SMB And DSMB: Identifying Your Marker Buoys

SMB And DSMB: Identifying Your Marker Buoys

A diver starts to open a DSMB

- Katrine Overbeck

SMB or DSMB is short for Surface Marker Buoy or Delayed Surface Marker Buoy.

Searching around the internet I found a lot of different opinions on this subject.

All agree that it’s a surface marker, and that DSMB is deployed underwater. But an SMB can either be a big round buoy dragged in a line during the whole dive or a long inflatable tube used by divers to get visual attention.

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SMB’s are also often used to mark your position on the safety stop. You deploy your inflated tube from 5 meters so boats don’t pass above you on your safety stop of ascent.

SMB – Surface Marker Buoy

This device can apparently have many forms. The first is a long bright collared tube deployed in the surface after a dive. This is done to get the attention of the boat crew and to let other boats know you are there.

This device is especially good to get attention if lost at sea or when an accident happens.

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Another shape of an SMB is small and round or typical buoy shaped, this is attached to a line and is dragged during the whole dive.

This makes the diver visible to boats and others, during the entire dive.

This way the boat crew can easily follow the divers.

An SMB signal is handier than a DSMB

A diver signaling a dive boat with an SMB - Credit: Dugongdoh

DSMB – Delayed Surface Marker Buoy

This is also a bright collared long tube, but a DSMB is deployed underwater just before ascent. The DSMB has an over inflation valve, much like the one on your BCD shoulder, which releases air as it expands on its way to the surface.

This way boats don’t sail over the divers on the way to the surface. The diver holds on to the DSMB with a line.

Learn more How to Safely and Effectively Launch a DSMB.

The length of the line varies from 5 meters and up. This way you will always be able to deploy it doing your safety stop.

It is a good idea to get the line of a DSMB attached to a Spool or a Reel, this way you won’t risk the line getting entangled.

A diver reeling a DSMB

A diver reeling a DSMB using a spool - Credit: CyberEak

Sizes of a DSMB

The length of an SMD and DSMB varies quite a lot from less than one meter to more than 2.5 meters. Knowing this you need to choose a (D)SMB that you can use.

You need one that is long enough to be seen from a distance, but at the same time it can’t take up too much space when rolled together for storage in the BCD pocket.

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Deploying a safety sausage

When you are on the surface and want to deploy the SMB, simply roll it out and blow it using your alternate air source.

Deploying a DSMB is a bit trickier, but still quite easy. You roll out the DMSB and free it from all equipment so it has free passage to the surface. Using your alternate air source you fill up the DSMB, holding on to the Spool, reel or line, whatever you use to hold on to it when it’s at the surface.

A diver deploys a DSMB

Be sure the DSMB line is unattached to your BCD during deployment - Credit: Thomas Grønfeldt Senger

It’s very important that you never ever attach the reel or line to your BCD when deploying a DSMB. If the line is entangled and stops in the reel, you will fly with the DSMB to the surface risking Decompression sickness

A visual signaling device makes you visible from a distance, to be safe always bring it on your dives. Better safe than sorry.

About The Author

Torben Lonne

Torben is a top skilled PADI MSDT instructor. He has worked several years with scuba diving in Indonesia and Thailand – and dived most of his life in most of the world.

He is also the co-founder and chief-editor of you can always catch him here [email protected]


  1. Scuba Pro

    This instructional leaves much to be desired in terms of best practices:

    1) Body orientation — Sideways to the current, with the upstream side on the right, so that the DSMB extends downstream to the left.

    2) Hand positions — DSMB in the left hand, spool in the right and held away from your equipment to minimize any danger of entanglement.

    3) Inflation — The use of the alternate air source is considered dangerous, as it poses an entanglement hazard. DSMBs should be inflated by tilting your head to the right and exhaling a full breath of air, capturing the gas from the exhaust port of the primary regulator.

    Many people also recommend partially deflating your BCD to become slightly negative, to offset the temporary lift of the DSMB before letting it go.

    • Torben Lonne

      That was a great add on! Thanks for commenting!

  2. David Tombs

    The dsmb is an essential skill in temperate diving. The method of inflation is hotly debated. Certainly many recommend that the buddy inflates the dsmb whilst the other diver holds onto the reel at the bottom.. It requires frequent practice in order to avoid entanglement and ascent issues. Deployment from the bottom should be mastered before mid-water deployment.


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