My two cents about Transmitters and Air Integration.

Technology, techniques and trends… they all evolve, some are quickly forgotten, some are here to stay. Transmitters are a frequent topic my students and followers want to know about so in January 2024, when I had just gotten my Shearwater Swift transmitters for the Belize expedition, I decided to interview a few people and write this article. This article was originally written during my time at ProTec Dive Centers, where I was the only member of the team to use transmitters on my side mount tanks. It was published in the ProTec Chronicles and in Duiken Magazine.

Let’s interview people!

 What seemed like a simple and easy idea for a casual quick series of stories turned into an elaborate conversation about the advantages and disadvantages of diving equipment and equipment selection philosophy. Because techies love to look at a question from a few different angles to make sure our opinion is fact based, informed and researched, here’s a set of ideas that might change the way you look at AI (as in Air Integration, not Artificial Intelligence!) and transmitters. 

Do we like transmitters? Most divers I come across say no…

But, let’s start from the beginning. In the past, almost every diver I ran into said a hard NO to transmitters when they first appeared in the market. We love and trust the tools we know, it may not be perfect but we’re familiar with it and we know the range of functionality as well as we are quite familiar with the range of failures, the likelihood and the seriousness of them. Pressure gauges, also referred to as SPGs (Submersible Pressure Gauge), are affordable and last a while with minimum maintenance.

SPGs are what’s common and standard among divers. Actually, I was surprised to work along many experienced diving instructors who have never used transmitters, it wasn’t until I dived and trained with Under the Jungle, that I found a transmitter-loving crowd… I now teach all my classes with transmitters and most of my students have or want to get transmitters in the near future. That has also made me think deep into gas management and calculations on transmitters! Maybe material for another post?

One of the people I interviewed is Kim Davidsson, a very experienced diver and explorer. When talking about choosing diving equipment, Kim said: “we want the right tool for the right job”. Even a single tank configuration could be the right tool for a given task, as long as it’s safe, and functional.

Kim is a practical man with extensive experience diving and teaching in the Mexican cenotes and caves, cold water, wrecks, mines, you name it. “The more configurations you master, the wider variety of environments you can access, and the more well-rounded diver you become”.

Kim’s personal philosophy when it comes to gear and accessories:

• Keeping it simple

• Standardizing gear

• Choosing items that are tough and durable

• Bringing only what you need

• Keeping an open mind

• Becoming a thinking and critical diver who takes educated decisions

In Kim’s opinion there is more than one way to do things but there’s no need to overthink it. If you’ve taken a class with Kim you’ve witnessed his approach and maybe you’ve even changed your mind about a few things after listening to him play the “What-if game”. His knowledge is inspiring and he does not hold back when he shares it.

During my tech diving class, whether it is entry level such as Open Water Sidemount or an advanced level such as Full Cave, I promote analytical thinking to increase your familiarity with failure points; during the Equipment presentation in all classes we analyze failures with likelihood versus seriousness. During most classes we study potential outcomes and possible solutions and implications of each failure. If you truly know how equipment works, you also know how it breaks and fails and that is essential in the overhead environment where swimming out with malfunctioning equipment can be inconvenient, to say the least. Knowing these details gives you an added layer of reassurance.

Failure points are a topic I like to talk about, while I try to avoid adding failure points to my systems, in some cases the benefit of adding a piece of gear to my setup outweighs the disadvantages, especially if the failure point has a low likelihood of occurring. In the case of transmitters, one of my biggest arguments is that transmitters reduce failure points compared to SPGs. That’s why I do not add a transmitter with an spg for redundancy or a short hp hose.

In Kim’s words “I didn’t like transmitters in the beginning but my opinion has changed over time with the evolution of technology and I have had the opportunity to see them in action; the technology of Shearwater products is there, welcome to 2024”. Kim cares to add that he is in no way associated with Shearwater, but he’s a true fan of their quality products and has been using them for years, his opinion is therefore driven by the products’ performance and the brand’s reliability.

What I recommend to our readers and divers is to make your own list of priorities, needs, pros and cons, don’t take my word but become informed and do your own research so that whatever decision you take, you will be certain that you’ve weighed the different variables in, without overthinking it, and truly believe in what you decide.

Going back to the What-if game, let’s look at SPGs  a little closer.

The advantages of using an SPG:

• it is cheap compared to transmitters

• readily available in most locations

• no battery needed

• easy and cheap to have a backup (or more) in your toolbox or to borrow one from another diver

The disadvantages of using an SPG:

• Adds more failure points

• Less accurate reading

• Generally heavier than transmitters

• Reading located out of sight (affects hose too)

Number of failure points on SPG:

(1) The SPG itself (it can break, flood or give a false reading),

(2) the 2 o-rings on the spindle/spool between the SPG and the hose

(1) the hose itself (including the crimp)

(1) Port o-ring (to first stage)

That’s a total of 5 failure points on one SPG, if we multiply this by 2 as we carry at least two tanks, that is a total of 10 failure points. 

We can also consider the SPG accuracy (and margins when rounding up or down) a downside of using analog instruments but we won’t add a failure point for that as it’s not the focus of this article.

Let’s now analyze the procedure we would put in place in case of an SPG failure.

Any gas failure should lead to the diver signaling the team, closing the leaking post, and turning the dive to exit safely. If your plan is solid -why wouldn’t it be!- there is enough gas in the other tank to exit (plus the reserve gas carried by your buddy, also part of a solid plan).

Feathering is also often introduced in our classes as a possible failure management strategy if the gas from a tank with a failure needs to be used. Feathering consists in keeping a hand on the valve and temporarily opening it to take a breath, closing it during exhale, and repeating over a period of time while swimming, this limits the amount of gas lost due to a failure but requires constant manipulation of the valve which is not always comfortable or efficient.

If an SPG gave us a wrong reading we may or may not catch it right away, there are a few ways of noticing it:

• Drastic and/or abnormal difference from pressure check at the shop compared to our pressure when tanks are in the water

• Noticeable difference in balance from one tank to the other (although this requires refined awareness)

• When taking an SPG off a tank it will mark a reading instead of going back to 0

Now let’s look at transmitters.

Advantages of using transmitters in cave diving: 

• Light and small

• Reading always within sight on handset

• Reduces failure points

Disadvantages of using transmitters in cave diving: 

• Requires pairing

• Requires batteries

• They aren’t as common as SPGs so replacing one on the go is not an option

Number of failure points on transmitters:

(1) The Transmitter itself (it can break, or flood)

(1) Battery screw or transmitter screws (depending on model, may lead to flooding although it is generally not a gas failure)

(1) Communication (the infamous loss of comms)

(1) OPV (this is the tiny black dot near the base)

Some people consider running out of batteries a failure point but battery usage and replacement depends purely on the user, so a diver forgetting or failing to change a battery when needed is considered user error. Just as running out of gas in your car would not be considered a car malfunction.

That means that a transmitter has only 4 failure points, which is less with a total of eight failure points on a tec setup, compared with 10 failure points that we have if we use SPGs. 

Transmitters pose less failure points than SPGs but the severity of those failures is something we also need to analyze, port o-rings in both devices would be equally severe, but the fact that transmitters aren’t manipulated during the dive as SPGs are (bending the hose to read several times in one dive), would indicate a port o-ring would be way less likely to come unseated on a transmitter than on SPGs.

The battery o-ring in a transmitter screw is static, except for when we change the battery, that o-ring is not moving during use (therefore suffering minimal wear and tear), unlike the swivel o-rings between a hose and an SPG, which are a common failure precisely because of the dynamic characteristics, these are made to allow for the SPG to turn, therefore sustain wear and tear with every use. 

It is generally accepted that the biggest fear when using a transmitter is loss of communications, which is not a gas failure per se: no gas is lost and all of it is available to the diver, but they aren’t able to monitor it. 

Divers tend to think though that a loss of transmission is equivalent to a fatal outcome, not being able to monitor gas? Forget it! Who wants to take that risk?

While monitoring gas is essential to diving, moreover to cave diving and any type of technical diving, not being able to read the gas is in our eyes more of an inconvenience in most situations. Keep reading.

So, what’s the procedure when transmitters fail? Exactly the same as with failing SPGs: turn the dive, exit safely.

When it comes to transmitters, the loss of the ability to read the gas pressure is not as high a concern because, as Kim puts it:

“Knowing how much gas you have, does not mean you have enough gas. You either have enough, or not, and if you don’t, it won’t matter if you can or cannot read it.”

What this ultimately boils down to is: if you made a solid plan, and followed it, during any stage of the dive, you must have enough gas to get out, plus a reserve, regardless of having comms. 

More about transmitter communications.

Failure to connect seems to be something that usually happens at the beginning of the dive, maybe related to having connected to the transmitter and then walking away to finish preparing for the dive (our tanks stay on the platform while we put on suits, etc). As Kim used to think when divers got in the water and suddenly couldn’t connect “If we only had SPGs, we could just go diving”, it definitely seemed that transmitters were an overly engineered, and not really needed, commodity. Another diver said: then you need a backup computer, which most of us have anyway.

Another common worry is transmitters on stages, they are connected, and as we drop them, we swim away, lose comms, and when we come back to them they fail to connect. I have used transmitters on the stages we use for the Vanilla Farm exploration project, currently, I had no failures connecting to a stage so far, and we are apart for several hours, sometimes we also leave the tank in the cave and come back the next day. 

Transmitters send an ultrasound signal to the computer. The transmitter, a.k.a. pod, receives the signal and pressure is displayed on your screen, and in some cases uses this information to make calculations such as remaining gas time or SAC rate.

In the past, some brands of transmitters used “channels” for pairing, this means that if a computer had three channels and more than three transmitters where in the same area, two of the computers would be receiving through the same channel, therefore causing the signals to collide, giving one computer the reading of another transmitter or losing comms altogether. This happened often and divers grew hesitant to use transmitters for this reason, they were deemed unreliable and having a backup SPG was recommended.

Transmitters and computers also used proximity in the paring process, meaning the computer would detect the transmitter which was closer and then the user would manually select it and paired it. But sometimes computers would still pick up the signal of another pod, that was perceived as a safety hazard.

Nowadays, companies like Shearwater, have created products that left behind that concept and are now using technology that allows a computer to pair with a transmitter based on a single serial number. Like this, a computer cannot perceive any other signal and pair itself with it. Only the one serial number entered will allow the one computer to be paired with it. This pairing is only done once and is permanent until the computer turns off that one transmitter, or deletes it from the list of transmitters on the handset. 

But some of you may remember this was not always the case. In 2019, Shearwater voluntarily recalled yellow transmitters as the transmission frequency was supposed to be different from the grey transmitters, allowing the use of two transmitters at the same time with one computer (think sidemount). The recall notice was issued when the yellow transmitters were, unfortunately, found to transmit at the same frequency, defeating their purpose. A couple of years later, the SWIFT transmitters were born with randomized transmitting intervals, making it potentially impossible to have two signals at the exact same time. These also came with a led that indicates when a signal is sent and if there is an interference. These transmitters are also smaller than the previous model, and like before, need no tools for installation. They are supposed to last about 300 dive hours which should allow the user to foresee a battery change on time. This speaks for the technology development and improvements that Shearwater is committed to, which is only possible using the feedback from divers through customer service. 

The perception on technology depends on the user’s experience, for me, SPG swivel o-rings fail all too often compared to transmitters. A week wouldn’t go by without having bubbles coming from an SPG on myself or one of my divers, I had the feeling that we were becoming lenient as this failure never seemed serious enough but happened regularly. When I had the chance to switch to transmitters I thought: It cannot be worse than SPGs, and I tried it. I haven’t had a failure since I switched.

Spending enough time with divers who had transmitters gave me the confidence to give them a go and since July 2023, I have been solely diving with Shearwater transmitters (the old model). Since the beginning of 2024 when I switched to the Swift morel I also haven’t had a single gas failure, and no communication issues. Whilst comparing the 7 months prior to the switch to transmitters, I had at least 10 o-ring failures and two hose failures related to SPGs. Not all of those failures where serious, but definitely inconvenient and required replacing the parts. Statistically higher than average? Maybe, but in this case using transmitters has proven quite reliable compared with transmitters. 

When talking about diving equipment, Kim Davidsson also states that Accessibility versus Streamlining is another line of thought we need to explore. SPGs are less accessible than the gas displayed on a handset, and getting rid of the SPGs also allows for better streamlining. This also leads us to talk about accuracy, the reading of a transmitter is more accurate, there is no need to change body position to read it, and the size of transmitters makes my setup more sleek, maybe the risk of failure and the seriousness of the potential failures are something we are willing to tolerate or adapt to. In Kim’s words: “This always comes down to how one feels about it, but knowing more about a tool will allow you to make an informed decision that you’re comfortable with”.

Some other people aren’t fans of technology, another important thing to consider is how tech savvy you are and how you adapt to new technology.

Most of my colleagues have always preferred analog SPGs but some would feel comfortable installing them on the O2 tank of their Sidewinder configuration after seeing mine. 

This is the perfect example of pondering risk versus advantage. If we usually dive with no reading on our O2, we could tolerate adding a couple failure points to gain on the reading size knowing that if the transmitter failed with a loss of comms, the scenario would be exactly the same as our previous configuration which we are already acquainted with: not having a reading on the O2 tank pressure.

Some people say they would try transmitters on stages first, since we account for total loss of gas on a stage during stage dives planning, a loss of comms would be less serious than what he is already comfortable with. Another example of analyzing advantages versus disadvantages, and thinking of possible outcomes. 

Last but not least, we have talked about redundancy a lot, and the concept is a word we use every day. Tec divers rely on backup plans, and sometimes have several layers of redundancy, not just the one, depending on the difficulty of the dive they are conducting. When it comes to transmitters, the first thing people want is redundancy. Let’s look at it from this point of view:

Rec divers have an SPG, and a single tank, on a single valve. This is the most common setup in SCUBA, although cold water divers may use H valves or Y valves as well. In a traditional setup there is no backup SPG, and most people never think of adding one. As we are fairly confident using that technology. 

On Sidemount or Backmounted doubles, we do not use analog SPG backups to our main SPG. On Backmount we are using only one SPG, which in the case of isolating the two posts, it would mean we can only monitor the left one. And this setup has been dived like this for the longest time. 

Now when we move to transmitters, having used no SPG backup historically on any of our setups, and using appropriate gas planning together with a proper conservative factor and team diving practices, is there really need for an analog SPG as a backup to our transmitters?

You either trust your gear, or you don’t. And if you don’t, you shouldn’t be using it…

For me, adding an SPG to a regulator as a Transmitter backup clogs the tank valve area, makes us less streamlined, makes the front of the profile heavier, adds considerable failure points, and brings little value to the majority of her dives. It’s ok to be more familiar and comfortable with analog SPGs, and it’s also ok to go for transmitters if that’s your jam. But adding up both elements only leaves you with more failure points and less advantages than before and a high likelihood that none of the two will fail, spending most of your dives diving a crowded first stage, posing entanglement issues, and missing on the advantages of using only one or the other. 

If you found this article interesting, please help me share it and send me your questions and suggestions for next post. Thanks for reading!