July, 2016
Choosing the best surface marker buoy (SMB) for your dive
Surface marker buoys are handy for a number of occasions, whether it’s to signal your position to your boat at the end of your dive or during emergency ascents.
When you need immediate help or when someone in your dive group needs to get to the surface quickly, you’d want to be able to deploy the bag without it causing other problems or making matters worse. That’s why choosing a suitable SMB for your dive is so important.
There are three main factors a diver should consider when choosing a surface marker buoy: its size, method of inflation and the length of its line.
- What size do you need?
To be useful, the marker must be visible on the water’s surface, so it should be as large as you can manage. My emphasis is on what you can manage. You could have the largest marker on the planet, but if you can’t inflate it properly, it would simply be a limp piece of plastic floating on the surface. That certainly won’t be noticeable from a distance — unless the boat crew is consulting Google Earth.
Therefore, the size of the SMB you choose should be the largest that you can reliably fill from depth. Personally I prefer a smaller, thinner bag that will stand upright when filled with a relatively small volume of gas. I use the Halcyon 1m SMB on all my dives. This bag will fill up completely with only a single regular breath at a depth of about 10m. If you are at a shallower depth, then you’d need to blow in a larger breath of air, but it’s definitely still possible to fill up the bag quickly and send it on its way without much stress.
Now you might be wondering, what if you’re diving at sites with large waves and surge? Wouldn’t a larger (more visible) surface marker be better? In response I would ask: Is the dive worth putting yourself in such a situation? If the answer is yes, then make sure you are prepared for it with a larger surface marker.
Remember that a larger bag must be filled with a greater volume of gas in order to stand upright on the water’s surface. This means you’d need to either blow more gas into it (by exhaling or purging from the regulator) or release the bag when you are at a greater depth to allow for more gas expansion. The latter would be a good option, but the downside would be the much longer line that you would have to reel in as you ascend.
I would normally only inflate these larger surface markers once arriving on the surface and the boat is further away. The bigger marker will be easier to spot from a distance, but will also be harder to manage while underwater.
- Which method of inflation should you use?
Open circuit SMBs are some of the commonest in the market. To inflate an open circuit SMB, a diver typically purges air from his alternate air source into the bag. However, I do not recommend this method of inflation for a number of reasons.
The large amount of air purged from the alternate air source would likely cause a fairly significant and sudden buoyancy change. In an emergency or stressful situation, a sudden change in buoyancy could easily spiral out of control.
The force generated by the large volume of gas also means that the SMB will take off towards the surface really quickly. If the diver does not manage the line well, the line could get tangled with the BCD or tank, and drag you up to the surface. Nobody wants to be a human SMB!
I would always opt for the oral inflation method, because it is quicker and safer. The amount of gas that you exhale would not cause a significant buoyancy change (unless you inhale an extra-large breath of air right before). This makes the buoyancy change much more manageable. You wouldn’t need to find your alternate air source, too.
If like me, you prefer the oral inflation method, what’s left is to choose an SMB that works best with it. It’s possible to orally inflate an open circuit SMB, but due to the line being attached near where the open end of the SMB, there is a higher risk that your regulator might get caught in the SMB line or the SMB itself. Definitely not my first choice.
There are many SMBs on the market that are designed for easy and effective oral inflation. They normally have an oral inflator with a one-way valve. This, in my view, is the best one to use because it guarantees that the gas goes directly into the SMB. It’s also really easy to use. The Halcyon SMB I use does not have a locking mechanism, so you won’t need to fiddle with extra bits to inflate the bag.
- How long should the line be?
Some SMBs come with a 5m line, which means you can deploy the SMB only at the 5m safety stop. Obviously this is limiting, as you might run into other situations where you need to deploy the SMB at a greater depth. My advice: Always get a longer line that’s wound around a spool.
SMBs do not always take a straight path up towards the water’s surface, and might ascend at an angle when there is a current. As such, always make sure your SMB’s line is longer than your deepest planned depth. This means that if you are doing a 30m dive, then a 30m spool is not going to be sufficient. A 45m spool would be a better choice. I would use a 30m spool for dives to depths shallower than 25m.
In summary
My recommendation is to get a small thin SMB that you can reliably fill via oral inflation, and use a spool with an appropriate amount of line. Also, remember to practise deploying your SMB after buying one! A seasoned diver can easily get a bag deployed in less than 15 seconds, so keep practising until it becomes second nature!
The correct way to do a back roll
Here in Bali, we tend to dive from small boats that require a back roll entry into the water. Very often, we encounter divers who do not know how to do a back roll effectively. Some go headfirst into the water while others flip over completely and struggle to get their legs beneath them. While this can be a hilarious sight, there is a safety issue here that shouldn’t be overlooked.
When performing the back roll, the scuba tank should hit the water first. This cushions the diver from impact, and protects the neck from undue stress. Divers commonly mistakenly throw their heads back to initiate the backward roll, and this usually results in the diver hitting the water headfirst.
There’s more than one reason why this isn’t ideal. Firstly, by throwing the head back, you’re likely to hit the first stage with the back of your head. Obviously that’s going to be uncomfortable. The mask strap might also slip off the head upon impact with the water. If the diver isn’t holding the front of his mask and regulator, the mask might very well slip off and drift away. In truth, many divers have lost their masks this way.
Thirdly, if the diver isn’t able to get his legs under him quickly enough in a high current situation, then he might surface far away from the boat and the rest of the divers, or heavens forbid, near the propellers at the back of the boat.
Here is how a back roll entry should be safely and effectively executed. Before getting into position, ensure all your gear is in order: Fins securely strapped on, BCD fully inflated, mask and regulators in place.
Step 1 – Sit as far back on the edge of the boat as possible. Lean forward to prevent the tank from hitting the side of the boat as you enter the water.
Step 2 – Keep your head facing forward, and place your right hand on the mask and second stage. Check again that the BCD is fully inflated to be doubly sure.
Step 3 – Cross feet (stack one fin on top of the other) to avoid hitting anything or anyone beside you.
Step 4 – Keeping your back straight, slowly lean back, as if lying back on your bed. The weight of the tank will pull you backwards into the water. Let the weight of the tank lead the backward roll. Avoid rocking backwards forcefully as this might cause your body to over-rotate. Ideally, the corner of the bottom of the tank should hit the water first, and this should slow your entry into the water.
A nice entry where the tank hits the water first
Step 5 – As you enter the water, keep your head, hands, legs and waist in roughly the same position as while you were seated on the edge. Avoid spreading your legs as your calves might hit the edge of the boat.
An over rotation, where the head is the lowest point on the entry
Step 6 – Once the tank hits the water, move your legs in a breaststroke kick to get them under you in the quickest time possible. This should also prevent you from drifting too far into the current.
Step 7 – Signal to the boat that you are okay.
An advanced option: As you lean back into the water, turn and angle your body slightly so that it faces where the current is coming from. This brings your legs and fins around into a better position to push back against the current if the need arises.
Should we use an inflated surface marker buoy throughout a dive?
Most divers recognise that the surface marker buoy, or SMB for short, is an essential piece of dive equipment. However, not everyone agrees on the point of whether to use it throughout a dive.
Some divers inflate a highly visible surface marker buoy before descending, and the buoy follows the group throughout the dive. You might see this happening at shallow bays or dive sites where boat traffic is high. It seems like a good idea, since the marker lets boats know that there are divers below, but is it really?
Now let’s look at what could go wrong in such a scenario.
Firstly, having to tow something along (in this case, an inflated marker on the surface connected to a line held by an underwater diver or attached to his BCD) is not only tiring but also hard to manage. The diver holding on to the reel or spool has the responsibility of releasing and taking in the line according to changes in depth. If your divemaster had to manage this, do you think he would have the capacity to also lead the dive and keep track of all the divers?
What’s more, divers might also swim into the line and get entangled, making the dive even more difficult.
Secondly, there are often winds or surface currents at many dive sites. This force pushing on the surface marker buoy may oppose the underwater current or the direction taken by the divers. Fighting the drag and getting the SMB to follow you during the dive would be a challenge.
Lastly, even though the surface marker buoy serves to warn boats, people do still make mistakes. In my years of diving, I’ve seen more than one boat drive right over an SMB. If the SMB line was attached to a BCD, what would happen if the line got caught in a propeller? I shudder to think of the possibilities.
In my view, surface markers are useful only when divers are surfacing or in situations where the conditions are such that the boat must follow the divers throughout the dive (for example, strong current, heavy surge and open ocean diving). The method of diving with an inflated SMB throughout a dive would not be a first choice for me, when planning dives in relatively good conditions.
What’s more important is ensuring the diver has good skills, especially buoyancy in this case. If a diver had excellent buoyancy and awareness, he would be aware of the loud noise generated by an approaching boat, and stay close to the bottom.
Finally, let’s consider two divers with excellent buoyancy skills: One has an inflated SMB attached to him and the other has none. A boat passes overhead. The diver with the line, through no fault of his own, might very well get pulled up into the boat’s propeller. The diver without the line, who upon hearing an oncoming boat, stays close to the reef or bottom and faces no such risk.