|
Divers wear weighting systems, weight belts or weights, generally made of lead, to counteract the buoyancy of other diving equipment, such as diving suits and aluminium diving cylinders. The Scuba diver must be weighted so that he or she is negatively buoyant by default, and then adjust the amount of air in his or her Buoyancy Compensation Device (BCD) in order to achieve neutral or positive buoyancy as needed. The weights can be distributed to trim the diver to suit the purpose of the dive. Surface-supplied divers are often weighted even heavier, and may be unable to achieve neutral buoyancy, and rely on the diving stage, bell, umbilical or lifeline for returning to the surface. Free divers may also use weights to counteract buoyancy of a wetsuit. However, they are more likely to weight for neutral buoyancy at a specific depth, and their weighting must take into account not only the compression of the suit with depth, but also the compression of the air in their lungs, and the consequent loss of buoyancy. If the weights have a method of quick release, they can provide a useful rescue mechanism: they can be dropped in an emergency to provide instant increase in buoyancy which may return the diver to the surface. Dropping weights increases the risk of barotrauma and decompression sickness due to the possibility of an uncontrollable ascent to the surface. This risk can only be justified when the emergency is life-threatening or the risk of decompression sickness is small, as is the case in free diving and scuba diving when the dive is well short of the no-decompression limit for the depth. Often divers take great care to ensure the weights are not dropped accidentally, and heavily weighted divers may arrange their weights so subsets of the total weight can be dropped individually, allowing for a somewhat more controlled emergency ascent. The quantity of weight required is determined by the overall positive buoyancy of the fully equipped diver, which depends on the diver's body composition, buoyancy of other diving gear worn (especially the diving suit), water salinity, and water temperature. It normally is in the range of 2 kg / 4 pounds to 15 kg / 33 pounds. Additional weight may be carried by surface-supplied divers to provide stability when working on the bottom. The weights are generally made of lead because of its high density, reasonably low cost, ease of casting into suitable shapes, and resistance to corrosion. The lead can be cast in blocks, cast shapes with slots for straps, or shaped as pellets often named "shot". ==Types of weight== Part of the weighting system may be carried in such a way that it can be quickly and easily jettisoned by the diver to increase buoyancy, the rest is usually attached more securely. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「diving weighting system」の詳細全文を読む スポンサード リンク
|