How and when to use a delayed surface marker buoy
A delayed surface marker buoy is used by a diver at the end of their dive. This is to either aid the diver ascent and/or to mark their position to the dive boat skipper.
A delayed surface marker buoy (DSMB), is similar to a surface marker buoy except that it's deployed at the end of your dive vs used for the duration of the dive. A DSMB, which is also known as a decompression buoy or a deco buoy, is often used for safe diving ascents from depth on decompression stop dives. They are also used to indicate a diver's position on ascent. This helps the dive boat skipper spot divers on the surface, especially in seas with a big swell.
What is a delayed surface marker buoy used for?
A delayed surface marker buoy (DSMB) is not to be confused with a surface marker buoy (SMB). SMB's are used for the duration of your dive. Where the buoy is on the surface to enable the dive boat skipper to follow you whilst you’re on a drift dive.
Whereas a DSMB is deployed at the end of your dive to aid ascent or to help mark your position on the surface to make it easier to be spotted by the dive boat.
A delayed surface marker buoy is deployed at the end of your dive from the bottom.
How a delayed surface marker buoy is inflated
The buoy is inflated either using your scuba mouthpiece or using a special air feed. Once you've filled the buoy with enough air at the bottom, you let it go and the buoy will shoot to the surface.
Once you've deployed your DSMB, you can then slowly reel in the line and use the line as an ascent line. See below for using the DSMB line for decompression stops.
So long as you've put sufficient air in the buoy before you've sent it to the surface, the buoyancy will be strong enough to support your ascent. You'll be able to hang off the line as you reel it in, even when you stop for decompression stops or for your safety stop.
Not only is a DSMB used as an aid to ascend, it's also used to mark your position on the surface. In the UK the seas can sometimes have quite big swells. This means it's sometimes quite difficult to see divers as they surface.
When a delayed SMB is used, this sticks higher above the water than your head does. This makes it much easier for the dive boat skipper to see surfaced divers.
However, it's important to make sure you inflate the DSMB buoy enough so that it does stick up in the water like a sausage. This is why DSMBs are also referred to as 'Safety Sausages'.
More Reading: How do you do a decompression stop vs a safety stop
Delayed surface marker buoy tips of use
These are a few handy tips when you use a delayed surface marker buoy for the first time.
DSMB tips for use underwater
- Always thoroughly wash your DSMB after use. This is because salt water can jam up the reel. A reel that jams can be dangerous when it's deployed.
- Make sure you have enough line to reach the surface. This is really only a concern on deeper dives. Most DSMBs have sufficient line for recreational dive depths.
- Make sure you either have something to hold on to when you fill the your DSMB or connect the reel to something on the bottom. Ideally if you're diving on a wreck, there will be many things to tie off your DSMB reel to.
- Before you leave the dive boat for your dive, make sure your reel is free running. Make sure the reel won't get stuck when you deploy your DSMB.
- Make sure you fill your buoy with plenty of air so that the buoy or 'safety sausage' stands up in the water on the surface. It's better to over-fill it than to under fill. If you over fill the buoy, the excess air will spill out on its way to the surface as the air expands.
Extra safety tips for DSMB use
A few more safety tips for using a surface marker buoy.
- Be careful you don't get dragged up with the buoy as it's deployed, as this could be extremely dangerous. This is especially true if you've gone into decompression stop time on your dive. This is something that could happen if the reel jams when it’s deployed.
- If you are on a decompression stop dive, make sure you leave enough time at the end of the dive to deploy your delayed surface marker buoy. Once you're into decompression stop time, the time you need to decompress clocks up very quickly.
Why is a DSMB used for safety?
More often than not a delayed SMB is used for decompression stop diving. This is why the alternative name of 'decompression buoy' or 'deco buoy' is used.
It's far easier to come to the surface slowly and in a controlled manner using a line. When you send your DSMB up to the surface, you have a line to follow to the surface.
Also, and assuming you're diving a decompression stop dive, it's far easier to maintain a set depth when you're holding on to a line. This is especially true if your decompression stop time is lengthy.
It's far easier to relax into your decompression stop when you are holding onto a line than it is controlling your buoyancy using your buoyancy control device or the air in your dry suit.
More Reading: Scuba Diving Buoyancy Control Device (Scuba BCD Reviews)
What's the difference between a delayed surface marker buoy and a surface marker buoy?
Earlier in this article I mentioned a 'Surface Marker Buoy' or SMB.
The main difference between a delayed surface marker buoy and a surface marker buoy is that a DSMB or safety sausage is taken down on the dive and only deployed at the end of the dive. Whereas an SMB stays on the surface for the duration of the dive.
The SMB is used so the dive boat skipper can see where the submerged divers are. He uses the buoy to follow the divers in a drift dive.
A delayed surface marker buoy provides the same role on the surface, but only at the end of the dive rather than its duration.
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