I often get the mistaken call enquiring how to get a driving license.
SCUBA Diving is actually very much like DRIVING A CAR: put your car on the road (buoyancy), load it with fuel (breathe), and drive around (dive).
This week we talk about BUOYANCY CONTROL. Without buoyancy control you are nowhere as a diver. Either you are (going) up (= POSITIVE buoyancy) or (going) down (= NEGATIVE buoyancy). The aim of every diver is to know just how much air to put into that jacket (or buoyancy control device ie BCD) to maintain NEUTRAL buoyancy and keep yourself at a certain depth (on the road).
The first thing we teach you is to study your BUOYANCY CONTROL DEVICE or Jacket, know all its parts, and how to Control your Buoyancy (how to use the inflator and deflator button).
Pressing the INFLATOR BUTTON to get some extra air in the jacket, is an easy one. You press and air will come. The trick is twofold: how often and how long do I press. You press once, wait for a few seconds, to allow the change in air volume to take effect on your buoyancy, and see what happens. If you are still sinking you repeat the process. Patience is the key here: divers who inflate too often or too long will always rise, it is important for you to give short little inputs and wait. Once you get the right amount of air you are set to dive at that depth.
Moreover I feel it is important to correct for negative buoyancy when you already are in a HORIZONTAL DIVING POSITION (to stay at your preferred depth). Your horizontal position together with the extra amount of air you put into the BCD allow both for a correction towards neutral buoyancy. First you go horizontal (first correction for negative buoyancy), then you inflate (second correction) to go neutral; a lot of students who do it the other way around tend to over inflate, and float back up after coming horizontal.
DEFLATING your BCD to let some air out and go down is technically a bit more difficult as it requires a lot of VERTICAL POSITIONING! When I teach deflation (negative buoyancy) I always tell:
1) Make sure you are in an UPRIGHT (upper) BODY POSITION (so that the air in your jacket can flow upwards). Maintaining a horizontal dive position will not help as the air has no incentive to flow out of your jacket (once you press the deflator button).
2) Make sure your DEFLATOR HOSE is UPRIGHT and fully stretched out (so the air can stream out of the hose). An obstruction or bend in the hose will again slow down the exit of air.
3) Make sure you PRESS the DEFLATOR BUTTON and LOOK up, so you actually allow the air to stream out (open the door) and see the bubbles coming out (a confirmation that you are actually deflating).
4) Finally you do this all when you are vertical WITHOUT you MOVING OR KICKING YOUR FINS. If at the time of vertical deflation you are still kicking the only way you are going is up and you want to descent!
If you do all of the 4 above points correctly for negative buoyancy but you are not coming down, you will have to correct with your BREATHING. Either you are holding your breath, or are not breathing out enough to give you that initial drive down. (PS, if you are still not coming down after deflation and breathing out, it means you require some extra weight!). Please do not forget to EQUALIZE your ears on the way down.
Of course there is always the possibility of using your DUMP VALVES although I am not an advocate of this. The level of buoyancy control is far less than when you use the deflator button, and reaching technical perfection in buoyancy control is paramount to become safe and comfortable diver.
Diving is PRESSURE, and the pressure CHANGES at every DEPTH, which in turn will have an effect on your BUOYANCY. If we are descending the pressure increases which in turn will compress the air in our jacket. This means that at deeper depth we sometimes need to put a bit more air, than at shallower depth, to stay neutrally buoyant. When we go back up, and the surrounding pressure reduces, the air in the jacket will expand, thus giving us a bit more positive buoyancy. Whenever you ascend, always be ready to release a bit of air to maintain your neutral buoyancy (or not go up too fast).
Once you are neutrally buoyant with the jacket (gross buoyancy), and want to maintain that perfect depth, the fine tuning of your buoyancy happens through your breath (fine buoyancy). Breathing I will explain in the next wisdom session.
Buoyancy control is an easy one: PATIENCE, PERSEVERANCE, BODY POSITIONING and TECHNICAL UNDERSTANDING of how to inflate / deflate your BCD will get you where you exactly want to be.
Oh ja once you reach back to the surface after a beautiful dive is actually the only time you really push hard on this inflator button to fill the whole jacket with air, so you stay afloat and relaxed.