Browsing Category Equipment
When to deploy a surface marker buoy (SMB)
The answer might seem obvious, but many divers neglect to shoot the bag early, and end up surfacing a long way away from their dive location and their boat. I’ve heard many stories of divers drifting for hours because of their boat crew could not locate them. Don’t let that happen to you.
I would always consult the diving conditions when deciding when to deploy my surface marker buoy. Generally, you should shoot the bag when you are starting the ascent in a normal dive, or whenever you are leaving the reef, whichever happens earlier.
However, if the conditions are bad, such as when there’s a strong current pulling you away from the reef, then you would need to deploy your SMB as early as possible before you get swept into the open ocean. Don’t delay getting the SMB to the surface!
Consider a situation where this wasn’t the case, for example, if the diver ascended to a safety stop before deploying the SMB, or in a situation where the spool wasn’t long enough to reach the depth the diver is at.
In these situations, the time taken to ascend to a shallower depth, coupled with the current, could mean that the diver drifts far away from the dive site. Given that the boat would be waiting for the diver to ascend near or on the dive site, this could mean the boat captain will not be looking out towards the ocean where the divers eventually surface.
Needless to say, it’s much harder for the boat captain to spot divers floating in the open ocean than next to the reef. Personally, I wouldn’t take it on faith that the boat captain will always know where to look for you when you surface. Do your part as well to guarantee that he can see you!
Finally, if you’re wondering whether to use an inflated SMB throughout your dive, read this article that discusses it in depth.
Differences between a jacket and a backplate and wing system
Looking at BCD systems and their merits will require an understanding of what they are there to do while you are diving. Obviously, a BCD is there to help control your buoyancy, but in terms of function, how does this actually work?
All BCDs have a way to inflate and deflate the air bladder. More gas in the bladder equals more positive buoyancy, and less gas equals less positive buoyancy. Simple!
However, how these devices are built and designed play a huge role in how easy it is to manage the gas within the BCD, and thus manage your buoyancy as a result.
Let’s look at jacket BCDs, which are the most common type of BCD found in almost every dive centre the world over. This is shaped like a vest or jacket, with arm holes and an air bladder that goes from the front to the back, with additional pockets and clips and adjustable straps for convenience.
The backplate and wing system, is a completely different looking piece of equipment, with a 5 point harness and crotch strap, attached to a rigid metal or plastic back plate, which in turn is bolted onto a round donut shaped air bladder.
Functionally, both types of BCD will allow inflation of gas into the air bladder through the inflator mechanism, and both will allow deflation of the gas from either the deflate button, or one or more dump valves.
However, the relative positions of the dump valves, and how the gas moves in the air bladder plays a critical role in how the BCD performs while diving. Ultimately, we need to know where the gas is located in the bladder while underwater, and that is how we can use these devices effectively.
Now if we can agree that a good diving position in the water would be a flat, horizontal trim to aid in streamlining, then where would the gas be in the BCD in that position? In a jacket BCD, the gas would be at the top, near where the tank strap is. Depending on the exact trim of the diver, this gas can be near the shoulders, or near the bottom of the tank. There could also be some gas trapped in the front pocket areas as well.
Most new divers learn to dump gas from their BCDs by extending the inflator hose upwards and pressing the deflate button. The diver would need to come into a head up position, to allow the gas to flow to the deflate button to be released.
This additional movement is not ideal, firstly because in that position, the diver would then need to come back to a horizontal position again, wasting energy and effort to move into and out of position.
Secondly, if the diver was in a runaway ascent, the best way to mitigate that would be to position head down and kick downwards, which would be really hard to do if the diver is angled upwards with their legs beneath them. Any additional movement in the legs would only exacerbate the problem by bringing them closer to the surface and causing the gas in the bladder to expand more.
Let’s contrast this with a backplate and wing system. While diving, the donut shaped wing will fold upwards, and wrap the tank on both sides. The gas in the bladder in this position then can only be in one position, at the highest point of the wing on both sides of the tank.
In this position, getting the gas out is relatively easy, as the dump valve on the wing is located near the bottom of the wing and close to the top edge. In most cases, the diver would not need to adjust his trim by a lot in order to remove the gas from the wing. He would just need to pull on the dump valve string upwards, trapping the gas between the dump valve and the tank. In this case, there isn’t anywhere for the gas to travel to, and will be easily dumped from the BCD.
BCDs should also minimize the amount of trapped gas that cannot be removed from the bladder, in terms of corners which can create pockets of gas that are not easily moved to the dump valves. The dump valve position should also allow for the maximum amount of gas to be removed from the bladder, so that every bit of gas is removed and won’t cause any additional positive buoyancy due to gas expansion on ascent.
If those are the key traits that make for an ideal BCD, then I feel a wing design makes the most sense. It’s round and doesn’t have any corners to trap gas, has a smaller internal surface area, the dump valve is located close to the edge of the wing, and it’s design prevents catastrophic failure in the event of a dump valve breakage.
The backplate system also has other benefits in terms of fit and streamlining, which ultimately leads to better control in the water.
BCDs these days come in all types and flavours, but choose wisely! It needs to be effective in the water, and not cause any additional complications.
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.
How do I attach a bolt snap to diving gear?
Attaching bolt snaps to dive gear like SPG hoses, regulators and backup lights makes for easier stowage. Now the question is: Should you use cable ties or nylon lines?
For me, the choice depends on where and how they will be used. Nylon lines are definitely superior to cable ties in most situations, however, they take some practice in order to be tied correctly and securely. Cable ties are quick and easy to secure, and are found everywhere, so they are a quick handy solution to connecting a bolt snap when you’re out diving.
Let’s dive in to the various situations in which either of these options might be suitable.
Attaching bolt snap to SPG hose: Cable tie
A bolt snap attached to an SPG hose with a cable tie.
The connection between the bolt snap and the SPG hose tends to be a static tie, that is, it would not move much in the course of its lifetime. The clip on the SPG hose need only flip forwards and backwards, and there would not be much turning along its vertical axis.
For static connections, a cable tie would be sufficient. A cable tie has strength along the length of the plastic tie, but does not handle rotational forces well. If a connection has a high possibility of rotating or turning sideways during use, then a cable tie is not ideal.
Attaching bolt snap to long hose or backup lights: Nylon line
The long hose is traditionally tied to a bolt snap with a knotted nylon line.
The long hose connection occasionally has some rotation, but will not be excessive. Likewise for backup lights, there might be some movement when they are clipped on. A cable tie is generally sufficient, but a knotted nylon line connection is definitely superior.
An SPG hose can also be tied to a bolt snap with a nylon line. This particular knot is probably 4 years old now.
The backup light should be tied with a nylon line connection to be secure.
Attaching bolt snap to backup lights, cameras and other large equipment: Nylon line + Cable tie
Due to the way the camera housings move in the water when clipped off, an extra cable tie over the knotted line is a good idea!
Alternatively, make sure your line is thick and tied really well! You wouldn’t want to lose a few thousand dollars worth of camera equipment due to a failed knot!
Connections to large, bulky or heavy equipment will certainly have rotational forces involved. Picture your camera dangling from the bolt snap attached to the D-ring of your shoulder straps. The weight will cause your gear and its connected bolt snap to sway in various directions as you move, and when your hands are busy with something else. The equipment will also rotate as you clip on and off. So, for a camera and other heavy equipment, I would say a knotted line is mandatory. I might even put a cable tie over it to be doubly sure that the connection is secure!
Looking at the camera housing when it’s clipped off to a d-ring gives you an idea of how it will move and swing when diving. I’d rather make this connection a secure one!