Browsing Tag wing design
Is sidemount diving relevant to open water dives?
Sidemount diving is slowly becoming more common and gaining some popularity.
More and more divers are seen diving sidemount in open water environments.
However, is this just a fad and is it relevant to the diving that we normally do?
Where did it come from?
Sidemount diving, which started with exploratory cave diving, was created so that cave explorers could access tighter and more restrictive holes, allowing exploration further into cave systems.
The benefits of sidemount include the freedom of not having large double tanks on your back, the feeling of being free and less weight to cause backaches, easier logistics from carrying smaller tanks to boats instead of larger doubles, etc.
However, do these benefits apply when diving in the open ocean? IMHO, not so much.
Sidemount from shore
In ocean diving, you would traditionally either dive off a boat or from shore.
Shore dives do see a small benefit from sidemount. Mostly from when you have to transport tanks to the waters’ edge, which may not necessarily be a comfortable beach entry.
There could be large waves or rocks that make carrying a large set of doubles tricky if not dangerous to the diver.
In this situation, yes, you would see some benefit from ferrying the tanks to the water in multiple trips, but this would still mean having to make several trips up and down the beach.
Me personally, I’d rather fight the waves once and get into the water quickly, rather than have to struggle multiple times.
Sidemount from a boat
What about diving from a boat?
There’s no requirement to move tanks around, but most divers will have to put on their tanks in the water next to the boat to prevent having to stand with tanks bouncing on your sides while the boat rocks in the waves.
Of course, it’s possible to put on the sidemount tanks on the boat and backroll with them between your legs. But anyone who has ever had a stage tank bash your head on impact with the water would think twice about this.
What happens if there’s some current on the surface?
This would make the process of clipping off the tanks one by one very troublesome while needing to hold on to the boat as well. In choppy seas, this is not an option I would even consider.
Carrying doubles on your back is a much easier option, as you would be way more stable with the weight on your back.
The water entry will be much easier too because you are free to move away from the boat once in the water.
What about during the dives?
Does the sidemount configuration provide any benefits while you’re diving? Well, there is a sense of freedom and increased maneuverability from not having a large mass on your back.
However, you do have to remember to keep the tanks streamlined by checking periodically that they are clipped on the appropriate D-rings as the tanks get lighter.
Plus, you also have to balance the tank usage by breathing from different tanks every once in a while.
This added task load is unavoidable in sidemount, and an additional task when compared with diving doubles.
I haven’t found a restriction in open water yet
In conclusion, there are some benefits to diving sidemount, but sadly, most of them don’t really apply to diving in the open water environment.
I would say that the configuration is an important one to practice with and get good at before attempting to dive a cave system, so practicing in open water makes sense.
However, I personally don’t think diving sidemount as a default configuration in open water really provides enough benefits to outweigh the added complications.
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.
Diving with Ditchable Weights: What You Should Know
Why dive with weights?
One of your first lessons when learning to scuba-dive would (should!) be buoyancy. Divers use weights to counteract the buoyancy of other diving equipment, such as diving suits and gas tanks. During the dive, you will control your buoyancy by adjusting the air volume in your buoyancy compensation device (BCD) or buoyancy bladder (commonly referred to as wing), and dry suit, if applicable. At the end of the dive, you’ll need enough weight to be neutrally buoyant when you have breathed down most of your gas, and when holding your position at safety or decompression stops.
What are ditchable weights?
Most divers are familiar with the concept of ditchable weights, especially if you are trained to scuba-dive in cold water. You probably have been taught that if you have trouble with your BCD and are unable to inflate it, you should get rid of the ditchable weights to achieve positive buoyancy and surface (or stay on the surface if you are already there). But should you get rid of all the weight at once in such an instance? More on that later.
This is in contrast to fixed or non-ditchable weights, such as a steel backplate, V-weights or steel tanks. These are weights that either cannot be removed, or should not be removed for safety reasons. These weights form an integral part of the diving system and will not be considered in this article. We will discuss how to choose them in another post.
Where should you place your ditchable weights?
I do not recommend wearing all of your weights in one location, especially on a weight belt. Not only do weight belts affect your balance, they are also notoriously prone to coming loose on their own. I would first consider putting as much weight as possible directly above the centre of gravity of the diver. Once these locations are full, put some weights in a location that is easily accessible and where the weights can easily be ditched.
How much weight do you need?
This depends on the diver’s mass and body composition, buoyancy of other diving gear worn, water salinity (fresh water or salt water), and water temperature (which relates to a choice of diving in a wetsuit or drysuit). Read more about this here. The weight required is directly related to the amount of thermal protection worn. A thicker undergarment (worn with a drysuit) or wetsuit will result in the need for more weight. This is something cold water divers tend to forget when they dive in warm water. They’ve changed to thinner wetsuits but insist on having the same amount of weight that they used back home!
Should you dump all your weights if your BCD fails?
Let’s use the example of a drysuit diver: In order to sink, a drysuit diver would normally need between 6 and 10 kg (or about 12 to 20 pounds) of weight on him. That’s quite hefty!
The big question that relates to ditchable weight is then this: In the event of a BCD failure, is it possible for the diver to swim up to the surface with all that weight?
Chances are, the answer is no, for most regular divers. It would appear then that the simple solution (which is also commonly taught around the world) is to drop all your ditchable weights in such a scenario.
However, I strongly advise against doing something like that, because of the risks involved. A runaway ascent is very likely, and it can result in multiple issues, such as lung overexpansion injury, decompression sickness, boat strikes and so on. There are other ways to deal with a BCD failure, so dropping weights need not be your first option.
The first thing I would think of in the event of a BCD or wing failure is: How did the BCD or wing fail, and can it hold any gas at all?
For example, the picture below shows a wing in use by a diver. The red arrows show the position of the gas in the wing. In the event of the dump valve failure, the gas would still be able to stay in the wing as the dump valve location is lower than where the gas would be.
In contrast, a bungeed wing (shown below), would lose most of the gas in the wing due to the tension created by the bungee. Because of the design of the wing, this failure would result in a greater loss of buoyancy for the diver.
Scenario 1: Damage on one side of the BCD / wing
In a typical puncture or breakage, the damage is likely to be located on only one side of the BCD, so it would be possible to position oneself such that the gas stays on the side of the BCD that does not have the hole. If the diver can do this, the failure is less of a problem.
Because the BCD still holds gas and provides some buoyancy control (although it is harder to manage it), there is no need to drop all the weights and shoot to the surface. The diver can and should make a comfortable ascent to the surface with the help of his teammates.
Scenario 2: Damage on the inflator mechanism
The breakage might be harder to rectify when the elbow connecting the inflator mechanism is detached from the BCD fabric. This problem makes it impossible to inflate the BCD, and also allows gas to escape from the BCD due to its location on the BCD. How then can we solve this?
I would consider depending on my teammates. If my team is nearby and my buddies were aware of the problem, they could definitely lend a hand. They could hold on to my arm, and control our buoyancy using their BCD or by kicking. I would also pass on heavy items that I am carrying to lessen the weight and provide some lift. Diving together with someone has definite benefits, and you should both be able to ascend in a controlled fashion without having to dump any weights.
Another thing I would attempt to do is inflate a surface marker buoy (SMB), send it to the surface and use the spool to assist with the loss of buoyancy. The SMB may not provide enough lift for me to completely dangle on the end of the line, but coupled with my teammate’s help, it would be easier to do a controlled ascent.
Fourthly, if I was wearing a drysuit, I might inflate it a little more than I normally would to help increase buoyancy. This is one of the last things I would consider doing however, as more air in the suit might make it harder to kick and move around.
Lastly (and this is a distant last option), I would remove some but not all of my weights to help with buoyancy. I would never remove all of my weights at the same time, because this would most likely result in a very rapid, uncontrolled ascent. The dangers of lung overexpansion, decompression sickness and unconsciousness on the surface cannot be understated here!
Of course, to be in the situation where I would resort to ditching weights, I would have to be alone, and be low enough on gas that I couldn’t risk wasting it by doing a strenuous swim to the surface. Needless to say, we should never put ourselves in such a fix to begin with.
To put things into context, in all my years of diving, I’ve never seen a BCD or wing fail so completely that it couldn’t hold any gas at all. Plus, most of the time, with good team awareness, proper equipment and correct weighting, a BCD failure is easily rectified without having to resort to ditching your weights.