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©James Lynott


SMB stands for surface marker buoy, a must have piece of dive safety equipment. You can get SMBs in various shapes and sizes, put simply they are an inflatable surface marker used when shore diving and boat diving for resting, marking a dive site, assisting another diver and carrying things. The most common devices are flags and long inflatable tubes, explained in more detail below.

Depending on the dive site and plan, you may anchor a surface float or tow it throughout the dive. In either case, you'll need a nylon or polypropylene rope not less than 15 metres/50 feet long for towing or anchoring. Carry the line on a reel or line caddy to avoid entanglements. Many SMBs provide a way of attaching a reel such as a loop or clip mechanism, more about reels below.

Dive Flags

You'll find that in many places where you like to dive, people enjoy other water sports including boating, waterskiing, jet skiing and so on. These kinds of things zipping back and forth above you pose a serious hazard as it is nearly impossible for them to see you when you're underwater. Therefore, for safety and required by some local law in boat traffic areas, it is necessary to carry a flag to warn of boaters and similar threats.

The appropriate flag depends on where and under what conditions you dive. A dive flag is either a red rectangle with a white diagonal stripe or blue and white double tailed pennant (Alpha flag), and large enough to see from at least 100 metres away. In some instances you may be required to fly both flags, particularly when boat diving. When diving from a boat, place the dive flag on a mast, radio antenna or other elevated location for maximum visibility. If you're diving from shore or have a long swim from the boat, you'll fly the flag from a surface float. In this case, your flag should have a wire to extend it into the "flying" position, and should ride at least a metre/three feet high so boaters can see it in choppy water.

Local laws (be sure to look these up when planning on diving somewhere new) stipulate how close you have to stay to your flag and also how far away boaters and skiers etc must stay away. For areas where there are no regulations, a general rule is for you to stay within 15 metres or 50 feet and for other people to stay 30 to 60 metres, 100 to 200 feet away. It is also important not to display the flag unless there are divers in the water.

Unfortunately, many boaters don't know what a dive flag means and sometimes they can't see your flag (when coming from upwind or in choppy waters). These boaters ay come a lot closer to you then they are supposed to so don't assume that just because you have a flag, people will steer clear of your area. Remain aware and ascend cautiously. In addition you should remain near your flag and carry an inflatable signal tube that allows you to alert boats of your presence in the water.

Surface Signalling Devices

Surface signalling devices, also referred to as delayed SMB's are almost mandatory for sea dives. They are called delayed as you use them at the end of a dive either to signal that you need help in an emergency, so that boaters will stay well away from you and if you accidentally drift/swim off a designated area thus informing the boat of your whereabouts. The latter can be especially important if you inadvertently end up too far down current and the boat must come pick you up.

Because they are used post dive, they save the hassle of managing the SMB throughout the dive. There are a number of different types for both visual and audible signalling, you should carry at least one of each. Visual include brightly coloured inflatable tubes or balls that you can blow up to be seen more easily, as well as signal mirrors, and for diving at night signal lights and flashers. Some inflatable tubes are self-sealing to stop air leaking out and some have their own inflation device. The cheaper SMB's however, may lose their buoyancy if they are caught in surface winds or rough waters. Audible devices are Whistles, powered both orally and by your low pressure inflator. The most popular place to keep these is on your BCD inflator hose, out of the way yet easily accessible in the case of an emergency.

See our full range of SMBs here >