This is possibly one of the most asked questions of new divers. When you are learning to dive you wonder how your instructor can use a smaller cylinder and still only use fifty bar whilst you suck your cylinder dry with the speed of a vacuum cleaner. In this post I will share some of the best advice of do's and don'ts of twenty years of diving experience to extend your bottom time. So how can you slow down how quickly you consume the air from your tank?
'Skip Breathing' You may have heard this term, but it's doubtful if it achieves your aim to reduce air consumption and is definitely not recommended. Essentially you try to breathe every other breath. However it has the flaw of meaning that in the time between breaths chances are you are holding your breath, a real bad idea as we all know. If you do manage to achieve it without holding your breath, then the chances are the next breath after the missed one is bigger than normal probably using as much air as two normal breaths would take.
How to reduce air consumption There are several elements to reducing your air consumption none of which you can normally force:
1. First is your body position, you need to be flat in the water, horizontal, so your profile as you fin through the water is minimised. This reduces drag and as such the amount of effort you have to put into moving yourself. With your muscles working less, the demand for oxygen is less and therefore your breathing rate will be less.
2. Secondly as your instructor will have highlighted during your initial diver training trimming your buoyancy so you are neutrally buoyant is important. If you are overweighted (as in your dive weights not your physique) and not correctly trimmed you will be constantly swimming at a slightly upwards angle to compensate for the weights pulling you down.
3. I would also say from personal experience that a good regulator can help hugely. When I first learned to dive my first regulator was a Conshelf SE2, which was a great shallow water regulator but the equivalent to sucking a very cold McDonalds milkshake through a straw below 20m, virtually impossible. An upgrade to Mares Voltrex (possibly my most loved regulator ever) and wow, I could breath at depth with ease. A further upgrade to a Scubapro Mk20 G500 and the regulator was virtually throwing air into my lungs. The point here is the better the regulator, the lower my air consumption because you don't need to work at breathing.
4. Take deep slow breaths, you want each inhalation and exhalation to move as much fresh and expelled air as possible (this is your lungs tidal volume). If you shallow breathe this causes old air to remain in the bottom of your lungs and reduce the amount of fresh air in your lungs, which increases the amount of carbon dioxide (which is the trigger for the urge to breathe) and reduces the amount of oxygen. Occasionally panicking student complain of not being able to breath properly, normally incorrectly citing the pressure of the water against their rib cage but it is in fact not flushing the lungs with proper breathing control.
5. Experience. Unfortunately not an easy thing to fix quickly. In point 3 I mentioned as I upgraded my regulators my air consumption dropped. However there could have been another variable at play, each time I changed I had logged significantly more dives each time. The more time you spend underwater the more confident and relaxed you become. Neither of these two qualities should lead to complacency or arrogance underwater, both of which are likely to cause accidents.
Possibly the most important element in my opinion is relaxing. It is closely linked to point four, but as you relax you will find your air consumption drops significantly. You will probably also discover as you become more comfortable in the water, the amount of lead weight you need to carry will reduce. Amazingly new divers bodies despite what they may think really don't want to sink, it's quite a leap of faith to convince your body it is a good idea to sink below the surface despite all the dive gear.
I hope you have found this post useful, if you have any advice or comments please post it here on the blog so people can read them in the future.