The quest for perfect buoyancy control is something that all scuba divers should aspire to. Aside from basic safety skills, it’s the most important aspect of learning to dive. Poor buoyancy control makes improving your air consumption or becoming a good photographer virtually impossible – and can lead to serious accidents. Former full-time instructor Mark ‘Crowley’ Russell gives us some pointers
Buoyancy control starts with correct weighting
The first step on the way to good buoyancy control is the weight check. Poorly weighted divers find it difficult to establish neutral buoyancy underwater leading to frustration, hard work, damage to the marine environment and – potentially – serious accidents. Weight checks are all too often rushed and improperly conducted, but taking a bit of extra time on the process, even if it substantially shortens your dive, is worth the effort in the long run.
When to make a weight check
You should make a weight check every time something changes. If the equipment is different, especially if it’s brand new, then a weight check is essential. Different types of tank (steel or aluminium; 12 or 15 litre) will affect your weight – aluminium is much lighter than steel and you will need to adjust your weighting accordingly if you change to a different type of tank between dives. If you’re moving from freshwater to saltwater you will need to add weight to compensate (and vice versa), and if you dive in the Red Sea, its high salt content means you will need more weight than if you were diving in other locations. If it’s been a few months since you last dived you may have gained or lost body fat or muscle mass (fat is much more buoyant than muscle), even if the bathroom scales say you weigh the same. Unless you’re diving every other day, it’s sensible to make a check at the beginning of every dive vacation.
How to make a proper weight check
The standard weight check is to: wear all your equipment in water too deep to stand up in, hang vertical and motionless and adjust your weight so that you float around eye-level with an empty BCD while holding a ‘normal’ breath of air. Motionless is key – any movement of the arms or fins will keep you at the surface. If you’re struggling to remain vertical at the surface, deflating your BCD a little before you start the weight check will help. A ‘normal’ breath is what you do when you’re not thinking about it. It’s difficult to quantify, but imagine filling your lungs half-way. Holding a deep breath will result in overweighting, and vice versa. As a test, once you’re neutrally buoyant at the surface, you should descend slowly when you exhale. Remember, it’s always best to make a weight-check with an empty, or nearly empty tank – 20-30bar (300-450psi) is ideal. Tanks shed around 2kg between full and empty, so if you have to make a weight check on a full tank, you will need to add around 2kg of lead to compensate for the change in buoyancy during a dive. If possible, make a second check at the end of the dive with a nearly empty tank.
Isn’t extra weight safer?
No. It’s an unfortunately common myth that extra weight is somehow ‘safer’. It’s not. Extra weight will definitely help you sink. It may well also make you float uncontrollably to the surface. If you want to perfect your buoyancy control, then you should dive with the weight you need and no more.
How do I know if I’m overweighted?
If you sink like a stone when you descend, are constantly bobbing up and down underwater, continually adding or removing air from your BCD to remain at a constant depth, holding your breath to remain above the bottom, then you’re overweighted. Remember, your BCD is there to help you establish neutral buoyancy, not move up and down. For single-tank recreational diving, a short, sharp, pffft of air is all you should need to add to your BCD as you descend. At any given depth, your BCD should feel like it’s almost empty. If it feels full, you’re overweighted. Fine-tuning your depth should be done by breath control alone.
How do I know if I’m underweighted?
Be careful with this one. Not being able to sink may be due to underweighting, but it may also be due to breathing too rapidly at the surface, or unnecessary finning and arm-flapping. This is where dive guides often throw extra weight at divers to get them underwater. Relax, control your breathing, remain motionless and exhale. If you still can’t get underwater, you may need some extra weight. If, underwater, you have a totally empty BCD and relaxed breathing but still find yourself head-down, feet-up trying to swim yourself down then you are probably underweighted, but make sure you check the BCD is empty first – and learn to use those dump valves!
Weight belts or weight pockets?
This is partly down to the design of BCD (jacket, hybrid, wing) and partly down to personal preference. But it doesn’t have to be a case of either/or. You can use both if it helps distribute the weight more evenly around your body. Also remember that weights don’t have to be concentrated around your middle. If you find it hard to keep your legs from sinking, you might want to try having weights around your tank strap to compensate. Accessory pockets are available for this purpose; some BCDs have them built in. If you have floaty feet (especially in a drysuit), you may need ankle weights. There’s no one-stop-shop for weight distribution.
Breath control is everything for buoyancy control
Once you have established neutral buoyancy using your BCD, moving up and down a metre or so should be controlled entirely by your breathing. If you are neutrally buoyant with half a lung full of air (see ‘normal’ breath, above), then anything over that makes you positively buoyant, and everything under makes you negative. You breathe in to ascend, and breath out to descend but – and this is the key to breath control – there is a delay between those things happening. If you breathe in, you will only start to ascend once you cross that half-way point and become positively buoyant. When you exhale, you will remain positive and keep rising until your lung volume falls below the same point. That ‘lag’ in between inhaling and exhaling and rising and falling is one of the most fundamental principles to buoyancy control through breathing.
The importance of trim for buoyancy control
Being horizontal and streamlined when you are swimming is more efficient and therefore requires less energy, but it also helps to keep you at a constant depth. If your legs point downwards then every fin kick propels you upwards, with the result that the expanding air in your BCD makes you positively buoyant, so you need to deflate and descend and start again. It’s fiddly, wasteful of air, tiring, annoying and – especially if you’re overweighted – can easily result in an uncontrolled, rapid ascent.
In terms of equipment, wings are often touted as better for keeping a diver in trim, but good trim does not guarantee good buoyancy control, and jacket-style BCDs do not mean you can’t be in trim. There are pros and cons to each design, but being able to correctly weight yourself and control your position using your breathing are of more critical importance than the equipment you are wearing. Concentrate on improving your buoyancy control before splashing out on gear that you may not need.
Practice makes perfect
Understanding that your equipment, weights and personal physiology work together as one holistic system and not as individual components is key to successful buoyancy control, and it’s not always practical or safe to do these things during a regular dive. There are plenty of training courses available, but also don’t be afraid to ask at the dive centre – be that your local club or a holiday resort – if there’s an instructor or experienced diver who could assist you in a pool or shallow water session.
Don’t be afraid to remediate and experiment where possible, even if that means starting from scratch on the bottom of the pool. While you need to be able to perform skills and dive while neutrally buoyant and mid-water, re-acquainting yourself with the basics can be incredibly helpful. Much as it might have fallen out of favour in recent years, the old-school ‘fin pivot’, for example, is a really useful tool for familiarising yourself with the delay between transitioning from positively buoyant to negatively buoyant during the breath cycle. It serves no practical purpose for diving, of course, but once you become more comfortable with the sensations, mid-water hovering and adjusting your depth in the water column using breath control alone become that much easier.
Experiment with different locations for your weights and how it feels to move them around, and also how adjusting your tank strap might affect your position in the water. Experiment with different breathing patterns so you can either move up and down as you hover, or remain in exactly the same position. Have fun, play games, practice hovering upside down, pretend to use a camera with both hands so you can only move by breathing and kicking while pretending to take pictures. Doing all of these in a safe and controlled environment will go a long way to making your next dive not only more enjoyable, but also safer for you, the diver, and the marine environment we seek to protect.