Previously, I wrote out some thoughts and a strategy for swimmers who struggle with sinking:
Since then those posts have received a good deal of attention and I’ve enjoyed hearing from various swimmers about their ideas and progress with overcoming the sinking problem. It also inspired me to get a better picture of how much variance there is in buoyancy among us humans-in-water. The first step was to measure my own.
My Neutral Buoyancy Point
Here is what I found:
(Sorry, I admit it’s a little creepy to see several of my body-less heads floating there, isn’t it?)
When I did this test in the sea, my normal training spot, my body with full inhale settled with the water line splitting my goggles. When I gently released all my air I started sinking as if I would never stop. The bottom was maybe 4 or 5m below so I didn’t bother to see how far.
When I did this test in a chlorinated pool my body with full inhale settled with the water line above the line of my swim cap on my forehead. When I gently released all my air I sank to the bottom (2m) immediately.
Now, with a little body mass/volume calculations I could estimate what % of my body I am allowed out of the water in my neutral position. Previously, we’ve referred to the roughly 95/5% iceberg principle- a human is permitted only about 5% of his mass above the surface of the water and if more than that he will be required to divert some portion of his energy to fighting gravity. By calculating my personal % I could find out if I come in above or below that approximate average %.
The third test I need to do is with my 0.5mm Sailfish Edge sleeveless speed suit on (which I might use occasionally in cold water/air conditions). That will affect my buoyancy further, but how much? It is certainly less buoyant than the typical 3/5mm wetsuits most people wear, but it is still adding something. I am curious.
Self-Test for Neutral Buoyancy Point
Without the aid of a nice physio-lab to measure things in, we might use this simple test anywhere we swim to get a reading on buoyancy and be able to compare it to one another. This in turn could help us pick which advice might work better for each kind of buoyancy situation.
And, as my diagram above reveals, different water composition will affect a swimmer’s buoyancy point. We are familiar with how much more buoyant we are in salt-water, and the sea is the Eastern Mediterranean is particularly salty, as salinity in seas and oceans go. But also natural fresh water, mineral-laden water, chlorine, bromine, saline pools may affect buoyancy to some noticeable degree also – it would be a interesting experiment to find out how much.
Now, I would like to invite you to conduct the experiment on yourself and send me your results!
This is how to do the self-test:
1) Find some water deep enough that you cannot touch the bottom with your feet. The water needs to be calm, free of turbulence and current.
If the bottom is close to your feet, you may bring your legs into a cross-legged position to bring them up, closer to your body, and you can hold them with your hands. But keep your torso and spine vertical.
2) Allow your body to gently settle so that you are using minimal amount of hand movement to keep your nose above the surface.
3) Lift your mouth and take a full inhale of breath and hold it.
4) Make sure your head and spine are fully aligned. You should be looking directly horizontal, keeping your neck ‘long’ so that the crown of your head and spine are pointing up directly up against gravity, as if you were standing on land.
5) As gently as possible allow your body to sink down to it’s neutral point – if there is one.
(That is the question we want to definitively answer for those who wonder if they are ‘total sinkers’.)
You want to ‘sit down’ onto the water until it holds you up. You want to create no momentum by moving your body parts, and create no turbulence in the water that will interrupt the balance of the natural forces acting on your body.
If you have been pushing up against gravity to breathe, when you let go gravity will push you down and the momentum of your body mass will carry you below your neutral point. Then, if you apply no force you will be waiting for water to push you up again and gravity to push you down again like a swing in super-slow-motion settling down. So the more gently you ‘sit down’ into the water the less up/down settling there will be.
Now, for those with higher body density it may be more difficult to get to this settled point – if there is one. You need to eliminate all momentum of your body sinking due to the initial drop of your body mass into the water – because that momentum will carry you down deeper than your neutral point, and it will take way too long (for holding your breath) for the forces to push your body back up to it.
Imagine one of those lift-chairs used to lower disabled or paralyzed swimmers into the water – imagine that chair very slowly lowering your body into the pool until the water takes over and the chair sinks away from under you. That is what you are looking for – the point where water will take over and you won’t sink further unless some force is added to the equation.
Sinkers need to realize that density is not the only factor sending your body deeper in the water so easily. You can’t easily change your body density, but you can work on those other factors to remove unnecessary difficulties to your swimming. So determining the facts about your neutral point is a first step in creating a more clear picture of the physics problem you must solve.
I would be delighted to hear your results and observations from this self-test for neutral buoyancy point. If you would include some basic body statistics or description that would be insightful too – weight, height, and description of body build (runner, weight-lifter, desk-jockey, etc) and your ‘density type’ – from ‘sink like a rock’ to ‘effortless floater’.
And, if you know how to use some simple photo or graphic editing software you can use these images below to cut/paste your head into the approximate position of your buoyancy point, just like I did with mine.
And the creepy body-less head…