Connect with us

Latest Features

mCCR Face-Off: Gemini vs Sidewinder

There’s lots of buzz these days among sidemount rebreather aficionados: there’s a new sidemount mCCR in town, which has resulted in increased noise on the socials. Here geeky Floridian cave explorer Grant Tobin dives into the weeds and reviews Fathom Dive Systems’ new Gemini mCCR rebreather and contrasts it to his previous breather, the popular KISS Sidewinder.



By Grant Tobin. Images courtesy of SJ Alice Bennett unless noted.

Photo by SJ Alice Bennett

I’d like to be able to give a fully independent review of the Fathom Dive Systems’ new Gemini sidemount rebreather, but I found myself unable to begin doing so without including a comparison with the KISS Sidewinder as well as my personal justifications for switching. 

Disclosures: I have no affiliation with KISS, a division of Polish-based XDeep (although I am certified to service the units). I have no business affiliation with Fathom but am sometimes involved with Karst Underwater research (KUR). Charlie Roberson, the proprietor of Fathom is on the KUR board of directors. Also, I really don’t think any sidemount unit should be a diver’s first rebreather. 

The Sidewinder. Photo courtesy of XDEEP

The Sidewinder

I can say, however, that the Sidewinder that was invented by Mike Young (and Edd Sorensen, and probably Matt Vinzant for the initial inspiration) has also been responsible for more cave line laid in the past five years than almost any other unit. I do firmly believe in dual oxygen monitoring. All opinions are my own and should be taken with your own grains of salt. [For detailed specs on the KISS Sidewinder see InDEPTH’s Holiday Rebreather Guide]

I did my initial training on the KISS Sidewinder in April 2019, first with Mike Young’s unit and then finishing on my own after it was delivered. I put approximately ~350 hours on the unit between April 2019 and Jan 2023. My max depth was 96 m/315 ft, and my longest dive was somewhere north of 6 hours. My lowest temperature dive was 1°C/34ºF. 

Here are the modifications I made to the Sidewinder:

  • Changed the KISS DSV to Golem Gear BOV to Golem Gear DSV (I dislike the KISS one. It was improved in the most recent update and is now easier to service, but I have a strong distaste for the circ-clips that hold it to the loop hoses, as well as the vertical DSV open close vs a horizontal twist). 
  • Added Loop covers (homemade from SuperFabric or whatever the armored milspec dotted stuff is) 
  • Added syntactic foam coating to the scrubber 
  • Changed the Omni-Swivel QDs for the ADV inlet to either QC6 or BC Inflator, depending on the team I’m diving with—Removed the ADV (it either needs an in-line shutoff, or to be removed, or to run on a lower diluent IP, or a stiffer ADV membrane, or two membranes) 
  • Removed the OPV (it’s in a great place to wet your unit if you happen to bump it into a restriction or unintentionally hit it with your elbow) 
  • Changed the Fischer-driven single monitor with Molex cells to dual monitor FathomHUD hardwired + Petrel 2/3 four-pin off an SMB splitter board (Fischer is silly—the argument for single monitor has improved with the advent of vibration in the Petrel 3, but I still am philosophically opposed). 
  • Changed the stock towers to Light Monkey towers (not only have there been various shades of manufacturing tolerances over the twenty years of KISS using these, but a few friends have popped theirs off grinding through restrictions) 
  • Changed the stock-blanked WellsMarine first stage and KISS single button oxygen add (GAV) to a Poseidon XStream MK3 on a KISS dual button orifice needle valve (remove depth limit, add needle flexibility, better access to first stage parts, integral OPV. The stock oxygen add is also prone to breaking when torqued by the wrong people) 
  • Switched from the plastic loop hose retaining clamps to metal hose clamps 

What remained an issue with the Sidewinder unit itself after making these changes? [Ed. note: Similar to other CCR manufacturers, KISS/XDeep does not sanction the modification of their equipment, as it can create safety issues.]

Some of the things that make the split-backmount-not-really-a-sidemount unit great also create other issues

  • Water removal. No water dump is available on the small lung. Brett Hemphill remains the only person I know who has used the DSMB style dump available on the larger lung, though I imagine Mike Young and a couple others have as well. Edd Sorensen speaks of intentionally flooding the unit and then proceeding to do a long cave dive on the unit “about 8 times” without ever having had a caustic, and he’s not the only one. The shape of the lung on the back makes it less likely for the caustic water to move from the exhale scrubber, through the counterlung, up the inhale scrubber, and into the cells (and eventually the inhale loop). I would not advise trying this yourself. 
  • Wet sorb. Lung butter and any moisture dumps from the exhale and onto the top of the exhale scrubber. In 22°C water, you can make a sandcastle out of the right-side scrubber after four-ish hours, and a partial sandcastle out of the inhale scrubber after five. Some of this is my drool, some is the byproduct of the scrubber reaction and lack of water trap on the unit. 
  • No gas inlet across cell faces. Some units (Fathom, for example, or a modified KISS Sidekick) have the diluent-in blowing across the face of the cells, allowing for instant cell verification. Others have cells oriented in a place that is less likely to get wet under normal diving conditions. In cold water, there is enough condensation on the inhale side of the hose that water drips down onto the back of the cells in the Sidewinder and into the Molex connectors. If the cell faces do end up wet, a few dil flushes may help stabilize, partially dry, and hopefully return the cells to function, but it’s often a roll of the dice if they all come back. 
  • Thread on scrubber canister heads. Some scrubbers do and some scrubbers do not have a line indicating max fill. Some scrubbers seem to have more and some fewer rotations of the head nut to lock down the heads on the scrubbers. There have been at least two instances of the user managing to grind through a restriction or otherwise and rotating the nut loose and knocking the head off. User error? Definitely possible. When the first reports of the tower to loop thread popping loose surfaced, the immediate reaction was to state user error and poor assembly. Having held a pair of the failed ones in my hand, I humbly disagree.
  • Scrubber to counterlung connection. These use another pair of the circ clips.
  • Internal mesh screen on the scrubber. For the first few years, the bottom of scrubbers had a glued-in circular disc with a mesh screen to support the sorb and keep it separate from the counterlung. I’ve managed to break two of them. Mike replaced them for me, though I still find the plastic crossbars thin. 
  • Water from the OPV can drip down into the back of the cells / into the cell head. Short people (and people that have been taught poorly) trigger the OPV each time they reach for their butt d ring or XDeep OPV with their right hand and it’s one of the few ways to get a quick caustic on a sidewinder. 
  • Various iterations of the SW MAVs and needles have had issues at extreme depths. Switching to higher durometer o-rings helped, but anybody that has taken their unit past 90 m/295 ft knows of these issues. Hint, they fail open and it’s a nice way to get yourself into a “boom drill.” It’s not a great trimix unit unless you need to squeeze through something at or on the way to these depths.

The above largely ignores any issues with parts that I’ve already replaced. An important thing to remember is that much of the Spirit series were simply built by parts on hand from the KISS Classic (and even the Sport). Have I been using this unit differently than intended? Certainly, or at very least differently than what Mike Young set out to make when he produced the units. With so many instructors screaming about how the SW is “the most versatile and simple rebreather made,” I did put it through its paces. By the time I retired it, my unit was, at most, half stock components. 

The Gemini

I began hearing rumors that Fathom was working on a prototype sidemount unit in early 2022. Charlie and the team he dives with are pretty experienced at home builds and have used various rebreathers over the years, from modified Fathoms to Billy Gambrill-esque Lowriders, to Sidekicks and SF2s and Choptimas and others, so I was eager to see what would pop out. Rumors beget rumors and poof, we got to the Diving Equipment and marketing Association (DEMA) trade show in Orlando, Nov 2022, and the Gemini was on display to the public. 

According to the Fathom Gemini CCR Spec Sheet:

  • $7695 
  • Dual scrubber (hence the name) 
  • Axial 
  • potted head using SMB connectors (JJ/Fathom cells) 
  • No ADV 
  • OPV/water dump on the lung itself 
  • Easy integration with GG BOV, GG DSV as stock 
  • Fathom dual button needle valve with blocked, stiff spring Apeks DS4 
  • Swappable scrubber baskets 
  • Integrated HUD 

The Gemini and the Sidewinder are obviously units of a similar skeleton (not unlike an xCCR vs a JJ-CCR vs a BMCL Liberty etc), and a few other comparisons can be drawn. That said, the stock and early manufactured Sidewinders (2018, 2019) are probably a Honda Fiat to the 2023 Gemini’s Toyota Corolla (or even the old Lexus LS 400)? The 2022-ish Sidewinders, properly configured with a bunch of aftermarket work, (imo) bring them closer to a Gemini. Some gaps are inevitable, though. 

Here’s some information that’s not in the spec sheet: 

  • Prelim EN14143 testing with 812 sorb has given a 2.5 hour duration at a breathing rate of 40 LPM with 1.6LPM CO2 injection on air at 4°C. My personal breathing rate is a quarter of that, and my CO2 production rate (extrapolated from my oxygen consumption) is ~0.375 that. Under normal conditions, that brings the expected duration to something more useful for me. 
  • Stock 44” LP hose from the DS4 to the Needle. 

Price comparison for a 2022 Sidewinder with dual monitors, as of 31 Dec 2022, to be “ready to dive” and excluding harness, regs, cylinder, and assuming one needs a MAV, and that Delrin is a less good insulator than Black Amalgon. The scrubber basket material matters for diving, and thus you need syntactic foam.

Note, a purchaser could do some other things to cheapen this, but I wished to use the KISS configurator to attempt to bring them together to something many view as safer. Blah, blah—always know your PO2. If two monitors saves one life, the quant in me says the math of everyone needing two monitors is positive expected value. Even better, an instructor can monitor student PPO2 on a Fathom HUD farther away than a Petrel (Even scarier: instructors that permit new students to only use a Shearwater Nerd).

What is still lacking on this hypothetical Sidewinder compared to a Gemini? The N@90 heads up display (HUD) is much worse than the Fathom version. You’d still be working with Molex cells and a head that isn’t potted. And you have a depth limit in the 70m/230 ft range. (*Mike has made and sent a few SMB style splitter boards, but they’re Molex in and SMB out, so you’re still drowning in six Molex connectors). 

  • Subscribe for free
  • Area 9
  • Halcyon Sidemount

If we were attempting to make this phantom Sidewinder match the Gemini as closely as possible in function (higher depth limit, cap ADV, etc), we’d be out the needle valve ($499 for the SubGravity, which is cheapest publicly available on market, but only allows for oxygen in, as opposed to the Fathom or KISS needle valves with two inlets, and thus eliminating the MAV) as well as appropriate first stage, stiffer spring, blanking cap, and OPV+ADV caps. The price discrepancy would then increase further. 

Can someone argue that the Sidewinder is designed to be simple and shouldn’t need splitters and dual monitoring and a needle, and that sump heads would solve some of these? Sure. It’s not how I use it, and it’s not how I think it should be taught. An uncertified user also isn’t “allowed” to order sump heads with a new unit. You could order the Sidewinder without dual monitoring, but you can’t order a Gemini without a HUD. I can’t see a NERD 2 in a true whiteout, but I can see the HUD, or I can feel a (vibrating) Petrel 3. I’d rather be able to stay on the loop and count via the HUD than stay on the unit and trust my—or most diver’s—ability to dick around counting breaths in semi-closed rebreather (SCR) mode. 

The above information is all pre-purchase for me. I put down a deposit at DEMA and took delivery in early-January. Current instructors as of this writing are Kelvin Davidson (instructor trainer), Jon Kieren, and Giovanni Gastaldo at Third Dimension in Tulum, Mexico, and Jon Bernot (instructor trainer) at Cave Country Dive Shop in High Springs, Florida. After a hiccup with my work coverage interfering with a class with Bernot, I was able to find a mutual timeframe to sneak to Mexico for some time with Kelvin. 

First Impressions

My unit arrived at my office on 4 January 2023 in a blue crate weighing about 12kg. My initial thoughts: 

  • Loop hoses are much shorter, but much more flexible.
  • Removable scrubber baskets mean I won’t be able to use that dead space for packing (I formerly put two computers and my oxygen first stage inside of scrubber cans.
  • Very tight tolerances on all connections. Almost “break an O-ring if you don’t lube them” tight.
  • Weed Wacker cable seals the bottoms and tops of the cans to the lid. Coincidentally, this is also how the one atmosphere exo suits work.
  • Not sure how I’m going to feel about the water dump placement. I debated for a long time drilling holes in the bottom of my sidewinder cans and installing Light Monkey tinkle valves. This way, I could dump water before it hits the lung. I elected not to proceed, as I worried it would harm resale value and, at the end of the day, rebreathers are a means to an end, and I don’t have emotional attachment to units.
  • I’m pretty compact, the two button Fathom needle valve is not. (I’ve had one in the past, this wasn’t really a shock)
  • No loop hose weights (I had them on the sidewinder and never experimented with removing them).
  • Holes on the scrubber screens are a little larger than expected. Fractions of a millimeter but would wait to put sorb in them to find out whether this concern was warranted.
  • The choice to flow gas from right to left means that for the oxygen valve to remain on the right side, the hose into the needle must pass along the bottom of the harness and up the left side of the back (as opposed to straight up the right side like the SW).
  • Cell placement is an improvement. In a horizontal swimming orientation, cell faces are down toward the ground rather than backwards toward your fins. Unlike Molex cells, backs of JJ and Fathom cells are covered with the wire lead. 


  • Lung (4.5L) 
  • Scrubbers 
  • Scrubber baskets 
  • Gas addition head 
  • Electronics head with HUD + 6” female 4-pin (Charlie will make it longer if you ask/need) 
  • 40” Inflator Hose DS4 w button gauge and beefy Apeks OPV 
  • Needle + hose to head 
  • QC6 male + hose to first stage 
  • Flow meter 
  • DSV + nipples
  • Three bolt snaps (can tops, bungee across front) 
  • Bungee 
  • Paracord 
  • Fathom hat and sticker 

Taking The Class

I built the Gemini to copy over the rigging from my Sidewinder but did not get it wet before class. I made it to Tulum, Mexico, and took care of my crossover. Kelvin was using a Razor 4, Lanny an XDeep Rec, and myself a Katana2. Takeaways are listed below in positive, neutral, and negative order. 

The Positives

+ SMB cells. Larger surface area, fewer small connections. Molex are trash, and I’m happy to fight anyone that says they prefer them. 

+ Proper threading on the head to loop connection. The LM ones aren’t super well machined, and most people have a chip on their first thread because of it. The KISS ones are…well KISS ones. Caveat: Dobbykins and I had the first retail set of LM towers, so I don’t know if this has been improved in the past two years. 

+ Connection from the cans to the CL do not have a circ clip that could break or be lost. 

+ Dewatering ability. I have not tested it. There’s enough alkalinity in the freshwater in the cenotes in Mexico that I was worried about frying the cells. Next time I have a bit of sorb time left and the ability to pull my cells out, I’ll hop back in the water and totally flood the thing a couple times to see what happens. Between Edd and one or two others’ experiences having flooded one side, I’m not super concerned with some moisture, assuming the inhale side remains unflooded. 

+ Easy BOV integration. I’ve danced both sides of the BOV DSV debate. On a Sidewinder, the integration with a BOV was either very messy, or needed Fathom parts, or would add an additional hose somewhere. I did the Jason Richards thing for a while but grew to hate the ADV and all the additional hardware necessary. On a Gemini, going from DSV to BOV requires a single 30” LP hose and an elbow (plus the BOV). One could ditch the necklaced backup and thus ease gearing up. On all CCRs, I firmly believe you need either a BOV or a necklaced backup that is always breathable. 

+ The two button needle (and the other Fathom needle and other Fathom MAV) are upstream. I’ll use a quote from Charlie here to avoid confusion: “The manual addition button flows gas opposite of normal buoyancy compensator inflators. We did it to prevent the leaks that the SW MAV is plagued with. Increased IP pushed it open in the normal downstream direction but assists in keeping it shut with upstream flow. It eliminates leaks and free flowing MAV. That also means that a HP seat failure on the oxygen 1st stage won’t result in a boom scenario.” I actually didn’t know this, and I don’t currently know why it isn’t advertised more heavily.

+ Swappable canisters. Credit is due to rEvo designer Paul Raymakers for conceiving of the split or dual scrubber canisters—the ability to swap scrubbers does present interesting possibilities. Say I fly down to Florida or Mexico for a week. Arrive by midday Saturday and want to get a shakedown dive in before doing much larger dives over the next few days. Now, I can get a two hour dive in, swap the old inhale into the new exhale, repack the new inhale side, and be happy putting in a very long dive (Caveat: you’ll all need to figure this out by yourself, and I’m not going to tell you my rules for sorb use. If you’re pushing max scrubber durations, you should be in a big boy or big girl state of mind and be able to evaluate these risks.) 

+ You’re more likely to hurt yourself trying to disassemble the unit topside than you are to hurt it under water. 

+ No battery box on the loop hoses 

+ WOB. I saved this one for last, as I don’t think humans can measure these things objectively by feel or with much precision, and I don’t want to lead readers astray. I feel that the Gemini breathes slightly better than the Sidewinder. 10%? 15%? And then I had to ask myself why (and question as well whether I was still in the honeymoon phase with the unit). I think, very simply, it has fewer bends for the gas path and slightly less turbulent flow through the hoses. The towers run straight out of the lid, there is less dead space in the heads, and the entry at the bottom of the scrubber is smoother. 

Hopefully xDeep/KISS will publish the results of the testing they did, Fathom will do the same, and we will have some data. The important thing to remember is the manner the cans and lungs are rigged will have the highest impact. 

  • Halcyon Sidemount
  • Subscribe for free
  • Area 9


  • SW users are split running their MAV and GAV across their chest vs over the shoulder. I will need to get used to this being on my left shoulder. 
  • Packing sorb is going to take longer. I’ll trade this for the ability to pull scrubbers out to let cells dry without needing third party caps or to be able to toss the scrubber baskets into a drybag. 
  • Haven’t squeezed into anything that makes me prefer the straight routing vs the angled-in routing of the KISS and LM towers. If the straight piping did improve build quality and WOB, I’m all for it, and I do believe the straight plumbing puts the incompressible parts lower on the body 
  • Flow right to left 
  • Fathom advertises Black Amalgon as 400x better insulation than aluminum. Aluminum 6061 is in the ~167 W/m-K range, Acetal (Delrin) is 0.23 W/m-K range, and epoxy coated fibrous synthetic materials seem to be in the ~0.04 W/m-K range. I don’t have the equipment to test whether the dual design of Amalgon + inner scrubber basket material is superior to the newer Sidewinder Delrin cans + syntactic foam coating. 

The Negatives

— HUD uses a 2032 battery. Time will tell how long this lasts me, and it’s another thing to keep in the kit. Takes about three minutes to carefully change. 

— My finger fits and has the dexterity to remove the heads via fingering. If one doesn’t, you’ll need a guitar pick or a spudger or a relatively high amount of grip strength to remove the heads when you need to disassemble the unit. I think Charlie should include a plastic bike tire lever, as I promise you someone is going to use a non-coated tool and either mark the cans or the head or chip the head loop connection. There is a trick to it, but GFL if you didn’t lube the o-rings sufficiently. 

— The fishing crimp on the end of the weedwacker line could mar the canister. The Gemini is a tool I’m going to scrape through rock, and the crimp is not in a place to cut my suit. That said, I wrapped it in heat shrink so I could grab it better with wet hands. 

— I’d like to see a notch machined into the head and canister to ensure future users always line the heads up properly. It’s minor, and matters less than on the Sidewinder because of the straight piping. The argument against doing this is that the bottom of the cans can also be removed (but seems to be more for maintenance and manufacturing ease than a need). Fathom would need to mark tops and bottoms or one could use a sharpie and be done with it. There’s an unfortunately high amount of variation among SW instructors on correct counterlung bung to head tower angle. 

— The mesh screen size is ever-so-slightly too big. I’m going to use some JJ scrim material (filter paper) on the cans to ensure less dust and no granules poking out. I popped through 5? 10? granules per time I packed the sorb. At very least, there needs to be a scrim on the side of the basket nearest the cells and one nearest the water dump on the lung. UPDATE: scrims are now included.

— I don’t think the spring on the scrubber basket adds much value. As more classes come through, I think a standard will end up developing. I’m kind of worried a muppet will bend the screen via the bolt, and the bottom screen (top as packed) isn’t of the same machining tolerance as every other piece of the unit. 

— No water trap. I’ve experimented with different ideas on the Sidewinder (including a very small t piece in the middle of a loop hose) to absorb the sickening amount of spit I drool into the cans), but as of now, drool path is the same. Sorb works decently whilst wet, but eh. Still a complaint people will have. 

— I have to suck it up and return to using an Apeks product. 

— I dislike the stock GG mouthpieces. I’ve switched to a Divex (JJ) which I like better than the soft Scubapro one, which I prefer over the Comfobite for CCR use. On OC, my needs are slightly different. I’ll inevitably end up with a gag strap should I move back to BOV use. 


The Gemini works about as I expected it to. It’s not wildly different from the Sidewinder, but it is better, and I trust it more. Any issues that I have with the Gemini are minor or are inherent in the design of split-backmount-not-really-a-sidemount-unit units. If you believe (as I do) that dual monitoring is a need, then I do not believe there is a reason to buy a new Sidewinder as of Jan 2023. 

If you do not believe in dual monitoring but do believe in reducing the number of things that can go wrong on your unit via plugs, or sump heads, or LM towers, or a new first stage, or not using Omni-Swivel QDs, or dislike circlips, etc., then the question is a little more difficult. If demand outweighs availability of the small instructor pool for the Gemini, there’s an inevitable bottleneck. Currently, there is also a three to 12-month lead time for a new Sidewinder, depending on who you ask. 

On an ending note, my motivation for putting such effort into this review comes from the fact that I have one of the first couple non-prototype units, and wanted to share what I learned.

Dive Deeper

InDEPTH: Not All mCCRs are Created Equal: The Case for the Needle Valve by Charles Roberson

InDEPTH: Keep It Simple Sidewinder By Jake Bulman and Skanda Coffield

InDEPTH: InDepth’s Holiday Rebreather Guide: 2022 Update

Grant Tobin is a derivatives trader and risk analyst based out of Chicago, IL. A native Floridian, he began diving in 2006 and cave diving in 2009. His last several years have been focused on dives and projects ranging from participating with Karst Underwater Research (KUR) in Florida, to caves in Missouri and Mexico, to the wrecks of Bikini, Scapa, and the Great Lakes with MWUE. Outside of diving, he can be found racing long distance triathlon and rock climbing.


Twenty-five Years in the Pursuit of Excellence – The Evolution and Future of GUE

Founder and president Jarrod Jablonski describes his more than a quarter of a century long quest to promote excellence in technical diving.




by Jarrod Jablonski. Images courtesy of J. Jablonski and GUE unless noted.

The most difficult challenges we confront in our lives are the most formative and are instrumental in shaping the person we become. When I founded Global Underwater Explorers (GUE), the younger version of myself could not have foreseen all the challenges I would face, but equally true is that he would not have known the joy, the cherished relationships, the sense of purpose, the rich adventures, the humbling expressions of appreciation from those impacted, or the satisfaction of seeing the organization evolve and reshape our industry. Many kindred souls and extraordinary events have shaped these last 25 years, and an annotated chronology of GUE is included in this issue of InDEPTH. This timeline, however, will fail to capture the heart behind the creation of GUE, it will miss the passionate determination currently directing GUE, or the committed dedication ready to guide the next 25 years.

Photo courtesy of Kirill Egorov

I don’t remember a time that I was not in, around, and under the water. Having learned to swim before I could walk, my mother helped infuse a deep connection to the aquatic world. I was scuba certified in South Florida with my father, and promptly took all our gear to North Florida where I became a dive instructor at the University of Florida. It was then that I began my infatuation with cave diving. I was in the perfect place for it, and my insatiable curiosity was multiplied while exploring new environments. I found myself with a strong desire to visit unique and hard-to-reach places, be they far inside a cave or deep within the ocean. 

My enthusiasm for learning was pressed into service as an educator, and I became enamored with sharing these special environments. Along with this desire to share the beauty and uniqueness of underwater caves was a focused wish to assist people in acquiring the skills I could see they needed to support their personal diving goals. It could be said that these early experiences were the seeds that would germinate, grow, mature, and bloom into the organizing principles for GUE.

Brent Scarabin, Jarrod and George “Trey” Irvine getting ready to dive.
Jarrod with his Halcyon PVR-BASC prototype.
George Irvine and Jarrod conducting the original DIR workshop.

The Pre-GUE Years

Before jumping into the formational days of GUE, allow me to help you visualize the environment that was the incubator for the idea that became GUE’s reality. By the mid-1990s, I was deeply involved in a variety of exploration activities and had been striving to refine my own teaching capacity alongside this growing obsession for exploratory diving. While teaching my open water students, I was in the habit of practicing to refine my own trim and buoyancy, noticing that the students quickly progressed and were mostly able to copy my position in the water. Rather than jump immediately into the skills that were prescribed, I started to take more time to refine their comfort and general competency. This subtle shift made a world of difference in the training outcomes, creating impressive divers with only slightly more time and a shift in focus. In fact, the local dive boats would often stare in disbelief when told these divers were freshly certified, saying they looked better than most open water instructors! 

Area 9

By this point in my career, I could see the problems I was confronting were more systemic and less individualistic. In retrospect, it seemed obvious that key principles had been missing in both my recreational and technical education, not to mention the instructor training I received. The lack of basic skill refinement seemed to occur at all levels of training, from the beginner to the advanced diver. Core skills like buoyancy or in-water control were mainly left for divers to figure out on their own and almost nobody had a meaningful emphasis on efficient movement in the water. It was nearly unheard of to fail people in scuba diving, and even delaying certification for people with weak skills was very unusual. This remains all too common to this day, but I believe GUE has shifted the focus in important ways, encouraging people to think of certification more as a process and less as a right granted to them because they paid for training. 

L2R: Jarrod Todd Kincaid and Rickard Lundgren plotting their 1999 Britannic expedition.

The weakness in skill refinement during dive training was further amplified by little-to-no training in how to handle problems when they developed while diving, as they always do. In those days, even technical/cave training had very little in the way of realistic training in problem resolution. The rare practice of failures was deeply disconnected from reality. For example, there was almost no realistic scenario training for things like a failed regulator or light. What little practice there was wasn’t integrated into the actual dive and seemed largely useless in preparing for real problems. I began testing some of my students with mock equipment failures, and I was shocked at how poorly even the best students performed. They were able to quickly develop the needed skills, but seeing how badly most handled their first attempts left me troubled about the response of most certified divers should they experience problems while diving, as they inevitably would. 

Diving Fatalities

Meanwhile, I was surrounded by a continual progression of diving fatalities, and most appeared entirely preventable. The loss of dear friends and close associates had a deep impact on my view of dive training and especially on the procedures being emphasized at that time within the community. The industry, in those early days, was wholly focused on deep air and solo diving. However, alarmingly lacking were clear bottle marking or gas switching protocols. It seemed to me to be no coincidence that diver after diver lost their lives simply because they breathed the wrong bottle at depth. Many others died mysteriously during solo dives or while deep diving with air. 

One of the more impactful fatalities was Bob McGuire, who was a drill sergeant, friend, and occasional dive buddy. He was normally very careful and focused. One day a small problem with one regulator caused him to switch regulators before getting in the water. He was using a system that used color-coded regulators to identify the gas breathed. When switching the broken regulator, he either did not remember or did not have an appropriately colored regulator. This small mistake cost him his life. I clearly remember turning that one around in my head quite a bit. Something that trivial should not result in the loss of a life. 

Also disturbing was the double fatality of good friends, Chris and Chrissy Rouse, who lost their lives while diving a German U-boat in 70 m/230 ft of water off the coast of New Jersey. I remember, as if the conversation with Chris were yesterday, asking him not to use air and even offering to support the cost as a counter to his argument about the cost of helium. And the tragedies continued: The loss of one of my closest friends Sherwood Schille, the death of my friend Steve Berman who lived next to me and with whom I had dived hundreds of times, the shock of losing pioneering explorer Sheck Exley, the regular stream of tech divers, and the half dozen body recoveries I made over only a couple years, which not only saddened me greatly, but also made me angry. Clearly, a radically different approach was needed.

  • Area 9

Learning to Explore

Meanwhile, my own exploration activities were expanding rapidly. Our teams were seeking every opportunity to grow their capability while reducing unnecessary risk. To that end, we ceased deep air diving and instituted a series of common protocols with standardized equipment configurations, both of which showed great promise in expanding safety, efficiency, and comfort. We got a lot of things wrong and experienced enough near misses to keep us sharp and in search of continual improvement. 

Casey McKinlay and Jarrod with stages and Gavin scooters in Wakulla Springs. Photo courtesy of David Rhea

But we looked carefully at every aspect of our diving, seeking ways to advance safety, efficiency, and all-around competency while focusing plenty of attention into the uncommon practice of large-scale, team diving, utilizing setup dives, safety divers, and inwater support. We developed diver propulsion vehicle (DPV) towing techniques, which is something that had not been done previously. We mostly ignored and then rewrote CNS oxygen toxicity calculations, developed novel strategies for calculating decompression time, and created and refined standard procedures for everything from bottle switching to equipment configurations. Many of these developments arose from simple necessity. There were no available decompression programs and no decompression tables available for the dives we were doing. Commonly used calculations designed to reduce the risk of oxygen toxicity were useless to our teams, because even our more casual dives were 10, 20, or even 30 times the allowable limit. The industry today takes most of this for granted, but in the early days of technical diving, we had very few tools, save a deep motivation to go where no one had gone before.

All in a dive of diving for the WKPP.

Many of these adventures included friends in the Woodville Karst Plain Project (WKPP), where I refined policies within the team and most directly with longtime dive buddy George Irvine. This “Doing it Right” (DIR) approach sought to create a more expansive system than Hogarthian diving, which itself had been born in the early years of the WKPP and was named after William Hogarth Main, a friend and frequent dive buddy of the time. By this point, I had been writing about and expanding upon Hogarthian diving for many years. More and more of the ideas we wanted to develop were not Bill Main’s priorities and lumping them into his namesake became impractical, especially given all the debate within the community over what was and was not Hogarthian. 

A similar move from DIR occurred some years later when GUE stepped away from the circular debates that sought to explain DIR and embraced a GUE configuration with standard protocols, something entirely within our scope to define.

These accumulating events reached critical mass in 1998. I had experienced strong resistance to any form of standardization, even having been asked to join a special meeting of the board of directors (BOD) for a prominent cave diving agency. Their intention was to discourage me from using any form of standard configuration, claiming that students should be allowed to do whatever they “felt’ was best. It was disconcerting for me, as a young instructor, to be challenged by pioneers in the sport; nevertheless, I couldn’t agree with the edict that someone who was doing something for the first time should be tasked with determining how it should be done. 

This sort of discussion was common, but the final straw occurred when I was approached by the head of a technical diving agency, an organization for which I had taught for many years. I was informed that he considered it a violation of standards not to teach air to a depth of at least 57 m/190 ft. This same individual told me that I had to stop using MOD bottle markings and fall in line with the other practices endorsed by his agency. Push had finally come to shove, and I set out to legitimize the training methods and dive protocols that had been incubating in my mind and refined with our teams over the previous decade. Years of trial and many errors while operating in dynamic and challenging environments were helping us to identify what practices were most successful in support of excellence, safety, and enjoyment.

Forming GUE

Forming GUE as a non-profit company was intended to neutralize the profit motivations that appeared to plague other agencies. We hoped to remove the incentive to train—and certify—the greatest number of divers as quickly as possible because it seemed at odds with ensuring comfortable and capable divers. The absence of a profit motive complemented the aspirational plans that longtime friend Todd Kincaid and I had dreamed of. We imagined a global organization that would facilitate the efforts of underwater explorers while supporting scientific research and conservation initiatives. 

I hoped to create an agency that placed most of the revenue in the hands of fully engaged and enthusiastic instructors, allowing them the chance to earn a good living and become professionals who might stay within the industry over many years. Of course, that required forgoing the personal benefit of ownership and reduced the revenue available to the agency, braking its growth and complicating expansion plans. This not only slowed growth but provided huge challenges in developing a proper support network while creating the agency I envisioned. There were years of stressful days and nights because of the need to forgo compensation and the deep dependance upon generous volunteers who had to fit GUE into their busy lives. If it were not for these individuals and our loyal members, we would likely never have been successful. Volunteer support and GUE membership have been and remain critical to the growing success of our agency. If you are now or have ever been a volunteer or GUE member, your contribution is a significant part of our success, and we thank you. 

Photo courtesy of Kirill Egorov

The challenges of the early years gave way to steady progress—always slower than desired, with ups and downs, but progress, nonetheless. Some challenges were not obvious at the outset. For example, many regions around the world were very poorly developed in technical diving. Agencies intent on growth seemed to ignore that problem, choosing whoever was available, and regardless of their experience in the discipline, they would soon be teaching. 

This decision to promote people with limited experience became especially problematic when it came to Instructor Trainers. People with almost no experience in something like trimix diving were qualifying trimix instructors. Watching this play out in agency after agency, and on continent after continent, was a troubling affair. Conversely, it took many years for GUE to develop and train people of appropriate experience, especially when looking to critical roles, including high-level tech and instructor trainers. At the same time, GUE’s efforts shaped the industry in no small fashion as agencies began to model their programs after GUE’s training protocols. Initially, having insisted that nobody would take something like Fundamentals, every agency followed suit in developing their own version of these programs, usually taught by divers that had followed GUE training. 

This evolving trend wasn’t without complexity but was largely a positive outcome. Agencies soon focused on fundamental skills, incorporated some form of problem-resolution training, adhered to GUE bottle and gas switching protocols, reduced insistence on deep air, and started talking more about developing skilled divers, among other changes. This evolution was significant when compared to the days of arguing about why a person could not learn to use trimix until they were good while diving deep on air. 

To be sure, a good share of these changes was more about maintaining business relevance than making substantive improvements. The changes themselves were often more style than substance, lacking objective performance standards and the appropriate retraining of instructors. Despite these weaknesses, they remain positive developments. Talking about something is an important first step and, in all cases, it makes room for strong instructors in any given agency to practice what is being preached. In fact, these evolving trends have allowed GUE to now push further in the effort to create skilled and experienced divers, enhancing our ability to run progressively more elaborate projects with increasingly more sophisticated outcomes. 

  • Halcyon Sidemount

The Future of GUE

The coming decades of GUE’s future appear very bright. Slow but steady growth has now placed the organization in a position to make wise investments, ensuring a vibrant and integrated approach. Meanwhile, evolving technology and a broad global base place GUE in a unique and formidable position. Key structural and personnel adjustments complement a growing range of virtual tools, enabling our diverse communities and representatives to collaborate and advance projects in a way that, prior to now, was not possible. Strong local communities can be easily connected with coordinated global missions; these activities include ever-more- sophisticated underwater initiatives as well as structural changes within the GUE ecosystem. One such forward-thinking project leverages AI-enabled, adaptive learning platforms to enhance both the quality and efficiency of GUE education. Most agencies, including GUE, have been using some form of online training for years, but GUE is taking big steps to reinvent the quality and efficiency of this form of training. This is not to replace, but rather to extend and augment inwater and in-person learning outcomes. Related tools further improve the fluidity, allowing GUE to seamlessly connect previously distant communities, enabling technology, training, and passion to notably expand our ability to realize our broad, global mission.

Photo courtesy of Kirill Egorov

Meanwhile, GUE and its range of global communities are utilizing evolving technologies to significantly expand the quality and scope of their project initiatives. Comparing the impressive capability of current GUE communities with those of our early years shows a radical and important shift, allowing results equal or even well beyond those possible when compared even with well-funded commercial projects. Coupled with GUE training and procedural support, these ongoing augmentations place our communities at the forefront of underwater research and conservation. This situation will only expand and be further enriched with the use of evolving technology and closely linked communities. Recent and planned expansions to our training programs present a host of important tools that will continue being refined in the years to come. Efforts to expand and improve upon the support provided to GUE projects with technology, people, and resources are now coming online and will undoubtedly be an important part of our evolving future.

The coming decades will undoubtedly present challenges. But I have no doubt that together we will not only overcome those obstacles but we will continue to thrive. I believe that GUE’s trajectory remains overwhelmingly positive, for we are an organization that is continually evolving—driven by a spirit of adventure, encouraged by your heartwarming stories, and inspired by the satisfaction of overcoming complex problems. Twenty-five years ago, when I took the path less traveled, the vision I had for GUE was admittedly ambitious. The reality, however, has exceeded anything I could have imagined. I know that GUE will never reach a point when it is complete but that it will be an exciting lifelong journey, one that, for me, will define a life well lived. I look forward our mutual ongoing “Quest for Excellence.”

See Listings Below For Additional Resources On GUE And GUE Diving!

Jarrod is an avid explorer, researcher, author, and instructor who teaches and dives in oceans and caves around the world. Trained as a geologist, Jarrod is the founder and president of GUE and CEO of Halcyon and Extreme Exposure while remaining active in conservation, exploration, and filming projects worldwide. His explorations regularly place him in the most remote locations in the world, including numerous world record cave dives with total immersions near 30 hours. Jarrod is also an author with dozens of publications, including three books.

A Few GUE Fundamentals

Similar to military, commercial and public safety divers, Global Underwater Explorers (GUE) is a standards-based diving community, with specific protocols, standard operating procedures (SOPs) and tools. Here are selected InDEPTH stories on some of the key aspects of GUE diving, including a four-part series on the history and development of GUE decompression procedures by founder and president Jarod Jablonski.

Anatomy of a Fundamentals Class

GUE Instructor Examiner Guy Shockey explains the thought and details that goes into GUE’s most popular course, Fundamentals, aka “Fundies,” which has been taken by numerous industry luminaries. Why all the fanfare? Shockey characterizes the magic as “simple things done precisely!

Back to Fundamentals: An Introduction to GUE’s Most Popular Diving Course

Instructor evaluator Rich Walker attempts to answer the question, “why is Fundamentals GUE’s most popular diving course?” Along the way, he clarifies some of the myths and misconceptions about GUE training. Hint: there is no Kool-Aid. 

The GUE Pre-dive Sequence

As you’d expect, Global Underwater Explorers (GUE) has a standardized approach to prepare your equipment for the dive, and its own pre-dive checklist: the GUE EDGE. Here explorer and filmmaker Dimitris Fifis preps you to take the plunge, GUE-style.

The Flexibility of Standard Operating Procedures

Instructor trainer Guy Shockey discusses the purpose, value, and yes, flexibility of standard operating procedures, or SOPs, in diving. Sound like an oxymoron? Shockey explains how SOPs can help offload some of our internal processing and situational awareness, so we can focus on the important part of the dive—having FUN!

Standard Gases: The Simplicity of Everyone Singing the Same Song

Like the military and commercial diving communities before them, Global Underwater Explorers (GUE) uses standardized breathing mixtures for various depth ranges and for decompression. Here British wrecker and instructor evaluator Rich Walker gets lyrical and presents the reasoning behind standard mixes and their advantages, compared with a “best mix” approach. Don’t worry, you won’t need your hymnal, though Walker may have you singing some blues.

Rules of Thumb: The Mysteries of Ratio Deco Revealed

Is it a secret algorithm developed by the WKPP to get you out of the water faster sans DCI, or an unsubstantiated decompression speculation promoted by Kool-Aid swilling quacks and charlatans? British tech instructor/instructor evaluator Rich Walker divulges the arcane mysteries behind GUE’s ratio decompression protocols in this first of a two part series.

The Thought Process Behind GUE’s CCR Configuration

Global Underwater Explorers is known for taking its own holistic approach to gear configuration. Here GUE board member and Instructor Trainer Richard Lundgren explains the reasoning behind its unique closed-circuit rebreather configuration. It’s all about the gas!

GUE and the Future of Open Circuit Tech Diving

Though they were late to the party, Global Underwater Explorers (GUE) is leaning forward on rebreathers, and members are following suit. So what’s to become of their open circuit-based TECH 2 course? InDepth’s Ashley Stewart has the deets.

Project Divers Are We

Diving projects, or expeditions—think Bill Stone’s Wakulla Springs 1987 project, or the original explorations of the Woodville Karst Plain’s Project (WKPP)—helped give birth to technical diving, and today continue as an important focal point and organizing principle for communities like Global Underwater Explorers (GUE). The organization this year unveiled a new Project Diver program, intended to elevate “community-led project dives to an entirely new level of sophistication.” Here, authors Guy Shockey and Francesco Cameli discuss the power of projects and take us behind the scenes of the new program

Decompression, Deep Stops and the Pursuit of Precision in a Complex World In this first of a four-part series, Global Underwater Explorers’ (GUE) founder and president Jarrod Jablonski explores the historical development of GUE decompression protocols, with a focus on technical diving and the evolving trends in decompression research.

  • Subscribe for free
  • Area 9
  • Halcyon Sidemount
Continue Reading


WordPress PopUp Plugin