30th. December 2013 – 12:30: Roll over Archimedes.

It’s quite simple in theory. According to Archimedes:

“Any object, wholly or partially immersed in a fluid, is buoyed up

by a force equal to the weight of the fluid displaced by the object.”

But before we can say "Eureka" and go diving it gets a bit more complex. Neutral buoyancy is not just about Archimedes’ principle alone because his physics only applies once the “body” either sinks fully to the bottom or is on the surface; which is exactly not where a diver wants to be.

So in fact for the object (the diver) to be neutrally buoyant, it has to be expressed as:

Mass x the force of gravity =  mass density of the fluid x volume displaced by the body actually in contact with the fluid  x the force of gravity = 0

Now if that’s not an eyeful then imaging what it must be like to try to control it in 9 metres of sea-water, little to no visibility and in the face of a current .

Down we went none-the-less. The focus on this dive was to concentrate on the one skill that we needed to control but would take a lifetime to master – neutral buoyancy. It was here that we saw yet again the value not just an instructor but that of a true master. The difference is that instructors teach the science of diving; masters take it to a whole new level where it is no longer a science but an art form. Even though I had seen it before, I watched the demonstration mesmerised and somewhat envious of how easy it all seemed.

Then it was my turn. With the memory of what I had just witnessed fresh in my head, I knelt on the sea-bed. Because of the weights I was carrying, I was negatively buoyant. I filled my lungs to capacity – nothing happened. I pumped a tiny bit of air into my BCD – nothing; a bit more – nothing. A tiny bit more and there it was: my knee lifted off the sea-bed. I filled my lungs to capacity. Too much, I was rising too fast. I exhaled and sank back down. A tiny bit more air in the BCD and shallower breathing did the trick. I got it to a point where I could control my rising and falling just by the amount that I was filling and emptying my lungs with. Mastering how much air you breathed in and out for the given conditions in order to remain suspended in the water; neither rising and falling is what the complex formula is all about.

The next step was to do the same thing but in the horizontal position. Enter, stage left, the fin pivot. Again a master stroke: my instructor noticed that with so much weight tied to my waist, it was almost impossible to remain horizontal as the weight was distributed unevenly. He instructed me to move the weights higher up to just below my rib-cage. Problem solved.

For a stroke of pure genius:  our instructor wanted to reinforce the fact that we did not need to keep fiddling with pumping air into or letting air out of the BCD to manage neutral buoyancy. You could achieve the same thing by breathing alone. After all, he told us on the surface, the lungs had a capacity of seven litres of air whereas the BCD, for the purposes of neutral buoyancy has just one.

To demonstrate the point, he exhaled, removed a weight that he had stored in his BCD and placed it on the sea-bed. Normally that would automatically result in positive buoyancy as soon as he breathed in. Quite the contrary; purely by controlling his breathing he remained perfectly neutrally buoyant. He then got us to do the same.  Initially, the moment I removed a weight, I started to rise. Soon however, I got the point. With shallower breathing I was able to not only maintain neutral buoyancy but also to rise and fall at will purely by controlling the amount of air that was going in and out of my lungs. The “secret” was that you should never have to fill your lungs to capacity just to get positively buoyant. Nor should you have to totally empty your lungs to go the other way. It is in shallower breathing that you ride the fine line that we know is neutrality.

What a moment that was and what was more, it was a very liberating experience. The dive became more enjoyable and closer to what the sport is all about when you did not have to concern yourself with the technology.

Once we were back on the surface, we practiced removal and replacement of the BCD and everything attached to it and then it was back on the boat for the last time in the course.

Here’s the Dive profile for the day: