BUOYANCY

If you’re a diver, you’ll know about positive, negative and, the Holy Grail of Diving, neutral buoyancy. “The power to float or rise in a fluid; relative lightness”, is dictionary.com’s primary description of the word buoyancy. For the non-divers, a object that floats on the surface of a body of water (such as a beach ball) is considered to have a positive buoyancy, whereas an object that sinks in water is considered to have negative buoyancy, and an object that neither floats nor sinks, you guessed it, has neutral buoyancy. While all three states of buoyancy are of interest to divers (as well as anyone on a sinking ship), positive and, in particular, neutral buoyancy are the two more pertinent states for divers.
POSITIVE BUOYANCY Divers use positive buoyancy so they can rest at the surface without expending energy doing so. They do so by adding air to their BCDs (Buoyancy Control Device) until they attain positive buoyancy and then just float on the surface. At the end of a dive and ONCE on the surface, a diver will then again inflate their BCDs so they can rest on the surface while awaiting their boat to pick them up.

NEGATIVE BUOYANCY BCDs, wetsuits and people are, in general, positively buoyant. Divers offset these factors by adding weight (usually in the form of lead blocks) to their equipment setup. They can do this via several methods but the most common versions are a belt with weights attached or a BCD that allows you to stow the weights in pouches which in turn are stowed in the BCD. It doesn’t matter which method is used to weight yourself, per se, they all do the same thing – make you heavy so you can sink.

NEUTRAL BUOYANCY The most important buoyancy state for a diver is “neutral buoyancy”, i.e. the diver neither rises nor sinks in the water but maintains a constant depth. Why is neutral buoyancy so important? There are several reasons:

• It is easier to move underwater when neutrally buoyant so, all things being equal, you’ll use less energy and air. Take a look at the two James Bond movies Thunderball (1965) and The Spy Who Loved Me (1977). Both films feature underwater action scenes, and both films were made before the advent of the modern BCD. Watch the divers, they have no way to control they buoyancy except by pointing themselves in their desired direction and kicking, and kicking, and kicking, and kicking, and kicking … they make me feel tired just watching them.
• Being neutrally buoyant allows you a greater view angle of the reef.
• It minimizes damage to the environment. If you have no buoyancy control you’ll likely to hit the reef either bodily – i.e. you literally crash in to the reef – or with your fins, neither of which are good for the habitat.
• If you’re neutrally buoyant, your equipment should not get damaged because you are not crashing in to the reef.

BCDs AND BUOYANCY
Divers mainly control their buoyancy via their BCDs. A BCD is basically a watertight bladder that we wear and can add air to or release from. It is the mainstay in obtaining our desired state of buoyancy. Air always rises to the highest point … huh? What the hell does that mean and what has that got to do with diving? Think of a half empty bottle of water (or, if you prefer, a half full bottle). Picture the bottle of water doing nothing but standing on a table. Notice how all the water is in the bottom half of the bottle and the air is in the top half? Okay, now take the bottle of water and invert it (i.e. turn it upside down) and, unless the laws of physics and hydrodynamics have gone on vacation, the water is still in the lower part of the bottle (even though that is the “top” of the bottle) and the air is still in the upper part of the bottle (even though that is the “bottom” of the bottle). Finally, lay the bottle on its side (making sure it doesn’t roll off your imaginary table) and again you find the water in the lower half portion of the bottle and the air is in the upper portion. The air constantly moves to the highest point. The same rules apply to the air in a divers BCD. If the diver is in an upright position, any air in the diver’s BCD would be at the top. If the diver was inverted, all the air would be in the bottom of their BCD, and finally, if the diver was horizontal all the air would be across the back of the BCD. Fortunately, modern BCDs have several dump valves to allow a diver to release air regardless of the diver’s body position in the water. Unfortunately a lot of divers during courses are only shown how to add or release air via the BCDs low pressure inflator (LPI), yet most modern BCDs come with 3 separate air release valves (or dumps). Most BCDs have a dump valve on their right shoulder, which you’d use when you can’t use your LPI (possibly because your left hand is holding some sunken treasure you’ve uncovered on your dive). And most modern BCDs have a kidney dump valve, located on the rear of your BCD, which you’d use when in an inverted position. You should take time when diving to practice using all your BCDs dump valves so that using them, and using the appropriate one, become second nature.

PRACTISE MAKES PERFECT
 It’s not only using your BCDs dump valves that you should practice, but buoyancy skills in general. Some simple and cheap ways to practice and/or improve your buoyancy are:

• Safety stops. Perfect for fine tuning your buoyancy. Watch your depth gauge or, more probably, your dive computer, and see if there is any fluctuation in your depth. If there is you may want to add or release a bit of air from your BCD, or add or subtract a kilo or two.
• There are numerous games you and your dive buddies can play underwater that are fun and help you improve your neutral buoyancy control. One of the most common ones is Leapfrog. Get your dive group to form a single line in front of you with approximately 4 meters between each diver. The first diver raises their arms to form a “Y”, the second diver spreads their legs (Oh, missus!) to form an inverted “Y”, the third raises their arms etc. etc. The aim of the game is, after you’ve established positive buoyancy, to swim over and under each diver using just your lungs to fine control your buoyancy. If you are neutrally buoyant, when you inhale you will rise slightly and, when you exhale, you will sink slightly.
• The Hover. One of the skills introduced in PADI’s Open Water Diver course is the Hover. In this exercise, a diver is required to hover mid-water using just their BCDs and lungs (without using their hands or fins). It’s a simple skill to practice and doesn’t require any special equipment.
• The same for forward and backwards rolls. Hopefully by now you understand that when an object is neutrally buoyant it neither rises nor sinks. An easy way to see how far or close you are to achieving neutral buoyancy is to hover while neutrally buoyant in a horizontal position and then perform a backward or forward roll (use your hands, aka doggie style, to propel yourself around). Once you’ve completed a 360 degree turn you should still be at the same depth.
• Finally, the Wall Walk. In a swimming pool, remove your fins, and place both your feet against one of the walls. Add a little air to your BCD until you are neutrally buoyant and then try to walk up the wall (don’t forget to release a little bit of air as you go). It’s can be rather tricky, certainly infuriating, but it’s great fun and a great way to perfect your buoyancy

There are also various diving courses that help you to improve your buoyancy, Peak Performance Buoyancy (PADI) and Perfect Buoyancy (SSI) being but two of them. Ask your LDC for information about buoyancy courses if you think it would be of a benefit to you.