Or How to Hover Like Guru!
Part 1 – Shake the Lead Out!
We have all been there. You’ve made your pre-dive checks, jacket – check, lead weights – check, releases – check, air – check, final O.K and your in the water. The dive begins and, just like our instructor told us, you let just enough air out of the Buoyancy Control Device, breath out and slowly sink into azure underwater world to glide effortlessly among the fish.
The reality is more like, let the air out of the Blasted Crappy Device and stay glued to the surface, or even more dramatically, trigger a roller coaster ride of ups and downs, inflates, deflates, hard finning to get down or flapping like a demented butterfly just to stop from sinking. Forget protecting delicate underwater life, all you want to do is stop yourself from becoming an addition to Davey Jones’ locker!
So how do the pros make it all look so easy? Of all the skills that we learn in our PADI Open Water Course, buoyancy Control is the most dynamic. There are so many factors that affect your positioning in the water; your wetsuit, your weights, your lung volume, the water you are diving in, the amount of air in your tank, what your tank is made from and not forgetting that Blasted Crappy Device!
A Weighty Matter!
Let’s look at weights first. This is probably the most misunderstood item of equipment. The amount of weight you need is just enough to counter the buoyancy of you, your wetsuit, the water that you are diving in and your tank when it is down to about 50 bar. Anything extra will just make life so much more difficult. When you are correctly weighted you will be negatively buoyant at the beginning of the dive and neutrally buoyant at the end. There is no typical amount of weight and the lead that you had on your dive in the Cayman Islands in a 3 mm shorty will not be the same as those that you need doing retro hard hat dive off Grimsby docks!
How to get the right amount of lead!
So, how do you go about making sure you have the correct amount of weight? First of all, just before you make your descent do a buoyancy check. With all of your gear in place and your regulator in your mouth, hang motionless in the water. That means no kicking! Next let all the air out of your jacket and take a good breath in. You should now find that you are floating at eye level. Now breathe out and you should slowly start to sink. If you are still floating, add a kilo and repeat the check. If you sink like a stone, remove a kilo and repeat. Finally, add one or two kilos to take care of tank buoyancy at the end of your dive. If you are using a steel tank you don’t need this last step.
Next, have a think about what is happening on your dives. Floating around on the surface like a bobbing cork is the obvious sign that a couple of kilos extra would not go amiss, as is that exciting head down, arse up and legs kicking position while trying to do your safety stop,( though that could be to do with trapped air. More about wind problems in the next thrilling instalment!) However, if you find yourself dropping like an abandoned anchor, that would suggest a weight loss progamme would be beneficial.
Get rid of the pounds!
Another more subtle sign of overweighting is having to constantly add and release air from your BCD. It does not seem to matter what you do, as soon as you start to swim you lose control and start the porpoise ride all over again. The reason is simple. Excess kilos on your belt means more air in your BCD, so any change in depth will mean that this air expands or contracts a lot and this has a big effect on your buoyancy. The less air you have in your jacket then the less effect it has on you when you change depth. Get rid of the extra weights and you get rid of the extra air.
Next time you go diving, have a look at your divemaster’s weight belt and ask yourself, “How low can you go?”