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What is a surface marker buoy and how to launch one? Dive Buddy Scuba's guide to DSMBs and SMBs

Larry Klinger   Oct 03, 2020

Delayed surface marker buoys are one of the most important pieces of safety equipment we carry as scuba divers. However, they’re often under-used and a lot of new divers aren’t armed with the knowledge of how to deploy a DSMB. With all the different names for dive floats you might be left scratching your head and wondering what they’re for, whilst questioning exactly how to use a dive surface marker buoy.

We’re here to guide you on everything you need to know about SMBs - read on to learn what a DSMB is for, the difference between SMBs and DSMBs, what to look for in a delayed surface marker buoy, and how you can learn to use one.

What is a marker buoy?

To put it super simply, a surface marker buoy shows that a diver is down and alerts the surface to exactly where you are in the water. They are any kind of inflatable device which will float at the surface of the water and can be seen either from the shore or the boat (depending on where you’re diving from). They can be extremely useful in locations with heavy boat traffic, both coastal and inland in lakes.
They’re often brightly colored or marked with a “diver down” flag, and there are regulations in place to determine how close a boat is allowed to get to a dive float or a DSMB. Generally, you should never be more than 15 feet away from your own marker and boats should never get within 50 feet of an SMB, therefore allowing a 30 feet buffer zone. However, this distance can vary depending on local regulations.

What’s the difference between an SMB and a DSMB?

The jargon and multitude of names is where it can start to get confusing, especially for new divers. Understanding the acronyms is a great place to start - if you haven’t already worked it out, SMB means “surface marker buoy” and the “D” in DSMB stands for delayed, giving us “delayed surface marker buoy”.

Surface marker buoys are brightly colored inflatable tubes which can be deployed at the surface to alert people to your position. These are sometimes made of a thin rubber material and designed for emergency use, and these types fit easily into a BCD pocket. You’ll often find these in rental BCD pockets, and every diver should know how to use one at the surface. Diving marker flags or dive floats are also a type of surface marker buoy; in some locations, it’s standard to tow a dive marker float with a diver down flag at the surface for your entire dive. This is usually in shallow coastal locations where there’s a high chance of boat traffic.

Delayed surface marker buoys are probably the most versatile option for divers. The “delayed” part refers to the fact that they can be put up during your dive (usually prior to completing your safety stop), rather than inflated at the beginning of your dive and towed during it. You partly fill the DSMB with air at depth in order to send it to the surface, whilst staying connected to it by holding on to a reel. These have some slightly more advanced features than their surface-only counterparts, so read on to learn what features to look for in a great DSMB.

Why should I carry a safety sausage?

Safety sausage is yet another name describing the same piece of equipment, and the clue to answering this question is in the word “safety”. Carrying an SMB keeps you safe in a number of different ways. As we’ve already learnt, first and foremost an SMB can protect you from dangerous boat traffic by alerting boats to your presence and, more importantly, letting boats know you’re ascending.
SMBs are also extremely important in locations with heavy current. A diver at the surface can be carried very far very quickly by a current, so having an SMB deployed makes you much more visible and means you can be found much quicker in an emergency situation. Similarly, deploying a DSMB during a drift dive means that a boat or your surface support can follow your location whilst the current is carrying you along.


Learning to use a DSMB

Learning how to use a DSMB has been a more recent addition to the Open Water course, however, under NAUI guidelines it’s up to the instructor to decide whether to teach deployment at the surface or underwater. Often, new divers only know how to use an SMB at the surface, but it’s important for every diver to learn this important skill rather than just relying on a dive professional to have a DSMB at all times. In a situation where you perhaps end up separated from a group, it’s important (and perhaps even life-saving) to ensure you can let boats know you’re ascending, and how fast you’re moving in a current.
If it wasn’t thoroughly covered in your entry level course, DSMB deployment may be included on a drift dive on your Advanced Open Water course, and some agencies may even offer a specific DSMB specialty course to perfect your skills. Your best approach is to get into contact with a local instructor and discuss with them the easiest way to learn. They’ll likely teach you in a combination of pool sessions and open water dives.

How to deploy a DSMB - Top Tips

In the interests of safety, we’ve chosen not to post a step-by-step of how to use a safety sausage and we would encourage you to seek out the guidance of a certified dive instructor as above. However, if you already have the basics down and you’re looking to perfect your SMB deployment here are some tips which you could find helpful.
Buoyancy First

You may find it easier to let a small amount of air out of your BCD before you deploy your DSMB to balance out the air which you’ll be putting into the bottom of the SMB. Remember that it’s also easier to deploy an SMB from slightly deeper (think 10-15m, rather than 5-8m) due to the differences in pressure being greater at shallower depth. These pressure gradients make it slightly more challenging to fine tune your buoyancy, and buoyancy is key to a great DSMB deployment.
Air Expands

Don’t forget the first thing you learned about diving physics - air expands as it returns to the surface. Your depth will determine how much air you need to add in to avoid over expanding your SMB at the surface; air from 10m will be twice the volume at the surface, therefore you need to fill your SMB halfway, and from 20m you will only need to fill it one third.
Safety Concerns

We should never attach anything to ourselves whilst underwater, and this rule definitely applies to a deployed SMB. Never clip it to your equipment once it’s been sent to the surface; if you need to be hands free for a moment, you can simply clip off your reel with the bolt snap, doubling your line around the top part of the clip, and allow it to float in front of you. You should also ensure you hold the SMB and reel at arms length away from you as you release it to the surface to avoid entanglement, and always carry a dive knife or line cutter in case an entanglement does occur.