What do we know about buoyancy? In general and buoyancy for freediving? You normally learn it on your Freediving course, but lets refresh it here.
Google tells us that buoyancy is the upward force applied by a fluid on an object when the object is put in or submerged in the fluid. In a more simple way for freedivers, it means “sink or float or stay on the same depth.”
Why does it have any meaning for us as freedivers? If you are not properly buoyant, it will cost you much more energy to cover the same distance. But as freedivers, we want to save energy as much as possible, not to spend it.
There are 3 types of buoyancy: positive, neutral and negative.
If we refer to Google again, we can find out that positive buoyancy occurs when an object is lighter than the fluid it displaces. The object will float because the buoyant force is greater than the object’s weight. Neutral buoyancy occurs when an object’s weight is equal to the fluid it displaces. Negative buoyancy occurs when an object is heavier than the fluid it displaces. The object will sink because its weight is greater than the buoyant force.
In more simple words, if the freediver is positively buoyant at a certain depth – he floats up without any effort. If the freediver is neutrally buoyant – he stays on the same depth and doesn’t move up or down at all. I believe we can compare it to zero gravity feeling. I have never been to space yet, but I guess neutral buoyancy is what we might feel while wondering in the universe. Negative buoyancy is when the freediver just keeps falling down if he relaxes and doesn’t move. This “phenomena” is called freefall and for many freedivers, this is the best and most favorite part of dive.
Buoyancy depends on different factors – personal and external.
A personal factor, which influences the buoyancy, is body composition. Different body tissues have different density – bones and muscles are heavier than fat. Skinny people are usually less buoyant then people who have some body fat.
When we are talking about external factors influencing the buoyancy, first we need to think about the environment. In saltwater freediver more buoyant than in the freshwater due to different water density. So don’t forget to adjust your weights correspondingly, if you change the diving conditions. Otherwise, duck dives in the sea will be a real challenge, if you take the same amount of weights, which you take normally in the lake.
The second important external factor is a wetsuit. Wetsuit does affect buoyancy. The thicker is a wetsuit, the more buoyant it is. And the new wetsuit is more buoyant than the old one. Which means, if you are diving for 2 years in the same wetsuit you may need fewer weights after a certain period of time, then you used when your outfit was a brand new one. Just opposite – if you get yourself a new wetsuit – don’t forget that you may need some extra weights.
What you can do if you are too positively buoyant? You can add weights on your weight belt or neck weight. It is more difficult to adjust the buoyancy if the freediver is “too heavy” in the water. The easiest way is a wetsuit – if you put it on – it will make you more buoyant. But, if for some reason you cannot wear a thicker wetsuit – maybe it would be too hot in it, and then nothing could be done. At least at the moment, freediving gear manufacturers cannot solve the problem of negatively buoyant freedivers. Who knows, maybe soon someone will create rash guards with tiny balloons all around? We’ll see 🙂
And now, let’s discuss how we can check if we have proper buoyancy for open water trainings.
First of all, the freediver needs to be positive buoyant on a surface – when he lies down on a surface he is not sinking. The reason for it – you want to be able to rest before and after the dive – before the dive, you want to relax and take time to prepare, and after the dive, you might be a bit tired and want to recover. If you need to kick to stay on the surface – it is not the most relaxing, right?
Except being positive buoyant on a surface you need to be positive buoyant even after passive exhale. What does it mean “passive exhale”? You do full inhale and then you exhale without any force, passively release a little bit of air. After this manipulation you still need to float on a surface – may be a few centimeters below the surface, but definitely not sinking (even slowly) down.
Why?
If the worst-case scenario happens and the freediver loses consciousness on the way up, he will still stay positively buoyant on ascending and the whole rescue procedure will be much easier to do. Because when the freediver loses consciousness, the diaphragm relaxes and goes to the neutral position, which results in a little exhale. So when we do a buoyancy check with a passive exhale on a surface, this is a kind of imitation of air release in case of a blackout.
Besides, the freediver should be also positively buoyant the last couple of meters of ascending. Because on the last few meters of ascend freediver passes the riskiest depth, so it would be more reasonable to save little energy and not to kick hard. In this situation, the freediver can slightly relax and save some energy (read oxygen) on the last 5-10 meters due to positive buoyancy, which helps to prevent shallow water blackout.
Neutral buoyancy should be somewhere around 10 meters. At this depth, you don’t sink or float up. How you can check it? You dive to 10 meters. You slightly hold the line – make some kind of loop with your fingers around the line, so you don’t actually touch the line. And you will see if you go down or up. Ideally, you should stay on the same level – this means you have neutral buoyancy at this depth.
The depth of neutral buoyancy depends on how deep the freediver is going to dive and for experienced freedivers depth of neutral buoyancy might be deeper. But if you are a beginner or intermediate level freediver, you need to be neutrally buoyant at 8-10 meters. There is a one really cool warm-up exercise which our students find enjoyable. If you feel comfortable at 10 meters, try to hang there for a while. If you close your eyes, you can imagine yourself an astronaut in the open space out of gravity. This exercise we call hangs. But don’t hang too long – always remember you still have 10 meters to go up to the surface.
And when the freediver passes neutral buoyancy he gets into the impact of negative buoyancy. At the beginning of 12-13 meters, you don’t feel it much, because it is still very light. If you relax for freefall at this depth, you will fall super slow and just waste your oxygen-treasured time. So I wouldn’t recommend you to start freefall shallower than 15 meters.
After your turn on the planned depth, you need to do the way up which is just opposite to the efforts on the way down – first, you need to kick really good and strong to struggle with negative buoyancy. After you pass neutral buoyancy, you get into the positive buoyancy world and can relax a bit. Last 5-6 meters you may just float up fully relaxed without moving or glide a lot between kicks or between pulls, depending on your freediving technique.
To make a conclusion I would like to underline once again the key points of this article – when you check the buoyancy – you check it first on a surface. Even after passive exhale you should be positively buoyant. If you start sinking after passive exhales – remove the weights. Check if you are neutrally buoyant at 8-10 meters. If you sink – remove some weights from your belt.
And the main things – don’t forget to enjoy your freefall and your hangs in space.
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By Svitlana Gaidai