Blog about Underwater Life and Scuba Diving

A Guide To BCDs – Your Personal Marine Elevator!

1 Star2 Stars3 Stars4 Stars5 Stars (No Ratings Yet)
Loading...Loading...

The Evolution of Buoyancy Compensation (No Win, No Fee!)

I’ve written about buoyancy before, where I extolled the virtues of learning and mastering perfect neutral buoyancy. I am of the staunch opinion that well maintained buoyancy is the doorway to excellent diving. The issue with this is that our bodies (read: lungs) are incapable of adjusting our buoyancy sufficiently to allow us to be very positive on the surface and negative underwater when we are in SCUBA gear. The solution that divers have been using for the vast majority of diving’s history is to weight themselves down with lead (using a weight belt) and then use a flexible container that they can fill or empty of air to compensate for the lead. When the container is empty of air, the lead pulls the diver down. When the container is filled with a little air, the diver will sit neutral in the water. You will find a full description here. When the diver fully fills the container on the surface, he will remain floating.

Of course, the diver would be both tired out and hampered if he had to hold this container of air in his hands, so the container was given straps that allowed the diver to mount this compensator on his back and leave his hands free. This, obviously, evolved into what we now call the buoyancy compensator device, or BCD (sometimes referred to as just BC). At first the BCD was nothing more than a vest that went over the head (like an airplane life vest) and was then secured by passing a cord through the diver’s legs and fastening it down. This was a clever remedy for a difficult problem, though it wasn’t the end of the design process. Dive gear manufacturers realized that the BCD could become more than just an air filled bag that strapped onto your crotch (that’s what she said, boom boom!), it could become the spine onto which all the scuba gear would attach. The modern BCD is the base station for all your SCUBA, it is your organizer, your mounting device and it also compensates for your weight belt’s negative buoyancy (it’s like Batman’s utility belt!)

The BCDs of Yesteryear Were Much Less Effective, But The Divers Were Much More Cool!

 

Styles

The BCD, having been around for so much of scuba diving’s history, has had plenty of opportunity to evolve into different sub-classes to suit the particular needs of many applications and diver preferences. Although there are many types of BCD, there are three broad categories that encompass most models. There are plenty of crossovers and half-breeds so this list isn’t a definitive breakdown of BCD classes.

Recreational Wing

This is the most common BCD on the market today. The reason I have used the differentiating tag of “recreational” is because there are two types of “wing” BCD, this the the common type. The common BCD has a large bladder of air (usually formed into two long lungs that run parallel to the tank) that flares out (more or less) at the sides to form something like a pair of balloon wings. Attached onto this inflated backpack is a pair of shoulder straps and a large waist belt. This BCD offers the best combination of stability, ease of release (for emergency situations) and storage solutions of all the styles of BCD, this is what has made it so popular.

The Standard BCD Format Is An All-Rounder, The Best BCD For The Average Diver.

 

Jacket

This is not a new technology, but it actually outperforms the recreation wing in terms of comfort and air distribution because the bladder is not just confined to the back of the BCD. The jacket’s bladder runs down the shoulders and into the straps themselves which gives a better distribution of buoyancy and is (arguably) more comfortable. In all other aspects the jacket BCD looks much like that of a recreational wing type BCD – it has pockets and hoops galore.

The issue with the jacket is there is trade off between comfort and safety which many divers cannot make. This compromise comes from the fact that a jacket’s straps cannot be released entirely in an emergency. The diver must slide out of them the same way one might doff a rucksack. Most other BCDs have the ability to completely detach all the straps, leaving you entirely disentangled from the BCD, should you need to get out of it easily or quickly in an emergency (most rescue training works on the basis that your BCD had quick release straps).

The Jacket BCD Delivers Great Buoyancy But Poor Release Options In An Emergency

Tec Wing

The divers that go Tec diving have a very different set of requirements from their BCDs. For one thing they want the ability to modify it themselves, they don’t want a pre-configured BCD. The Tec wing BCDs are much more simple looking, and can be bought as a separate back plate, straps and bladder so they can mix and match the equipment to their exact needs. Their bladders are usually much larger, round UFO-shaped balloons. They need the extra volume in their bladders because they tend to dive with a huge amount of gear and tanks (at least two of every item and up to eight tanks!). They also need them to be large and flat to give them stability with all this gear, a normal recreational BCD would leave the diver spinning and tilting!

The Tec BCD Allows For Great Customisation, But Is Too Serious For The Lay Recreational Diver.

The back plates on a Tec BCD are designed to accommodate an array of tank sizes and can be fitted with racks of up to four tanks. The Tec diver can also use compression straps that are fitted all around the BCD to pull the bladder into the shape they desire. A wreck diver needs to be able to turn fluidly, and a big wide bladder would slow his turns and make him less agile, so he’d probably dive with a skinnier bladder shape than a photographer who requires stable diving above anything else.

The Tec BCD usually doesn’t have much in the way of storage on it (though it can be modified to have more) so they often wear a vest with pockets on it and attach pockets to their drysuits.

There has been a trend to create semi-Tec BCDs that have the same size, shape and look as a Tec BCD but they are tamer and pre-built into one unit. These help the bolster the current expansion into the amateur Tec diving (basic nitrox use and simple two-tank diving).

Cross-Breed BCDs That Cater For The Half-Way Divers That Want Tec Performance And Rec Simplicity.

 

Bladders

I’ve mentioned bladders quite a bit so far which might have left a few of you thinking about the toilet more than the sea. The bladder is the part inside the BCD that actually holds the air. It might be part of the fabric of the BCD, called a single-bladder, or it might be a separate balloon inside the BCDs shell, called a double-bladder.

On a single-bladder BCD the material is usually a tight nylon weave with an impermeable coating on the inside (polyurethane or some other plastic). This system works well and generally will survive most abuse. However it can be prone to leaking at the seams and welds because that is where the BCD takes the most strain. It cannot really be repaired (beyond tiny leaks) because the structural integrity is compromised if the bladder bursts. Because there is less material and the manufacturing is simple, this tends to be the format that recreational BCDs take to make them more affordable and because the lay recreational diver doesn’t normally require peak performance from their BCD.

The double bladder is much more pricey because it requires a complex manufacturing process. It does reward this extra expenditure by offering a more robust BCD (less likely to puncture) and a BCD that can be repaired. By housing the air in a separate bladder it  allows the designers to use different materials for the outer shell which offers the Tec diver even more options, like trading lightness for strength (something a Tec diver likes very much!).

 

Auto Inflater

The BCD, being an air-filled bag, requires both filling and emptying of air. This could be a problem if you had to do this orally (imagine blowing up a balloon and emptying thirty times in an hour!) so the clever guys at the dive gear factories made a system that allows air to blast from your tank into the BCD on demand. This makes buoyancy compensation as easy as pressing the button in an elevator. They even made it analogue so you could put in small amounts of air for fine-tuning or big blasts of air for fully inflating the BCD in a hurry on the surface.

The auto inflator comes in a range of sizes and shapes (some even have a regulator built into them) but ultimately it is just a small valve that you open by pressing a button with your thumb and, when you release it the spring shuts the gate which stops the flow of air. Some of these buttons can be really stiff so make sure you test the feel of the button before buying a BCD.

Auto Inflators Come In All Shapes And Sizes, Make Sure Your One Fits Your Hand And Your Strength.

Features To Look For When Choosing Your BCD

Because the BCD is the keystone of your diving rig it is not enough for it just to be the shape you need, but you will also require it to have a number of other features so you can fully make it your own setup:

  • Pockets – This is where, if you’re like me, you’ll house everything plus the kitchen skin (and a tool kit to fix the sink should it spring a leak…underwater…). A good BCD will have many pockets in many areas which will allow you to configure things just how you like it. The pockets must also close securely but be wide when you open them. I like to have a zip closing on mine because you can’t always tell if a Velcro pocket is fully shut (and how gutted would you be if you lost your £200 torch because of a loose piece of Velcro!).
  • Rings and Hoops – Another storage requirement for me is a ton of hoops and rings that should be dotted about the BCD in any place the designer can fit one. The more rings you have the better you can arrange your gear. I like to have my SMB, compass and knife on my rings. I’ll also use them to hang my teaching slate off for a short while, and attach my octo to my chest. Lots of hoops means lots of configuration options.
  • Good Tank Band – This is a pet peeve of mine, I hate when a BCD has a poor strap design. Ultimately a strap is a strap, there is little to it. But when a strap takes super manpower to tighten it enough to hold the tank in place, it’s just bad design.

    If Your BCD Has A Poor Tank Band Then You Can Buy Replacements From Other Manufacturers So You Get Excellent Performance.

  • Double Tank Mount – Talking of tanks, some divers like to (or need to) take two tanks on a dive. In this case before buying a BCD you should check what tank configurations it can accept (most mid-range and top-spec recreational BCDs can take two tanks given the appropriate modification).
  • Knife Holder – This is a little feature, but I like it. On my BCD I have an unsightly knife sheath tie-wrapped onto the outside of it which sticks out a lot and can be a hassle when putting my BCD on in a busy boat room. An integrated knife holder is a nice touch that keeps your profile smooth. Aim to keep your BCD sleek, because loose or dangly gear will catch on things and cause drag while swimming – avoid looking like a Christmas tree!

    An Integrated Knife Holder Looks Great, But Check The Knife Because Sometimes The Blades Are Cheap.

  • Integrated Weights – This is a very big deal on the BCD market and has made a big difference to the way buoyancy is adjusted. With integrated weights you don’t take a weight belt (which is great because they are a pain to make up and they are uncomfortable), instead you put the lead into two removable pockets that slip into your BCD. These pockets are quick release so you can dump them just as easily as you can dump a weight belt. They are much more comfortable although they make your BCD much heavier which could be an issue if you struggle to carry a BCD and tank as it is. Some BCDs with integrated weight systems also include trim pockets at the rear which allow the diver to configure his weights to his exact specification.
  • Convenient Dump Valves – All BCDs have dump valves these days, but not all of them are easy to operate which is their whole purpose in life – to be easily accessible ways of rapidly emptying your BCD! On some BCDs the rear dump valve toggle is on the front of the BCD, which I hate. I much prefer to reach to the rear intuitively in an emergency, rather than trying to remember where my toggle is! As an instructor I also approve of a dump valve being incorporated into the low pressure inflator hose (pull the hose downward and the air will dump) because if a student bolts for the surface then it is easier to reach for a long hose than a small toggle.

BCD Tips

BCDs are often poorly introduced to new divers, and sometimes even experienced divers haven’t fully come to grips with this important piece of kit. Here’s a few tips and tricks that help me ensure my BCD performs as it should.

Use Your Cummerbund!

Pardon me? Use my what? The cummerbund is the large, usually Velcro, strap that you pass around your waist, it is then further secured by a large buckle. This is, surprisingly, the most important strap on your BCD because it is what hugs the BCD to the body when submerged. On land the shoulder straps reign king, but underwater it is vital you have a tight fitting cummerbund. It is wise to refit your cummerbund once you have entered the water because when you are wet it will feel more loose, and it’s imperative that you keep that strap tight, unless you enjoy your BCD riding up and down your back!

This tightening strategy goes for all your straps. Ensure that just before you go down, you further tighten every buckle. The closer the BCD is to your body, the more natural you will feel as you swim and the better your buoyancy will be.

Tie Wrap Everything!

This is possibly a slight exaggeration, you shouldn’t tie wrap everything, but it is strongly advised that you carry five or six wraps of different sizes with you in your BCD pocket because they are amazingly useful. They can be used to attach gear to your BCD (knifes, compass, etc), they can be used to keep teaching slates together (clip a bras hook onto the tie wrap and you can hang them from your BCD ring while doing skills) and they can be a quick fix (or long term one) if a strap breaks or a hoop gives out. They are water resistant, nearly indestructible and very portable, have them with you all the time!

Inevitably You Will Need To Tie Wrap Something, Carry Them With You At All Times!

 

Minimise The Movement Of Gear

If you value your gear and your BCD then you will pay specific attention to this point. If you have big pockets then you will no doubt find that gear rattles around in there. If you put the wrong combination of items in together (nice torch and reel with heavy brass clip) then you may end up with tatty or broken gear quicker than you’d like. It is also worth mentioning to those of you that carry extra weight for students or novice divers that lead blocks bouncing around in a pocket are a shortcut to a burst pocket.

The solution is to organise your gear so that it doesn’t rattle (put a squashy SMB with your torch to keep it from moving) or hang it on the BCD rings. Organising you BCD properly has many advantages and only takes half an hour of playing when you get it home from the dive store.

 

Don’t Overweight

A heavily overweighted diver will require more air in their BCD to attain neutral buoyancy. This means their BCD is inflated into a big size which will cause drag in the water (a swimmers arch nemesis) and will restrict their movement, not to mention what it would do to their buoyancy itself! A smart diver aims to have very little air in their BCD when they are neutral, this will make them more efficient which saves air and energy – both of which are high-value resources when diving.

 

Service, Service, Service!

Everyone knows they need to service their regulator every six months (that doesn’t mean they’ll do it though) but not everyone thinks to service their BCD. A BCD takes serious wear and tear, yet we rarely do much more than rinse it after a dive. A smart diver will flush his whole BCD out with fresh, clean water (you can add a little disinfectant too) after every couple of dives (or before he puts it away in the shed) by unscrewing the dump valve and filling the BCD entirely with water then flushing it out again. This clears it of salt and mould which accumulates over time.

You should also pay attention to the low pressure inflator hose because they have a tendency to leak. If they do then it’s time to change the O-rings in the auto inflator. It’s a simple job but many divers will ignore the bubbles until the button is almost useless. Don’t be a lazy diver, look after your gear!

 

Final Thoughts

Your BCD is the helm of your SCUBA setup, it is where you steer your small submarine from. As such it should be fitted to you, in size, shape, style, function and features. Don’t be afraid to modify your BCD to your own requirements, the more you make it fit you the more prepared you’ll feel when your twenty metres deep. Learn it’s features, adjust straps, move gear from a pocket to a hoop to a strap and practice donning it and doffing it using the quick releases. If you know your BCD, then you know your gear.

Do you have a favorite BCD style? What do you look for in a BCD? Is there any modification or feature that you just couldn’t live without? If so, please share with us and leave a comment using the section below.

Happy (buoyant) Bubbles!

By Jamie Campbell


Tagged as:


Blog Roll