How do I deploy a DSMB safely?
It’s a Question time and time again we are asked in the dive centre.
In my view, a Surface Marker Buoy is a must have piece of safety equipment, which, in many cases, is required by local law. So exactly what is a Surface Marker Buoy (“SMB”) and when should you use one?
SMBs come in many different shapes and sizes. Quite simply, they are an inflatable surface marker used to mark the location of a diver or dive group. Such devices can include inflatable dive flags that float on the surface and are attached to a line that a diver drags along, marking the location of the group to boat traffic or the lookout. However, most people associate SMBs with an inflatable tube, also known as a “Safety Sausage”. Safety sausages are invaluable for marking your location in instances where you may have been “navigationally challenged” and surfaced a distance away from the boat, allowing you to be spotted from a much greater distance. They are also essential when you are drift diving and require a boat pick up at the end of your dive. In this instance, a Delayed SMB is even better.
A Delayed SMB (“DSMB”) is effectively a safety sausage that is deployed at depth rather than on the surface. DSMBs are essential in areas of high boat traffic, assuming that boat crew are aware of what a DSMB is used for. I do recall a very hairy moment whilst diving in Thailand however, where a longtail boat drove straight over my deployed DSMB whilst on my safety stop, but that is another story! Delayed SMBs are also useful when completing a safety stop in a current, allowing the dive boat to track you. For instance, in a two knot current you can drift up to 400m (1/4 mile) during a 5 minute safety stop. It makes good sense to deploy your SMB during your safety stop if you haven’t returned to the boat.
DSMBs are also used heavily by technical divers to mark their location whilst completing their decompression stops. Many tech divers will have their name written on their DSMB so that the lookouts know who is decompressing and who may be missing.
So now you understand the uses and importance of an SMB (or DSMB), but before you head out and buy one, let’s discuss how to use one. As a safety device, DSMBs are potentially lethal pieces of equipment in the wrong hands.
The biggest risk areas when deploying a DSMB can broadly be categorised into the following 3 areas:
1. Problems with the reel jamming or line entanglement
There is a vast array of reels on the market, many of which are prone to jamming. Ask around your dive buddies for recommendations and consult online forums. Quite often, the simplest reels, such as a finger spool, are the least prone to jamming. Make sure you get one that works well and ensure that you look after it by regularly lubricating the mechanism and always ensuring you rinse it well in fresh water after use.
A key part of helping to avoid entanglement is to be extremely diligent in winding the reel up after use. I have, on a number of occasions allowed instructors to borrow my reel and it has come back in a dangerous state, the line in knots, reeled up in haste and increasing the chances of jamming on its next use. This is one area that it is well worth being very methodical about. So, after use, I recommend reeling the line out, attaching the end to a fixed point and laying the line out flat may help. Then, slowly reel the line back in to ensure the line is neat and taught. A line that is not tightly reeled up on a finger spool or unenclosed reel is likely to unravel over the reel side and potentially cause entanglement.
I have seen some divers mark distance on their reel line using knots or pieces of coloured ribbon tied on. This is not something that I would recommend as it increases the chances of the reel jamming. Instead, if you want to mark distance on your reel use a permanent marker pen which works well on the white reel line. I use a small mark at the 5m mark for safety stops and then a larger line at the 10m mark, 2 lines at the 20m mark, 3 lines at the 30m mark and so on.
Ensuring the SMB is packed away correctly helps to avoid issues on deployment.
2. Problems with the diver’s equipment getting caught in the SMB
If you have the reel attached to you, always ensure that it is detached prior to the deployment of the SMB. I have witnessed cases where a diver has been dragged up to the surface by an SMB that jammed on deployment and was still attached. If this happens, you need to be able to let go of the reel completely to avoid a rapid ascent. You may want to consider tying the reel to a wreck or rocks prior to inflation and deployment to avoid the chance of being dragged up by a jammed reel.
The first few metres below the surface, which is where you will be performing the majority of your safety stops and deployment, is where the pressure differential is most marked and small changes in depth has a marked impact on air spaces and volumes. With this in mind, you want to ensure you are ready to quickly dump your own buoyancy in your BCD as you fill the SMB. For this reason, it is worthwhile being slightly negatively buoyant to minimise issues with being dragged up during inflation.
Some simple SMBs designed for deployment from a 5m safety stop come with a pretied length of loose line. The loose line on such SMBs can easily become tangled and, for this reason, I would recommend attaching a reel instead. Some SMBs come with an attach length of webbing for deployment and these are excellent provided that you are diligent in folding away the webbing deployment system (as with a reel) neatly. I have an iSMB with webbing, it’s own inflation cylinder by AP Vales and have found it excellent.
3. Problems with inflation
Depending on the SMB, inflation may be performed via gently purging the alternate air source into the SMB opening or via a valve inflation using an inflator hose or oral inflation technique. Some SMBs have their own air supply in the form of a small cylinder.
For SMBs where oral inflation is required it is worth considering the risk associated with removing your regulator to inflate. With this in mind, it may be worth considering an SMB which does not require oral inflation. If you are a competent diver, the risk associated with regulator removal would be minimal. Some SMBs have their own air source attached via a small onboard cylinder. The advantage of these is that you do not haveto remove your regulator!
For open ended SMBs that are inflated using an alternate air source, the principles of inflation are the same as that of operating a lift bag. Roll out the SMB and then hold the open ended part above your alternate air source. You need to ensure the opening is fully open by prizing it open with your fingers. Then place your alternate air source (mouthpiece facing up towards the surface) at the opening and purge small quick bursts of air into the buoy. It is worth remembering that the buoy will not require much air before you release it, as whatever air is inside will expand with the decrease in pressure on ascent.
Using an SMB with a built-in 6m tape avoids requiring a reel.
An alternative inflation method for an open ended buoy is to utilise your exhaled air rather than your alternate air source. Whilst tilting your head to one side, simply hold the open end of the buoy above the primary demand valve and direct several exhalations up into the SMB. For both methods, small bursts of air should be added with care rather than a rapid purge that will result in an rapid ascent of the bag and associated risk of being dragged up with it.
Where a SMB requires oral inflation via a valve, the diver removes the primary regulator from his or her mouth to inflate the buoy and applies small short exhales into the bag to inflate. Similarly, where a low pressure inflator hose is attached to inflate the bag, small short bursts of air should be applied. Using a low pressure inflator hose to inflate from either the divers BCD or dry suit does not necessarily increase the chances of a rapid diver ascent as, unlike the BCD/Drysuit quick connect valve, the SMB valve does not retain the hose connector and can be easily disconnected by pulling off when required.
4. How do I choose the right DSMB?
Like diving with a computer, a DSMB should not be shared between buddy pairs. It is acceptable for just one member of the buddy team to deploy their SMB, however if the buddy pair did get separated, both members would obviously need to deploy. Further, having a second SMB provides a back up should problems such as reel jamming, perished bag or loss should arise with the deployment of the first SMB. Some operators require every diver to release a DSMB, rather than just one per buddy pair. That way they know when everyone is accounted for and on the way up.
If you simply want an SMB for deploying on your 5m safety stop, then an SMB with a 6m length of webbing tape attached to the SMB is probably the simplest and safest option. If you would like the ability to deploy the SMB from a greater depth, then a simple finger reel is probably the next best solution. Finger reels come in lengths up to 30m. Anything deeper and you will need to use a hand reel.
Some divers carry two reels with the line from the second reel attached to the handle of the first. The idea being that if the first reel jams while deploying the DSMB, you can let it go and deploy line from the second. Where possible, arguably a better solution to counter risk associated with jamming would be to use a single reel and tie it on to the wreck, rock or other potential anchor point for deployment. Alternatively, a finger reel is much less likely to jam as there is no mechanism to jam.
Practice deploying your DSMB in a swimming pool or shallow water. When you have the hang of it, practice with your eyes shut – you may just have to do it all in zero visibility! And keep practicing regularly to keep your skills fresh and ensure deployment is second nature when it is required.