Creating
Ideal Buoyancy
The idea of Ideal Buoyancy is
one not commonly understood very well. Too many divers, of all certification
levels, act as if staying off the bottom and under the top equates to
good buoyancy. If you feel that way ... read on!
Ideal buoyancy is characterized by
a diver who moments after he takes a normal SCUBA breath rises a bit in
the water column. Moments after exhaling, he descends back to
where he was. The idea that a "neutrally" buoyant diver stays in the
same place is not only wrong, it also makes it very difficult to
learn ideal buoyancy. In fact, let's dispel the idea of
"Neutral Buoyancy" and take it out of
our vocabulary altogether.
A diver with "Ideal Buoyancy" does move
up and down in the water. Period! An object with neutral buoyancy
cannot have expanding gasses in it without a fluid or dynamic counter balance.
The fact that we breathe gas that expands in our air ways, and then exhale it
means, that in a practical sense we will never be neutrally
buoyant. So why try to get there?
If you could diagram a diver swimming with
ideal buoyancy his path would look like a gentle sine wave. With each crest
being proceeded by an exhalation and each valley being preceded by an
inhalation. Something like this:
The delay from breath to crest or
valley is the time it takes for the new buoyancy force to have effect.
So how do you get there? It is really
pretty easy.
Here is what you will need:
- An empty (500 PSI or where ever
you would normally end your dive) SCUBA cylinder. The same size and make
up you will be diving with. i.e. an aluminium 80 or maybe a steel 72.
- Your full SCUBA kit that you
will be wearing while diving.
- Water...not to drink, the water
you will be diving in. The depth does not need to be much deeper than you
are tall. Remember a salt water pool does not normally have the same
salinity at the oceans and seas.
- Weights: preferably including
several one and two pound weights.
- Integrated weight pockets.
(If you own a weight belt, please use it for something other than
SCUBA diving.)
- A dive buddy in full gear,
including an alternate air source and a full tank of air.
The
Process
1) Getting the correct amount of weight.
But first "The Incident":
Find your water; put on your full kit EXCEPT your
weights. Here is why. I was at a popular certification site doing some OWD
certifications on May 4th and 5th this year. This is a fresh water site with
about a 90' bottom and vertical rock sides. A student from another dive
center was apparently drastically over weighted. In retrospect, I can see
the instructor did not have control of his class and she was NOT in his sight.
She went to the bottom. I mean out of control decent! She later said she
thought she was drowning. She spit out her regulator at depth, dumped her
weights, inflated her BC and kicked like a dolphin! I first spotted her at
about 30 feet. She passed 20 feet away from me at 15' of depth looking like a
Trident Missile! The short version is: I did a solo surface rescue. (No, her
shop personnel did not realize she had gone missing.) She had frothy blood from
her mouth and nose, was bleeding out of her eye sockets and had the appearance
of rather remarkable facial subcutaneous emphysema. She was conscious, allowing
me to gather quite a bit of information from her as the paramedics arrived.
Bottom line for us: No accidents! Therefore:
- Buddy in the water before you, with a full tank of
air, alternate air source(s) and a fully inflated B.C.D.
- Shallow water is better than deep
- Fully inflate your B.C D. prior to
entering the water
- Regulator in your mouth
- Enter the water
- Start without weights
Come out in the water to
your buddy and have him/her get a good grip on your vest. When you are ready,
hold your breath and slowly let the air out of your B.C.D. You should float
like a cork as you are not wearing weights. Now let your breath out. You most
likely will still be a cork. But you may not. Now return to the water's edge
and add 1 to 2 lbs to your weight pockets. Make sure there is an equal amount
of weight in each pocket. (I will cover weight distribution a bit later.)
Repeat this process until
you float about eye level in the water with a full breath of air, and when you
let your air out you barley sink. Now you have the correct amount of weight for
the end of your dive. This means, with a full tank, you should gently
sink. An aluminum 80 at the end of a dive will give you somewhere around 4 lbs
of positive buoyancy or upward lift depending on the amount of breathing gas
left in it. Which means the same tank, with a full load of breathing gas will
give you about 4 lbs of negative buoyancy, when compared to the
"empty" tank at the end of a dive. Don't forget that! I
actually lighten up a bit from there so I need to swim myself down two or three
feet before I sink. In any case the "sinking" should be slow and
EASILY controlled.
Also, you do not want to be
so light at the end of the dive you are struggling to stay at a safety stop or
are not 100% in control of your entire accent. When it comes to weighting,
"practice makes perfect".
2) Ideal weight
distribution.
When determining your
proper weighting, you were in an upright position and floating comfortably on
the surface. This is less than an ideal position for diving. Have you ever
noticed divers swimming past whose heads are higher in the water column than
their feet? They resemble an air plane in take off! Humm. Why is that?
Typically what you are looking at is the cool stuff underneath you, not so much
in front and above you. Your most natural ergonomic posture is essentially a
comfortable upright, standing posture. Now put on your imagining caps and
rotate that position to prone. Yep, just like lying down on a massage table.
... Nice thought! That is the position of ideal buoyancy. Maybe, we should call
it the "massage position"? ... Maybe not.
Weight distribution is how
we get there. Trim weights is the term commonly used.
Your body mass, adipose
(that is a nice word for fat if you are unsure!) and muscle distribution
combined with your equipment will determine how much weight to trim with and
where to place the trim weight. The best part? It is not hard to do. But it is
very individual. Let me try to give you some ideas.
I use three different
B.C.D.s: A ScubaPro Knight Hawk when I teach, a Dive Rite Trans Pac with a wing
for most of my dive trips and a back plate and wing for my doubles. I use two
tank bands on my wing rigs. My Knight Hawk has trim pockets located in between
the bladder and the back of my shoulders. I am also fairly solid at 5' 10"
and 185 lbs. My shoulders are about 42" and my waist about 33". Plus
I my mother often told me I have rocks in my head.
My darling wife on the
other hand is 5' 2". She is
rather curvy (narrow waist with an hour glass figure topped of with ... yes, a
pretty good size bust.) She has also been very athletic and has a solid
build.
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| Coleen |
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| Coleen and Ebby |
Is there any reason to
think our trim weights would be in the same places or in the same percentages
of the whole? Uh, no.
The last factor
acting like a variable is the wet suite/exposure protection. I weight my Nova Scotia
different than a dive skin.
Generally speaking I put
about 80% of the weights in pockets on my hips and 20% on the lower tank band.
Don't forget, you can always add a tank band for the purpose of adding weight
pockets for your trim weights.
Coleen on the other hand,
puts about 50% of her weight on her hips and 50% on her upper tank band to
compensate for the adipose in her chest. (Wasn't that a tactful way of putting
it?)
I have seen other divers
use the same ankle weights that dry suite divers commonly use. These weights
can be added on to nearly any part of you gear.
By way of caution it is
useful to remember trim weights are not easily removed while in your
gear.
Whatever combination works
for you be absolutely symmetrical. If you find yourself twisting in the water,
your weights are the likely suspects.
The Result
The result of ideal
weighting is relaxation. You are not fighting to stay in the proper position,
twisting, staying at your desired depth, or filling your B.C.D. with air
at depth. You will also notice you can adjust your depth with merely breath
control. This goes a long way to become a "Zen" diver.
The bonuses: One, you are
more relaxed and having a better, safer time. Two, your gas consumption rate
goes down. That's good stuff right there!
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| Coleen |
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| Lance |
