A useful safety device for most divers is the surface marker buoy. In essence it is an easily seen surface float which is connected to the diver by means of a thin, strong line, usually carried on a reel. Its main function is to allow the surface cover to know where the divers are at all times, and to provide the cover with a means of communicating with the divers should the need arise.
The marker float should be of sufficient buoyancy to ensure that it cannot be inadvertently pulled underwater by the divers. At the same time, it should not be so big that it is difficult to carry or is likely to be caught by the wind or surface current. It should have 10-20 Kg of buoyancy. If the buoy is inflatable, it has the additional advantage of being easy to carry when not in use. The material and colour of the surface marker buoy should be such that it is visible over a range of 200m. Several types of SMB are available including permanent and delayed.
The reel should carry sufficient line for the planned depth of dive and possess a winding mechanism to allow the line to be rewound on ascent. A very useful feature is the ability to lock off the line using a ratchet device. Rather than carry it throughout the dive, most divers clip the reel to themselves by means by a short length of cord.
