Underwater World is the Philadelphia Region's Premier Scuba Shop and Training Facility!
|
495 Easton Rd - Route 611 - Horsham PA 19044 - (215) 672-4180 STORE HOURS: Monday - Friday 1:00 - 9:00 · Saturday 10:00 - 6:00
SCUBA DIVING SAFETY
Click here for more informative Underwater World articles Buoyancy Control - The Keystone of Good Diving
I have long taught my students that there are two things that
separate good
divers from the pack. That is
buoyancy control and dive planning.
And there is
more to both of them than you think. Read on and then gather up
your gear and
go out and practice because if the last time you practiced buoyancy control
was during your basic course, I can assure you that your buoyancy control
leaves a lot to be desired.
Three Buoyancy Compensators (BC's)
to better buoyancy control.
That's right, three bcs. First of all, there is your buoyancy
compensator,
which is what most people think about when we talk buoyancy.
But there are
two other bcs, Breath Control and Body Control. Let's take
them in that order.
Your Buoyancy Compensator
The buoyancy compensator is used for gross changes in buoyancy. These changes
take place due to wet suit compression, compression of air in our bc, and
changes in the weight of our tank as we use up our air. There are a few
things that are important to remember about our bc. First of all it is not an
elevator,! We do not use our bc to bring us to the surface and allow us to
sink. We use our bc to maintain neutral buoyancy at all times. This is a very
important concept. Let's look at the proper use of a bc during a dive.
You add a little air to your bc prior to entering the water. This assures
that after hitting the water, you return to the surface immediately. This
allows you to make sure your mask strap is still in place, your weight belt
is not sliding down, and you are with your buddy. It also allows you to
signal the boat crew that you are ok. (Admittedly, some very experienced
divers enter the water with no air in their bc and commence their descent
immediately. But these are very experienced divers.) To start your descent,
you should let all the air out of your bc and then using either a line or a
surface dive, begin your dive. I prefer to swim downward on a slight angle,
clearing my ears as I go. Remember, if you are descending feet first, the
greatest drag created is by your fins. This will usually cause you to lean
backwards and you will find yourself descending butt first! At this point you
are actually falling through the water. If you can not clear your ears, it is
difficult to stop your descent immediately. If you are swimming down, all you
need to do is level off to stop the descent. Now, as you continue your
descent, you need to add air to your bc to maintain neutral buoyancy or at
least be close to neutral. Do not wait until you reach the bottom to start
adding air. If you do that, then you need to add a lot of air to get it
right. If you make big changes, then you can make big mistakes. Make small
changes and you will only make small errors that are easier to correct.
Throughout your dive you will need to make changes as you change depths or as
your tank gets lighter due to air consumption.
At the end of the dive, as you start your ascent, you must start letting some
air out of your bc in order to maintain neutral buoyancy during the ascent.
If you do not, the air in your bc will start to expand, your wetsuit will
start to recover from its compression, and you will start to be carried to
the surface by your buoyancy. This is not buoyancy control. If all of a
sudden a boat motor starts or a boat starts to approach the area, you can not
stop your ascent easily. If you were neutrally buoyant, you would stop where
you stopped kicking. That is a controlled ascent.
It is also important that you know your bc. If you want to learn more about
bcs, look at our equipment section for the piece I wrote on bcs.
The bottom line is: you let all your air out to start your descent, then you
add air as your descent continues. As you ascend you let air out until you
reach the surface, then you add air to keep you afloat at the surface. Got
that?
Our second "BC" is body control. Understand that your body wants to go in the
direction that the top of your head is pointed. If your point your head up,
your body goes up, if you point your head down, your body goes down. That
said, let's explore body control.
Newton's Second Law states that "For every reaction, there is a direct and
opposite reaction." First of all note that Newton said for "every" action.
That means if you are at the surface and have let the air out of your bc and
you expect to sink, that the best way to do that is not feet first. That is
because every move you make tends to push you back to the surface. If you
just move your legs to balance yourself, that action has an opposite reaction
(pushing you up). If you move your hands through the water, there is an
opposite reaction to that action. Your best bet is to do a surface dive and
then the movement of your fins pushes you downward.
Remember as a kid, holding your hand out the car window to ride the air
waves". Tilt your hand up and it goes up, tilt your hand down and it goes
down. Your body acts like that in the water. If your are swimming along and
you tilt your head up, your body goes up. Therefore your body must be
parallel to a depth if you expect to remain at that depth. The problem comes
in the way we where our equipment. If we are wearing our weight belt around
our waist, it is really in the wrong place. We should be wearing it around
the center of buoyancy. For most of us that is probably 8 - 10 inches above
our waist. Of course, it is not practical to wear a weight belt there so we
wear it lower. But that pulls our legs down, which means our head is pointed
upward and we go up. How do we deal with that? We add more weight! And our
legs sink even more. We made the problem worse. This circle continues until
we have add so much weight that no matter where our head is pointed, we are
not going up! And now when we get to the bottom we need to add that much more
air to our bc to compensate for this excess weight. Of course, that air goes
around the top half of our body and compounds the problem. Our body control
is not under control. At this point we are now pushing our body through the
water on an angle and not in a streamlined head-first position and we are
pushing our bc through the water half full of air. Try pushing an empty bc
through the water and try pushing a bc full of air through the water and see
the difference. So the amount of weight that you use corresponds to your body
position as you push it through the water.
Notice the way a shark swims as it moves through the water. It is propelled
by its tail (as we are propelled by our fins). When he wants to turn, he
draws in a pectoral inward tilting his body in the direction of the turn. He
then arches his back and glides through the turn. You can do the same thing.
You want to turn? Drop one shoulder, arch your back, continue to kick and
watch your body go through the turn. Your hands never leave your side. It is
like flying. Practice it and you will be amazed at how effortless it is.
We all know that every time we inhale we go up and every time we exhale we go
down. So it must have some effect on our buoyancy. It definitely does. We can
use that effect to our advantage.
When someone realizes that they are too buoyant, the first thing they do is
reach for their inflator hose and bring it up above their head to dump air.
Two other things happen at the same time. By going into a head-up position,
they proceed to move even shallower and, secondly, they are now pointed in a
position to move them even shallower yet. What they should have done is
quickly exhale and held that breath out. Yes, I did say hold your breath, but
I said hold it "out." By exhaling you quickly get rid of several pounds of
buoyancy. That buys you little time to get a hold of you inflator hose and
dump some air. Remember, you don't need to dump it all, just a little. You
should just be a little off. Also, make sure that you use the rapid exhaust
at the top of your inflator hose or the dump on the back of your bc to do
this. If you are not sure how these work, talk to one of our staff and they
will demonstrate it for you.
So, you can see that you can use breath control to your advantage.
The bottom line is that proper buoyancy control takes all three of these
methods. And proper buoyancy control is not something that just happens. If
you think that someday it will just come to you, look in your Day-timer.
Someday is not there. But if you practice these techniques, take an advanced
course, think about how your movements and prescence in the water translates,
and you work on buoyancy for the next 25 dives that you do, you will never
have to think about it again. And you will be part of that group of divers
that every one admires because you make it look so easy. Go for it.
You -- Your Knowledge and Your Physical Condition
Your Equipment
Where Are We Going?
The Day Before
The Dive - Finally
The Missing Link
See, you have to read on to what the missing link is. Well, it is the one action that nobody takes in dive planning - the debriefing.
If you don't talk about what happened you will see the same problems come back to haunt you again and again. Discuss those
problems even if they are minor. it will prevent them from growing.
As you can see, the bottom line is that if you only spend a few minutes planning a dive, you are compromising the safety, fun
and comaraderie of diving. So get your diving planning act together.
|