Human Dim Sim in space - or how not to use your SMB!


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.


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.

Having established the bone fides of such equipment it is essential that the diver is familiar with its use.


Having now discussed the methodology for correct use - a small anecdote is appropriate.

Son Fletcher and Human Dim Sim Tim Smith recently scallop diving off Rye Victoria in 7 metres of water. The Human Dim Sim decided to show Son Fletcher how his new SMB worked.

The reel was loaded in a standard 15 metres of cordage - the Human Dim Sim released the drag/lock and let the reel fall to the sea floor (the cordage was longer than the bottom depth) - he then commenced inflation with his occy. An important note here is to ensure that you have hold of the SMB at time of inflation!!!!

At partial inflation Tim lost his grip on the SMB and his regulator - consequently he was propelled upward to surface at a rate of 4m/sec/sec - only stopping when his belly button broke the surface.  Looking not unlike a nuclear submarine breaching the surface on an emergency ascent.

Luckily no damage - but a potentially dangerous experience- imagine the same scenario at 30 metres. SMB are very valuable pieces of equipment but in the wrong hands or used incorrectly can be a rapid invitation to lung expansion and associated problems.

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