Buoyancy

How can I get Buoyancy Control!

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.. It acts in the upward direction at the centre of mass of the displaced fluid.

So what does that actually mean?

Why is buoyancy so important? How can experienced divers make it look so easy? Well the truth is that simply understanding the principle of Archimedes isn’t the answer. Knowing how to practice your breathing skills, continuing your diving experience and making equipment adjustments is a good place to start. I always tell divers that it takes someone on average between 50 to 100 dives to be comfortable in the water and achieve good buoyancy control. So how can you improve your buoyancy? and what should you look for when adjusting your trim? Everyone is different and what works for one person might not work for another, so achieving buoyancy control really is about diving down (excuse the pun) and practicing with what looks and feels right, for you.

One of the first things you should focus on 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 early on. Reasons for this body position is probably due to the diver being incorrectly weighted.

Centre of Gravity

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. they then inflate the BCD increasing the air volume above the centre of gravity causing the top part of the body to float upwards. Naturally this pushes the fins 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. If they stop they sink!

Positioning

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; I don’t have to move to monitor my computers and it 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 if you increase the angle, your hand would 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 of your COG you need to adjust.

Weights

Weight belt or integrated system? Maybe Both! The best way to adjust is to have smaller weights making up your total weight at 1kg or 2kg 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 of 50 – 60 bar. Next, we would need to move some weight up. This can be done by using trim pockets or tank weights. An option is to move 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 and adjust again if required.

Breathing

As well as adjusting your position and weights we need to look at how we breathe and use the BCD inflator. We often see many divers with their inflators in their hands inflating and deflating as they navigate through the site. The outcome is usually to end the dive 20 minutes before anyone else.

For those divers with air consumption difficulties, I would recommend the Peak Performance Buoyancy specialty 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 help to reduce the amount of air you use in your BCD and reduce air consumption. For big depth changes you would of course still use your BCD.

Buoyancy Control - PADI SIdemount buoyancy
dive centre procedures

Log your configuration

If you dive regularly with the same equipment it is easy to keep a note on what weights you are using and where you position them once you have done all your and checks. For some of us that use different kit and/or dive in different environments this is where a log book comes in handy. Many divers ask me “surely you don’t still keep a log book after thousands of dives?” Well 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 versus a 5mm wetsuit or 7mm semidry. I still look back and use this information until this day!

I hope this has given you some guidance around ways of improving your buoyancy control 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 finish the course carrying less weights and with better air consumption.

Dan