kydex/SS BP as an even lighter weight BP option, but it is .7 pounds negative, so it is only a .4 pound difference.

Does this all look right?

References:
http://www.ajdesigner.com/phpspecif...vity_equation_submerged_water_weight_loss.php
http://www.reade.com/Particle_Briefings/spec_gra2.html
http://www.reade.com/Particle_Briefings/spec_gra.html
http://www.onlineconversion.com/weight_all.htm

~Jess

 

[*Floater*]

First things first, how negative is a pound of aluminum underwater? What about stainless steel? lead?
I did a little bit of math using specific gravity and came up with the following numbers, could someone please tell me if they are right? Obviously this is only for fresh water, but what really matters is the relationship to lead.

Aluminum: 0.621212121 pound
Stainless Steel: 0.87012987 pound
Lead: 0.911894273 pound

So my aluminum bp from hammerhead scuba weighs 1.8 pounds, this would mean it is 1.1 pounds negative, or equal to 1.2 pounds of lead.

I was thinking about the DSS Kydex/SS BP as an even lighter weight BP option, but it is .7 pounds negative, so it is only a .4 pound difference.

Does this all look right?

References:
http://www.ajdesigner.com/phpspecif...vity_equation_submerged_water_weight_loss.php
http://www.reade.com/Particle_Briefings/spec_gra2.html
http://www.reade.com/Particle_Briefings/spec_gra.html
http://www.onlineconversion.com/weight_all.htm

~Jess

I got the same numbers using a method I've seen used here before.

As you point out the DSS plate isn't much lighter underwater (or above), so I would not get it for that reason if you already have an AL plate unless you really need to lose another half pound. It's a nice plate though. I like mine.

 

[donacheson]

...

Aluminum: 0.621212121 pound
Stainless Steel: 0.87012987 pound
Lead: 0.911894273 pound
...
Does this all look right?
...

Close enough for diiving estimates.

BTW, to get 9 significant digits of accuracy, you should specify the temperature, alloy, and water purity. <G>

 

[JessH]

BTW, to get 9 significant digits of accuracy, you should specify the temperature, alloy, and water purity. <G>

Yeah, I realize this, plus that many is totally unneeded in this sitaution. I was simply cutting and pasting and didn't bother to get rid of them.

~Jess

 

[victor]

Whats the answer in salt water?

As I am planning for warm water, max 3mm one piece I am worried about weight.
In my skin I think I would be negative with any doubles combination, true not by much with some ALU80's.
I would hate to have to add buoyancy just to overcome the weight of the doubles.

 

[ScottB]

I just did quick and dirty math (inverse proportion) based off of JessH's figures to 4 significant digits.. basing the weight of a cubic foot of fresh water at 62.4 pounds, a cubic foot of salt water at 64 pounds..

1 pound of aluminum will have approximately 0.6057 pounds negative buoyoancy
1 pound of stainless steel will have approximately 0.8483 pounds negative buoyoancy
1 pound of lead will have approximately 0.8891 pounds negative buoyoancy

*example of math:

(buoyancy in salt water) = (buoyancy in fresh)*(weight of freshwater)/(weight of saltwater)
(buoyancy 1lb AL in sw) = (0.6212 pounds)*(62.4 pounds/cuft)/(64 pounds/cuft)
(buoyancy 1lb AL in sw) = 0.6057 pounds