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 self-inflating 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.

I use: AP Valves self-inflating dSMB, AquaTec self-sealing dSMB for backup. Large McMahon reel, Halcyon spool for backup

There are two choices for SMB colouring - red and yellow. Studies have shown that these are the two most visible colours at sea. If you look around a dive shop, you will see up to three SMB colours: All red; all yellow; and one side red, one side yellow.

Red is far and away the most common SMB colour. This leads some new divers to buy a yellow SMB so theirs will stand out more when at a busy site. Others buy the two-colour SMBs because these must surely be the ideal for high-visibility.

However!

In the UK, and many other parts of the world, there is a convention used by more advanced divers that a yellow SMB is an emergency signal, to be responded to by sending down a cylinder of gas, or a rescue diver, or both.

Whilst for the most part recreational divers do not have or need such a signal, it is possible for both types of diver to be on the same site. If one group of divers is using yellow as an emergency signal and the other group uses yellow as standard, this could lead to confusion and even to a genuine emergency signal being ignored.

For this reason, unless you have a very strong reason for wanting a yellow SMB as standard, please buy an all-red one.

If you decide that you simply MUST have something yellow with you in case you get lost at sea, flourescent yellow fold-up flags are available at all good dive shops that have been shown to be better for location purposes than any SMB. Diver article

If you decide that you would like to use a yellow SMB as an emergency signal yourself, two precautions to take are: Make sure your surface cover knows this convention; and mark the SMB with "help", "SOS" or some other such message in large, clear black letters to ensure there is no doubt that you a diver in distress and not just a diver who thought yellow looked nicer than red.