Buoyancy Compensator

Is Buoyancy the Single Most Important Scuba Diving Skill?

When starting out scuba diving most trainees struggle with their buoyancy for a while. They are introduced to an alien environment and find that they are either floating or sinking. Unfortunately, many divers with years of scuba diving behind them still have problems with their buoyancy. In the shallow confines of a training pool bad buoyancy can be corrected by the instructor. When deep diving for extended periods of time this is not possible and poor buoyancy could be extremely dangerous.

The physicals laws of buoyancy are described by Archimedes Principle – that most of us encountered at school. It states that a body immersed in a liquid experiences an up-thrust on it that is equal in size to the weight of the liquid that it is displacing. Therefore if a boat displaces water equal in weight to itself then this will be experienced as a force pushing it upwards so that it floats on the surface. Conversely a stone will sink because being denser than water it displaces a volume weighing less than itself. The up-thrust is less than its own weight and it therefore sinks.

The boat is exhibiting positive buoyancy whereas the stone is negatively buoyant. We scuba divers do not want to flop on the surface or sink like a stone. We need to be neutral in the water so that with a lazy kick of our fins we can move up or down. If we floated we would have to paddle hard to duck beneath the surface and if we sank, we would always be struggling to compensate for the tendency to sink.

Neutrally buoyant means less effort and therefore less air consumption. It allows us the best control of our attitude within the water and is more comfortable than always having to swim to keep a position. Scuba diving enthusiasts get to be neutral by balancing their diving equipment. Often this is by trial and error and because a thick insulating wetsuit or dry suit is usually worn it will mean adding lead weights to the scuba gear. Often several kilos of lead are added by way of a weight belt or alternatively in weight pouches in the buoyancy jacket. The time to adjust weighting is at the end of the dive, when most of the air has been drained from the tanks. As the air that has been breathed can weigh a couple of kilos, depending on the size and configuration of tanks being used, the diver is at his or her lightest at the end of the dive and at this point must adjust their weighting to achieve neutral buoyancy. Carrying this out at the start of the dive could result in the diver being very positively buoyant by the end of the dive!

The weight belt and weight pouches can be removed by the diver quickly. The weight belt has a quick release buckle and the pouches are usually attached by Velcro. Thus, in an emergency the diver, or his buddy, can remove the weights and the diver will shoot to the surface where he can be rescued. This is a controversial rescue method, and the deeper and longer the dives being conducted, the more dangerous as an emergency procedure this becomes. A rapid ascent in only a few meters of water by a panicking diver after a twenty minute dive is likely to lead to a safe rescue. A similar buoyant ascent from 40 meters after an hour under water will lead to severe diving illness such as burst lung and decompression sickness. Even if a safe ascent is made, the diving computer used to monitor the dive will probably lock you out from diving for a day or more after a too swift ascent.

For such extended range diving it is often advisable to reduce the emergency jettison weights, to ensure that an emergency ascent is not too swift. Many divers have a combination of pouches and weight belts so that only part has to be removed to achieve slight positive buoyancy. A technical diver may even use integral weights in his twin set that cannot be removed. They know that a rapid ascent would be just as final as drowning. Some will wear a couple of removable kilo weights in small pouches – some do not.

Buoyancy is seen as a critical skill in scuba diving. Without good control, it is impossible to swim over delicate coral without doing damage or hard to hover while carrying out safety stops or decompression procedures. Being over weighted can be dangerous and even worse, wearing ill fitting or badly secured weights can result in unexpected buoyant ascents and the consequential damage this can do to a diver’s body.

About the Author

Mark Jenner is a BSAC Dive Leader and Open Water Instructor. He has been diving for over 20 years and enjoys writing about the sport. You can read more about key diving skills and scuba gear reviews on his diving web site and about important scuba diving decompression subjects such as which dive computer to use on his diving blog site.

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