Surface Marker Buoy

What is it?
The surface marker buoy (or SMB) is an essential piece of equipment which allows a dive team to mark their position either on the surface or underwater.

Why should I have one?
Just as with backup lights, SMB's are not only for technical divers. Marking one's position in the water with an SMB may be the only form of communication between the boat and the diver in less than optimal conditions.

In recreational diving, deploying an SMB may prevent a number of unsavory outcomes. In areas of high boat traffic, the SMB may be deployed to prevent an unsolicited "haircut" from a prop. In high current, the SMB may assist the boat captain in either tracking your dive group, or in noting the fact that you have drifted off the dive site. Finally upon arrival at the surface, the SMB may facilitate tracking of the team, and also prevent other boaters from colliding with you.

In technical diving, the SMB is used to prevent separation between dive team and boat. It allows a dive boat to deliver a support diver, who can easily follow the line down to the team to relieve them of spent bottles or scooters. It may also signal the boat that the team is drifting, and allow them to unhook, or follow at a safe distance.

What are the important characteristics?
Surface marker buoys come in a variety of shapes and sizes, with many different features.

Open Circuit vs. Closed Circuit
Open circuit SMB's are distinguished by a simple opening found at the bottom of the bag, by which it can be inflated or deflated. Meanwhile, closed circuit bags usually have either a single inflate/deflate mechanism, or separate in and out mechanisms.

The benefits of an open circuit bag are simplicity, and easy inflation using the regulator as opposed to an LP inflator hose. This is better for wetsuit divers, who may not have an additional hose, as disconnecting the primary inflator (i.e the BC hose) is not recommended for anything aside from auto-inflation. However, in general, open circuit bags are less reliable, as they are prone to deflating at the surface. While the gas inside the bag keeps the SMB upright underwater, upon surfacing, the SMB is further weighted down by the material forming the bag itself. Some SMBs now feature baffles, which reduce the chance of the bag deflating accidentally. Pulling down on the bag will also help keep it vertical, which further improves your chances of keeping the gas in the bag. However, between gas switches and bottle movement, the ability to maintain constant tension on the SMB is unlikely. Furthermore, larger swells may make it even more difficult.

Closed circuit bags almost completely eliminate the risk of accidental deflation, but introduce some other issues worth considering. First, the added complexity of the SMB means more mechanisms. These may include either a one-way flapper valve for inflation, and/or an additional over-pressure/dump valve, much like that found on a wing. However, the likelihood of these simple devices failing catastrophically is minimal. Another drawback is the risk of over-inflation and subsequent catastrophic failure (think: boom). An easy solution is not to overfill the bag; the simple relationship of volume and ATA says that, depending on your depth, you only inflate enough to make it full on the surface. For example, at 70'/21m (roughly 3 ATA) you only need to fill the SMB 1/3rd of the its volume to have a nice full SMB at the surface.

Depending on your local diving conditions, your specific needs may vary. SMB's commonly range in size from ~3'/1m to 6.6'/2m and larger. While some may not believe it, bigger is not always better as a large SMB may be difficult to control underwater, reducing the chance of a controlled deployment. It will also exacerbate any entanglement issues. The larger bags may cause more problems underwater, and in the real world, may not be any easier to view at the surface, due to the difficulty in keeping a larger, heavier bag upright.

Attachment Point
Each bag, regardless of size or type, must have a clean point for attachment. Ideally, it's a stainless steel d-ring that will allow a double ender (commonly the 4" found on the spool) to pass through. Plastic will work, but is not as durable. You should definitely avoid any quick clips or "suicide clips" that may accidentally "acquire" line.

Avoid using the double ender to clip to any part of the bag; the line may slip out of the double ender, and you'll need the double ender to lock down the spool.

Where do I put it?
The small SMB stows neatly in a bellows pocket. To make it easier to deploy, it may be stored pre-rigged with a spool. This also allows you to use one double ender to secure both the spool and the SMB.

Larger SMB's may need to be stored in the backplate pak. Be sure to store the bag in such a way that the valves are position in the hollow of the back, usually at the bottom 1/3 of the plate. Clip the bolt snap to the tail d-ring, which allows you to unclip, and then pull out the SMB from the storage area.

How do I maintain it?
Soaking will prevent salt buildup. If you can unscrew the OPV, you'll also be able to rinse the inside of the bag with freshwater. Take some time to flush some freshwater through the one-way inflation valve in order to prevent any leakage due to salt crystal buildup. Dry and store unfurled, to prevent any creasing that will weaken the material.

Which one should I get?
In Monterey, we most often use the 3.3'/1m with a lot of success. The benefit of a smaller sized bag is twofold: the small size when stowed means it can easily be placed inside a pocket, and the small amount of lift (6 pounds when full) makes it easier to handle underwater. From entanglements to simple communication, having an easy to handle bag means that your SMB deployment can go from a harried release to a controlled, safe procedure. Even with larger swells, the bag is easy to see is good conditions.

We also often carry the Halcyon 4.5' marker. Our experience found the larger bag to be no easier to see, as the increased weight of the bag made it more difficult to keep erect. When lying down, it wasn't easier any easier to locate than the 1m/3.3' sausage. However, the larger diameter of the sausage means it provides more lift, up to 40 pounds. It still retains all the benefits of the smaller sausage, including a closed-circuit design that can be either orally or power inflated, and the 40# lift is still manageable, especially considering proper inflation technique based on depth. We most often carry it when scooter diving, as it can be used to lift a smaller scooter to the surface. Obviously, if your scooter weighs more than 40# on the surface, it will need a larger bag to rescue it.

The marker should be held out in front of the diver at arms length. With the free hand, unclip a spool and slip the looped end of the line through the eye of the stainless steel bolt snap at the bottom of the marker. Pass the spool through the loop, thus securing it to the marker. Now a final charge of gas appropriate to the depth of release is added and the marker is released. Allow the spool to turn freely while maintaining tension on the line as the marker rises to the surface.
It is important to note that the line is used for reference and is not to hang from. It can be spooled up incrementally and locked down at each decompression stop when used as a free-floating deco station. For divers wearing thick or rough gloves and who struggle to control the spool when free running, simply make an "OK" sign around the line, just above the spool, with the line playing out between the thumb and forefinger of the "OK". The spool will not plummet to the depths; rather it will dance about seeming to hover below your hand, while the marker travels upward.