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Why carry a (Delayed) Surface Marker Buoy (DSMB)?

Updated: Nov 7, 2022

Why carry an SMB when diving
To be seen from afar

A friend was recently asking me what were the most important pieces of equipment she should buy to go on a dive trip to a remote part of Indonesia. She was surprised when I put the DSMB near the very top of my list of essentials. Why is it such an important part of your dive kit? And why should you have one on you on every dive to ensure your safety?


First, let's start by clarifying this confusing issue. Most pro divers who dive off boats ( or not) use DSMBs but will refer to them as SMBs just because it's quicker and easier to say. The safety sausage or DSMB is a long (1m to 2,5m) buoy that you inflate underwater at the end of your dive then send up to the surface (hence the name: delayed). The SMB can be the same device or a round inflatable buoy but that you inflate before you descend and that you drag along for the duration of your dive to signal your presence, or, leave at your point of entry. It's often used when doing monitoring, shallow dives, or to signal divers' underneath entry/exit points.

The DSMB is a standard for all boat diving since it has the twin role of a) signalling your presence to other boats as you get ready to ascend protecting you from propellers during your safety stop/ascent and b) signalling to your boat that you have finished your dive so that they can get ready to come to pick you up.

Why the SMB is it such an important piece of equipment?

So apart from protecting you from overhead boats and helping your boat find you, it is of course also much much easier to spot you from afar if you were to drift away and get lost. Finding a 1,5-meter bright orange sausage in the big blue sea is much easier than a small 30 cm hooded head...If you also bring along a torch it can also serve as a bright beacon in the night/heavy rain to help rescuers find you as you shine your light up the big orange shaft ( why does that sound kinky?).

Holding a SMB at the safety stop
Extra safety and visual reference at the safety stop

How do you use it?

When you decide it's time to prepare the* ascent to your safety stop is a good time to send up the DSMB. Many people like to send it up from 10 m because it inflates more easily (the volume of air increases more as the pressure drops), you are still in a completely safe zone and it gives time to everyone to adjust their buoyancy to make sure they are neutrally buoyant when arriving around 5 m for the safety stop ( so they don't bob up by mistake). It makes life easier if the DSMB is on a reel with a string around 10 to 15 m long that you can just let spool out once you've added air to the safety sausage with your alternate air source (though there are other funky methods that I won't go into here). You then slowly roll in the reel until you reach 5m where you do your safety stop with the added visual reference of the buoy.

The most important point: make sure that the string and anything that could snag on you is away from you and that your fingers or BCD are not tangled or attached in any way to the DSMB/string. That way it cannot pull you up to the surface with it, risking an uncontrolled ascent and the possibility of / decompression accident.

You may also want to check overhead before launching it that there are no boats or other obstacles that it may become entangled with or damaged by.

Diver underwater with a SMB
A reel to prevent entanglement and a bag to store it

Which DSMB to buy?

Brands don't really matter. What you do want to look out for though is, preferably not a plastic one, but a fabric one with strong seams. This piece of kit needs to last and the plastic ones just don't. It needs to be a bright colour, my personal favourite is orange but bright yellow, red or pink can work just as well. It needs to have a reel and a sufficient amount of string. It needs to roll up neatly and be secured in a rolled-up position and be easy to attach and detach from your dive kit when you need it. Some of them have a reflective band on the top, which is a bonus. Any practical little bag or elastic strap system to secure it nicely and good clips are a good buy too. Many dive guides write their name on theirs in permanent marker, making it easier for their boat to find them at busy dive sites.

Don't leave home without it

It really is an essential piece of kit that EVERY diver should have on them on EVERY dive. In places with strong currents (or even without), all rental gear should at least have an SMB in the pocket (if you are wondering if we do this, the answer is yes we do: all our BCDs are equipped with an SMB and a whistle). This for the simple reason that if one diver is lost, they should have their own SMB so they can be found easily and fast by rescuers.

If you're going diving and you only take 2 pieces of (personal) kit, take your dive computer and your SMB!


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