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What’s A SMB?

When I was new to diving I never knew the difference between a dSMB and an SMB or what they were really for so I figure there are other divers out there who don’t know either.  Nowadays more and more agencies and courses are teaching how and when to use SMBs which is great and more and more dive operators around the world won’t let you off the boat unless at least one of you have a SMB. 


Your SMB is an essential piece of kit to help you be seen and found in the water to avoid being hit by boats as you surface or getting lost or left behind.  On the surface from a distance you are just a small head and shoulders on the surface and typically dark coloured so a bright red sausage can make you more obvious in the water. SMBs come in a range of sizes, shapes and colours for different needs and they have a range of features to make your life easier so lets take a closer look at SMBs.  


An SMB or Surface Marker Buoy is a simple device that floats on the surface to mark a location.  ‘SMB’ often refers to both permanent buoys and delayed buoys but they are made to mark a location in the water or communicate with the surface. Permanent SMBs are inflated at the beginning of the dive and you tow them with you on the dive so there is always a marker above you on the surface to mark your position so boats stay away.  Because SMBs stay on the surface they can be more intricate and include pockets for spares, small diver down flags and can be used as a floatation device if you get tired. Typically red and white to match the diver down colour they contrast against the water well. SMBs tend to be round or torpedo shaped and often have a ballast section on the bottom with a weight or section that can be filled with water.  


A dSMB is a Delayed Surface Marker Bouy that scuba divers take with them underwater with a reel or spool.  When you begin to ascend or if you need to contact the surface you can attach the dSMB to your reel and inflate it so it bobs up to the surface. dSMBs are quickly becoming essential equipment around the world but don’t take up much space and aren’t complicated to use.  When you start to ascend and begin your safety stop you send up your dSMB and hold onto it with line from your reel or spool so boats in the area know you’re there to either stay away or to come pick you up.  After you’re reached the surface keep it inflated so you’re obvious and boats can keep an eye on you but remember that not all boat users may know what an SMB means so ascend carefully.




Meanings change depending on where you are but these are the most common colours and meanings/reasons for using them.  The different colours are often assessed by different agencies in different conditions for which is easiest to spot. Yellow is currently leading the pack but the heritage of the colour is holding it back. 


Red SMBs are Location Markers, they mark a location in the water to return to or to avoid or tell boats that there is a diver below about to ascend. Red is a good all-round colour that contrasts well with the water and can be seen far off.


Yellow SMBs are for Emergencies in some circles but simple Location Markers elsewhere, you will often see EMERGENCY written down the length of a yellow dSMB and are used by advanced divers that can’t ascend to the surface but need help or equipment from the surface without surfacing. Recent studies have shown that yellow is easier to see in the water so there might be a culture shift in the next generation of SMBs.


Black SMBs are Location Markers like the Red, new to the diver market black SMBs are said to contrast well against the water especially in bright conditions where the sun is behind you but they have sparked some debate and some skippers dislike them.


Multi-Colour SMBs are also Location Markers, made to stand out more by creating a flashing effect as they turn on the surface so two-tone SMBs draw your eyes to be better seen.  



The size and shape depends on where you intend to dive, if you’re in flat and calm waters a small dSMB can be enough to be seen so a compact dSMB can be best as they pack down small and don’t weigh a lot.  If you’re diving in rough waters a large SMB can get you found faster and even in calm waters a large SMB will be easier to see. Permanent SMBs tend to be round or torpedo shaped with a flag out the top.  round ones are better as static SMBs as torpedo buoys will glide through the water smoother so freediving for depth or marking a location to come back to round buoys are best but if you’re moving through the water and trailing the SMB behind you torpedos are easier.  



Permanent SMBs just have Simple Valves that you blow up orally before the dive and close before you jump in. dSMBs have a range of inflation methods, the most basic of which is an Open End that you exhale into or use your octo to fill to send it up to the surface.  Open ended dSMBs are quite cheap to manufacture but you have to keep tension on the line as if they flop over on the surface the air inside can escape and the SMB sinks.  Because of this you will often see Fluted SMBs that are open ended but when inflated the opening is closed by the air pressure inside pinching it closed. Many dSMBs have a Nozzle that has the same fitting as your BCD so all you have to do is push your BCD hose onto it to inflate the SMB and up it goes.  Closed Cell dSMBs often have this inflator and will stay inflated even if they flop over so they always stay inflated.  Because the air you put into the dSMB will expand as it ascends closed and fluted dSMBs will have an Over Pressure Valve that allows expanding air to escape so the dSMB doesn’t explode but keeps them inflated and taught at the surface. Some SMBs even have their own cylinders known as Buddy Bottles that are filled up from your main cylinder before the dive and then inflate your dSMB by simply opening the valve.  The small cylinder holds enough gas to inflate the dSMB and can be easier to use as you just have to open a valve and off it goes. Reflective Tape reflects light so shines back when a light is shone in its direction so you really stand out in the water especially at night. Communication Pockets are clear sections that you can roll a notebook page into to send a note to the surface or insert a glow stick to stand out on the surface, especially at night. Some dSMBs have Bungees, Velcro or Pouches to store them in and wrap them up during the dive so they don’t unravel.  



All SMBs require some kind of line to hold it in position so it doesn’t just float away. Most permanent and some dSMBs come with some line but you often have to buy a spool or reel separate.  Good line management is essential and practice is the only way to improve. Rope and lines are dangerous in water and act very different to what you expect so take care and keep an eye on your lines.  If your SMB comes with a length of line cut off only what you are going to need as the excess line will tangle and can cause a problem in the water.  If you’re only going to use a dSMB for 5m safety stops just cut a 6m length of line with a weight on one end so you don’t have too much excess line that can wrap you up and tangle. As you ascend reel in your line, if you don’t you’ll end up with 5m of line wrapping around you, your gear and your buddy.