| Backing |
If a wind is Backing it is shifting in an anti-clockwise direction, for example, shifting over time from the West to South West. The opposite of this is veering. |
| Backup |
The concept of carrying fully functional backup systems to replace primaries in the event of failure. |
| Bailout |
A small cylinder, (usually 3-4 litre) commonly used as an emergency breathing system in commercial diving, also known as a Pony bottle. |
| Ballast |
Any solid or liquid weight carried in a vessel to increase the draught, to improve trim or to regulate stability. |
| Bathyscape |
A strong, hollow vessel designed for underwater exploration with its own system of buoyancy control so that an attached cable is not needed to control descent and ascent |
| Bar |
A measure of pressure, 1 bar = atmospheric pressure or about 15lbs per square inch. |
| Barodontalgia |
Pain & discomfort caused by the volume and pressure changes in teeth |
| Barotrauma |
Injuries resulting from the inability of expanding gasses to exit the body. For example, ear drum rupture, lung over expansion injury, pneumothorax, squeeze, sinusitis. |
| BCD |
Buoyancy Control Device, sometimes called a stab jacket (stability). An inflatable jacket worn by divers. This provides buoyancy and holds the diving cylinder. |
| Beacon |
Any object that serves as a signal or indication for guidance or warning. A fixed (non-floating) aid to navigation. |
| Beam |
The widest part of a vessel measured between the gunwales. |
| Bearing |
Horizontal direction of an object from an observer, expressed as an angle from a reference direction (e.g. compass bearing, true bearing, relative bearing). |
| Bear Off |
Steer away from the wind, shore or any object. |
| Bend |
A knot that joins two lines of unequal thickness. |
| Bends |
See: DCS |
| Bioluminescence |
Simply light produced by a chemical reaction which originates in an organism. |
| Bight |
The part of the rope between the end and the standing part. A loop formed by folding the rope back on itself. |
| Bitter End |
The free end of a line or rope. |
| Bollard |
Stout post on wharf or pier for securing mooring lines. |
| Booties |
The boots that are worn with fins. Also used to describe the thick socks worn under the drysuit. |
| Bottom Mix |
A breathing mixture used at the deepest portion of a dive. |
| Bottom Time |
Often calculated from the start of the diver's descent until the beginning of his ascent, or to the safety stop or first decompression stop. Note: This measurement varies widely from organisation to organisation, and some divers do not calculate the safety stop into their total bottom time. |
| Bow |
The front end of a vessel. |
| Bowline |
A knot used to form a temporary loop in the end of a line. See Knots. |
| Boyles Law |
At a constant temperature, the volume of a given mass of gas is inversely proportional to the absolute pressure; if the pressure
goes up the volume goes down and vice versa. |
| Bradycardia |
A heartbeat of less than 60 beats per minute. |
| Broach |
The turning of a vessel broadside (90°) to the wind or waves, subjecting it to possible capsize (to turn over). |
| BSAC |
British Sub Aqua Club. |
| BSOUP |
British Society Of Underwater Photographers |
| BT |
Bottom Time |
| Buddy |
Your diving partner. BSAC strongly recommend that divers always dive in pairs for safety. |
| Buddy Breathing |
An emergency out-of-air procedure where two divers share one second stage regulator while ascending to the surface. |
| Buddy Check |
A pre-dive check where two divers familiarise themselves and check each others equipment prior to a dive. |
| Bulkhead |
A vertical partition or wall. |
| Buoy |
Anchored floating object, marking a channel, hidden dangers, etc. |
| Buoyancy |
The upward force equal to the weight of water which is being displaced by an immersed object. |
| Burst Disk |
a part of a tank valve that prevents the pressure in a scuba tank from exceeding maximum operating pressure by bursting and venting the tank. |
