Buoyancy of body fat

[Alex in L.A.]

I'm not sure what forum this belongs in, so I thought I'd try this here.

Let's say I get my gear and weights balanced so that I'm perfectly neutral at a depth of 15 feet with 500 psi in my tank at the end of a dive.

Then, over the holidays, I partake in, err, a bit of eggnog and cookies and whatnot, and when I step on the scales in January I am carrying 5 more pounds than previously. Let's also assume for the sake of simplicity that we know these five pounds are all body fat.

Here's my question. Exactly how much weight will I have to add to my belt to rebalance precisely (assuming I'm diving in saltwater)? Which is to say, exactly how positively buoyant is a pure pound of body fat, all other factors excluded? Thanks for any help on this.

 

[TCooperWFI]

Though it's not true that 5 pounds is 5 pounds, it's pretty darn close.
I added a couple of links, but I would like to see the math. I hope someone has an exact answer.

Diver Mag 2001

The Physics of Diving

 

[baenglish73]

Let me try.

According to Archimedes, the additional Bouyant Force will be equal to the density of water times the new volume of water displaced.

The weight of your fat will be the density of fat times the new volume of the fat.

The new volume of the fat should be equal to the new volume of water displaced.

Calculate the additional bouyant force, subtract the additional weight and add that much more weight to be neutral again.

or

New Weight = Additional Volume ( Density of water - Density of new fat)

If you added 5 lbs, look up the density of fat, and you'll have all the info you need. Of course, I haven't considered the last time you went to the bathroom.

 

[FredT]

Then, over the holidays, I partake in, err, a bit of eggnog and cookies and whatnot, and when I step on the scales in January I am carrying 5 more pounds than previously. Let's also assume for the sake of simplicity that we know these five pounds are all body fat.

Here's my question. Exactly how much weight will I have to add to my belt to rebalance precisely (assuming I'm diving in saltwater)? Which is to say, exactly how positively buoyant is a pure pound of body fat, all other factors excluded? Thanks for any help on this.

Specific gravity of similar hydrocarbons is about .8-.9, so to approximate your increased buoyancy requirement will be:

Weight of fat ( 1 - .85)

For a 5 pound fat gain this is 5*0.15 = 0.75 pounds.

FT

 

[TCooperWFI]

I don't have that size weight.
:biggrin:

 

[roakey]

I don't have that size weight.
:biggrin:

Lead is soft, just use an ordinary kitchen knife to shave a one-pounter down. Make sure it's a kitchen knife of someone you don't like, and replace it without washing...

Roak

 

[TCooperWFI]

Now if I could just get around that court order barring me from holding knives.... :ninja:

 

[chrpai]

Lead is soft, just use an ordinary kitchen knife to shave a one-pounter down. Make sure it's a kitchen knife of someone you don't like, and replace it without washing...

Roak

OMG, when I first read this I thought you said

"Fat is soft, just use an ordinary kitchen knife to shave...."

 

[Dwain]

OMG, when I first read this I thought you said

"Fat is soft, just use an ordinary kitchen knife to shave...."

That is true. maybe shave a bit O fat.

 

[TCooperWFI]

:ninja: It still won't get me past that stupid court order, make one little mistake (or six) and people remember it forever! Jeez!