Archimedes' principle is the fundamental natural law of buoyancy, first identified by the Greek mathematician and inventor Archimedes in the 3d century BC. It states that any object floating upon or submerged in a fluid is buoyed upward by a force equal to the weight of the displaced fluid.

This buoyant force is caused by the weight of the fluid, which causes the fluid pressure to increase steadily with increasing depth from the surface. Any submerged object is subject to a greater pressure force on its lower surface than on its upper surface, creating a tendency for the object to rise. This tendency is counteracted by the weight of the object, which will sink if it is heavier than the surrounding fluid and will rise if it is lighter. If the object weighs the same as an equivalent volume of the fluid, it will be in equilibrium and remain motionless. Buoyancy may be thought of as the DENSITY of a fluid relative to the densities of objects submerged in it.




STRESS
A diver normally does not realize that they are stressed!
Why do divers get stressed?

  1. They have not dived for a long time.
  2. They are diving with equipment they have not used before or equipment that has failed previously, and are worried that the equipment will not work correctly.
  3. They are diving with a buddy that they do not want to dive with, or there are divers in the group that make them nervous.
  4. They are doing a dive that is beyond there capabilities. (They are not ready to do that type of dive.) E.g. Night Dive, but are not happy on a day dive.
  5. Everyone is diving with a computer, but you do not have one. You are worried about your dive tables as you are on the limits. Naughty! Naughty! Stay out of the water. The exception to diving on the limits, or into decompression is only if you are a technical diver, where you are trained to do compulsory decompression stops.
  6. The diver has buoyancy problems. The bigger the problem the more the stress.

Most stress related problems can be solved by going to a swimming pool and doing 1 or more dives there. E.g. testing your new equipment, practicing skills you are worried about.

If you are unhappy about doing a specific dive, don’t dive. You are responsible for yourself. No one can make you do a dive.
WEIGHTING
As a scuba diver we should be wearing as little weight as possible.

Most divers carry excess weight, resulting in extra air in the BC. Get your buddy to stand in their gear and then inflate the BC to the maximum. Does that not look very bulky? That bulky equipment is what you have to propel through the water.

How much weight should a diver wear?
A diver should only carry enough weight to be able to stay at 5M for the safety stop at the end of a dive with an almost empty tank. About 30 bar pressure remaining.

Why at the end of the dive?
Air in your tank has a mass. Depending on the size of your tank it could be as much as 4kg. Therefore if you checked your weight before the dive and you were neutral buoyant, at the end of the dive you would be positive buoyant by the amount of the air used. Many divers have problems at the end of a dive because the air used was not taken into account when checking buoyancy.

FITNESS
The fitter the diver is the less air they will use for the dive. Ladies are generally lighter on air than men.

BREATHING PATTERN
The correct way to breath underwater is slow, deep inhalation and a slow exhalation. Do not hold your breath. Breath holding is known as skip breathing and will result in a headache. This is dangerous.

DIVING POSITION
There are only three positions to talk about:

  1. Horizontal in the water.
  2. Head down position.
  3. Head up position.

Diving horizontally in the water is the most streamlined way of diving. Any other position uses more energy and will result in higher air consumption. Keep all gear tucked in, as well as the hands. Many divers that dive horizontally still use their hands to change position. This creates undue drag.

Head down position is used when diving in water where there is a layer of silt on the bottom. This will redirect the thrust form your fins, away from the bottom, thereby not disturbing the silt, enabling the diver to turn around and swim past the same area again. This position requires the diver to be slightly positive buoyant at all times. This is more strenuous than horizontal diving, but can be a very pleasing way to dive. Your head is closer to the small creatures that you would normally not see.

Head up position is the classic position that most new divers use. They are not neutral or positive buoyant and therefore have to fin to keep off the bottom. This results in the silt being kicked up in a silty environment or when on a reef the coral is damaged.

 
Bottom time is affected by various factors:

= Stress
= Weighting (Buoyancy)
= Fitness
= Breathing Pattern
= Diving Position

 
© Kenneth Wessels 2013