 The reel or spool used to store and roll up the line usually has slightly negative buoyancy, so that if released it will hang down and not float away.A "delayed" or "deployable" surface marker buoy (DSMB) is a soft inflatable tube which is attached to a reel or spool line at one end, and is inflated by the diver under water and released to float to the surface, deploying the line as it ascends.This provides information to the surface that the diver is about to ascend, and where he is.