Buoyancy

Buoyancy & Descents

PADI teaches divers to dive safely. They teach buoyancy by using the fin pivot skill and the hover. This should be enough to get a feel for buoyancy. But their only real guidelines are to add air to your BCD as you descend and to release air from the BCD as you ascend.

Is that it? Is that the only guidance an instructor can give?

The first thing to do is to get your weighting right. PADI teach this with the Buoyancy check.

If your weighting is wrong you will struggle. Too much weight and you will sink rapidly and need to add a lot of air to your BCD to compensate. This means more air to compress as you descend to greater pressure and more air to expand as you ascend to lesser pressure. You will need to make more adjustments as you go. If you aren't aware of the need to adjust until you are moving quickly up or down you will find yourself constantly battling.

A good sign of someone being overweighted is seeing their legs hanging down behind them while diving. Being correctly weighted makes it easy to lay down flat underwater. Any extra weight pulls the legs down, while the air needed to maintain neutral buoyancy pulls the chest up. Worse, if the BCD does not have enough air then the diver has constantly to kick to stop from sinking. When they add air to become neutral they may find that they swim upwards as much as forwards. They then dump air to stop from rising upwards and can get locked in a cycle of adding air and rising upwards before dumping it again. Waving hands are another sign of the need to add air to the BCD. The brain may not have realised you are sinking, but the hands know to tread water just as they would on the surface.

Let's make a quick recap about buoyancy. It's a simple thing to understand. If we took a mould of you and your equipment and filled it with water we would compare the weight of the water with you and your equipment. If the water weighs more you will float. If you weigh more you will sink. If you are the same you will neither sink nor rise - you are neutrally buoyant. We add weights that are heavy, but small, to adjust our weight without adjusting our size, to help us sink. We add air to change our size, but minimally change our weight, to be more buoyant.

Let's assume you have done a weight check and have the right amount of weights. You should actually have slightly more than you need to descend as you are making allowances for the tank weighing less at the end of the dive. (Yes, the air in the tank weighs something and as you breathe it the tank gets lighter.) You now swim out to an area that is too deep to stand and are ready to descend.

S - Signal to your buddy that you are ready to descend

O - Orient or Observe. Check where you are by looking at what is beneath you and for landmarks for navigation.

R - Regulator. Swap you snorkel for your regulator. Always blow into the reg before taking a breath

T - Time. Check the time we are starting the dive

E - Elevate your BCD hose. Expel the air from your BCD. Exhale. Equalise

D - Descend

Hold the deflator hose high with your left shoulder raised so that it is the highest point. If you are relaxed, and not holding air in the bottom of your lungs, you should drop under the surface. Empty your lungs. Imagine you are deflating yourself. Relax your muscles. A tense body is less likely to sink. Being in an upright position helps you to cut through the water. If you can't resist your legs kicking then fold them under you. If you fall backwards allow it to happen. Your land reflexes will tell you to catch yourself, but it is simpler to let it happen and then roll over - welcome to moving in 3D. Once you have the inflator hose almost completely underwater you can stop deflating as you are already descending. Equalise. If you are upright then lean forwards and pull your legs up and then push them out behind you.

Get a visual reference. How do you know if you are sinking down or rising up unless you have something to compare yourself to? The closer the visual reference the more helpful it is. This is one reason why descending with a line is such a good idea. A dive computer is invaluable here as it will tell you to a 1/10th of a metre what your depth is.

Unless you are experienced, you will find yourself still dropping as you are negatively buoyant from the descent. So add a small burst of air to your BCD. Check what effect it has had. Remember from doing the fin pivot that it doesn't have an immediate effect. If you need to speed the process up you can take a deeper breath and use your lungs to help you adjust.

We want to breath normally. If we are neutrally buoyant yet needing to take a deep breath then the simple solution is to add a little air to the BCD and go back to breathing normally. Always add a little air and give it a chance to have effect. You can always add a little more if it isn't enough. Try not to add too much and then trying to release air as you will end up constantly trying to catch neutral buoyancy. Remember, make small changes.

The more neoprene you have the more material there is to be squashed and expanded and the more often you will need to adjust your buoyancy. It's always easier when the water is warm and you need less wetsuit to cover you.

If you need to dump a little air you need the deflator to be at the highest point. Arching your back lifting the hose upwards (not forwards) and tipping so your left shoulder is higher up should be enough to have the air rise towards the deflator. Again, make small adjustments. Look at the end of the hose to see the air coming out. This will help you gauge how much you have released. If you see that you are not letting any air out you can try adjusting your position to try and shift the air out. If the BCD is empty there is no point holding the hose open as you are only letting water in.

Find a visual reference - reef wall, line or the bottom - that is close to you and stop moving. Watch to see if you are stationary. If you are going up or down make an adjustment to your BCD and check again. By doing this throughout the dive you can keep yourself neutral before a problem arises. Be aware of sloping bottom formations as you may think you are keeping level when you are actually changing depth. This is where your SPG comes in very handy - as well as making sure you are not breaking your max depth. - or better still, a dive computer.

If you have realised too late that you are floating up and are moving quickly, you should dump a lot of air. Arch your back and lift the left shoulder. Get upright so the dump is at the highest point. Then you treat it like a descent. Get a visual reference if you can (may not be easy in midwater). As you drop you will need to add air to the BCD and to equalise your ears. You can slow the descent by laying down, rather than staying upright. Still make small changes unless you are dropping quickly.

Try to establish a connection between your ears needing popping (equalising) and your BCD needing more air (equalising). One should remind you of the other. As you descend to greater pressure the air in the BCD is compressed - you take up less space in the water and become more and more negatively buoyant. You add air to get the BCD back to the size that makes you neutral. The ears have a similar need. They are squeezed by the pressure and you add air by equalising to get them back to their comfortable size. You may find that the need to equalise indicates the need to add air to the BCD. Or maybe your ears are more sensitive and it is every other equalisation that indicates the need for air in the BCD.

Swim slowly with minimal movement as this will stop your speed and movement from treading water. If you are always moving you can't tell if your buoyancy is correct. Stop moving and see if you sink or rise and then make a small adjustment. You will also save air as your demand for breath will be less.

Remember to breathe normally so that you can use your lungs to help you rise or fall. If you want to swim over a coral then take a slow, deep breath to get you to rise up. If you are neutral you will rise up like with the fin pivot (but without leaving your fins on the bottom). To drop down you empty everything from your lungs, not just a normal exhale but a full exhale.

For an ascent

S - Signal you are ready to ascend

T - Take the time of the end of the dive. Bottom time for the RDP is when you are ready to ascend to the surface or your safety stop

E - Elevate the hose. Get ready to release air from the BCD

L - Lift your right arm to protect yourself

L - Look where you are going

A - Ascend. Start going up by taking a long deep breath or kicking upwards. Do not add air to the BCD.

R - Rotate so you can see all around you and don't have a blind spot.

As you start to ascend you will need to have your deflator hose up and ready to deflate the BCD. Make sure the left shoulder is the highest point so the air will flow upwards towards it. Vent little bits of air as you feel yourself being pulled upwards. If you dump too much you can always fin upwards. What you really want to avoid is a speedy ascent. As you improve you will find you can allow positive buoyancy to lift you up and you control the rate of ascent by releasing air and slowing yourself down. A visual reference is very important at this point - a computer is even better - for checking your ascent rate.

Once on the surface you inflate the BCD and get yourself positively buoyant. This is the first step before you take your reg out or take your mask off. You should be able to rest on the BCD and not have to fin or kick to stay up.

I hope this helps to refresh anyone reading that is about to go diving again and maybe helps you pick up a trick or two that you missed while taking in so much on your Open Water course. For me it is all down to the descent. If you crack that part the rest just follows.