Browsing Category Education
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.
GUE vs PADI: What’s the difference?
GUE and PADI are two different organizations, right? Whose certification is more recognized internationally? Which is better?
At Living Seas, we’re often asked these questions when newcomers dive with us.
Yes, GUE and PADI are two different organizations that are unrelated to each other. GUE stands for Global Underwater Explorers, and PADI stands for Professional Association of Diving Instructors.
As a certification body, PADI is more well known internationally because it has been around for a longer time. It also spends a lot on marketing. GUE is a non-profit organization with the primary goals of advancing aquatic education, conservation and exploration. That being said, GUE is widely recognized as being the best in the industry because of its emphasis on quality control and stringent standards. Increasingly more people are beginning to know about GUE, too.
The PADI certification will allow you to dive around the world (within the limits of what you’re certified for, of course). You could think of PADI as a key that grants you access to the underwater world.
Once you walk (or more literally, swim) through that door, your dive education should continue. Going through a GUE course, in my opinion, is more about the skills and the knowledge that you acquire in the process. The certification that comes with it is secondary.
That’s why Living Seas offers both PADI and GUE courses. We believe in being qualified for the diving that we do, beyond being certified to do those dives. (If you’re curious about our diving philosophy, read our earlier reflections on what it means to be an “advanced” diver and the fundamental skills all divers should have.)
For those who believe in challenging themselves to dive better, I urge you to think in terms of qualification instead of certification. Forget chasing certificates, and instead focus on being more competent and comfortable at the dives you want to do!
True competency isn’t measured by the number of certificates you have or the equipment you own. It’s gained through time spent in the water, practicing and improving.
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.
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.
What kind of dive education do you want?
This is one question I pose to my students when they ask me about the differences between diver training agencies, and why fees vary between dive centres purportedly offering the same course.
Your answer probably depends, in part, on why you decided to pick up scuba diving in the first place.
But I’m not talking about diving specialties that you can delve into after completing your open water diving course.
I’m talking about your learning process and outcome.
As an extreme sport, scuba diving is inherently dangerous. After all, humans are not designed to survive underwater, and external conditions can greatly impact the safety of a dive.
That said, scuba diving can and should be done safely. A good dive education is the starting point.
Education can lead to various outcomes:
- Intellectually knowing something
- Understanding how things work
- Copying an action without understanding
- Knowing and doing something well so that it becomes second nature
Personally, I believe that we ought to get to that last stage in terms of our diving ability. To be specific, a diver should at least get the basics—buoyancy, positioning and body position—right. It’s difficult to progress if you aren’t completely at ease in the water!
A committed dive instructor will work towards ensuring that you have a sound theoretical understanding and good practical proficiency. With guidance, practice and experience, you will improve your scuba diving skills and comfort level.
So do think about it: What kind of dive education do you want? A healthy attitude towards dive education—both on the part of the learner and instructor—definitely makes better and safer divers.
Why are Living Seas courses so expensive?
At face value, the Open Water and Advanced Open Water courses offered at Living Seas are more expensive than other dive shops.
We are priced higher for a number of reasons, and we encourage you to read on and decide for yourself whether the extra you pay is worthwhile.
1. We teach a longer course
We conduct our Open Water course over four days instead of the typical three. This includes two days for a theory lesson and a pool practice (confined water dive) session , followed by another two days of ocean (open water) dives.
Our Advanced Open Water (AOW) course includes a theory class and a pool session on top of two days of diving. For certification bodies like PADI, the AOW course requires the student to complete five leisure dives with the instructor. This is typically done over two days, and the e-learning component is done in the student’s own time.
Between the ocean dives, Living Seas instructors take time to introduce and discuss concepts that would be relevant when you proceed to do leisure dives in the future on your own. We believe in preparing our students well and ensuring you are real divers, not just people who can do drills underwater.
2. We teach face-to-face, not online
You get more time learning with an instructor by your side, as opposed to doing much of your learning online by yourself. In our classroom, you’re able to ask questions, get feedback, and work through difficult concepts with your classmates and instructor.
Our instructors are also trained to guide students through the material, instead of just delivering what’s in the textbook. We think it’s important that our students truly understand what we teach, and be able to tease out the connecting threads between different concepts.
Diving is ultimately a sport, so practical training gets special emphasis. After our students understand the theoretical basis of concepts like buoyancy, we systematically guide our students through drills with thorough explanations of good diving practices.
We do not adopt a traditional “Just do as I say” method of instruction, and we don’t think it’s something that anyone should stand for these days.
3. We keep classes small
Our student to instructor ratio is always kept low—no more than four students are assigned to one instructor for any in-water activity. Safety is our priority, and keeping classes small means our students get more focused attention from our instructor.
With fewer students to supervise, your instructor is more likely to catch and correct your mistakes as you make them. With timely feedback, you’ll learn faster and more effectively. You also spend less time waiting, whether it’s for the other students to complete their drills or for your instructor to check your gear one by one.
Learn well during the pool session and you’ll have more time during the open water dives to swim around, get comfortable in your gear, and hone your diving skills.
This is Elaine who learnt how to dive in early 2016. Although this video shows her third-ever dive, she looks comfortable and controls her position well.
4. We include your hotel stay
Our Living Seas Open Water course package includes theory and practical lessons, gear rental and your hotel accommodation. The hotels we partner offer comfortable stays and decent amenities. If you opt to take the course in Bali, the hotel is also where our Indonesian office is based. The hotel pool spans 100-plus metres and is four metres deep. As it’s a big pool, you’ll have more opportunity to swim around and gain more experience before diving in open water. In Bali, no traveling is required on the days the course is conducted. Your room, the classroom, pool and restaurant are less than two minutes away from one another.
For courses based out of Singapore, we’ve also chosen a hotel partner that offers us the best logistics in terms of diving, accommodation and transfers. Who wants to go on a trip where more time is wasted on traveling than diving? Rimba Resort on Sibu Island is our base of choice as it allows for smoother transfers, a more relaxed schedule and a more comfortable stay.
5. We don’t upsell
As an ethical business, Living Seas believes in fair pricing. We do not support the practice of using open water courses as loss leaders. We would rather focus our attention on teaching our students to dive well, than on our bottom line.
Your learning is our priority
We believe that learning has to come first. We go the distance to make sure you have ample time, space and practice as well as comfortable accommodation, so you are less stressed and more focused on learning to dive safely.
It’s our commitment at Living Seas to make sure that you get the best learning, in the best way and format possible.
How is the GUE Fundamentals course relevant to recreational divers?
You might have heard about the Global Underwater Explorers (GUE) Fundamentals course through your “hard-core” diving friends who love exploring caves and wrecks.
Or perhaps you came across it while googling for information on how to improve your scuba diving and buoyancy control.
Either way, you’re probably wondering: Is this course relevant to me, if I’m simply into recreational diving?
We get this question a lot. Contrary to popular belief, the GUE Fundamentals course is ultimately a recreational course. It doesn’t have to lead to technical or cave diving, although the course is also a gateway to GUE’s more advanced diver training options.
The skills taught in the course are relevant to any diver regardless of certification level and where you dive. It doesn’t matter whether you’re diving over a reef, in a cave, on a wreck or 50m deep—the importance of being able to handle yourself well in any type of underwater location simply can’t be understated.
One of the objectives of the Fundamentals course is to allow you to become better at the basics of diving, that is, to improve your awareness, buoyancy and communication underwater. Coupled with a focus of diving in a team, the GUE Fundamentals course makes you a much better dive partner. You’ll emerge from the course with a better knowledge and understanding of how to interact with others while diving, and how to deal with situations that arise.
Some might also ask: Shouldn’t I have already acquired these skills at the Open Water courses? Well, the short answer is no.
The GUE Fundamentals course doesn’t just hone your skills of buoyancy, trim, balance and propulsion, but it also teaches you to streamline your equipment configuration, plan a dive, manage your gas, and master a number of drills, including how to deploy a surface marker safely and effectively. More details here.
A useful analogy likens regular recreational diving to amateur dance classes, while the GUE methodology is more akin to ballet, where the strict focus on form and technique produces a dancer with a much higher skill level.
Whether you progress to more advanced diving after the GUE Fundamentals course is completely up to you. Even on a recreational dive, having solid underwater skills is useful. After all, having fun on a reef is an objective in itself.
Plus, if everyone has better skills, we’ll enjoy the underwater environment without causing damage to the reef—or to ourselves!
Is the Advanced Open Water course just about going deeper?
Most new divers will be excited to do and learn more once they’ve gotten their Open Water certification. From here, there are two easy next steps: Book another dive trip and/or take the Advanced Open Water (AOW) course.
(Note: A number of diver training agencies offer an advanced open water course. As can be expected, the syllabuses and prerequisites vary. Wikipedia offers a good overview here. One of the most widely known AOW courses is offered by PADI.)
On the face of it, the AOW course seems to be just about going deeper, past the 18m limit that the OW certification imposes on new divers. And unfortunately, this is how some instructors conduct the Advanced course—where it’s more like a leisure diving weekend than a course—and why some divers complain afterwards that they didn’t learn anything.
While the Open Water course focuses on the basics of diving safely, it doesn’t offer the time or scope to do much else. It makes sense then that the Advanced course should give divers the opportunity to hone their skills—and get more comfortable underwater.
The Advanced Open Water course is also an excellent gateway to inspire imagination and fire up the urge to explore in new divers. Be it deep dives, wrecks, caverns, dives in strong current, open ocean pinnacle dives, photography or videography, the possibilities are endless!
We at Living Seas believe that in order to call oneself an “Advanced” diver, you should have control over your position in the water, so we introduce manoeuvring techniques such as the various frog and flutter kicks, the backward kick and the helicopter turn. After all, if you plan to do more challenging dives, you’d definitely want to have more control in the water!
Besides teaching new skills, the advanced course should involve experiencing different types of dives, such as Navigation, Deep Dives (20m to 30m), Drift Dives, Boat Dives, Night Dives, and more. Exposing new divers to a diversity of dives—under supervision of course—helps to broaden their perspectives of what diving is and can be.
Hopefully, something sparks an intense desire within them to continue diving and exploring. I’ve always believed that if someone is interested and passionate about diving, they can’t not want to care and conserve it for future generations.
Whether you’re teaching or learning the AOW, seize the opportunity to inspire—or be inspired! The AOW is not just about going deeper; it’s an opportunity to broaden one’s horizons, and see what more diving can offer. It’s a really wide world of oceans, after all.
Why use double tanks?
When asked this question, most people would answer that we use double tanks to get more gas for our dive. This is a valid answer, of course, but I think the more important reason is redundancy.
Redundancy: The inclusion of extra components which are not strictly necessary to functioning, in case of failure in other components (OED)
Running low on gas during a dive can be frustrating – we all know what it feels like to want to stay down longer and enjoy ourselves! The next logical step to overcome this limitation is to carry more gas, especially on deeper dives where a diver’s gas consumption will be much higher.
Without going into a discussion on decompression here, increasing gas capacity can be done in different ways, by carrying a larger tank, using a steel tank so you can fill it to a higher pressure, or carrying multiple tanks.
If one chooses the last option of carrying multiple tanks, one could consider simply strapping two single tanks together (called a sidemount or independent doubles configuration) to effectively double the available gas. So why not just do that? Consider a situation when a failure happens (for example, a faulty o-ring on a regulator or tank valve). The result is you lose the ability to access an entire tank of gas.
Another problem with the sidemount or independent doubles configuration is that you’ll have to double up on regulator hoses. You’ll need a primary and secondary second stage, an inflator hose and an SPG on each of the first stages. This in turn doubles the number of possible failure points. Not ideal.
That aside, we also have the issue of deciding which tank to breathe on. If we breathe on one tank fully, then what happens if failure occurs on the full tank that you were planning to switch to? (Sidemount divers will argue that there are ways to prevent this from happening, such as switching tanks at defined intervals to balance the gas consumption between both tanks, but these measures could lead to additional complications, IMHO.)
We can mitigate against some failures by using DIN instead of Yoke valves on our tanks, and by minimizing the number of hoses that we need, but the best method I’ve found is to dive with a double tank configuration with an isolator manifold.
So how is redundancy built into this configuration?
One important feature is the isolator manifold. In this configuration, we have two first stages, each connected to a tank valve, which are in turn connected to each other via the isolator manifold.
Two 300 bar scuba cylinders connected by an isolating manifold
With this set-up, a single failure on a regulator will not result in an immediate loss of half your gas. We could shut off the valve that the failed regulator is connected to, and effectively shut down the leak. Because of the manifold, we can still access all of the gas in that tank. In this situation, one failure will result only in the loss of some functions (one second stage and either the inflator hose or the SPG), but not in any loss of gas.
But what if the manifold itself fails, you ask? Well, this is where the isolator comes in. If any side of the manifold, or tank valve fails, then we could isolate the two tanks by closing the isolator valve. This cuts off the flow of gas from one side to the other, resulting in only one of the tanks draining, as opposed to both, if the valve was left open, or if there was no isolator.
When doing more extreme dives, whether you’re going deeper or diving in an overhead environment, you’ll want the confidence of knowing that failures won’t result in you losing so much gas that you won’t be able to get to surface safely. Personally, I’d say that’s a pretty good reason to have the heavy weight of a set of double tanks on your back!