Surface markers
A non-delayed SMB is inflated at the surface prior to the
dive, and towed throughout the dive. A dSMB is carried deflated during the
dive, and inflated when needed. Because it's not fun towing a marker throughout
a dive, it is preferable to use a dSMB whenever possible.
There are several types of dSMB, however. The first was simply a tube sealed at
one end, that required constant downward pressure from the diver to keep
upright and inflated.
A much better solution is the self-sealing dSMB, which is designed so that the
act of inflation seals the inside, ensuring that it stays inflated and at the
surface. An over-pressure valve is fitted, to prevent the SMB from bursting on
ascent.
Even more recently, the and the closed-circuit
dSMB have come on to the market. The dSMBi is a
self-inflating dSMB, which has a crack-bottle or CO2 cylinder built in. By
carrying their own supply of gas, these negate the need for a diver to risk
entanglement or freeflow when deploying a dSMB, and also guarantee that the
dSMB will be completely full when arriving at the surface.
The closed-circuit design, instead of being open at the end, has instead a
small fitting that a direct feed hose can be attached to.
The main advantage or these newer designs is to cut down on the risk entailed
in deploying a dSMB - using a demand valve risks freeflow, using an airgun requires either an extra LP hose or swapping around
of direct feeds, using exhaled gas risks entangling the regulator with the
dSMB. They can also be easily filled at the surface, and used as a non-delayed
SMB as well, whereas standard dSMBs are more awkward
to fill above water.
Non-delayed SMB's, the only real choice is shape. The
traditional blob is dying out slowly, as the cylindrical 'sausage' is proving
to be better at riding the waves, and the 'torpedo' easier to drag.
Lastly, SMBs tend to be fairly anonymous red
cylinders. For safety and convenience, mark your SMB so that your surface cover
know which SMB is yours. Black duck tape is handy for making big, highly
visible letters or shapes, and can also increase your SMB's
visibility.
