What is and Do I require a ‘DSMB’?

What is a DSMB?

Do I need a DSMB? The delayed Surface Marker Buoy, known in the diving jargon as a ‘DSMB’ has several uses. There is also the ‘SMB’. So what is the difference and why do I require one?

Surface Marker Buoy – SMB

First and foremost, an SMB means Surface Marker Buoy – often known as ‘safety sausage’. This marker buoy is inflated at the surface or, it remains totally inflated during the duration of  your dive. The SMB at the surface can be used to signal to boat traffic. You can indicate you are ready for pick-up, and it’s an easy marker for the boat captain to see your position.

You can inflate the SMB on the surface, then descend, leaving the SMB topside. By towing the SMB behind you, you indicate to boat traffice your whereabouts under water. This method is often used on a drift dive, indicating to your boat captain your direction of travel.

Delayed Surface Marker Buoy – DSMB

The delayed surface marker buoy is often deployed around 8-10 m when divers prepare to perform their safety stop. This signals to your boat captain that divers will be ascending very shortly. You can use it to assist divers in the safety stop area, if making a ‘stop in the blue’ without any form of reference. The DSMB maybe used as a positional marker signal if you ascend far away from your intentional exit point, or boat.

A DSMB is attached to a reel or spool.

You should have a clear understanding what is a reel, what is a spool and how they work. After deploying the DSMB to the surface, you should begin to reel in excess line until you arrive at the correct safety stop depth. I prefer to mark my depths on the line so I know where the 5 metre depth line length ends and again one at 10 metres.


What is the advantage over a coloured line?

Here we have a choice of orange, white or lime-yellow. Often white lines in clear water are hard to spot. This may cause us problems with other ascending divers if they dive into, or across you reel-line path. Coloured lines are easier to see, both for yourself and other divers close by.

Many Instructors and dive guides use, and deploy DSMB’s on a daily basis. Most give little thought to those who have never deployed one before. It is important to learn this skill in your PADI Open Water Course correctly. Entanglement, getting the line caught around the BCD or fins, dropping the reel or spool, as well as not enough air in the DSMB are very common beginner problems. Just as important, is the stowing of the DSMB, reel/spool after you have reached the surface. This should be done in the water, otherwise you will have feet/metres of line floating at the surface when trying to exit the water. This may cause divers to become entangled or trip over the spool line.


Some types of DSMB have a resrictor built inside, just above the open end. This narrowing is there to prevent the expanding air coming out of the tube, as the DSMB travels to the surface. The narrow restriction causes the end of the DSMB to close over and stop the buoye from deflating.

If you need more practice deploying a DSMB, why not take the PADI DSMB Course? Learn how to manage and deploy one correctly. Use it as a safety stop indicator, how it can help with the trim on a safety stop and stow it away correctly before exiting the water.

Come and join us for a DSMB course at DiveSMART Gozo.