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
A RECENTLY QUALIFIED diver joins a group swimming through the shallows of a coral reef. The young guide ahead moves effortlessly, occasionally standing on his head in midwater to check on his charges or look under a rock.
The new diver isn’t really enjoying himself. He is constantly distracted as he first injects air into his BC because he is sinking, then dumps it seconds later because he is rising.
His mask is leaking and a little fogged up, and every time he glances at his pressure gauge his air seems to have plummeted. Fear of running out before they get back to wherever the boat is increases his breathing rate.
He may not recognise it, but he is experiencing a bad dive. He may eventually decide that diving is not fun and pack it in, or else continue and muddle through.
At worst, he’ll spiral into an incident endangering or possibly killing himself and others.
The diver is badly trained, has been certified before he is ready and doesn’t realise it. Unless someone levels with him, his situation is unlikely to improve.
DIVING HAS LONG SUFFERED FROM a high drop-out rate, but now far fewer people are taking up the sport to replace those leaving it. Many divers are also largely inactive, making only a few dives a year, so they spend less money purchasing the services on which the diving industry survives.
A little late in the day, that industry is trying to stem the outflow of divers.
Divers often drop out if they feel uncomfortable under water or have a bad experience, and the two may be linked. Lack of core-diving competence can easily create a situation in which the diver has a bad experience, gets a fright and loses confidence.
Proper pre-screening of students and thorough entry-level training should prevent most divers getting into difficulties most of the time.
Training should also provide the mindset and skills base to enable even the novice diver to extricate himself with minimal drama long before a situation gets out of control.
One of the main causes of losing control under water and a major contributory factor in serious diving incidents and fatalities is really basic – poor buoyancy skills.
So many divers struggle with one of scuba’s most important skill-sets, and if the problem lies in the teaching, the solution lies there too.
But divers must also take their share of responsibility, demand better training and be prepared to pay for it.
FORMAL DIVER TRAINING from the major agencies often lags far behind useful developments because of a lack of foresight and imagination by industry leaders. BCs, octopus rigs, dive computers and nitrox all ran into heavy resistance from instructors before later becoming incorporated into mainstream recreational diving.
Buoyancy-control training has changed little in the 30 years since the last major revision to how entry-level diving is taught.
Optional buoyancy courses (a number of which featured in divEr’s summer Skills Booster supplement) are an anomaly, an admission that a skill-set everyone agrees is essential is not being taught adequately to new divers.
Drivers take lessons, pass their test and get a licence. Imagine then being told that a speciality driving course exists called “Braking” – but that you don’t have to take it.
As instructors we designed our own course, inspired by an American instructor prepared to buck the system.
Twenty years ago, multi-agency-qualified Peter Wallingford came up with his Diamond Reef buoyancy-control training programme and tried to interest training agencies Stateside, but they were indifferent.
Our Precision Buoyancy course was not endorsed by any training agency. We realised that divers seeking out buoyancy-control training wanted results, not badges.
The programme centred on teaching proper weighting, the relationship between this and breath control, spatial awareness and problem-avoidance and management.
Training agencies stipulate that new skills should be learned and practised only under the supervision of a qualified instructor and we endorse that.
We don’t currently run the course, but we hope all divers will find tips here that they can apply to make their next dives safer and more enjoyable.
THE WEIGHT CHECK
Overweighting is a running theme in fatalities, near-misses, runaway ascents, crashed safety stops, over-breathing and general diver discomfort.
Training manuals stress the importance of formal weight-checks, but this skill does not seem to be being taught adequately by all instructors or remembered by students.
In the UK many divers learn to dive in warm freshwater pools, wearing thin wetsuits provided by the school. Steel cylinder will often make them several kilos overweight to begin with, and adding more weight to plant them on the bottom adds to the overweighting.
If it was explained to students that a little deliberate overweighting might help to begin with, but that as they relax weight could be removed, and if they did this on the course, they would learn valuable lessons about proper weighting and the need to be ready to adjust it.
A weight-check should be made during all beginner pool sessions and entry-level training dives in the same way as a buddy-check, mask-clearing, alternative air source use and other performance-based skills to ram home its importance.
You can learn proper weighting only if you need to add weight. Most dive-gear sinks if you throw it into a pool,
as do people, at least to the top of their heads. So students need to wear a suit buoyant enough to overcome the dead weight of their scuba gear and their body, and start the course positively buoyant.
This implies a coldwater wetsuit. We suggest that entry-level training should be done in suits thick enough to require at least 4kg of lead to attain neutral buoyancy with a full tank. The goal is to replicate how students will dive for real.
The weight check doesn’t need to be done with a near-empty cylinder. There’s a simple formula for calculating how much additional weight will be needed to compensate for a near-empty tank at the end of the dive.
Air weighs 1.25g per litre. Multiply the volume of the cylinder, say 10 litres, by its pressure, say 200 bar, to get 2000 litres. Multiply this by 1.25 to get 2.5kg. This figure will prove useful shortly.
The weight-check is done in standing depth. Air-trapping can be a problem with a BC, especially if it is the wrong size or improperly adjusted, making it hard to vent completely – and divers can’t see what’s happening behind their heads. An air-pocket will make them over-buoyant at the surface and con them into adding more weight.
Under pressure an air-pocket will lose buoyancy, and once a diver levels out or up-ends and dumps again, it’s likely to vent completely. The instructor or a buddy should look for this problem and may be able to see a position that can be adopted to fully vent the BC.
Air-pockets can also form in suits, and exhaled air easily gets caught in hoods folded back behind a diver’s neck. Such air usually makes its way out while making the weight-check.
IT’S BEST TO DUMP through the dump-valves rather than by holding up the oral inflator hose, which tends to let water into the BC and can be used only in specific attitudes.
Most BCs have several dump-valves that permit dumping in almost any position and restrict water ingress. Dump-valve controls usually have less room for movement than inflator hoses, so can be quicker to locate. This makes them faster to operate if an ascent begins to speed up.
Teaching divers to reach for the dump-valve itself, then run a hand over it to find the pull-cord, helps them to locate controls quickly. The more they do this, the more instinctive and easier it becomes.
Students can be passed weight until, holding a half-breath, they float at eye-level. If they keep their mask on and regulator in, they can simply tuck in their knees to bring their feet off the bottom, so this skill can be done in shallow water.
Once the proper weighting with a full tank is established, add enough weight to balance the amount the tank will lose during the dive. Students can calculate this using the 1.25g rule mentioned earlier. Small weights help with making fine adjustments and emphasise the importance of precision weighting rather than a make-do approach.
THE DROP TEST
To further demonstrate the effect of overweighting, we would freefall to the pool floor twice with the students timing us. The first time we would be properly weighted for the start of a dive. The second, we would be carrying an extra weight.
Adding just 2kg roughly doubles our descent speed. We would not have students practise this – the demo is sufficient.
You can get a sense at the surface of how essential breath control is to easy diving, simply by inflating your BC fully and experiencing how far you rise and fall with each inhalation and exhalation.
Experimenting with both shallow and deep breathing reveals the effect that breath control has on your buoyancy, much as when making a fin–pivot or hover.
We would descend and review the fin-pivots and hovering that should have been learnt on any beginner course. The instructor holds out a hand in front of students practising fin-pivots to indicate where they should halt.
Hovering again should require a reference point to indicate the depth students need to maintain. Hitting the mark makes them think about how deep a breath they can take.
Repeating fin-pivots and hovers several times at different heights, even with accomplished students, ensures that they really are in control and not just fluking it!
DESCENTS & ASCENTS
Our next skill-sets, finely controlled descents and ascents, are just an extension of hovering. While BCs have made diving safer, they also allow divers to dive overweighted. Lazy instruction has led even experienced divers with advanced training to think diving overweighted and depending on the BC to compensate is normal.
Before BCs were invented, divers learned to balance their weight precisely to control their buoyancy. There are limits to this technique, depending on suit thickness and compression characteristics (neoprene does not compress and lose buoyancy according to Boyle’s Law), cylinder specifications and volume, lung capacity and even the density of the water.
For fun we sometimes dive without BCs. It’s liberating, because buoyancy control is so easy if you understand the principles of proper weighting and breath-control. The next set of exercises are designed to wean the diver off over-reliance on the BC.
When overweighted divers dump air from their BC they tend to drop quickly, which can lead to buddy separation, hurt ears and getting into deeper water than intended. Combine a deep wall, nitrox and an unskilled and unaware diver, and you are inviting an incident.
A properly weighted diver falls much more slowly. The aim of the Elevator is to slow the descent and make the diver much more aware of controlling it.
Divers slowly release air from the BC until, by exhaling, they begin to sink gradually. They inhale to slow or pause the descent, reinforcing the role of proper breath control.
Overweighted divers run a higher risk of making uncontrolled rapid ascents. We would teach divers to ascend with minimal air in their BC and, again, to initiate the ascent by inhaling, ascending in stops and starts by inhaling and exhaling and without finning (but not, of course, holding their breath).
Many precisely weighted divers, even using thick wetsuits, do not need to add air to the BC during the descent, landing even in 6m extremely softly.
A little air usually has to be added to initiate the ascent, but many students find they don’t even need to dump this, controlling the entire ascent through breath control.
Buddy-pairs can practise descent and ascent skills facing each other, instructed to keep pace and stay within reach of each other and make descents and ascents as slowly as possible.
The goal is for them to control their buoyancy and maintain buddy awareness. Teaching buddy teams to rotate during ascents to look for boats or other hazards causes divers to lose sight of their partners, so we would prefer each of the diver to stay face to face, looking out for their buddy by scanning behind and above them.
Once an ascent begins, the diver should not redescend unless intentionally. Overweighted divers
tend to over-inflate, then over-dump, as is commonly reported to occur during rescues.
Divers should position gauges to be read without losing sight of the buddy, and keep monitoring the depth display to confirm that they are ascending and control their ascent speed.
They can take hold of their inflate or dump controls before ascent or descent – fumbling for them, especially if over-weighted, can mean loss of control of speeds.
OVERWEIGHTED DIVERS compensate by adding large volumes of air: about one litre for every kilo of lead they
don’t need. The rapid and dramatic contraction and expansion of this air in their BC makes it far more difficult to accurately control buoyancy, and they can quickly be overcome, especially on safety stops, by excess air in their BC taking control of them.
A properly weighted diver can rise or fall only relatively slowly in the water column, so there is more time in which to notice and bring under control any hint of a developing runaway descent or ascent.
Adding and venting air from the BC should be the final part of the precision buoyancy control programme – quite unlike the usual sequence of adding too much weight and then adding large volumes of air to the BC to compensate, with breath-control coming a poor third.
NEXT MONTH: Part Two of Precision Buoyancy Control looks at how better understanding can help to save lives and bring into play midwater skills – which in turn make divers not only safer but more environmentally friendly.