Calculating Bouyancy Requirements

Ok, I am probably being dense here (having a bad day) but how do you go about calculating how much bouyancy you need to hand to get yourself from the bottom back to fresh air again given a certain depth & equipment configuration?

Anyone got a handy formula they would like to share?

Ta,
Steve

[zepp]

One litre of air at the ambient pressure will lift one kilo of weight. So, if you are 5 kilos heavy, you will need to put a volume of 5 ltrs of air in your BCD/Dry-suit to become neutral........

[Narked@50]

Hi Steve

You also have to remember your weighting depends very much upon the abount of gas, and type of cylinders you carry: http://www.subaqua.co.uk/cgi-bin/cyl...i?units=metric

This link will help you calculate it.

James

[up 4 it]

Hi Steve

There isn't actually a formula for the scenario you are asking, however, if you were with a buddy at the surface at the waters edge, and he hooked a set of the spring fishing scales to the back of your tank and you then dumped all your air, he would be able to see your weight in water... ie how much you weigh negatively buoyant.

If as in the previous example you were 5kg negative, this would require 5 litres of air to make it neutral and a little bit more to lift.

If you then multiply the 5L by the absolute pressure for the depth you are at, this would give you the amount of air required to lift you. eg at 30m - absolute = 4bar therefore air required = 4 x 5L = 20L

When you are rising the pressure reduces therefore at 20m - absolute = 3bar therefore air required = 3 x 5L = 15L therefore you would need to dump air.

Steve

[zepp]

Originally Posted by up 4 it

Hi Steve




If you then multiply the 5L by the absolute pressure for the depth you are at, this would give you the amount of air required to lift you. eg at 30m - absolute = 4bar therefore air required = 4 x 5L = 20L

When you are rising the pressure reduces therefore at 20m - absolute = 3bar therefore air required = 3 x 5L = 15L therefore you would need to dump air.

Steve

I did state in my post "One litre of air at the ambient pressure will lift one kilo of weight"