Divers who have mastered precision buoyancy make diving look effortless. They are more comfortable and streamlined and use less energy and hence less gas
Precision buoyancy control Part 2
DIVERS CAN’T KEEP THEIR mouth and nose above the surface indefinitely while treading water, and we often dive in rougher water than even strong swimmers might enter (swimming standards are set low for divers).
If you’re out of air, wearing dive-gear won’t help unless you use it to make yourself buoyant by ditching the heavy bits. The proof lies in the many fatalities in which victims have been seen to reach the surface before sinking back.
If we assume that these divers are out of air, we need to demonstrate the contribution that overweighting can make to a surface emergency.
Divers, some highly experienced or instructors, have also been known to enter the water or accidentally fall in with their air turned off, sink and drown.
You might want to keep your BC partially inflated where a risk of falling in exists, and to check that your air is really on. We prefer to confirm this for ourselves rather than have a buddy check the tank-valve by hand, because the risk exists that they’ll turn the air off.
The speed at which even a properly weighted diver becomes exhausted and incapacitated and sinks can be appreciated by a simple exercise.
Move into water too deep to stand up in while properly weighted. Vent all air from your BC and tread water, keeping your head clear. Stop as soon as you feel uncomfortable, and don’t be surprised if you don’t make a minute.
Keep close to shallow water for safety, or within easy reach of the poolside or a ladder, with an instructor ready to assist if needed. Repeating this exercise holding an additional 2kg weight only reinforces how quickly fatigue sets in with just a little overweighting.
THIS IS THE SITUATION in which one diver found himself after stepping off a dive-boat into deep water with his air off, either because he forgot to turn it on or it was switched off, or off and back half a turn, by his partner.
He sank immediately, failed to drop his weights and was lucky to be rescued by a divemaster who was both very close and very attentive.
An empty cylinder won’t make a properly weighted diver usefully buoyant at the surface. Most empty 12-litre cylinders would provide less than 1kg positive buoyancy, even if the diver was carefully weighted to be neutrally buoyant at the safety-stop with a quarter of the air left.
An average BC, by contrast, provides around 14kg. This is needed to raise the diver’s head, which weighs around 8kg, high enough above the waterline for breathing.
Many divers are now trained to wear a snorkel on their mask at all times. Learning to switch to this quickly on reaching the surface in an out-of-air scenario can make it much easier to breathe and control the situation – if the diver is not overweighted.
An overweighted diver may be unable to keep the snorkel tip clear of the water without finning hard, which is exhausting, in which case the snorkel may have little value.
The proper weighting test described last month is designed for going diving. Even if properly weighted, keeping your head clear of the water and able to breathe requires you to tread water holding the equivalent of an 8kg weight.
This is because the weight-check means that you arrive back at the surface, even with an empty tank, with your mouth and nose pretty much at or below water level.
Swimmers without additional flotation must work to keep their mouth and nose clear of the water to breathe, and a scuba diver is little different.
To survive an out-of-air situation on the surface, it’s vital to recognise how quickly this can become an emergency, and act swiftly and decisively.
The next exercise provides part of the solution…
Divers who reach the surface out of air and then drop back and drown have failed to carry out the one simple and near instantaneous act that would make them positively buoyant, float at the surface and probably save their lives. They didn’t ditch their weights.
Many new divers have not practised weightbelt-ditching except, in recent years, as part of the CESA (Controlled Emergency Swimming Ascent) skills conducted by some, though not all, training agencies.
It seems likely that most people diving today have never practised emergency weight-jettisoning. Instructors may worry about damaging pool floors, but this skill is so fundamental that ways should be found to practise it repeatedly.
Soft weights are a good option. If we exclude this skill from entry-level, rescue, scuba refresher and buoyancy courses, which other skills will we decide to neglect
Weights ditched, you can achieve greater buoyancy by inflating your
Divers and their instructors have been taught to fear rapid ascents.
Even our perception of what “rapid” means has changed. Ascents directly to the surface at 18m per minute were once standard. Today, most computers call for ascents of barely half that speed, and demand a safety stop too.
Research indicates that lung injury is usually preventable at the speeds achieved with a fully inflated BC from recreational depths, but shows no useful evidence of drowning victims ever returning from the grave.
For us, the buoyant ascent, promising a very good chance of survival, wins over the certainty of death.
Letting students try a buoyant ascent for real is not a good idea, because they may fail to follow instructions to the letter. As instructors we would demonstrate it ourselves, holding onto a weight on the pool-bottom at 5-6m, ditching weights and fully inflating our BC before letting go.
The first demonstration can be done vertically to decrease drag and increase speed, the second spread-eagled, to show how flaring typically halves the ascent rate.
By demonstrating our own confidence in the buoyant ascent, our hope would be that our students would be less scared of resorting to it in an emergency.
However we must underscore that we don’t recommend that anyone who is untrained practises this exercise – and that all the skills here should be practised only under the supervision of a qualified scuba instructor. Teaching yourself could cause injury or worse.
UK divers often learn in small, shallow pools, unrepresentative of how they will actually dive. Entry-level divers need to be trained in at least 3m or more of water, which provides space for starting to master ascents, descents and midwater exercises.
Scuba courses stress the need for divers to avoid direct contact with the seabed to protect the environment and maintain visibility, as well as preventing indirect contact from fin-wash.
Students need space to practise and master midwater skills, including trim control, spatial awareness and finning techniques.
Diving requires a lot of multi-tasking. When buoyancy control distracts you, it not only takes your attention away from enjoying your dive but compromises safety. You may be too preoccupied to monitor your air properly, for example.
Our goal is to make buoyancy control almost subliminal, requiring less concentration, but being usually a combination rather than a single skill, it requires multi-tasking in itself.
Practice not only makes perfect but makes it easier to divide your attention safely – perhaps to take pictures.
Many factors, some man-made, others natural, play a part in damaging coral reefs. The significance of diver damage may be disputed, but if the environment is undamaged before we dive on it, it shouldn’t be damaged afterwards.
Accidental contact is not 100% avoidable, but good buoyancy control skills are a vital preventative measure.
A diver can achieve perfectly neutral buoyancy in almost any attitude, including upright with feet dangling. To be safe to yourself, your buddy and your surroundings, you need to master both trim control and spatial awareness.
The next exercises aim to build ability to perfect trim control and hone spatial awareness in progressive steps.
HOVERING AND SPACE
Obstacles can be used to teach spatial awareness, which also factors into trim-control. They help students learn how to avoid accidental contact with corals, for example.
Swim-through frames provide an objective, non-negotiable method of measuring Performance.
Hoops can be used, though we prefer Pete Wallingford’s Diamond Reef Hover Stations. Their diamond shape better replicates a diver in cross-section, with the cylinder passing through the top, shoulders through the sides and legs through the bottom.
The Hover Stations are tight enough to hook stray equipment such as dangling gauges and improperly secured octopuses. Their open top helps prevent the diver becoming trapped in the framework, which adds safety. They look quite large when you first see them but they’re deceptive and regularly catch out instructors, including us.
Moored using two 1kg weights, the Hover Stations will move if students make contact with them. The instructor can see and the student can usually feel the contact, so feedback is immediate and unambiguous.
Many divers swim badly trimmed, because humans naturally adopt a feet-down, head-up position in the water.
Apart from sedentary marine life, everything else is built to move efficiently through water, and as we should want to swim more like a tuna than a seahorse, trim control becomes important.
The combination of different bodies’ flotation characteristics and different diving equipment’s buoyancy means that getting horizontal isn’t always easy.
Students can start by trying to hover horizontally with their body midway through the frame of the Hover Station.
Many will find it difficult to stay horizontal, stressing that achieving neutral buoyancy is only part of the process of mastering buoyancy control.
Divers who can swim horizontally are more streamlined, use less air and are less likely to kick up silt or collide with coral. They need to learn how to redistribute weights to bring themselves onto an even keel.
Ankle- and small block-weights that can be clipped on quickly can help compensate for any bias. Buddies or instructors can often see if you are pitching fin-down or head-down more easily than you can feel it.
All diving equipment and its position on the diver will add weight or buoyancy and affect trim, so this exercise is about redistributing weight.
If students add trim weights, they must remove a corresponding amount of ballast to avoid being overweighted.
MAKE LIKE A SEAHORSE
Hovering upright in the foetal position and sculling through a Hover Station is an exercise we call the Seahorse.
You need to make fine, thoughtful adjustments to your midwater position to pass your fins over the lower part of the frame by inhaling and then exhaling to drop yourself slightly to pass your body and head under the upper part.
Once you can do this going forward, you can try going through backwards. You learn to scull through with your hands. It ramps up the task-loading, because you have to think about the position of your fins, your breath control to precisely adjust your position as you limbo through the frame, and your hand movements to avoid the slightest contact with the Diamond.
Mask-clearing often leads to a large shift in buoyancy. Many divers exhale far more than necessary to clear even a fully flooded mask, and a big breath out is usually followed by a big breath in! This leads to a yo-yo effect, with the diver first sinking, then rising significantly.
Most divers can easily clear a modern low-volume face-mask 6-10 times on one breath. By learning to use just enough air to clear the water from your mask, the importance of thinking about breath-control is again reinforced.
Divers often practise mask-clearing and removal during training while kneeling overweighted on the pool bottom, so don’t experience a rapid descent when they exhale violently to clear the mask, as they would in midwater. Yet it is in midwater that they are most likely to have to do this for real.
By practising mask-clearing, then removal and refitting, while lying prone in a Hover Station off the bottom, students are better prepared for open water. They will be able to complete this exercise without touching the frame, using a very simple trick – breathing normally.
Divers’ fins have no nerve-endings and are often badly scarred from contact with rocks, corals and wreckage. Their thrust creates a lot of fin-wash, too. Over sand, even experienced but unaware divers leave an easily followed silt trail.
Learning about fin-control begins by swimming through the Hover Stations. Divers often underestimate how far fins move through the arc of the up-kick and downstroke cycle. Instant feedback from clipping the Hover Station helps to bring this home, and divers quickly become more aware of the position of their fins relative to what’s below, above and behind them.
Sculling fins to swim backwards is a skill useful to divers with their hands full of cameras, for instance. Another is propulsion using only the upper fin when there’s any risk of disturbing silt. The other fin, kept below it, deflects the wash away from the seabed.
The Helipad encourages divers to combine their understanding of breath-control and spatial awareness as well as fin-wash. Using six lightly weighted skittles, a rectangle slightly longer than the diver and marginally wider is marked out.
Students swim over the top and, by exhaling, drop into the rectangle without knocking over a skittle. Next, using mostly breath control with BC inflation only if necessary, they lift up and away without disturbing the skittles either by direct impact or through fin-wash.
Divers are encouraged to get half a metre or so above the Helipad and horizontal before moving away with careful finning, so as not to disturb the skittles.
Students can try carrying a bag containing a 2kg weight through Hover Stations set just off the bottom, in midwater and just under the surface.
They have to add air to their BC and work hard to maintain proper buoyancy control by carefully combining the adding and dumping of air with fine-tuning from breath control.
It’s another reminder of the importance of proper weighting and trim and brings in a little multi-tasking.
Divers must think about how to position the bag to prevent it upsetting their trim and causing them to collide with any part of the Hover Station.
To help divers combine learning how to control their trim with spatial awareness, a short tunnel can be made from three Hover Stations. The students have to swim slowly through without making contact.
Once achieved, more multi-tasking is introduced. They may be asked to pick up and carry through the bag with the diving weights inside or, later, unspool and rewind a reel on their way.
The exercises should be fun as well as confidence-building, so we might also have them swim through on their backs.
We don’t accept that these skills are beyond the reach of a diver in the early stages of training. Better buoyancy-control skills need to be integrated into entry-level scuba training across all agencies.
The diving industry has made a rod for its own back, with courses that are too cheap and too short, and entrenched attitudes. Teaching better buoyancy control seems destined to remain a low priority, but enterprising instructors armed with some diamond-frames, skittles and patience can go a long way to improving the situation.