The Buoyancy Control Device, Buoyancy compensator or BCD forms the hub of our SCUBA system. It serves two main purposes, firstly the practical in that it allows us to carry a tank on our back and take it under water. The second purpose and the most essential is, as it’s name implies, allows us to compensate for our buoyancy.
As SCUBA divers the skill that most beginners find the biggest challenge is the most important skill for us to master and that is being able to achieve neutral buoyancy. It would be impossible without the BCD.
When we go for a dive and descend from the surface the air in our bodies and equipment compresses. This means that the deeper we go the less buoyant we are and the faster we start to sink. To counter act this loss of buoyancy we experience through the compressing of air spaces, we replace that air by adding it from our tank into our BCD and that is what gives us our buoyancy compensation.
It’s an extremely important concept that is at the heart of successful and safe SCUBA diving. It’s also something that you will need to consider when choosing a BCD of your own. It’s particularly relevant to diving in cooler water where you will need to wear thicker exposure protection as this will become one of the biggest air spaces you will need to manage and compensate for.
If your diving aspirations consist of tropical vacations where you will wear light or little exposure protection such as a dive skin or thin wetsuit you will rely a great deal less on your BCD to achieve buoyancy control. But, if you dive in areas where you will need to wear a 5-7mm wetsuit or a drysuit, buoyancy control without relying on your BCD becomes impossible. This is because the more exposure protection we wear, the more air spaces we create and this makes us very positively buoyant on the surface. To counteract the positive buoyancy on the surface we need to add more weights to our system but as we descend and those air spaces compress our extra weights act as an anchor that will quickly plunge us to the bottom without our BCDs.
Different Types of BCs for Diving
There are quite a few different types of BCDS but they fall into two main categories relating to how it’s air cell functions. The first category is where we find the more traditional BCD and still the most common for recreational divers and that is the Jacket or Vest Style. The second category of SCUBA BCDs is the rear inflation or wing style BCs. Both have their advantages and disadvantages and the one that suits you best will depend on what type of diving you do or plan to do in the future.
Jacket Style BCDs
Jacket BCDs get their name because you wear them just like a sleeveless jacket or more accurately like a vest. The BC surrounds the diver’s torso and covers the shoulders and fastens around the waist. The air cell is incorporated into the entire jacket so as you put air into the BC it can move around the entire torso of the diver.
Jacket style BCDs are often seen as the preferred choice for novice divers and most likely the type you used or will use on an Open Water Course. This is mostly because of the way the air is positioned around the diver it makes it easier to maintain a vertical position in the water, particularly on the surface. While a great benefit to beginners and those that undertake long shore dives with extended time on the surface, a vertical position isn’t of much benefit in most diving situations.
Another useful benefit of of Jackets is they often have more in the way of pockets for carrying accessories and they are mostly weight integrated. Weight integration just means that your dive weights are carried on board the BCD in quick release pockets rather than being carried by the diver separately on a weight belt.
Again, as the name implies, a rear inflation BCD has an air cell that only inflates behind the diver and does not continue around the torso. The BCD can be one complete unit or can be a modular system made up of a harness, back plate and wing (air cell).
The are a number of benefits of rear inflation. Most notable is that rear inflation tends to promote better positioning of the diver in the water making them more horizontal with less effort. This more streamlined position is often referred to as a divers trim and good trim is something we should always be striving for. The more streamlined we are in the water, the less effort it will take us to swim forward.
Rear inflation BCs also tend to have less on the front of the BC, usually just a harness configuration like a backpack which can make them feel less cluttered. They also often have a greater lift capacity by having an air cell capable of holding more air. The modular systems made up of a separate harness and wing gives the added capacity of changing wings and air cell size to suit the diving conditions and applications. This is most obvious when changing from diving with a single cylinder to using twin cylinders.
If you’re a beginning diver their are a couple of things to be aware of if you are considering a rear inflation BCD.
First, when you are on the surface of the water and the air cell is inflated behind you, the BCD will try to keep you horizontal and push your face back into the water. It’s no big deal, you will learn to instinctively lean back into the BC on the surface and you will do it without thinking before long.
Second and more importantly is how the BCs react when you need to dump air out of them. With a jacket style BCD it’s easy and just like you were taught during your open water training. Flip yourself vertical, raise the BCD inflator and the air will make it’s way out.
With rear inflation you will most likely find it more challenging to get vertical and will want to dump air while swimming horizontally. As air rises to the highest point, in a wing that usually means that it wraps up around the tank on your back and it makes dumping out of your inflator hose while horizontal virtually impossible. Instead you need to reach behind you and find a dump valve on the wing itself and dump it from there, often sticking your bum up to make sure that the dump valve is the highest point of the BCD.
Features of BCDs
All BCDs regardless of what style they are must incorporate the following features to do their job
Have an expandable air cell. The air cell can increase in size when air is added to it and shrink in size as it forces their air out of it.
Low pressure inflator hose which is where the air from the tank is attached to the BCD. The inflator hose typically has two buttons on it, one to let the air in and the other to let the air out. Inflator hoses also include a mouth piece so that you can orally inflate the BC which is particularly useful if you are low on air while on the surface.
Dump valves and over pressure valve. There must be ample exits for air to leave the BCD when you want to deflate it. It also must have over pressure valves to avoid over inflating the BCD past it’s capacity.
Adjustable straps and buckles. You must be able to ensure a snug fit and allow adjustment for when you wear different levels of exposure protection.
Adjustable tank band to secure the cylinder to your BCD and a sturdy back plate to keep your system nice and rigid.
TIP: Almost all tank bands are made from a webbing material. This material will stretch when it’s new and becomes wet for the first time. Before diving in a brand new BCD you should try and stretch this strap otherwise you will find that your tank slips out from the BCD and almost without fail it will be mid-dive. The easiest way to do this is to give the tank strap a good soak in water and fasten it to a tank over night, tightening the straps a few times over the evening and doing this before your first dive with your new equipment.
Other BCD features to consider
Weight integration. Carrying your dive weights on board your BCD has become pretty much standard for recreational divers. Mainly for the added comfort it has over carrying weight on a waist belt. BCD weight pockets must have a quick release feature so that you can remove the weights in one quick and easy action.
D-rings are the semi circle shaped loops on a BCD usually made out of stainless steel or plastic and allow you to clip off accessories such as a torch or camera, they also give you a way to clip off regulator and gauge hoses so that you don’t drag them across the ocean floor or reef.
Pockets which are usually zippered or covered with a Velcro flap also give you good storage space for accessories.
Alternate air sources can be added to the BCD inflator. This combines your BCD inflator with your octopus regulator.
Choosing A BCD
At first the having to make a choice between BCDs can be over whelming, for many people it can be downright intimidating but it doesn’t need to be. The better idea you have of about the type of diving you will be doing in it, the easier your choice becomes. You should even be ale to narrow your choice down based on things like your body size and the temperature of the water you will be diving in. Let’s take a closer look of some of these considerations.
Comfort and Fit
If it’s not comfortable or doesn’t fit, it’s no good. Comfort is a hard thing to judge without wearing a buoyancy compensator in the water but there are a few things to be aware of.
If you’re going to be doing most of your diving in tropical conditions, wearing only a skin or rash vest, pay particular attention to what type of padding a BC has. You’ll want an adequate spine pad and possibly a cushioned trim around the neck and arm holes.
Ladies may also be more comfortable in a BCD that doesn’t inflate around the chest. There are BCs that are specifically designed for women, with comfort being their priority. These vests are lower cut under the arms to avoid squeezing the chest. They often have extra padding and are cut at the base with a ladies hips in mind.
When fitting a buoyancy compensator what aiming at a snug fit. You need to avoid any movement of the tank and BC unless you instigate it yourself. A BC that is loose in the shoulders or at the waist will move from side to side as you dive and as your tank drains and becomes more buoyant, it will try to lift it’s self off your back.
All most all buoyancy compensators today have an integrated weight system and they have made our sport infinitely more comfortable. When choosing a BCD take note of how much weight it can carry in it’s pockets and that it’s enough for what you carry in your thickest dive suit. Most BCs will have weight pockets at the front and hopefully it will also have smaller weight pockets at the back next to the tank strap. These are often referred to as trim weights.
An easy weight release system is necessary. You need to be able to pull out the pocket and ditch the weights with one hand and with one action.
If accessory pockets are important to you, be aware that in many BCs these sit over the top of the weight pockets. So, when the weight pockets are full of lead it is taking up the room from the accessory pocket.
Caring For Your BCD
The proper care and maintenance of your BCD will not only extend it’s life but will also ensure it’s safe operation. One of the most common safety concerns of an un-maintained BC is a sticky power inflator. With a build up of salt, sand and corrosion a BC’s inflate button can stick in the on position and has the potential to send an unprepared diver on an uncontrolled ascent to the service. If you find yourself in this situation you may need to disconnect your inflator hose and control your BCD orally.
SCUBA BCD Do’s and Don’ts
Here’s a few tips to help prolong the life of your BCD.
Avoid using your BCD in chlorinated water. Chlorine is incredibly corrosive and will ‘eat’ almost any gear that suffers from prolonged exposure to it. It can fade your BCD material but more importantly after a period the material will start to break down and become brittle. The webbing that forms the shoulder straps can also lose any elasticity it has and be more prone to breaking when under pressure.
If you are doing scuba training in a pool, ask the training facility if you can use one of their BCs, if you must use your own make sure to wash it thoroughly as soon as you can after being in the chlorine.
Avoid carrying weights in the BC when not in use. If you have a weight integrated BCD do not carry loaded weight pockets in it when not in the water. The weight from the pockets can put extra stress on the seams and stitching of the BCD as well as extra stress on the shoulder straps. Sometimes you won’t be able to avoid this but whenever you can, carry your weights separately.
Avoid sharp objects. Particularly in transit or storage, make sure there are no sharp edges or objects like a knife in the vicinity of your BCD.
Cleaning your BCD
When cleaning your BCD there are three ares that you should pay attention to. The outside material of the BC, the bladder or internal material of the BC and the power inflator mechanism.
The essential ingredient in BCD cleaning is freash clean water. You can use a mild detergent or a commercial product such as McNETTS BC life and conditioner. Personally all my gear including my BCDs go in McNETT’s wetsuit wash and it works extremely well.
The first step in washing your BCD is to remove any water that is inside the air cell. The easiest way to do this is inflate the BCD (orally), turn it up side down so the inflator hose and left shoulder are the lowest point and press the deflate button. Any water inside the BCD will empty out via the inflator hose.
The next step is to give the BCD a good rinse through the fresh or soapy water and allow the BCD a good soak. If you have time to leave it soak for 30 minutes, that will be ample.