Lid28 januari 2005 om 10:53
WHY DO I BREATHE SO HEAVILY?
Factors governing a diver’s air consumption fall into three categories:
Physical: Basic diver training teaches us Boyle’s law, that the volume of a gas is inversely proportional to pressure. The deeper we go, the more gas each breath will take from a diving cylinder.
Physiological: If we swim hard or work under water, we breathe more, because our bodies metabolise food and oxygen to produce energy. The harder we work, the more energy we need, the more oxygen we need to provide that energy, and the more air we need to breathe. We also require energy to keep our bodies warm, so a cold diver will breathe harder.
Psychological: Worried or nervous divers get through their air more rapidly because they breathe faster than necessary.
HOW TO LOWER YOUR RMV
Whatever you do, don’t try to save air by breath-holding or deliberately breathing shallowly. At best you will surface with a headache, but you could end up with a burst lung or worse. The way to use less air is to tackle the problem, not its symptoms.
Buoyancy control: This might seem like a topic for novices, but the buoyancy control of many “experienced” divers is less than perfect. A buoyant diver will be swimming down all the time. A heavy diver will have to swim upwards or bounce along the bottom, reducing the visibility for everyone else or damaging the marine life. Maintaining neutral buoyancy throughout a dive avoids unnecessary effort, improves comfort, and reduces RMV.
Over-weighting: An overweighted diver will have to put extra air into a BC or drysuit to maintain neutral buoyancy. By itself, this is insignificant compared to the amount of gas a diver breathes, but it will have a bad effect on your position in the water, tending to turn you upright. Swimming requires greater effort due to the unnatural angle in the water and increased water resistance, with a consequent increase in RMV.
Finning: Poor finning technique such as a bicycle kick wastes effort and increases RMV. It can be difficult to spot problems in your own finning technique, so ask your buddy to keep an eye on it and give you some feedback; you might be surprised at the results. Efficient finning uses strong, gentle strokes of the whole leg, taking each kick through to completion.
Equipment: Think about the gear you carry and how it is adjusted. A poorly adjusted regulator with a high breathing resistance will require extra effort just to breathe, again increasing RMV. A loose weightbelt will often rotate round a diver’s waist, pulling you off balance, making the dive uncomfortable and causing you to expend effort to compensate. It can also slip downwards, pulling you upright and making swimming more difficult. In both cases the consequence will be increased RMV, not just from the effort, but because a diver will feel generally awkward and uncomfortable. Any loose, badly sized or poorly adjusted equipment can have a similar effect, pulling a diver off balance or making control difficult. And having the right diving suit for the water temperature will also help to reduce RMV, because a cold diver breathes more.
Overall, be comfortable and happy in the water. Become familiar with your equipment. Learn to move gracefully and economically, with good buoyancy control and finning technique. Once these factors are under control your RMV will take care of itself. A low RMV is a Zen thing.