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  EXTRA

May 2000

COMPENSATION
CLAIMS

It's another big Diver test: we asked manufacturers to come up with two or three examples of their BCs to reflect today's market. Then we took all 39 devices under water. John Bantin returned weary but enlightened - use his findings to help you make your own BC choice.

In the 1970s, the Watergill Atpac was introduced to an unprepared diving market. It became the most hated and vilified item of diving equipment ever. Why?
At the time divers had to be very accurate about the amount of lead they wore. As they went deeper, they had to take greater lungfuls of air from the poorly performing regulators of the time to maintain their buoyancy. The Atpac was probably the first buoyancy-compensating device which allowed them to stay perfectly neutral at any depth, just like fish with their swim-bladders.
So why was it ill-received? It was worn behind the diver like a wing. He put air into it as he went deeper and released air as he came back up. Sound familiar?
The Atpac was not a life-jacket; in fact, it would float an unconscious diver face down. However, people at the time could not mentally separate such an item from a life-jacket and indeed the first BC to be accepted was the very effective but very uncomfortable Adjustable Buoyancy Life-Jacket, or ABLJ.
When I first heard about the ABLJ, I was told it was like a parachute in reverse. If you got into trouble, you filled it with air and it sent you straight back to the surface. With that sort of misinformation going round, it's not surprising that so many untrained and unsuspecting Watergill Atpac users ended up face down and unconscious on the surface!
Some traditional divers still swear by their ABLJs, though everyone else suspects that this can only be because they have never tried a modern BC. The sophistication of some of these is amazing - as is the price range. But none of them are life-jackets, and none can be said to float an unconscious diver face-up at the surface.
Nowadays wing-style BCs are the ones that are criticised for pushing divers face forwards. Wings with massive amounts of buoyancy available will certainly do this if you insist on using all of that buoyancy. But with all styles it's a question of your height and build, your suit, how you rig your tank and position your weights.
If you buy any new BC you should experiment with it before using it for any serious diving. As a guide, if you are not very tall and do not specifically need a wing, you're probably better off with a traditional-style BC.

Maximum lift: weight supported by the inflated BC. Surface-to-mouth height, BC fully inflated.

SURFACE SUPPORT
One of many functions a modern BC must perform is supporting a conscious diver comfortably at the surface. If you intend only to dive in calm, easy conditions, you might not need your head held very high above the surface. However, if you plan to dive where there are waves, you might feel more secure with a BC that lifts you clear of the surface.
In our test the surface-to-mouth height was measured with each BC fully inflated on the diver (me) and is intended simply for purposes of comparison. We used the same 12 litre steel tank throughout. This weighed more than 18kg in air but around 6kg in water.

LIFT
Maximum buoyancy available is another important factor, although remember that those parts of the inflated BC which are above the waves add nothing to surface buoyancy. A good rule of thumb is that a properly weighted diver needs no more maximum buoyancy in his BC than he has lead on his belt.
However, if you intend to use twin cylinders, especially steel ones, it's comforting to know that you can float your rig, without you, at the surface without it sinking. With twins we suggest you need at least 20kg of maximum buoyancy.
Many manufacturers obtain maximum buoyancy figures by measuring the internal volume of the BC buoyancy bag and the maximum amount of water it can contain.
A litre equals a kilogram of lift but this method does not take into account torso-squeeze, when a BC inflates inwards as much as it does outwards. We discovered a couple of uncomfortable examples during the test.
Then there is the weight of the item itself, including, sometimes, lots of heavy stainless-steel D-rings.
To gauge buoyancy we inflated each BC while I was wearing it as much as we could without it starting to hurt. We then removed it and measured how much lead the inflated BC could support in the water. Again, the figures are for comparison only.
We asked all the distributors to send us examples in size Medium, though you will notice that we received some in size Large. Presumably this was because Medium was not available, rather than a ploy to get any advantage from the buoyancy figures in the test!
Usually larger sizes mean bigger buoyancy bags, so the figures achieved for those products cannot be directly compared with the other BCs in the chart.
All BCs are meant to fill from their direct-feed (power inflator) fast enough to meet CE specifications, but we checked to see how easy it was to dump air during a normal horizontal swim. Air can get trapped in some of the poorer designs, which means a little more inconvenience in use, but among our selection these proved few and far between.
People are still taught to dump air by raising the corrugated hose, but this tends to let water back in the other way. We used the corrugated hose-operated shoulder-dump and also the pull-cord dump where fitted. The dump valve at the lower back is used in case the diver finds himself inverted and ascending.

BANDS, POCKETS & RINGS
The BC also holds your tank on your back. Most use only one camband but others use two, which must introduce extra security. One or two, it's best to wet them before fitting to a tank, as they often stretch.
Most BCs have pockets, some more useful than others. Until recently, the only BCs with stainless-steel D-rings were those intended for tekkies to hang stage-cylinders from. Now there are more around than you can shake a stick at!

INTEGRATED WEIGHTS
We were surprised that this collection of BCs more often than not featured integrated weights. Many also offered pockets at the back of the BC, usually high up, to accommodate weights to trim the diver's attitude in the water.
The latter are especially useful when using aluminium cylinders, although, unlike the main integrated-weight system, the lead cannot be jettisoned in an emergency.
There is no reason why a correctly weighted diver using a BC correctly to achieve neutral buoyancy should ever need to drop weights unless out of air, but at least if you can pull out your weights easily you can pass them up into the boat.

CONSTRUCTION
Few contemporary BCs use a soft backpack but many use a small, hard backpack combined with a cushion. Only a few had a hard carrying handle and some made do with a loop of webbing, mainly useful for hanging the BC up to dry. Some BCs had both, one had none.
Some BCs are constructed using a single bag which is made airtight by combining the material with something tough like polyurethane. In other cases an airtight bag is used inside an outer fabric bag.
The double-bag construction allows the inner bag to be easily changed should it get damaged and leak. The single-bag concept allows for a design that can be more streamlined and there is little evidence to show that it is more vulnerable in use.

Whichever BC you choose, get one that is neither too big nor too small for you. It should fit comfortably and not ride up above your shoulders when you are under water.
Finding one that is not black might prove harder.
In carrying out these tests I was ably helped by Mike Seares, whose input proved very useful. Thanks must also go to John Stanton of G&H Diving Services, for providing and calibrating all the lead we used.

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FITTINGS - THE DEVIL IS IN THE DETAIL

Above: Weights located at the back compensate for tank buoyancy Above right: Velcroed cummerbund with zipped key pocket. Right: Corrugated hose dump

Above: How many D-rings do you need? How many do you want? Above left: Integrated weight system with quick-release mechanism. Left: Weight pocket at the side of the BC

Intro | Table | £150-199 | £200-249 | £250-299 | £300-349 | £350-399 | £400-500 | Conclusions

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Appeared in DIVER - May 2000

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