NAUI Scuba Diver
20 Continual Improvement
or negative buoyancy easily. If you are over-weighted, it
is hard to keep your head above water at the surface or to
control your descents and ascents. To counterbalance the
excess weight, you will have to add greater amounts of air
to your BC underwater. You will not be able to streamline
your movement through the water because your weighted
waist and buoyant BC will position your body at an angle.
You will expend much more energy than necessary just
moving through the water. On the other hand, if you do
not have enough weight, it is a constant struggle to get
beneath the surface and stay at depth.
Individual buoyancy is affected by many factors,
both personal and equipment related. Muscle and bone
mass, wetsuit or dry suit buoyancy, cylinder material and
size, neoprene padding on weight belts, backpacks and
cummerbunds, all affect your buoyancy. Moreover, the
air cells in neoprene wetsuits compress due to increasing
pressure as you descend, and you must compensate
for this loss of volume by adding air to your BC. During
ascent, as your wetsuit and the air in your BC re-expand,
you will have to vent this air from your BC.
If you are properly weighted, you will be able to
achieve neutral buoyancy at depth with a minimal
amount of air in your BC, and you will be able to easily
maintain a horizontal position as you swim. You will
expend less energy, have greater control, and be able to
avoid stirring up silt (figure 2-8).
If your buoyancy is adjusted properly, you can use
the amount of air in your lungs to fine-tune your buoyancy.
Whether you breathe with your lungs fuller or
emptier can make a difference of as much as 3 kg (7 lbs)
in buoyancy, depending on lung volume. With practice,
very slight adjustments of your kick will control your trim
as you breathe and swim underwater. You will be able to
control your vertical motion in the water with breathing
control. Deeper breaths will slow your descent or actually
allow you to rise in the water column. Longer exhalations
will reduce your lung volume and allow you to descend
without effort.
Remember to perform a buoyancy check whenever
you change your equipment or exposure suit configuration.
A surface buoyancy check is an approximation. After
setting your weighting with a buoyancy check, you may
FIGURE 2-7. Fine tuned buoyancy control is the mark of a skilled
diver.
still need to make minor adjustments to your weighting
to dive comfortably.
The guiding principle in weight adjustment is to use
the minimum amount of weight that will enable you to
be neutrally buoyant with an empty BC during your safety
stop at 5 meters (15 feet). As you end the dive, the air in
your cylinder is depleted, and the cylinder will be significantly
more buoyant. The criterion for a surface buoy-