What is buoyancy

Archimedes’ principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and it acts in the upward direction at the centre of mass of the displaced fluid.

So what does it mean? Why is buoyancy so important in the world of Scuba Diving? How can experienced divers make it look so easy?
Well the truth of the matter is that knowing the principle of Archimedes or trying to figure it all out on this blog is not the answer… the answer is simply practice, experience and adjust.. I always tell divers that it takes someone on average between 50 to 100 dives to be comfortable in the water and have very good buoyancy skills. In this blog I will talk about ways to improve buoyancy and what to look for to adjust your trim but everyone is different and what works for one person might not work for another, therefore if it works then use it, if it doesn’t then try something different..


One of the first things you should look at is how you are positioned in the water, the majority of divers will be head up with ineffective  fin kicking upwards, this is normal for beginners but it is something that should be looked at and fixed right at the beginning. The main reason for this is being overweighted.

The extra weight will change our centre of gravity… COG.. those into car racing or flying will know that it is very important to understand and monitor the COG. In diving it is the same, the more weight you carry on the belt (below the centre of gravity), the more air compensation you need and so the BCD is inflated which increases the air volume above the centre of gravity, this will cause the top part of the body to float upwards and the fins to go down.

Most divers will notice this when they stop fining such as on a safety stop or taking a photo. When moving forwards they are constantly finning upwards therefore compensating for the negative buoyancy and being able to hold their depth somewhat, but when they stop they sink.

Another area to look at is how horizontal you are, my position is pretty much horizontal with my arms in front of me, and this plays two roles, 1 I don’t have to move to monitor my computers and 2 adds weight to the top of my COG. If I was to bring my upper body up it would also cause more friction against my body when moving forward, To demonstrate the effect simply put your hand outside your car window when moving and hold it horizontal, it would be streamlined but when you increase the angle your hand will be pushed upwards…

Try to practice swimming in a skydiver position where your shoulders are inline with your hips and your back slightly arched. Once you start to get into this position you will soon realise which part you will need to adjust.


Weight belt or integrated?? “Maybe Both”!! The best way to adjust is to have smaller weights making up your total weight, 1kg or 2kg at maximum. There are many options for weights and it will be different for everyone. Some options are; harness system, integrated weight pouches, weight belt, tank weights, BCD trim weight pockets, ankle weights, and clipped weights.

Imagine a diver who has all their weights on their waist and complaining of not being able to stay horizontal… my first question would be, are they carrying too much weight? first step is to do a weight check with an empty tank 50 to 60 bar. Next, we would need to move some weight up, this can be done by using trim pockets or tank weights. Another option is the tank position, moving the tank up would increase the weight above the COG therefore bringing the upper body down.

Distribute your weight as much as you can and try out different configurations, if it feels good then use it for a while then adjust if required.

As well as adjusting your position and weights we need to look at how we breathe and use the BCD inflator..  I see many divers with their inflators in their hands inflating and deflating as they navigate through the site, only to find out that they have to turn back and exit 20 minutes before anyone else… if this is you, I would recommend the Peak Performance Buoyancy with me where I look at breathing techniques and decreasing your air consumption.

Without holding your breath at any time you should be able to use your breathing control to move vertically in the water. Small depth changes can be done by breathing a bit deeper or releasing that extra air from your lungs will start a descent on a  sloping bottom, this will reduce the amount of air you use in your BCD and reduce air consumption. For big depth changes you would ofcourse still use your BCD.

Log your configuration

For those that dive regularly with the same equipment it is easy to keep a note on your mind as to what weights and where you position them once you have done all your testing and checks. For some of us that use different kit and/or dive in different environment this is where a log book comes in handy… many divers ask me.. surely you don’t keep a log book still after thousands of dives… the answer is yes I do, I can give you the hours I’ve spent underwater and how many pleasure dives and courses I have done,  I log configuration details and weight used such as sidemount, twinset, single cylinder, single cylinder with a stage bottle or when I use a shorty vs a 5mm wetsuit or 7mm semidry.

I hope this has given you some guidance around ways of improving your buoyancy, and if you need more help and guidance get yourself on the Peak Performance Buoyancy course… we run them all the time and most divers come out of the course carrying less weights and better air consumption..


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