Info Article | Buoyancy and the evolution of the BCD

Scuba divers world wide are familiar with the BCD – Buoyancy Control Device, this is the “jacket type” piece of dive gear that assists the divers with 2 valuable functions: 

Maintaining proper buoyancy control and having a device to attach the tank to the diver.

Buoyancy control is very important to divers as it allows proper horizontal or depth control while diving, allowing divers to dive safely (for equalisation), comfortably and avoid crashing into underwater plants, topography and structures (yes, conservation and self preservation are important); in other words, buoyancy control is as essential to diving as “balancing” is to riding a bicycle.

If you’ve  been diving less than 20 years you are probably most familiar with the “modern  jacket type” bcd). The main parts of the bcd are: adjustable shoulder straps, the BPI (or basic power inflator), cummerband, dump valves, tank band/strap and utlity pockets. The adjustable shoulder straps and cummerband ensure correct fit for comfort. The BPI allows the diver to add or subtract air for the correct buoyancy oreintation it is basically a puck or box with a “put air in” button and a “let air out” button; most bpi’s also have a mouthpiece allowing the diver to orally inflate the bcd.  

Let’s take a look and see how the bcd evolved

Way back when (> 25 yrs ago) there was a buoyancy device that divers called the horse collar: basially a round tube with a hole for the diver’s head, an inflation device, a couple of straps and maybe a utility pocket in the front – no comfortable cummerband or adjustable shoulder straps. To attach the tank, an additional device called a “backpack” was necessary. It consisted of a rigid plastic “plate” a tank band and shoulder straps.  Divers strapped on the back plate with tank and then donned the horse collar. A mission, yes,  but this was state of the art way back when (i.e. before the internet or cell phones)!

Moving along the development curve, Scuba Pro came up with the STAB (stabilising) JACKET. Really neat! It combined the functions of the horse collar and backpack into a single unit with a comfortable cummerband, tank strap and air chambers in the shoulder straps, and also utility pockets. A really comfortable unit, however not very popular in SA as there are no adjustments to the fixed shoulder straps; most scuba diving in SA is done from “Ribs” or Rubber Ducks (they have no ladder). At the end of the dive, the diver unclips the shoulder straps, hands the bcd to the skipper and hauls him/herself over the pontoon sides of the duck, inelegantly bellyflopping onto the deck. 

In Europe, Australia and many other countries,  the diver hands his fins to the deck hand and gracefully walks up the ladder with bcd (and tank) on his back.  In case you are wondering, the blue image on the left above is a rib or dive duck.  Note the height of the pontoon above the water. (We don’t actually dive from the little rubber duck at the top of this article)! Stab jackets are still enjoyed by many underwater photographers as the “all around air chamber” does what it’s name implies – “stabilises”.

Ok here we are, back to the modern bcd, so now we need to add a few more modifications to jazz up everything! Notice that there is no wrap around jacket near the “rib cage” and voila, we have a back inflation bcd! A bit more comforable for some divers as there is no air pushing against one’s ribs. Look at the little red “handles” in the front left and right lower sides of the jacket – these are pull handles for integrated weight pockets – another invention, that some divers find more comfortable than the traditional weight belt! (Psst – most divers dive overweighted – but that is for another article)!

Ok, what next?

Normal recreational scuba diving doesn’t provide enough adrenalin for some divers so along comes the technical diving “wing”. This type of buoyancy device kind of looks like a back inflation (which it is) the main difference is that it is usually an upside down “U” bladder, with a minimum of utility pockets and accessories. Techies prefer this type of device as it is more streamlined, often has a crotch strap (yep! for comfort and proper fit) and minimised mass and bulk.

The one that works for you!

Yep jump in the water with several different ones until you find the one that works for you! All your reputable dive shops have demo models that you can take for a test dive. The horse collar and stab jacket are not readily available so you are most likely going to experience the jacket type, the back inflation and the wing are your popular choices.  If you test drive more than 6 bc’s and can’t find one you like – you are probably not going about this correctly. 

A tiny bit of trivia  –  the ancient looking orange thing here is the only buoyancy device that qualifies as a life jacket – as it keeps the diver’s face out of the water!



–  Article provided by Russ Davies, Normalair Equipment Officer 


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Spring Braai Run Down

On Saturday the 2nd of September we hosted our annual NUC Spring Braai, the weather was perfect and a good turn out meant we had an absolute blast of day. The snoek braai, prepared by Marcel and Spy went down a treat, so did all the ice cold beer!

We also hosted our very first NUC beer pong competition, which provided much entertainment all round and set the tone for the rest of the afternoon. Well done to Tom and ‘The Dragon’ for winning the beer pong competition and the floating trophy in a hotly contested final which went down to sudden death with Daleen and Mark, we hope you will be back next year to defend your title.

The typical booze cruise that followed on Bert’s Tub was short but hilarious and enjoyed by all aboard, for me this is always a highlight of any NUC function on the dam!.
Well done to Vince, Tom and Marcel for cleaning up the awesome spread in the raffle, from dive trips, model cars, dive and spearo knives and Jeep gear. A big thank you also to everyone who bought tickets for supporting the club and to the sponsors of the prizes (African Dive Adventures, ORCA and Arnold Chatz Cars).

These social events are not only what makes our club unique but also are also an important part of our fundraising to be able to keep the oldest dive club in Joburg alive. Thank you to everyone who came and enjoyed the day with us.
In case you missed out; don’t dispair! The NUC committee are already hard at work preparing for our next event, the annual Beerfest on the 28th of October – as per usual, everyone is welcome and all are encouraged to bring a guest or two.

We also have a trip planned to Ponto at the end of September, if you are keen you can find details about this trip below, on our website and Facebook page. If you have any questions please feel free to give us a shout.
Again a huge thank you to all who helped organise and who attended for making the day a success – here’s to many more.