Non-divers who want to be a scuba diver one day naturally don’t have any idea about the buoyancy underwater. Because when we swim, we don’t need any balance or buoyancy, our body does it all! But this changes when we use a scuba diving suit, a tank, weights and a bcd. All these equipment make a diver to get unbalanced both underwater and on the surface. This is something unguessable unless you have experienced scuba diving once. The National Geographic Channel doesn’t show inexperienced scuba divers without perfect buoyancy on their documentaries. Thus, an arm-chair explorer thinks that when scuba divers jump into water first time, they have buoyancy underwater naturally, without any aid, just like a baby newborn gazelle walking after just a couple of minutes from the birth.
What Is Buoyancy Underwater?
When we look at the dictionary, we see that buoyancy has several meanings like “ability to swim”, “force of flotation” and “not to sink“. First, we should understand that buoyancy is necessary and important for scuba divers not only underwater but also on the surface. I have chosen the topic as “Buoyancy Underwater” because most of the scuba divers and non-divers think that buoyancy is only (or mostly) important underwater. They search the whole buoyancy topic as “Buoyancy Underwater“. I wanted to catch this kind of search on the web and try to explain the topic as it has to be.
Let’s return to the topic. To be able to explain the term “buoyancy”, I want to give an example.
If you throw a stone to the sea, it sinks. Which we call “the stone is negatively buoyant”.
If you inflate a balloon and throw it to the sea, it swims on the surface. Which we call “the inflated balloon is positively buoyant”.
Divers should be positively buoyant when they are on the surface. We can do it by inflating our bcd. And if this is not enough (in emergencies for example, if you have weights on you more than you need) you can remove your weight belt and become “positively buoyant”. By this way, you don’t have to kick your fins to be able to stay on the surface and don’t loose energy. You stay out-of-water and breathe comfortably.
Positive and negative buoyancy are two terms important to understand the buoyancy, but not enough. We also should know the term: “Neutral Buoyancy”.
Neutral Buoyancy Underwater
The objects neither sink nor swim on the surface is called “neutrally buoyant objects”. But how this happens? The term “density” is explaining this to us.
For example, if you buy 1 lt (volume) of fresh water from a market and put it on the libra, you’ll see that it is also 1 kg (mass). The density of the fresh water makes 1.
If we go on with this, the density of sea-water is accepted as 1.025. If the density of an object is greater than 1.025, then it sinks (negatively buoyant). If an object has a density less than 1.025, then it floats (swims) (positively buoyant). Therefore, if you remember the stone and the balloon example, the balloon has a less density and the stone has greater density than 1.025.
And if an object has a density of 1.025, what happens? The magical think that divers love happens; The object “hovers” in the water (has neutral buoyancy underwater)
We divers always want to be neutrally buoyant underwater. That’s because divers:
- want to have a larger angle of view
- don’t want to harm the habitat
- don’t want to damage their equipment
How to Obtain the Same Density With the Sea Water (Neutral Buoyancy Underwater)
Staying positively buoyant on the surface is okay. You inflate your bcd, remove your weights if needed. Boom! You are positive. You can swim like this to the dive boat/shore with your buddy without any other help.
However, buoyancy underwater is another issue. Having the same density with the sea water you are diving in (having the neutral buoyancy) requires alittle bit more technique.
Use Your BCD
If we are talking about buoyancy underwater, bcd -the buoyancy control device- should be the first thing to talk about. Divers should use a proper size and comfortable BCD, preferentially their own. A BCD gives us the chance to take the air inside (inflate it) and release the air to the water (deflate it) whenever we want to. In other words, when we inflate our BCD, we decrease our density (because we increase our volume, from the formula density=mass/volume). And it is vice versa when we deflate our BCD.
This is excatly the same logic with the submarines. They full their air tanks to be able to surface and then pump some water to their tanks to be able to descent. Inflate your bcd to raise a little bit, deflate it to descent. When you have the optimization, your density will be the same with the sea water and you are going to have neutral buoyancy underwater.
Understand the Mechanics of a BCD
All beginners in scuba diving complain about “not being able to use their BCD“. They try to raise a little bit, pushes the inflator button of their BCD for a couple of times but WTH ? They start to ascent fast and deflate all the air in their BCD and touche the bottom. And this time, they start to crawl at the bottom.
This is because it takes a little bit of time to understand the mechanics of a bcd. When divers want to go up a little bit and try to be neutrally buoyant, they push the inflator button for a couple of times. The air gets inside their bcd. First, because of the duress, the air reaches to the waist and tail end part of the bcd. But as we all know, air always move “up” in the water. So, air collected on the waist and tail end part starts a journey inside of the divers bcd. The direction is the shoulder part of it. İn a couple of seconds, air gets collected on the shoulders of our bcds. Only after this process, the air tries to raise a diver.
If i sum up, a bcd inflator is not a joystick. You don’t start to rise when you touch the inflator. What you should do is to give small bursts each time (two pushes for one second each) and wait for at least 15 seconds for the air to start to raise you. After 15 seconds, if you are not swimming neutrally, give two more small bursts and wait 15 seconds more. And this goes on like this.
If you push the inflator more, after a couple of seconds, the cumulative air in your bcd will start to raise you. However, this raise will turn into a fast ascent which is very dangerous for the divers.
Use Your Lungs
Our lungs are just like balloons; they take 500 milliliters (0.5 liters) of air each time we inhale. So, not only our bcd, but also our lungs have an important role on buoyancy underwater. For sensitive buoyancy, we can use our lungs.
Imagine your self trying to descent. Don’t deflate all the air inside your bcd. Instead, deflate 3/4 of it then exhale and give all the air in your lungs out slowly. This will make you start descending. Inhale normally then. You’ll see that because you have started to descent, your volume has also started to get smaller (you get negative buoyancy). After this period, even if you inhale normally, you’ll go on descending slowly.
When you reach the bottom, you’ll still have some air in your bcd that you haven’t deflated at the beginning of your dive. You can use this air for gaining neutral buoyancy underwater. This will both help you in air saving and a good slow descent. A slow descent gives you enough time for equalizing your ears and your mask. It also prevents “nitrogen narcosis”.
Use Proper Weights
You should use proper amount of weights. Many say that the amount of weights a diver should use depends on the diver’s own weight. This is a right but not enough. A diver’s weight, the suit, bcd seize, tank type (aluminum or steel) are factors affecting the amount of weight. I use 8 kilos in my dives. But in summer, everything else staying constant, i use a 5 millimiters of shorty. Just because of this, i start to use 6 kilos instead of 8 kilos.
Diver Weight Calculation
There are thousands of web-sites which says they have the diver weight calculator. This is pointless. Every divers is unique. Even me and my buddy weigh the same, our fat, bone and muscle ratio is completely different where fat makes us float but muscle makes us sink ?! We don’t use the same suit and equipment. Even using different kinds of diving boots affect divers differently. So how are we going to make the diver weight calculation?
A diver with all the gear gets in the water where the sea level is higher than the diver’s height. The diver deflates the bcd all and inhales normally. The diver holds this breath (diver’s regulator should be on the diver’s mouth) . With an empty bcd and a normal breath hold, the sea level should be on the diver’s eye-level. If the sea level is on the diver’s shoulders, the diver should increase the amount of weight. If the diver is starting to descent, in this position, then the diver should decrease the amount of weight. First, increase/decrease 2 kg and then repeat the process. At last, the diver will find the optimum amount of weight.
Take a Course for Buoyancy
To be able to learn the buoyancy concept and apply this to your actual diving experiences, you should take a course about buoyancy. There are courses on this subject in different diving systems. For example, in PADI, it is Peak Performance Buoyancy and in SSI, it is Perfect Buoyancy.
You are learning to use your bcd, lungs and weights in this course. You hover in different positions (feet down, head down, by side etc.). A diver taking this course notices the importance of buoyancy underwater and on the surface is important for his/her dive carreer.
Almost every branch of scuba diving requires very good buoyancy. Cave diving, deep diving, underwater photography… All can be succeded with perfect buoyancy skills.
A Typical Perfect Buoyancy Course Content
Last weekend, i had three students who are ready for SSI Perfect Buoyancy Course. First, i have given a briefing about the day and the content of the SSI Perfect Buoyancy Course. Because of its nature, buoyancy courses are always fun! There is nothing essential but also excited than challenging the gravity. Only the divers and the astronauts feel this. Doesn’t it even sound great?
In our first dive, we have worked on the fin-pivot. By using our bcd and our lungs, we try to hover a little bit, our fins touching the bottom. By this way, a diver starts to learn about the mechanism of a bcd.
Our second skill was to hover horizontally. Do you remember Ethan Hunt in Mission Impossible trying to steal the diamond in this position?
As a third skill, i wanted my SSI Perfect Buoyancy Course students to hover like sitting on a chair, hands on the kneels. This was the funny part for me. A student who is performing this skill is a great fun for an instructor. Sorry guys, but i have to admit it. But they all have started to master the buoyancy underwater.
The idea in the fist dive is to give the logic behind the buoyancy underwater to the student. And in the second dive, the student gets in the water knowing this and starting to master the skills needed.
In the second dive, first skill was to flip-flop underwater. This skill gives an idea how a diver feels in different positions and how the regulator reacts to this. Next skill was to hover a handstand (head-down). This is an important and a challenging skill for the students. They should get neutral buoyancy underwater, plus everything is reverse. In addition to these, breathing from a regulator in this position is also more difficult.
Next skill was “screwed swim“. The objective here is to swim by turning yourself while staying neutrally buoyant. This skill is again for adaption. A diver with perfect buoyancy skills should experience every position underwater and can stay neutrally buoyant in every one of them.
Our last skill was to sit cross-legged in the mid-water (hover). First, the divers gains neutral buoyancy underwater by inflating the bcd with small bursts. Then the divers position themselves as if they are sitting in the mid-water. Last thing is to cross-leg while sitting. If the depth is 6 meters, the diver should be hovering in 3 meters in this position, just like a planet hovering in space.
This last skill is the last part and it is often considered as “diff’cult to perform” by students. However, this skill will help them fully understanding the bcd, weight and lung relationship. They get the idea: “bcd should not control them, they should control their bcd and as a result, their buoyancy underwater“.
Baris, Hugo and Kemal. You all showed great performance in all skills. However, the last skill was not a training dive, it was a thrilling buoyancy show! Every buoyancy photos in this article have been taken during this course (except the one near the first pharagraph). And these guys only have 10 logged dives right now, they are not dive pros, which means every diver regardless of the level can take this course and master in buoyancy underwater. Congratulations for becoming SSI Perfect Buoyancy Divers. That was a strong and fun course.
Thank you for attending.
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