A surface marker buoy, SMB or simply a blob is an inflatable buoy used by scuba divers, with a line, to indicate the diver's position to their surface safety boat while the diver is underwater.
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SMBs are inflated on the surface before diving to mark the diver's position during drift dives, night dives, mist or disturbed sea conditions such as Beaufort force 2 or greater. The buoy lets the dive boat follow the divers and highlights their position to other boat traffic.
Divers need to consider some configuration options and features when using SMBs.[1] A closed SMB, with a valve through which the user blows, is likely to be more reliable, by remaining inflated, than an open ended buoy or a delayed buoy which seals itself as it inflates.
To avoid losing the reel, a lanyard attaches the diving reel to the diver. This lanyard can clip to the buoyancy compensator or go around the wrist. Alternatively, the lanyard can be long enough to float above the diver and stay out of the way. If the lanyard clips to the buoyancy compensator, the user should take care to release if there is surface boating activity, as boats may drag divers up by their SMB reels.
The DIR diving philosophy considers unsafe any attachment to equipment or objects which end above the water surface, due to high risk associated with dragging the diver upwards in spite of their decompression obligation or maximum ascent speed limit.
A delayed surface marker buoy (DSMB), decompression buoy or deco buoy is similar to a surface marker buoy but is deployed whilst the diver is submerged and generally only towards the end of the dive. The buoy marks the diver's position underwater so the boat safety cover can locate the diver even though the diver may have drifted some distance from the dive site while doing decompression stops. A reel and line connect the buoy on the surface to the diver beneath the surface. Alternative means of marking one's position while doing decompression stops are diving shots and decompression trapezes.
A decompression buoy is not intended to be used to lift heavy weights: in this case divers use a lifting bag.
There are at least four methods of keeping the air in the inflated deco buoy. The buoy can be:[1]
Divers of some training organisations carry two differently coloured deco buoys underwater so that they can signal to their surface support for help and still remain underwater decompressing. For example, in some circles in Europe, a red buoy indicates normal decompression and a yellow buoy indicates a problem, such as shortage of gas, that the surface support should investigate and resolve. Although in other circles, two buoys (any colour) up one line means the same, currently the protocol is not universally accepted even within Europe.
Some types of buoy provide an attachment for a strobe light, cyalume stick or writing slate, which can convey signals to the surface support.
Several common problems are encountered when deploying deco buoys.
A safety sausage is a buoy used when the diver is at the surface to indicate the diver's position to the dive boat, reducing the risk of losing contact when air, light or sea conditions decrease the visibility of the divers from the boat.[2][3] The sausage is a plastic tube that is normally inflated by putting one end under water and purging the second stage underneath to inflate it. Inflated tubes are normally about 6 feet (2 m) tall. Uninflated sausages roll up and fit in a buoyancy compensator pocket. Commercial boat dive operations, especially at offshore reefs or areas known for strong currents or mercurial weather, may require divers to carry safety sausages. A safety sausage is not a substitute for a surface marker buoy or diver down flag.