The Neptune Warrior

Facts

Sea water weights 64 lbs / cubic ft.

Fresh water weights 62.4 lbs / cubic ft.

Sea water exerts 1 ATM. pressure every 33 ft.

Fresh water exerts 1ATM. pressure every 34 ft.

Atmospheric Pressure @ sea level = 1 ATM or 14.7 p.s.i.

Absolute Pressure = Water Pressure + Atmospheric Pressure

Absolute Temperature

oKelvin = oCelsius + 273

oRankin = oFahrenheit + 460

Air = 78.084% N2 + 20.946% O2 + 0.033% CO2 + 0.934 Inert gases

Equations

1. Absolute Pressure ( ATA ) = ( depth/33 ) + 1 ( or 34 if fresh water )

2. Wet weight = Dry weight . Buoyancy

3. Buoyancy = volume x 64 ( or 62.4 if fresh water )

4. Surface Air Consumption ( SAC ) = rate at depth/ATA

5. Consumption Rate at depth = SAC x ATA

6. Cylinder contents = (contents in psi/working pressure) x Cylinder size

in cubic ft

7. Cylinder contents = (contents in cubic ft/cylinder size ) x working pressure

in psi

8. Partial Pressure (pp) of a gas at depth = pp at surface x ATA

( note . No 7 and 8 – working pressure in commonly 3000 psi and cylinder size is

commonly 80 Cubic ft. )

Gas Laws

Boyles Law . Pressure and volume of a gas in a flexible or open container are inversely

proportional.

P1 V1 = P2 V2 ( assuming temperature is constant )

Charles Law . Temperature and volume of a gas are directly proportional

V1/T1 = V2/T2 ( assuming pressure is constant )

Amontons Law ( also known as Lussacs Law ) . Temperature and pressure are directly

proportional

P1/T1 = P2/T2 ( assuming volume is constant)

General Gas Law

P1V1 = P2V2

T1 T2

** always use absolute temperature and absolute pressure in the above equations

Archimedes. Principle : an object partially or wholly immersed in a fluid is buoyed up

by a force equal to the weight of the fluid displaced by that object.

Henry.s Law: The amount of gas that will dissolve into solution is directly proportional to

the partial pressure of the gas and inversely proportional to the absolute temperature.

Dalton.s Law: The pressure exerted by a mixed gas is equal to the sum of the partial

pressures of its components. (The partial pressure of a gas is the pressure it would exert

if it alone occupied the entire volume of a mixture.)

Sample Questions.

Q1. What is the difference in weight between 5 cubic ft of sea water and 5 cubic ft

of fresh water?

A1. Using the facts

Sea water weights 64 lbs / cubic ft.

Fresh water weights 62.4 lbs / cubic ft.

5 cubic ft of sea water weights 5 x 64 = 320 lbs

5 cubic ft of fresh water weights 5 x 62.4 = 312 lbs

therefore the difference is 320 . 312 = 8 lbs

Q2. How many 50 lb lift bags are required to recover an anchor from the ocean

with a dry weight of 320 lbs and a volume of 2 cubic ft.?

A2. Using the following equations

2. Wet weight = Dry weight . Buoyancy

3. Buoyancy = volume x 64

Buoyancy = 2 x 64 = 128 lbs

Wet weight = 320 . 128 = 192

Therefore total number of 50lb lift bags = 192/50 = 4

Q3. What is the absolute pressure at 57 ft of sea water?

A3.

Using the equation

1. Absolute Pressure ( ATA ) = ( depth/33 ) + 1

ATA = (57/33) + 1 = 2.727 ATA

Q4. A balloon has a volume of 12 cubic inches at 33 fsw ( feet of sea water ) what

is the volume at 132 fsw?

A4. Using equation

1. Absolute Pressure ( ATA ) = ( depth/33 ) + 1

Absolute Pressure @ 33fsw ( P1 ) = (33/33 ) + 1 = 2 ATA

Absolute Pressure @ 132fsw ( P2 ) = (132/33) + 1 = 5 ATA

And then using Boyles Law

P1 V1 = P2 V2

2 x 12 = 5 x V2

V2 = (2 x 12)/5 = 4.8 cubic inches

Q5. How much is an air consumption rate of 40 psi/min using a standard 3000psi /

80 Cubic ft tank in cubic ft per min.

A5. Using equation

6. Cylinder contents = (contents in psi/working pressure) x Cylinder size

in cubic ft

Rate in cubic ft / min = (40/3000) x 80 = 1.067 cubic ft / min

Q6. If you have a SAC rate of 25 psi / min how long will a tank charged to 3000 psi

last at 90ft if the diver wishes to start the asent with 1000 psi.

A6 Using equation

2. Absolute Pressure ( ATA ) = ( depth/33 ) + 1

ATA @ 90ft = ( 90/33 ) + 1 = 3.7 ATA

And then

5. Consumption Rate at depth = SAC x ATA

Consumption Rate at 90ft = 25 x 3.7 = 92.5

The diver has 3000 psi but wishes to asend with 1000 remaining therefore we need to

calculate how long 3000 . 1000 = 2000 psi will last

2000/92.5 = 21 mins. ( approx. )

Q6. How much air ( in cubic feet ) is in a 3000 psi / 80- cubic ft tank when the

guage reads 2400 psi ?

A6. Using equation

6. Cylinder contents = (contents in psi/working pressure) x Cylinder size

in cubic ft

Cylinder contents in cubic ft = (2400/3000) x 80 = 64 cubic ft.

Q7. What is the ppO2 ( partial pressure of oxygen ) in ATA at 50ft

A7. Using equation

1. Absolute Pressure ( ATA ) = ( depth/33 ) + 1

ATA = (50/33) + 1 = 2.5

And then

Air = 78.084% N2 + 20.946% O2 + 0.033% CO2 + 0.934 Inert gases

8. Partial Pressure (pp) of a gas at depth = pp at surface x ATA

ppO2 @ 50ft = .20946 x 2.5 = .52365 ATA

Q8. A diver is at 20ft in a lake, the temperature is 75 oF, she has 4 liters of air in her

BC. She descends to 60ft where the temperature is 55 oF, how many liters of air is

in her BC now ?

A8. Using General Gas Law

P1V1 = P2V2

T1 T2

Remember to convert all pressures and temperatures to ABSOLUTE values, and note

this is a LAKE .. so this must be FRESH water.

P1 = (20/34) + 1 = 1.59

V1 = 4 (** liters is a measure of volume)

T1 = 75 + 460 = 535

P2 = (60/34) +1 = 2.76

V2 = ??

T2 = 55 + 460 = 515

1.59 x 4 = 2.76 x V2

535 515

V2 = 1.59 x 4 x 515 = 2.21

535 x 2.76