SCUBA - Self-Contained Underwater Breathing Apparatus 09
SCUBA - Self-Contained Underwater Breathing Apparatus 09 : Diver Mobility: The diver needs to be mobile underwater. Streamlining dive gear will reduce drag and improve mobility. Personal mobility is enhanced by swimfins and Diver Propulsion Vehicles. (1) Controlling buoyancy underwater: Diver under the Salt Pier in Bonaire. To dive safely, divers must control their rate of descent and ascent in the water. Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether he ascends or descends. Equipment such as diving weighting systems, diving suits (wet, dry or semi-dry suits are used depending on the water temperature) and buoyancy compensators can be used to adjust the overall buoyancy. When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes gas consumption caused by swimming to maintain depth. The buoyancy force on the diver is the weight of the volume of the liquid that he and his equipment displace minus the weight of the diver and his equipment; if the result is positive, that force is upwards. The buoyancy of any object immersed in water is also affected by the density of the water. The density of fresh water is about 3% less than that of ocean water. Therefore, divers who are neutrally buoyant at one dive destination (e. g. a fresh water lake) will predictably be positively or negatively buoyant when using the same equipment at destinations with different water densities (e. g. a tropical coral reef). The removal ("ditching" or "shedding") of diver weighting systems can be used to reduce the diver's weight and cause a buoyant ascent in an emergency
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