Myth No 1 . The more buoyant lift available, the better the jacket. When the first adjustable buoyancy jackets for divers came on the market, leisure diving was in its infancy. From the start, these devices were the subject of misnomer, misinformation and misunderstanding.
ABLJs (adjustable bouyancy life-jackets) - as the early devices were known - were sometimes described as 'reverse-parachutes'. It was believed that if you got into trouble you simply inflated your ABLJ and sped safely to the surface. Unfortunately, several people suffered severe lung damage before it was concluded that these jackets were extremely dangerous unless you'd had 'special training' in their use. Owners of ABLJs filled their attendant 400ml bottles with trepidation and thought of using them only in cases of dire emergency.
This little reservoir of air, however, had another magic property. It was said that you could breathe from it via the buoyancy bag - as a last resort. It probably would have been! Party tricks in the pool were one thing - and often led to lung infections from the bacteria growing in the warm, damp conditions found in an unsterilised bag. In a crisis in the sea, however, trying to breathe from the ABLJ was more likely to cause either loss of the last vestige of buoyancy, resulting in rapid progress downwards; or in an over-filled bag and out-of-control ascent.
So it was that a philosophy developed that everyone should have an ABLJ - but no-one should try to use it!
Of course, we've moved on since then. We've discovered the joy and safety of neutral buoyancy. We now use medium-pressure air fed directly from our regulator's 1st stage to add buoyancy in a controlled way. And the modern jackets which we have come to know as BCs are, almost without exception, compact, comfortable and available in a range of styles to suit the demands of all types of diver.
Myths, however, persist - not least in the club environment, where individuals may have their credibility invested in inaccurate information. There are, for instance, still BSAC branches where all the members perservere with the discomfort of toilet seat-style ABLJs because the branch notables don't believe in stab-jackets! So let's try to debunk some of the myths and misinformation which still surround the BC, BCD, ABLJ, stab(iliser)-jacket, or whatever else you wish to call it.
Myth No 1 . The more buoyant lift available, the better the jacket.
Wrong! Bigger jackets can contain more air, displace more water and provide more lift. Bigger jackets also provide more drag, causing you to work harder under water and consume more air from your aqualung cylinder.
A diver should be neutrally buoyant at all stages of the dive. This includes when vertically at the surface with no air in the jacket (eyes above the water). If additional buoyancy is needed, there's too much lead on the weightbelt. Putting air in the jacket at the surface should float you comfortably with head well above it. Air contained in the jacket above the surface of the water (eg. above the shoulders) does not contribute to buoyancy at this time.
As a simple guide, you should not need any more buoyancy in your jacket than you have weight on your belt, plus the negative buoyancy of any additional peripheral equipment (eg, torches & winder reels) you may wish to carry with you. If you are neutrally buoyant at the surface, you will only need to add air to compensate for wetsuit compression as you go deeper. If you're wearing a drysuit you need sufficient reserve only to compensate should you suffer a severe failure of its air-tightness or direct feed.
Myth No 2 . BCs or ABLJs will rocket you out of control to the surface.
Wrong! Properly trained divers don't lose control. It's certainly the experience of most beginner divers, learning neutral buoyancy techniques in the pool, that they find themselves drawn irresistibly towards the surface. But then, the pressure changes in the shallow water found there are dramatic.
Try inflating your BC fully while at 30m or more. You'll discover that the effect of this dramatic displacement of the water is gradual, and you will certainly have time to take control, dump the offending air and return to a safe condition before you've gone very far. However, the inattententive diver, not noticing the start of a buoyant ascent, will find himself speeding upwards at a great rate of knots and probably have difficulty finding the appropriate dump controls in time.
The moral of this is to be aware of where you are, monitor your depth gauge or computer, and be sure to understand that your exhaled bubbles should appear to pass upwards at all times.
Myth No 3. Direct Feed controls are a major cause of out-of-control ascents. Wrong! Badly maintained direct feeds have been known to stick open. If you find this happens to you, disconnect the hose, reconnecting it should you need more air. Most experienced divers have had to do this at some time, and, in the light of what we've said about Myth No 2, you've got plenty of time to do it. Remember, since you will be achieving the deepest part of your dive first, once you have put in the maximum amount of air needed for a particular depth, you should only need to release air as you ascend to shallower depths.
Myth No 4 . Oral Inflation of the BC saves air. Probably wrong! Under water, there is no evidence to suggest this. Using exhaled air to put in your BC may sound like a good idea, but the extra effort needed for this action usually means you breathe more heavily afterwards. Complicated manoeuvres with mouthpieces are probably not advisable for out-of-practice divers. If you are safely at the surface, why not blow by mouth, if it makes you happy? But you will be amazed at how little the use of the direct feed depletes your air supplies.
Myth No 5. All BCs should float you face-up at the surface.
Wrong! It's just not essential. The adjustable buoyancy life-jacket (ABLJ) was actually not a life-jacket because it did not have permanent buoyancy. It might have floated you face up when inflated, but a diver who fell out of a boat, knocking himself unconscious on the way, was unlikely to be in a fit state to crack open the little emergency bottle. Manufacturers of modern BCs go to great lengths to disclaim that they are "life-jackets".
Some BCs will float an unattended and unconscious diver on his back when inflated at the surface. This could be useful for anyone who dives alone, but then they probably wouldn't make it to the surface anyway. Some BCs, notably the wings style, will float you on your front when used in conjunction with a lightweight aluminium tank. How-ever, it's not an overwhelming effect.
The attitude of a passively floating diver is more affected by the buoyancy of his tank (fully pumped steel is negative; empty aluminium is positive), together with the position of his weights, than the position or shape of his BC.
In a worst-case scenario, one hopes one's buddy will be able to cope. Another diver can turn you face up, ditch equipment and begin resuscitation. Towing a casualty with any sort of BC inflated is not a problem - but then some training agencies recommend discarding the BC and tank of the casualty altogether before attempting the tow.
Myth No 6. BCs with soft back packs are not for serious divers.
Wrong! A particular brand of BC has found favour with the majority of British club divers. The styles available are all substantial, bulky, and almost military in their approach to design. They are a good product. They all use a hard backpack..
On a world scale, however, they have only a tiny share of the market. Most divers now use BCs with soft backpacks simply because they take up less room in the travel bag. Who is right? It's different strokes for different folks. Many new 'tekkie' designs use a soft backpack unless they are fitted to twin cylinders
Myth No 7. Integrated weight systems are dangerous.
Probably wrong! In an emergency, positive buoyancy can be achieved by dropping the weightbelt. Divers who are trained to do this, will.
Those who have more recently taken up the sport probably would forget this option during a crisis because they are not used to doing it. During a crisis one resorts to familiar procedures.
Then again, a diver weighted for neutral buoyancy needs only to ascend a little for the residual air in the jacket or suit to expand and help him on his way. The 'controlled buoyant lift' has replaced 'dropping the weightbelt' as a safe way up to the surface. BCs with integral weight systems allow for emergency jettisoning of the lead. The only dangerous part of using one is the tendency to give hernias to those unlucky enough to have to try to lift a fully-rigged set out of the water.
Myth No 8. You don't need a BC if you're using a neoprene drysuit.
Wrong! There are divers who eschew the use of a BC on the basis that the copious amounts of air normally injected into the suit mean that the BC is redundant. However, planned redundancy is a key (and worthwhile) idea in the new philosophy of the 'tekkie' diver, and the BC is still useful for surface buoyancy or for the correction of irreversible inversion of the diver under water.
Myth No 9 . You need to put air in both BC and drysuit during the sub-surface part of the dive.
Hopefully wrong! You need only to maintain the volume of air in the suit - by direct-feed - as it becomes compressed by the pressure of depth; and, in case of thick neoprene suits, to add air to compensate for the compression of the neoprene. If you start off neutrally buoyant, you should not need to put air in your BC as well. If you do, it probably indicates that you're over weighted, or that your suit is a poor fit.
Divers often demonstrate a bizarre inclination to become obsessive over non-issues when it comes to equipment. The wing-style BC is a classic example of this tendency. American divers were recently reminded of the story of the Watergill At-Pac. This was a truly innovative BC back in 1972 when people were only just getting to grips with toilet-seat style ABLJs. It was remarkably similar to today's 'revolutionary' wings.
The At-Pac was also the first BC to incorporate low pressure direct feed inflation and weight integrated as a standard feature. I'm sure any modern diver transported back in time to those days would have chosen the At-Pac over any contemporary alternative. Yet it was labelled, according to a recent report in the Dive Rite newsletter, by an over-cautious American diving public as the 'Killer BC'! What were the reasons for this?
By the standards of those days, the At-Pac was a complex piece of equipment and the manufacturers elected to sell it only through dive stores which were sufficiently knowledgeable in its use. Unfortunately, they chose to supply only shops associated with one particular training agency, which left other dive shops in the same town in a quandary.
When faced with enquiries about an obviously desirable piece of equipment they did not stock, with no similar alternative available, and the only supplier also teaching a rival and hated training system, shop owners chose to look for technical reasons why their customers should not buy one.
Ignorance makes fertile ground for misinformation, and the generally worthy At-Pac was soon accorded the ignoble distinction of being one of the most hated and vilified pieces of equipment in the history of leisure diving. They said: "The Watergill At-Pac is dangerous. It floats an unconscious diver face down!"
A product which could have revolutionised buoyancy control back in the early 70s thus ended up sold to a relatively small number of divers.
It was not until the massive marketing power of the American Scubapro company was put behind their stabilising jacket in 1977, that the American diving public was prepared to accept anything other than chest-mounted ABLJs.
