Buoyancy control

Buoyancy control is the most fundamental of all the basic diving skills. The feeling of weightlessness that is the reason why many people want to dive is dependant on having good buoyancy control. With good buoyancy control a diver uses less air, will feel more comfortable in the water and is less likely to suffer an uncontrolled buoyant ascent. Despite being such a key skill, most of the UK diver training agencies have noticed a reduction in general buoyancy skills. This reduction in skills is not restricted to novices; many experienced divers have poor buoyancy control.

The level of control that divers have in managing their buoyancy can be split into four levels. The first is where the diver has very little idea about how to control their buoyancy and they are often unable to maintain any level of control. Someone learning to dive for the first time would usually start like this but they usually move past this by the end of their initial training. The second level is where the diver understands the principles of buoyancy control and can manage their own buoyancy to a large extent. They may still have to work very hard at it and divers at this level are easily identified by the fact that they keep a constant hold on their BC inflator hose. Some divers never progress past this level, especially if they only dive very occasionally. The third level is where the diver is growing in confidence and can hold their buoyancy without constantly thinking about it. They will appear to be fully in control and to be able to maintain position at the depth required. The majority of divers will get to this third level but then do not progress any further. They may seem to have mastered buoyancy control however when they become distracted, by sending up a DSMB or dealing with some type of problem then their buoyancy is affected and they may start to fall or rise in the water. They may not realise that a higher level of control is desirable, or even possible, as they may get into the habit of sending up a DSMB from the bottom and unless they get into trouble will not realise that a problem will interfere with their ability to control their buoyancy. The fourth level of buoyancy control is where the diver can control their buoyancy precisely, even when they are focusing on other tasks or dealing with a problem.

For technical diving it is essential that we aim to reach the fourth level of buoyancy control. There are a number of reasons why we must aim for this level and not be content to remain at the third level. Technical diving inevitably means decompression diving and a decompression ceiling puts restrictions on how far we can ascend without risking DCI. If a problem at depth results in a loss of buoyancy control then a rapid ascent may result. Technical divers must be able to deal with any problem at depth without risking a rapid ascent and so must be able to deal with any problem while still maintaining their buoyancy control. Obviously this level of control is also useful for recreational divers who will then also be able to deal with problems without a subsequent loss of buoyancy. In addition to the risk of an uncontrolled ascent there is also the risk of sinking further. A diver who becomes fixated on dealing with a task and is unaware of their buoyancy may sink deeper. This can make the original problem much more serious. By sinking deeper the diver is using up their breathing gas faster, they will experience a higher level of narcosis and finally they will be incurring an even greater decompression penalty.

Finally decompression dives will involve significant periods of decompression stops. These stops may be longer than the bottom part of the dive. These are often done in mid-water with very little visual reference. In order to follow the decompression schedule the diver will need to accurately control their ascent rate and then be able to hold their position at the required depth in order to complete their decompression stop. Unless your buoyancy control is good enough to hold a safety stop without moving up or down more than half a metre then you should not even think about doing decompression diving. If you are unable to hold a safety stop then it is likely that you will be unable to hold a decompression stop and missing a decompression stop is likely to result in a decompression incident. For this reason it is good practice to do at least a one-minute safety stop on every dive in order to perfect this skill. Once you can reliably hold the safety stop for at least a minute without exceeding half a metre variation from the target depth then you can start to think about decompression dives. Ideally you should be aiming for a variation of +/- 0.3m or less from the stop depth.

For cave divers or wreck penetration divers, buoyancy control becomes even more important. Dropping down onto the bottom or floating up into the ceiling can produce a blinding cloud of silt that can reduce the visibility to zero. When swimming through an overhead environment it is vital that we can hold our position in the water without excessive use of the hands or fins to maintain position. Excessive use of the hands or fins can also kick up significant amounts of silt and further reduce the visibility. In order to navigate through a wreck or cave without touching the bottom, ceiling or either of the sides we need to have full control over our buoyancy.

The first step to good buoyancy control is correct weighting. The majority of divers carry more weight then they need, this ranges from a couple of kilos to tens of kilos overweight. Again this is not just restricted to novices. Experienced divers are often over weighted, some to a remarkable extent. They set up their weight belt and then never change it. In the mean time, with experience, they need less weight; their equipment may change, they may add pony cylinders, switch to a twinset, add deco cylinders, torches, etc. As a result they may be significantly overweight without realising it. They have come to think that it is normal and change their diving technique to compensate for being over weighted.

If you dive over-weighted then you must put more air into your wing/BCD or drysuit in order to achieve neutral buoyancy. This additional air significantly increases the risk of an uncontrolled buoyant ascent because as you ascend there is more air in the suit or wing/BCD to expand. This leads to the surprising situation where, by adding weight, you can make yourself more buoyant on your ascent rather than less. By reducing the amount of over-weighting you reduce the chances of an uncontrolled buoyant ascent. It is good practice for all divers, no matter how experienced, to do a buoyancy check at the start of each diving season, mid-way through the diving season and whenever they dive with a new or different kit configuration.

Once you are correctly weighted that isn’t the end of the story. Any time you change your equipment you will need to re-check your weight. If you switch between cylinders then you will need to adjust your weight and even two cylinders with the same capacity can vary in weight by 2 or 3kg. A new drysuit can vary considerably in buoyancy characteristics and even wearing an extra layer under your drysuit can make a significant difference to your buoyancy – remember layers keep you warm by trapping air and that air is going to change your buoyancy. There is a definite link between divers suffering uncontrolled ascents and the use of new or different equipment. If you are using any new equipment – even a new set of fleecy underwear – then do a buoyancy check before diving.

In open water you should try to keep your buoyancy under control at all times. This starts with the descent. Do not just dump all your air and sink to the bottom like a stone; instead you should be doing a controlled descent where you can stop the descent at any point. I once dived with a buddy who used to descend so fast that even with no air in my BCD and suffering with suit squeeze in my drysuit I couldn’t keep up with him on the descent. After struggling to keep up with him for a few dives I convinced him to do a weight check - we managed to remove 6kg from his weight belt while still allowing him to descend easily.

A controlled descent will help in a number of areas; it will help in avoiding narcosis, as rapid descents are a predisposing factor to nitrogen narcosis; it will help if you have trouble clearing your ears as you have time to clear them or stop and ascend slightly. A controlled descent is especially important if the dive site is deeper than you expected. There are numerous examples of experienced divers jumping into the water after being told that the site is 30m, doing an express descent to the bottom without checking their gauges and getting to the bottom only to find that they are at 40m rather than 30m. This will ruin even the best-planned dive plan and if diving on nitrox could be fatal.

Once on the bottom it is important to maintain neutral buoyancy rather than just bump along the bottom. In many countries British divers have a bad reputation for buoyancy control due to their habit of crawling over the bottom rather than swimming over it. This is due to their tendency to be negatively buoyant as a result of not putting enough air into their wing/BCD or drysuit. Once you reach the bottom take a few seconds to adjust your buoyancy so that you are neutrally buoyant. This will make the rest of the dive much more comfortable and is likely to reduce your overall air consumption as struggling with incorrect buoyancy during the dive will cause you to breathe harder or more irregularly than if you are neutrally buoyant. Being neutrally buoyant also gives a much more enjoyable feel to the dive as you really do feel weightless and can move effortlessly in three dimensions. If, on the other hand you are negatively buoyant on the bottom then you do not get the feeling of weightlessness and can only move in the same two dimensions as on land.

Hopefully it is clear that buoyancy control is a key skill that should be reviewed regularly by all divers. Reducing over-weighting, regular weight checks, practicing buoyancy control exercises and being aware of the impact of new equipment can all help to perfect your buoyancy control skills. With increased buoyancy control you will be more comfortable in the water, use less air, reduce your risk of an uncontrolled ascent and generally enjoy your diving much more.