page_title: Surface marker buoy
section_title: Deployment practice
hierarchical_section_title: Surface marker buoy / Decompression buoy / Deployment practice
caption_attribution_description: English: Surface Marker Buoy
context_page_description: A surface marker buoy, SMB, dive float or simply a blob is a buoy used by scuba divers, at the end of a line from the diver, intended to indicate the diver's position to people at the surface while the diver is underwater. Two kinds are used; one is towed for the whole dive, and indicates the position of the dive group throughout the dive, and the other, a delayed surface marker buoy, DSMB or decompression buoy, is deployed towards the end of the dive as a signal to the surface that the divers have started to ascend, and where they are going to surface. Both types can also function as a depth reference for controlling speed of ascent and accurately maintaining depth at decompression stops. Surface marker buoys are also used by freedivers in open water, to indicate the approximate position of the diver when submerged. They may also be used to support a catch bag or fish stringer by underwater hunters and collectors.
context_section_description: Reliably safe deployment in difficult conditions depends on sufficient practice and familiarity with the equipment and the specific technique to be used for inflation.
  Deployment may be from the bottom, as an aid to ascent and signal indicating position, from midwater, to indicate position maintain decompression depth and warn boat traffic, or at the surface as a means of attracting attention.
  The DSMB bag is unrolled. It may be necessary to connect it to the line on the reef or spool, but in many cases it is stored already connected. A quick but secure method of connection such as a bolt snap avoids delays and task loading distraction.
  The reel or spool is unclipped from the diver's harness if this has not already been done. The risk of uncontrolled ascent if the reel jams during deployment and is connected to the diver is generally considered unacceptable.
  A small amount of gas is introduced into the bag to vertically align the buoy, and allow the diver to check that the assembly is ready to deploy the line freely. Any clip or locking device restricting line deployment is released. A friction brake should allow easy but slightly restrained rotation to prevent inertia overwind. The diver adjusts buoyancy to ensure that they do not float upwards excessively during the deployment. The amount of buoyancy adjustment will vary with depth and the method of filling the buoy.
  Sufficient gas to adequately inflate the buoy when at the surface is introduced, taking into account the expansion due to reduced ambient pressure during ascent, by one of the following methods, and the bag released to ascend. A ratchet reel should be held with the pawl disengaged, a spool allowed to spin on a finger or in a cupped hand:
  The valve of the integral inflation cylinder is cracked open.
  The bottom opening of the buoy is held open above the exhaust opening of the demand valve in use for breathing, and a few breaths exhaled.
  A demand valve mouthpiece is held under the bottom opening and the DV purged.
  A low pressure inflation hose end is pushed onto the inflation tube of the buoy, which automatically releases gas into the buoy. When released it will automatically disconnect.
  The mouthpiece of the buoyancy compensator control valve is held under the bottom opening and the contents of the BC discharged into the buoy. If more gas is needed, the inflate and dump valves are opened together and gas flows into the buoy bypassing the BCD.
  A dedicated valve on an extra low pressure hose can be used at the bottom opening of the buoy.
  The diver can orally inflate the buoy through an oral inflation valve, if fitted.
  In all cases, the amount of slack line should be kept to a minimum to reduce the risk of fouling on the diver or equipment, and the reel or spool held away from the diver while unrolling. The diver should ensure slightly negative buoyancy to allow sufficient filling without being dragged up by the partly filled buoy to a depth where expanding gas makes buoyancy control difficult. This is easier at depth, but the risk of injury if dragged up is also greater.
  The diver checks that there are no line snags on any equipment, and takes up any slack by winding the line onto the reel or spool, before starting the ascent.
  Tension should be maintained on the line during ascent to avoid entanglement, by reeling it in as fast as the diver ascends. This is easily controlled by maintaining slight negative buoyancy at all times.
caption: Deco buoy with diver at the surface
exif: {}