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Equipment

Heads Up Swimmers and Divers Who Swim

Wouldn’t it be great to have your essential swim metrics right in front of your face, so you wouldn’t have to slow down to steal a glance at the clock, or flick a wrist and read your swim watch? Now you can! (Never mind that agencies only require you to paddle 300-400m at a jellyfish pace—you do keep up your swimming don’t you??) Here InD exec editor Michael Menduno, a passionate swimmer, reviews the latest in performance swimming technology. Can diving be far behind?

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By Michael Menduno

I am a water person. I swim four to five days a week. I am a diver. I’m also a technologist and gearhead. So, when I saw the FORM ‘smart’ (augmented reality) swim goggles, I knew I had to try a pair.

FORM goggles offer the swimmer key user selectable metrics such as time elapsed; distance swam, split times, interval times, pace per 50/100 yards or meters, stroke rate/SWOLF, or even calories burned in a concise, bright-yellow heads up display that appears to float in your field of vision. Note that the metrics are based on the trailing length; they’re not instantaneous.  The heads up display also cleverly sequences metrics as the swim progresses. For example, it shows the new split time after the swimmer performs their turn. Also, the eyepieces are symmetric so that display can be positioned in either your right or left eye. 

As a result, you don’t have to stop swimming to look at your swim watch or deck clock for timing, and it counts your laps in case your early morning swim brain loses track. According to the company, the goggles free up your mental bandwidth so you can focus on your form, hence the name. Did I mention they currently have no competition?

FORM goggles can be readily set for lap swimming, intervals or drills (ah those kick sets!) with the two tiny toggle buttons on the side of the goggles; they don’t have GPS and so don’t work for open water swims. At the end of your workout, you save the swim using the menu buttons, and it’s uploaded to the companion app on your smartphone via Bluetooth, where it is stored and can be shared. Your swim data can also be uploaded to Strava or Training Peaks, though currently FORM is not integrated with Swim.com, which partners with the U.S. Masters Swimming (USMS) log. That’s where I upload my Apple watch swim data. 

Oh, and the goggles also talk to the Polar OH1 optical heart rate sensor, which can be fitted to the google straps, allowing the device to display your heart rate in real time. They can also upload heart data from a Garmin watch. All in all, FORM can only be described as a remarkable piece of engineering. 

Interestingly, when I first called the Vancouver B.C. Canada-based company to inquire about their goggles, one of my first questions was, “Are you also planning to offer an augmented reality diving mask?” NOT! 

FORM’s marketing director explained to me that there are an estimated 30 million swimmers in the U.S. and 240 million globally making it the largest sport in the world—roughly one to two orders of magnitude larger than diving, including both free and compressed gas divers—and that’s who they plan to focus on. That of course would include triathletes and Iron-people who swim too.

I also realize now that FORM’s secret sauce is a lot more than simply displaying computer data on an in-mask optics display. Though the diminutive optics screen, which is about the size of a 64GB SanDisk card, and the small thumb drive-sized computer positioned at the temples, could easily be incorporated in a diving mask. Shearwater and Thalatoo take note.

The Ghost In The Machine

FORM is the brainchild of 44-year old competitor swimmer cum mechanical engineer, Dan Eisenhardt. He first conceived of the idea for smart swim goggles for his MBA project in 2006, but the available technology, particularly the state of machine learning (ML), at that time made it infeasible. Instead, he and his colleagues created a heads-up display ski mask and went on to form a venture-funded start-up called Recon Instruments, which Eisenhardt incorporated in 2008. He eventually sold the company to Intel in 2015, after creating five generations of smart glass products. He left Intel in late 2016 to return to his original vision, creating a smart swim goggle.   

Compared to a swim watch, which is attached to a single ‘stroking’ appendage; detecting starts and stops and strokes—not the Irvine kind (inside joke)—from a device positioned on your head is arguably a harder problem. But FORM appears to handle it with aplomb. Eisenhardt told me that they want to be accurate to within 99% of the metrics and it’s rare to see a mistake. Interestingly the goggles were able to correctly detect my stroke (fly), when my Apple watch didn’t. More on that later.

At the heart of the goggles, is a three-axis accelerometer and a three-axis gyro that interprets what’s going on in the rest of the body i.e. doing freestyle, doing fly, cranking out 80 or 115 strokes a minute, burning calories, based on that sensor input. That’s where machine learning comes in. FORM trained its algorithms using machine learning, with actual data feeds from many different types of swimmers, including the award-winning University of British Columbia’s Thunderbirds swim team, who were all recorded with video cameras. The various types of movements were labeled and then fed back into the algorithms, which were then tweaked and tested again, etc. Rinse and repeat!

Eisenhardt compared machine learning to opening up a Pandora’s box. “We had no idea back then how hard it would be,” he said. “We would change something over here and it would get better, but then something over there would break. It was always a moving target so we had to find an optimum point based on our goals and objectives. That was a big one!”

Other challenges? “It ends up being a combination of things, a kind of an engineering matrix,” Eisenhardt explained. “Low-power optics, machine learning, and bulk; those were three massive constraints, above and beyond price. Because price, is actually the most important. You have to constantly have that price rationale in the background.” 

FORM goggles retail for US$199. By comparison, ordinary swim goggles sell for US$15-30 up to US$59 for my MAGIC5 custom-fit goggles. Of course, like many of my swimmates, I have accumulated quite a collection of goggles over time.

My Experience

I found downloading and setting up the FORM app and goggles was easy. The goggles are high quality with a soft sleeve and come with a selection of different sized nose bridges for an optimal fit. I found them very comfortable and watertight, and they didn’t fog. Though they weigh about twice that of an ordinary pair of swim goggles: 2.3 ounces/65 grams compared to about 1.3-1.5 oz/37-43 g, I didn’t notice any difference once they were on my face.

My first experience using the goggles in an outside pool was disappointing. While the heads up display and metrics, which I had positioned in my right eye, were brilliant, I had a hard time seeing out of my left eye. FORM’s lenses are barrel-shaped with a flat forward surface. For me, it looks like a sunglass lens in the middle of my field of view. What’s more is that I kept seeing what looked like cavitation bubbles along the flat surface. As a result, I felt like I couldn’t see the pool well. My view also looked a bit wonky when I approached the wall to turn. FORM says the goggles take a little getting used to. Yup! I tested them in two different outdoor pools with the same result.

I asked Eisenhardt about seeing cavitation bubbles. He said that only two other people out of hundreds or more reported this problem, both of them in outside pools; something about the light perhaps.  So I tested them again in an indoor pool. This was my fourth workout session with the goggles. The sunglass effect was definitely diminished, and though I still saw some cavitation bubbles against the glass, my visibility had improved, though not as good as my MAGIC5, which of course, does not include a heads up display. This made me think that with time my vision and or brain would adjust.

I mentioned discovering that the FORM goggles correctly identified my butterfly while my Apple Watch 4 did not. This is often a problem with the watch. It also has trouble identifying breaststroke. Even more interesting, when I compared my split times from my watch on swim.com to those of FORM (I was wearing devices during my trials), the times showed significant differences sometimes amounting to a few seconds. A little unnerving! How fast do I really swim?

This, of course, raises the question, “How accurate is the [name of device]?” The answer of course is, “Compared to what?” It would be useful to compare both to an electronic pad used in swimming comps.

I was already aware of timing problems with the watch. For example, ending a lap by touching with my [left] watch hand yields a different time than touching with my right. Eisenhardt said that FORM’s accuracy is based on matching swim data to video recordings to within a certain tolerance, which is how they derive their 99% accuracy figure. “It’s very rare that you would touch the wall and get a time where you’re like, oh, that doesn’t seem like the right time. It’s just a very rare event. It’s hard to say exactly how accurate we are, but we are definitely accurate enough for you to never have to second-guess a metric.”

So there you have it. I LOVE the FORM display and the data; however, I am not yet happy with the visibility. I wish it integrated with the Swim.com cloud and consequently my official USMS log. ;-( I am also now intrigued with interval and split times, and plan to do more investigation with both devices. Are the FORM goggles worth $199? Never mind how much I’ve already invested in swim goggles, does the money really matter for a sport one feels passionate about? I am going to keep swimming with FORM, and keep my watch on, for now.

Heads up people. Watch this space.

Additional Resources (from FORM)

https://www.formswim.com

https://www.youtube.com/c/formswim


Michael Menduno is InDepth’s executive editor and, an award-winning reporter and technologist who has written about diving and diving technology for 30 years. He coined the term “technical diving.” His magazine “aquaCORPS: The Journal for Technical Diving”(1990-1996), helped usher tech diving into mainstream sports diving. He also produced the first Tek, EUROTek, and ASIATek conferences, and organized Rebreather Forums 1.0 and 2.0. Michael received the OZTEKMedia Excellence Award in 2011, the EUROTek Lifetime Achievement Award in 2012, and the TEKDive USA Media Award in 2018.

Equipment

The RB80 Semi-closed Rebreather: A Successful Exploration Tool

What rebreather has arguably logged the most exploration kilometers since its market introduction in 1998—an estimated 160 km plus (100 miles plus for you Imperialists)—and continues to rack up the klicks? It’s Halcyon’s RB80 passive-addition, semi-closed rebreather. Here WKPP greybeard and RB80 instructor trainer David Rhea reports on the RB80’s history, design & workings, training, and he offers the lowdown on its new sidemount progeny, the RBK. Looking for an electronics-free, sidemount bailout rebreather? Halcyon may just have your number.

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By David Rhea

Header image by David Rhea

Full Disclosure: Halcyon Dive Systems is a sponsor of InDepth.

In the early 1990s, the cave exploration conducted by the Woodville Karst Plains Project (WKPP) in the Woodville Karst Plains of Florida, especially Wakulla Springs, was becoming quite complicated. With dives averaging depths of 89 m/290 ft, with penetration being measured in miles, and decompression taking hours, it was becoming obvious that rebreathers would be necessary to move forward. In 1996/97, the WKPP began using a semi-closed circuit rebreather known as a Passive Variable Ratio-biased Addition Semiclosed Rebreather (PVR-BASR), nicknamed “The Fridge,” to extend their exploration and decompression obligations. This piece of equipment was a very large, bulky, and complex unit, and while it was uncomfortable above and below the water, the PVR managed to do what was intended and allowed for further exploration.

George Irvine and Anthony Rue with the Halcyon “Fridge” rebreather prepping for a WKPP dive. Photo from the GUE archives.

In 1996, a team of European explorers called the European Karst Plains Project (EKPP), who utilized the “Doing It Right” (DIR) techniques and philosophy of the WKPP, began using a semi-closed rebreather called the RB-2000. The unit was developed by the EKPP founder and director Dr. Reinhard Buchaly, who was inspired by the great success of French cave explorer Olivier Isler had at Doux de Coly and other cave systems using a custom made, triple redundant, semi-closed rebreather, the RI 2000 designed with the help of French engineer Alain Ronjat.

The RB-2000 unit was much smaller than the PVR-BASR, and utilized a very clever, intuitive, and reliable design. This design complemented the DIR philosophy used by both teams, and would become the choice for both groups moving forward.  By 1999, WKPP explorer Jarrod Jablonski and Robert Carmichael, the owners of Halcyon Dive Systems, worked out a deal with Buchaly to have Halcyon manufacture, sell, and service an American version known as the RB80.  

Designing a Semi-closed Rebreather

Being a cylindrical design 185 mm/7.28 in. in diameter, and 660 mm/25.98 in. tall —virtually identical to the size of an aluminum 80 cylinder—helped the RB80 get its name. The RB80 was designed to fit between the cylinders of a double tank configuration utilizing a specially designed frame, manifold, and switch block system. The economy of parts allows for maximum efficiency with only about 130 parts total. 

Images (L2R): The RB80 ready to rock, (R) Blake Wilson headed for the spring. Bottom: The RB80 dissembled. Note the countering bellows in foreground center right. Photos by David Rhea.

This design complemented the DIR philosophy of maintaining all of the diver’s back gas for emergencies, utilizing stage tanks for exploration and decompression. The gas switches utilized the same procedures taught by Global Underwater Explorers (GUE) but instead of swapping regulators from the mouth, the diver plugs a special QC6 swagelok fitted hose from the stage bottle into a switch block that feeds the gas into the rebreather. 

The stage bottle regulator is a standard open circuit (OC) configuration with the addition of one extra hose with a QC6 connector. The switchback also allows for a hose from the back gas to be plugged into the block in case of a stage failure or other emergency. 

Figure 1. Schematic of the RB80.
1. Dive/surface loop with non-return valves
2. Exhalation hose
3. Counterlung fore-chamber
4. Non-return valve to discharge bellows
5. Discharge bellows
6. Overpressure valve
7. Main counterlung bellows
8. Addition valve
9. Scrubber (axial flow)
10. Inhalation hose
11. Breathing gas storage cylinder
12. Cylinder valve
13. Regulator first stage
14. Submersible pressure gauge
15. Bailout demand valve

The vertical design of the RB80 has a very clever water removal tube that runs directly through the center of the scrubber bed and vents water along with a small volume of discharge gas. The unit is a passive addition semi-closed design, with no depth compensation and is tied to the diver’s respiratory rate. Roughly 1/10 of the respired volume of breathing gas is discharged into the water with each breathing cycle via the inner bellows and a familiar over pressure relief valve (OPV), commonly used on most dry suits. See Figure 2 and 3 below.

The RB80 utilizes a dual bellows counterlung system (versus traditional counter lungs), which reduces the loop volume each breathing cycle. When the loop volume is sufficiently reduced, it triggers the injectors made of components of an open circuit regulator that function quite similarly. Once the injectors fire, the loop volume is replenished with fresh gas. The unit has dual injectors for redundancy, which can be isolated at the switchblock if necessary.

The scrubber bed lies above the bellows in this vertical design and is manually filled by the diver before each dive. The scrubber is a 3.2 kg/7.05 lb design and will last approximately ten hours, based on more than twenty years of operational experience. Note that semi-closed rebreathers generally get longer duration on a scrubber given that a percentage of the breathed gas is expelled and replaced with fresh gas. 

The mouthpiece design incorporates a bail out valve (BOV) allowing the diver to switch from the rebreather to OC at the turn of a lever conveniently located in the center of the mouthpiece block. A hose routed from the right post regulator of the back gas is always live and gives gas immediately once the lever is turned. 

Assessing the Work of Breathing

New rebreather divers often state they feel the RB80 has a lot of breathing resistance. This is generally due to the fact that they are accustomed to modern OC second stages which deliver almost effortless on-demand breathing. Typically, modern second stages use VIVA (Ventura-Initiated Vacuum Assist) technology. This technology, along with the geometry of the second stage and the fact that the second stage is balanced, make for incredible light cracking effort. Upon inhalation, the initial cracking effort lowers the gas volume in the case, which pulls down the flexible diaphragm, activating the lever that opens the valve and allowing gas to flow to the diver. The VIVA then keeps the gas flowing at the same rate without the need for the diver to continue to draw on the regulator.  

By comparison with the RB80, the diver is simply pulling the gas through a one-way check valve, drawing the available gas in through the right inhalation hose, beyond the valve, into the mouthpiece block, and into the divers mouth. This entire system of gas flow does not have any boost effect like its OC sister and therefore feels as if you are working hard when, in fact, it is quite effortless. As a “virtually” closed loop, one simply draws the available gas through the inhalation hose into the diver’s mouth, and then exhales out a one-way valve at the mouthpiece, back through the left exhaust hose into the breather where the gas is scrubbed of CO2, water is removed, and the gas is replenished. 



Similar to OC, the rebreather does vary in breathing performance based on the diver’s position. If you have ever stood on your head diving OC, you feel a change in performance, as the second stage is much deeper than the lungs. The RB80 historically being a back mounted rebreather keeps the unit at a slightly shallower depth than the diver’s lungs, making inhalation slightly harder and exhalation slightly easier.  This difference is virtually indistinguishable; however, extreme head down or head up positions can seriously affect rebreather breathing efforts.  When worn in a side mount or stage position, the unit is in equal position with the lungs, making for very easy breathing. Fortunately, when a  diver is in near perfect trim, the RB80 performs best, as this is the ideal position for ease of breathing. 

Extending a Diver’s Breathing Gas

The RB80 is a serious gas extension device, providing 8-10 times the gas mileage of OC. By rebreathing one’s gas and only losing 1/10 of each breathing cycle into the environment, the RB80 can take a single aluminum 80 cf/11 ltr stage bottle and turn it into roughly 640 cf/18m3, or the equivalent of eight AL 80s. 

In cave exploration, we always start a project by setting up the cave with “safeties.” These are caches consisting of two bottles each equipped with a stage regulator complete with an OC second stage as well as a QC6 equipped drive hose to plug into the RB80, and a submersible pressure gauge (SPG). These bottles are placed roughly every 3,000-5,000 ft/900-1,500 m in the cave, and will remain there throughout the exploration. The safeties are checked by support divers prior to every push to ensure function and adequate gas volume. The bottles are properly filled and marked with the proper Maximum Operating Depth (MOD) gas for the dive, and they are labeled “SAFETY.” 

With rebreather diving, it is paramount that adequate bailout gas be available in case of a single point failure on the rebreather. Rebreathers, while quite robust, have many single failure points, i.e., the breathing hoses, one way valves, OPV, the bellows in the case of the RB80, and even the diver’s mouthpiece. As mentioned, the injectors have redundancy and can be isolated in case of issues, and a spare mouthpiece is always carried by the diver in case of a serious tear or damage. 

Any other single point failure could render the rebreather inoperable, forcing the diver to return and complete all decompression on OC, demanding eight times the amount of gas that had been used at this point in the dive. So, in addition to 100% of the back gas being maintained for bailout, cave exploration demands the discipline of staging the cave with safety bottles, safety scooters, as well caches of decompression gas, and proper support personnel.

RB80 vs. an Electronic-controlled Closed Circuit Rebreather (eCCR)

A variety of eCCRs are available by manufacturers. These units are extremely efficient, as no gas is lost from the breathing loop. The eCCR can be 25-50 times more efficient than OC. However, in addition to the single point failures listed above, which are common on all types of RBs, the eCCR, has additional concerns that prevent it from being a consideration for many cave exploration groups like the WKPP and GUE-affiliated El Centro Investigador del Sistema Acuífero de Quintana Roo (CINDAQ) foundation, which hosts the  Mexico Cave Exploration Project (MCEP) in the Yucatan. 

Most eCCRs have three oxygen sensor cells that must be meticulously maintained and work together with a solenoid and an electronic controller, using a concept called voting logic. Together with an oxygen bottle and a diluent bottle, the eCCR mixes the diver’s gas during the dive within a (PO2) set point range that is predetermined by the divers. By having three oxygen cells, the controller will side with the two that have the most similar reading if one were to start to read differently from the other two. 

Lauren Fanning and Blake Wilson diving their RB80s at Emerald Sink, FL. Photo by Kirill Egorov.

Unfortunately, voting logic is inferior to the gold standard—triple redundancy: main unit, back up, back up for the back up—and has been known to be incorrect i.e., in the case of a double cell failure. Discipline, and pre- and post-dive maintenance, are the key to maintaining good sensor reliability.

When diving an eCCR, it is necessary for the diver to constantly monitor the gas mix in their loop in order to ensure that they safely avoid hypoxia or hyperoxia. For an easy-to-see reminder that the unit is working within the safe limits set by the diver, most eCCRs rely on a heads-up display (HUD)— generally mounted to the inhalation hose—that shows a small series of lights indicating green for good, yellow for caution, and red for danger, in case the PO2 in the breathing loop is getting out of range. This is of course driven by a controller that gives real time PO2 that can be viewed on the diver’s handset. Most eCCRs provide at least one handset as well as the HUD to ensure proper redundancy.  

One of the reasons many cave exploration groups like the WKPP strictly use the RB80 is its simplistic mechanical, reliable design. With the RB80, the gas is premixed into the stage bottles, and the back gas is always mixed for the MOD of the max depth expected to be reached during the dive. With the RB80, there is no gas mixing during the dive; the gas is plugged into the switch block similar to doing an open circuit gas switch. The gas is filled, properly analyzed, and the content label is attached to the neck of the bottle prior to leaving the dive center. 

The bottles all have properly placed MOD stickers on two sides of the bottle for easy identification by both the diver and his team mates, plus a MOD sticker placed on the bottom of the cylinder that can be identified by teammates when being viewed from behind. In the water, the proper stage bottle is selected for the MOD, and the gas is safely plugged in at the proper switch depth, but only after the bottle has been properly identified, verified by the buddy, and the drive hose confirmed with the bottle that has been chosen, similar to open circuit gas switches. 

WKPP explorer David Doolette measuring a mastodon bone in Wakulla Springs B Tunnel. Dr. John Rose in background. Photo by David Rhea

The most dangerous thing about the RB80 (and semi-closed units in general), is the oxygen drop, especially in shallow water [See the Loop Gas calculations section of the RB80 page in Wikipedia]. Due to the fact that oxygen is being consumed during respiration, and gas is discharged from the inner bellows with each exhalation, the oxygen drops slightly with each breathing cycle until fresh gas is replenished from the injectors, typically every two to four breaths. For this reason, one must be cautious when using the RB80 at shallow depths (when the ambient pressure is low) or when using mixes with a lower oxygen fraction as a travel gas. 

The drop in oxygen levels also means there is a slight increase in inert gas that remains in the loop and that needs to be taken into consideration for decompression. Both of these nuances of the RB80 are easy to calculate and adjust for prior to the dive. 

During RB80 training, both the oxygen drop and the increase in inert gas load are addressed and easily able to be factored in. The theory is discussed in an RB80 class, and software is available to easily do quick calculations.  All of this can then be programmed into GUE’s Buhlmann-based desktop decompression program, DecoPlanner, for proper dive planning.  Like most rebreathers, the RB80 has additional complexities requiring proper pre-dive assembly, testing, maintenance, and post-dive discipline. 

Training on the RB80

The WKPP was established in 1995, and from the beginning, adopted a standardized approach to gear configuration and procedures. Initially, this approach was called “Hogarthian,” after early WKPP pioneer Bill Hogarth Main. Later, project director George Irvine added to the standardization and coined the phrase “Doing It Right,” or DIR, to represent this standardized approach.  In 1998, Jarrod Jablonski founded GUE, which offered exploration-based training utilizing WKPP’s standardized approach and gear configuration. Once Halcyon started building the RB80, GUE began offering formal training. Currently they are the only training agency to do so. 

From the beginning, GUE’s RB80 training has been exploration-based, with a heavy emphasis on failure-based training i.e. dealing with equipment failures as a team, similar to other GUE courses. Exploration-level cave diving has complex exposures that require divers to return from deep inside the cave, and then make a vertical ascent to return to the surface. With the addition of the RB80, divers are able to extend their penetrations exponentially, adding as much as 12-14 hours of decompression on some dives alone. Conventional rebreather training does not properly prepare someone for these types of exposures. 

RB80 Divers on the wreck of the freighter Judge Hart in Rossport, Canada. Photo by David Rhea

GUE divers have historically been required to take Fundamentals, Tech 1, and Tech 2 with a minimum of 25 dives at each level between classes prior to beginning their RB80 training. This is in addition to the Cave 1 and 2 level training and experience required to begin cave exploration.  The investment of time, energy, and resources necessary to become a GUE/WKPP exploration cave diver makes for a very serious explorer who has the skills and experience necessary to conduct dives with this level of exposure. The failure-based training also builds the diver’s confidence, repetitive learning, and instincts necessary to safely explore. 

One of the many reasons for the long term success of the RB80 has been this extremely regimented training by GUE’s four active RB80 instructors. In addition to the most intense and demanding rebreather training available, GUE RB80 students must purchase the unit prior to taking the training. This alone narrows the attendance to only the most serious explorer, as no rental option is considered. 

Until fairly recently, GUE divers were the only ones using the RB80. Even then, only those willing to take the robust training who had an exploration mindset learned to dive the unit. Currently there are 150-200 GUE divers certified to dive the RB80. The discipline and attitude of these explorers has ensured that the RB80 has been responsible for more kilometers/miles of cave exploration than any other rebreather in the world. I estimate that more than 161.6 km/100 mi of cave passage has been explored using the RB80. 

The discipline and attitude of these explorers has ensured that the RB80 has been responsible for more kilometers/miles of cave exploration than any other rebreather in the world. I estimate that more than 161.6 km/100 mi of cave passage has been explored using the RB80.

A Specialized Exploration Tool

For 30 years the WKPP has been mapping the underwater labyrinth of the Woodville Karst Plain, having mapped over 56,609 m/185,000 ft of cave passage with more than 35,189 m/115,000 ft below 58 m/190 ft. The RB80 has been one of the most vital keys to this success, including the world record dives in Wakulla and the following traverse. It is the only rebreather used for exploration on Woodville Karst Plain projects. Presently, virtually all exploration being conducted by the WKPP below 61 m/200 ft is exclusively done on the RB80. 

WKPP dives in Florida on the RB80. Photo by David Rhea.

Over the years, and especially during the Wakulla exploration heydays, one of the growing concerns was running out of scrubber material during the dive. On the biggest dives, the entire RB80 double tank configuration would be swapped at the deep portions of the decompression for a fresh ‘breather with smaller double five-liter bottles and fresh scrubber material. Note: an advantage of the RB80 over an eCCR is that the valves can be closed and the unit reliably stored underwater like a stage bottle for bailout.  It can then be quickly turned on and dived.

In 2008, CINDAQ’s MCEP project also adopted the RB80 and has done countless hours of exploration in the caves of the Yucatán. Between January 2018 and December 2020, for example, MCEP exploration divers mapped in excess of 180,000 m/594,000 ft of new cave passage in Ox Bel Ha alone using RB80 technology. 

As CINDAQ board member and co-owner of Zero Gravity Dive Center, Christophe Le Maillot, explained, “It is such a sturdy and intuitive unit. In all the years we used it, we have never had to terminate or cancel a dive because of a malfunction. It’s a real work horse!” Like their sister WKPP team, the MCEP exclusively uses GUE-trained RB80 divers for their exploration dives. 

GUE divers have also utilized the RB80 for cave exploration projects in China, the Nullarbor caves in Australia, caves in the south of France, cave and wrecks of Italy including the Pantelleria project, the Alviela cave project in Spain, and other karst areas around the world. In addition to cave exploration, the RB80 has been utilized by GUE divers on the west coast for the ghost net removal, and by GUE wreck divers in Canada and around the world. 

Introducing the RBK, a Sidemount RB80

In response to explorers wanting a stageable version of the RB80 as both a travel and/or bailout rebreather, Halcyon began working to develop a modified sidemount version of the RB80, called the RBK. The first version was called the RBK1 and after several years of modifications Halcyon produced two more revisions, the RBK 2 and the RBK 3, referred to simply as the RBK.

Halcyon COO Mark Messersmith diving the RBK in Mexico. Photo by Sam Meacham.
Sam Meecham with a pair of RBKs. Photo courtesy of CINDAQ.

The overall diameter of the RBK is the same as the RB80, but by reducing the height of each section, the overall length of the unit has been reduced to 50 cm.  Though the scrubber was reduced in volume to 2.4 kg/5.29 lb, the scrubber duration is rated for approximately eight hours based on user experience [See InDepth’s Rebreather Holiday Shopping Guide for add’l spec details]. Because of the smaller form factor, the RBK offers a 6-8:1 gas extension versus 8-10:1 on the full RB80.

The sidemount RBK has been used as a sidemount, travel, and bailout rebreather by both the WKPP and the MCEP, which has been testing and helping to refine various RBK prototypes since 2015. On recent long-range explorations through small passages, the RBK has proven to be an outstanding tool for shallower, long distance cave exploration. MCEP instructors are now working with the GUE board of directors and other RB80 instructors to develop a RBK sidemount training course, which should be available in the not-too-distant future.    

New Non-GUE Users

Andy Pitkin with a sidemounted RBK bailout rebreather. Photo by Kirill Egorov.

Over the last few years, Halcyon has made the RBK available to select non-GUE divers. They have sold custom versions of the RBK to militaries around the world. In addition, they have provided RBK units to exploration divers from Karst Underwater Research (KUR), who have been using the RB80 as a side mounted bailout breather for their recent long range exploration dives at Weeki Wachee Springs and other systems. The divers received their RBK training directly from Halcyon. 

As KUR project director Andy Pitkin put it, “It is undeniably true that ‘simplicity is the ultimate sophistication,’ as Leonardo Da Vinci once noted. The RBK has proved itself to be close to a perfect tool for our particular application, far exceeding my initial reserved expectations.“  

From its conception, it was quickly obvious that the RB80 would be around for a very long time. The simplicity, safety, and the robust mechanical nature of the unit, combined with rigorous training, and highly experienced users, arguably make RB80 and RBK the ultimate exploration tools.

Additional Resources:

InDepth’s Rebreather Holiday Shopping Guide (2020)

Halcyon: Using The RB80 As A Sidemounted Bailout Rebreather by Andy Pitkin, Karst Underwater Research (2018)

GUE: DOUX DE COLY: GUE Expedition with RB80 (2004)

Introducing the RB80 by Michael Waldbrenner and Dr. Reinhard Buchaly 

Deep Tech: Victory At Last (1998): Olivier Isler is setting penetration records with a triple-redundant semi-closed rebreather

RB80 Series on GUE.tv


David Rhea is an active GUE instructor and instructor evaluator, having been with GUE since the earliest days. An avid explorer with the WKPP since 1998, David has explored caves in China, Florida, Australia, Mexico, and France. A passion for diving started at age six, leading David to make his first dives at age nine. He became a scuba instructor at age 18. David has worked full time in the scuba industry for over 40 years, and has worked for Scubapro since 1995. David is as passionate today about exploration, teaching, and underwater photography and managing his Florida Scubapro territory as he has ever been. 

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