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 (SMB) 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.
Volume
The volume is determined by the profile, as the buoys are circular in cross section. There should be sufficient volume for adequate visibility. A large volume can make the buoy difficult to deploy safely if the gas source is not carried by the buoy.
Air retention
There are at least four methods of keeping the air in the inflated decompression buoy. The buoy can be:
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