| When starting out scuba diving most trainees | | | | tanks being used, the diver is at his or her lightest at |
| struggle with their buoyancy for a while. They are | | | | the end of the dive and at this point must adjust |
| introduced to an alien environment and find that they | | | | their weighting to achieve neutral buoyancy. Carrying |
| are either floating or sinking. Unfortunately, many | | | | this out at the start of the dive could result in the |
| divers with years of scuba diving behind them still | | | | diver being very positively buoyant by the end of |
| have problems with their buoyancy. In the shallow | | | | the dive! |
| confines of a training pool bad buoyancy can be | | | | The weight belt and weight pouches can be removed |
| corrected by the instructor. When deep diving for | | | | by the diver quickly. The weight belt has a quick |
| extended periods of time this is not possible and | | | | release buckle and the pouches are usually attached |
| poor buoyancy could be extremely dangerous. | | | | by Velcro. Thus, in an emergency the diver, or his |
| The physicals laws of buoyancy are described by | | | | buddy, can remove the weights and the diver will |
| Archimedes Principle - that most of us encountered | | | | shoot to the surface where he can be rescued. This |
| at school. It states that a body immersed in a liquid | | | | is a controversial rescue method, and the deeper and |
| experiences an up-thrust on it that is equal in size to | | | | longer the dives being conducted, the more |
| the weight of the liquid that it is displacing. Therefore | | | | dangerous as an emergency procedure this becomes. |
| if a boat displaces water equal in weight to itself then | | | | A rapid ascent in only a few meters of water by a |
| this will be experienced as a force pushing it upwards | | | | panicking diver after a twenty minute dive is likely to |
| so that it floats on the surface. Conversely a stone | | | | lead to a safe rescue. A similar buoyant ascent from |
| will sink because being denser than water it displaces | | | | 40 meters after an hour under water will lead to |
| a volume weighing less than itself. The up-thrust is | | | | severe diving illness such as burst lung and |
| less than its own weight and it therefore sinks. | | | | decompression sickness. Even if a safe ascent is |
| The boat is exhibiting positive buoyancy whereas the | | | | made, the diving computer used to monitor the dive |
| stone is negatively buoyant. We scuba divers do not | | | | will probably lock you out from diving for a day or |
| want to flop on the surface or sink like a stone. We | | | | more after a too swift ascent. |
| need to be neutral in the water so that with a lazy | | | | For such extended range diving it is often advisable |
| kick of our fins we can move up or down. If we | | | | to reduce the emergency jettison weights, to ensure |
| floated we would have to paddle hard to duck | | | | that an emergency ascent is not too swift. Many |
| beneath the surface and if we sank, we would | | | | divers have a combination of pouches and weight |
| always be struggling to compensate for the | | | | belts so that only part has to be removed to achieve |
| tendency to sink. | | | | slight positive buoyancy. A technical diver may even |
| Neutrally buoyant means less effort and therefore | | | | use integral weights in his twin set that cannot be |
| less air consumption. It allows us the best control of | | | | removed. They know that a rapid ascent would be |
| our attitude within the water and is more | | | | just as final as drowning. Some will wear a couple of |
| comfortable than always having to swim to keep a | | | | removable kilo weights in small pouches - some do |
| position. Scuba diving enthusiasts get to be neutral by | | | | not. |
| balancing their diving equipment. Often this is by trial | | | | Buoyancy is seen as a critical skill in scuba diving. |
| and error and because a thick insulating wetsuit or | | | | Without good control, it is impossible to swim over |
| dry suit is usually worn it will mean adding lead | | | | delicate coral without doing damage or hard to hover |
| weights to the scuba gear. Often several kilos of lead | | | | while carrying out safety stops or decompression |
| are added by way of a weight belt or alternatively in | | | | procedures. Being over weighted can be dangerous |
| weight pouches in the buoyancy jacket. The time to | | | | and even worse, wearing ill fitting or badly secured |
| adjust weighting is at the end of the dive, when | | | | weights can result in unexpected buoyant ascents |
| most of the air has been drained from the tanks. As | | | | and the consequential damage this can do to a diver's |
| the air that has been breathed can weigh a couple of | | | | body. |
| kilos, depending on the size and configuration of | | | | |