Well not really wind but trapped air. Similar really and pretty problematic! No one wants trapped air! Last month the mystical Art of Buoyancy Control was looking at the sinky bits. This month we are looking at the floaty bits, so let’s start by having a look at the main floaty bit. The BCD.
BCD also known as a Stab Jacket!
The BCD is your main way of changing your state of buoyancy. Remember back to those Open Water lessons? Positively Buoyant, good for hanging loose on the surface and having pre and post dive chats. Negatively Buoyant, the way to go down…. And then that mystical state. Neutrally Buoyant, the condition your dive guide seems to attain with no visible effort while you are still using the inflator hose like a demented bag pipe strangler!
The thing to remember about air is that it loves to float. So it will always rise to the highest point (the point closest to the surface) of your BCD. This means that air can get trapped in all sorts of silly nooks and crannies. BCD manufacturers have recognised this and have put dump valves and the deflator hose in appropriate places.
Getting Rid of Wind.
The standard way releasing air from the jacket is to raise the deflator hose and the left shoulder so it becomes the point closest to the surface and then let out the air. Sometimes water has got into this hose so keep the deflator button depressed until you see or hear the air coming out. This can take a few seconds. If you are swimming horizontally, roll so that you left hand side is upmost and point the deflator toward the surface.
What about dumps? Most BCDs now have dump valves on the right shoulder and the right lower corner of the jacket. These are quick ways of getting that air out and loose buoyancy. If you want to dump then you must make sure that the valve is at the high point, i.e. closest to the surface. I have seen a number of divers attempting to use the bottom dump valve when in a head up position. The only way you can use this valve is in a head down position as when you are duck diving.
Trapped air? Yes this can happen but it is minimised by having a correctly fitting jacket with all the buckles and clips correctly adjusted and clipped up. This keeps the BCD in the best position for air to easily find its way out. The best way of getting rid of trapped air is to get your body into a head up position. Raise the deflator, left shoulder high and be patient. Squeezing the BCD with your elbows will not do much except make you look like you are doing the funky chicken at some strange northern night club!
So you’ve successfully descended, you have the right weights and your trapped wind problems are sorted. How do you get the buoyancy just right? The secret is in the word adjustment. With the right amount of weight on, it should not take that much air in your BCD to become neutral.
As you descend, add small amounts of air every five metres or so. That will compensate for the compression of the air still in your BCD. While you are still getting to grips with it, get upright, find a visual reference, a bit of reef, a point on the shot or anchor line, but please, not a fish!
With this reference keep adding small amounts of air until you can stay level with your reference. Remember….keep breathing! If you find yourself floating up, let out small amounts of air and breath out all the way. Don’t dump all of the air unless you are imitating a Polaris missile. If you do you will have to start the process all over again. Also remember that it takes time for the adjustments to take effect, inertia is a very powerful force and with all of your gear on you have a mass of around 100 kilos, so adding half a kilo of lift is not a big force. So be patient. Make your changes and then wait a few breaths.
Contraction and expansion.
As you go deeper you will need to add air to your jacket. There are other floaty bits that start to affect things at this stage but more of that in the next thrilling blog!
So you have plunged the depths and are now heading away from the wonders of the deep. As you head up, all that air that you put into the BCD will start to expand as the pressure around you gets less. It is important to release a little bit of that air as you come up. As a starting point, make your ascent the same way as you went down, five metres at a time and then adjust your buoyancy again. You will soon get into the habit of automatically adding or letting air out of the jacket as you head down or go up.
From this point on it is practice makes perfect.
Next month we will look at your other floaty bits and get you in trim!