Surface Marker Buoy
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A Surface Marker Buoy, SMB or simply a blob is an inflatable buoy used by SCUBA divers, with a line, to mark the diver's position to their surface, safety boat while the diver is underwater.
SMBs are inflated on the surface before diving to mark the diver's position during a drift dive or night dive so the dive boat can follow the divers, or where there is boat traffic making diving more hazardous.
Divers need to consider some configuration options and features when using SMBs. 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.
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[edit] Decompression buoy
A decompression buoy is similar to Surface Marker Buoys but deco buoys are launched whilst the diver is submerged. Alternative solutions to marking one's position while doing decompression stops are diving shots and decompression trapezes.
Deco buoys are inflated underwater before or during the ascent phase of the dive. A reel and line connect the buoy on the surface to the diver beneath the surface. The buoy marks the diver's position underwater so the boat safety cover can locate the diver.
[edit] Design
There are at least four methods of keeping the air in the inflated deco buoy. The buoy can be:
- open ended (preferably with small independent weight to keep the opening submerged)
- open ended self sealing buoys (the air in the buoy expands as the buoy ascends closing a neck at the bottom of the buoy)
- sealed, with an inflation valve and a pressure relief valve
- sealed, with a built in air supply and a pressure relief valve
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 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.
Some types of buoy provide an attachment for a strobe light, cyalume stick or writing slate, which can convey signals to the surface support.
[edit] Deployment problems
Several common problems are encountered when deploying deco buoys :
- The diving reel jams after the buoy is inflated (dragging the diver up). To avoid this:
- use a simpler system or a reel which cannot jam (e.g. a weighted spool of line)
- detach the lanyard connecting the diver to the reel before inflating the buoy (and ensure no equipment is trapped in the buoy or reel)
- attach two reels to each other in series. If one fails the other is unlocked to reel out its line.
- Part of the diver's equipment gets trapped in the deco buoy (dragging the diver up). To avoid this tie the lanyard of the reel to something solid on the sea bed before inflating the buoy (so you have time to sort the problem out)
- The diver removes the primary demand valve from his or her mouth to inflate the buoy, and is therefore at a disadvantage in dealing with any other problems that might arise as the deco buoy goes off. There are a number of ways to avoid this:
- Use a deco buoy with its own air supply
- Use a secondary demand valve, such as an octopus, to inflate the buoy
- Use a sealed buoy with an inflation valve, which is filled by blowing directly into the valve inlet or by attaching a medium-pressure inflation hose from the buoyancy compensator or dry suit. The valve does not retain the hose connector, like the BCD or suit inflator valve, and the hose can be easily pulled off the valve when the buoy is sufficiently filled.
- Hold an open ended buoy above the primary demand valve and direct several exhalations up into the open end of the buoy. This technique is also useful in cold conditions to prevent freeflows caused by pressing purge buttons.
[edit] Lifting Bag
A lifting bag is an item of diving equipment consisting of a robust and air-tight bag with strops, which is used to lift heavy objects underwater by means of the bag's buoyancy. The heavy object can either be moved horizontally underwater by the diver or sent unaccompanied to the surface.
The volume of the bag determines its lifting capacity: a 100 litre / 4 cubic feet bag can lift a 100 kg / 220 pound underwater object.
The shape of the bag should distribute the volume in a vertical rather than a horizontal direction so that the open end of the bag always remains underwater. If the open end reaches the surface, air will escape from the bag and it may re-descend. A partially filled bag will accelerate as it ascends because the air in the bag expands as the pressure reduces on the ascent, following Boyles law, increasing the bag's buoyancy.
