BCD FAQ

1. What is a BCD?

The acronym BCD commonly is considered to stand for either Buoyancy Compensating Device or Buoyancy Control Device.  Generally when a diver refers to a BCD they are describing an inflatable piece of diving equipment which takes the shape of a sleeveless jacket. This jacket performs two main functions. Firstly, it provides the support and mounting mechanism that holds the scuba cylinder in place, when the BCD is worn by the diver the BCD jacket supports the weight of the cylinder and allows the diver to “carry” their air supply for the dive. Secondly, and perhaps most importantly, the BCD can be inflated using Air from the scuba cylinder. On the surface, fully inflated, the BCD provides great amounts of positive buoyancy allowing the diver to rest and relax on the surface without the fear of sinking. Whilst underwater, small quantities of air can be added to, or subtracted  from, the BCD to control the diver’s buoyancy and position underwater. BCDs come in many shapes and sizes, from the familiar jacket styles that most scuba students will complete their courses in, to the harness and “wing” style (a large inflatable bladder),  preferred by technical divers.  

2. What is better for diving, a weight integrated BCD or weight belts and non-weight integrated BCD?

BCD’s which have weight integration generally provide additional comfort and a better fit over non weight integrated BCDs and weight belts.  Wearing a weight belt can cause bruising and discomfort around the hips, particularly after a long dive.  Because the weight is more evenly distributed in a weight integrated BCD this should prevent any areas from rubbing or bruising as with a weight belt.  BCD's can also provide additional padding against the weight of the air tank which can be more comfortable. However, weight integrated BCD's may not provide enough weight in certain circumstances, so wearing additional weight on a weight belt may be more appropriate. 

3. How do I choose the right size BCD?

You will need to check the chart size from the manufacturer to help you choose the right size BCD.  Each design will be slightly different but in general for jacket style BCDs you should opt for a BCD that once worn, the edges of the pockets, where the BCD secures in front of the stomach, are no further apart than 4 to 6 inches (10 to 12cms). It is generally better to try on BCDs, to ensure the fit is correct. Through discussion with instructors and retailers can often lead to good advice and a great fit for new products using the a comparison from the brand and size of jacket you wore during your training or have used in the past.  

4.  Will I still need a weight belt if I am wearing a BCD?

It depends on the whether the BCD you have chosen is weight integrated, which have removeable pouches that hold your diving weights in the jacket or if it is a non-integrated style BCD. In most cases if you are wearing a weight integrated BCD you will not need a weight belt as well.  However if you are diving in cold waters and wearing a thick wetsuit or a dry suit then the BCD may not hold enough weight and you may also need to wear a weight belt as well.

5.  How are BCD's weighted?

Buoyancy is controlled by adding air to you BCD and additional weight is integrated through special removable pockets.  These can be quickly removed in an emergency situation and you can also take them off and hand them to the boat crew to make it easier to lift yourself up out of the water.  You should always ensure you are not over-weighted on a dive as this can make you tire much more quickly and will also affect your buoyancy.  You do need to allow for any additional equipment you are carrying as well when you work out your BCD lift capacity.  In general these weight ranges will apply in the following conditions:

  • Warm water diving (thin or no wetsuit) – 8 to 12kg
  • Recreational diving (full wetsuit) – 10 to 20kg
  • Technical diving (dry suit and challenging conditions) – 20 to 40kg

6. What styles of BCD's are available?

BCD's come in two main styles, wings or jackets.  The normal jacket style is easy to put on and comfortable to wear and provides good all-round buoyancy. The wing style BCD has inflation at the rear which keeps your front section clear. This can provide additional mobility in the water although the rear inflation has a tendency to push divers forward whilst on the surface, which can be disorientating for new divers.  Another benefit of wing designs are that they pack down very compactly which is ideal for storage and transportation.  Wing designs are preferred by more experienced and technical divers, as they are ideal for use in confined environments such as caverns and wrecks. The lack of the bulky pockets which are present on the jacket style, make the wing a more streamlined option, with less chance of snagging or entanglement at the front.  Jacket style BCDs are much more suitable for beginners as they will be similar to the jackets used whilst on dive courses, and provide an upright floating position whilst on the surface, a feeling as though the diver is being “held up, under the armpits”.

7.  Are there any lightweight designs for travelling?

Yes, most manufacturers include at least one BCD specifically designed to be lightweight and smaller in size to easily pack. Most BCD's can be quite heavy and bulky to transport around so if you do need to do a lot of travelling with your equipment, you can opt for one of the special travel versions.  These travel BCD's are made from lighter materials and have only basic features.  The steel D-rings may also be replaced by durable plastic versions which are much lighter (but still very strong).  These lightweight travel BCD's are suitable for warm water conditions and minimize weight and bulk.

8. How many dump valves should you have on a BCD?

Dump valves are important safety features and allow you to adjust the air in your BCD quickly.  The more dump valves there are the better and most BCD's have a least two.  These are typically located on both shoulders, one either side. These allow the diver to expel air from the BCD easily and quickly, though since air naturally wants to float to the highest point in the jacket, these dump valve are only effective when the diver has a “heads up” orientation.  Most new divers should be encouraged to look for BCDs that have an extra dump valve at the bottom of the jacket to the rear, often in region of the right hip or buttock. These valves allow air to expelled form the bottom of the jacket when the diver is swimming in the more natural horizontal orientation underwater. Or in the event of an uncontrolled assent, where the instinctive reaction is to orientate yourself head down and try to overcome the buoyancy of the jacket buy finning hard to swim to the bottom, the hip valve now becomes the highest point of the BCD and air can be quickly expelled from this to stop the assent and regain buoyancy control.  Make sure you know where these valves are located and that you can find them by feel, so that you can use them quickly and easily when you need to.

9. How many pockets do I need on my BCD and how big should they be?

The amount and size of pockets you will need on your BCD will depend on the kind of diving you are doing and how much you need to carry. Instructors and Dive masters generally opt for as much pocket space as possible, whereas recreational divers make a choice between pocket space and the streamlining achieved from small or no pockets. In warm water conditions you will only need a few pockets so that you can carry items such as fish identification cards and writing slates.  In colder water conditions you may want more pockets for additional items such as spare mask straps, lightweight underwater torches and dive reels.  

10. How do you inflate BCD's?

There are two methods to inflate a BCD's. Generally, scuba students are taught to inflate their BCD using a low pressure hose, which connects air form the scuba cylinder via the first stage regulator to the inflator button on the BCD. This is traditionally located at the end of the corrugated hose assembly that hangs from the divers left shoulder, know as the low pressure inflator assembly. As a backup, and for safety sake, all students are also taught how to use the second method of inflation, which is to manually (orally) inflate the BCD, where exhaled air for the divers lungs is used to inflate the jacket via a mouthpiece. One of the new emerging styles of inflator assemblies being see these days is the ‘air trim’.  This is very straightforward to use and the integrated inflation/deflation device is activate by two oversized buttons, located on the left hand pocket of the BCD, which are easy to operate.  The air trim system is ideal for beginners and offers a simple way to control buoyancy when diving.  Another method is the Balanced Power Inflator (BPI). This is one of the most accurate ways to control buoyancy and offers an additional benefit over air trim in that you can inflate at high speed even at depth.  You can also breathe the air from these types of BCD's and exhale into the water in extreme emergencies.