Archimedes Principle is understood by every sailor, boat owner, and scuba divers the world over. It is a physics law that governs buoyancy and object displacement on the water. It is a simple principle that can simply applied. The law is expressed mathematically thus:
buoyancy = weight of displace fluid
This means that any object may buoy itself positively if the objects displaces more weight than the objects weighs. This applies to gases and liquids as well. If an object buoys itself by displacing 1kg, then the force buoying it is equal or greater than 1kg.
Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.
A submarines sinks at will, because it takes on water into its’ ballast tanks, thus lessening the buoying force of the object. In effect a submarine takes on enough water to allow it to sink to a controlled depth, and propel itself at that depth smoothly. A diver does the same, but with lead weights instead. The neoprene of the wetsuit, the cylinder (depending on the cylinder type), and the actual diver all contribute to positive buoyancy. This positive or neutral buoyancy is affected at the end of the dive as well; depending on the cylinder type; which may add positively displaced weight to the diver. This is more effected by saltwater, than freshwater, as saltwater is more dense than freshwater, and so easier to buoy an object. The lead weights that a diver wears, trims this displacement so that a diver may actually “sink”. Obviously a diver doesn’t want to continue sinking (especially in open ocean, where the drop is 1 or more miles; that fall could actually kill a diver long before the sudden stop at the bottom). So recreational SCUBA divers wear buoyancy compensators (BCDs) that allow the diver to place compressed gas into the BCDs to offset the weight of the lead; allowing the diver to fine-tune their trim underwater. Like a submarine, a diver can achieve total neutral buoyancy and; using his/her breath; ascend or descend at will. Most of the sanctioning bodies teach methods to achieve and maintain neutral buoyancy in some form or another. It is very important to use archimedes principle to attain and maintain neutral buoyancy in order to ,ultimately, conserve air because moving about at depth requires less energy consumption while maintaining neutral buoyancy. The weight required is only just enough to submerge the diver by creating negative buoyancy. The BCD will fine-tune the trim. Proper instruction from a reputable dive center will give any diver the skills and knowledge to apply Archimedes principle to their dives, which will in-turn improve the diver’s Surface Air Consumption rates.
You now have a more detailed grasp of Archimedes Principle and how it affects recreational SCUBA divers. My sincere hope is that this understanding helps you in your diving adventures. For more information on attaining and maintaining neutral buoyancy, you should seek out a reputable instructor or dive center and take a buoyancy speciality. And remember, every dive is a good opportunity for practicing your buoyancy skills.
Coming Soon: SAC (Surface Air Consumption) Rates
Dive Safe. Dive Often.