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The Who’s Who of Sidemount



Michael Thomas

Michael Thomas is the Training Officer of the British Cave Diving Group (CDG) Somerset Section. The CDG is credited with being the first organization to develop sidemount diving in the early 1960s.  Mike is an avid promoter of sidemount and cave diving and he is also a Full Cave instructor, and a sidemount and tech instructor with TDI. In addition to being a Fellow of the Royal Geographic Society, he is on the British Cave Rescue call list.

What is sidemount to you?

Sidemount is a tool for a job underwater. There I said it, now let me backup a bit and explain. I have been a dry caver or speleologist since I was a child. Both my parents are also cavers. I started diving in 1987 and started cave diving in 1992. Now if you start cave diving in the UK with the Cave Diving Group (CDG ) you also start sidemount diving. My first cave dive in Hurtle Pot Cave in the Yorkshire Dales in 1992 was also my first sidemount dive. I was taught cave diving and sidemount diving by a core of four divers, one lady and three gentlemen that had learnt to sidemount cave dive in the 1980s. As a diver I work and play underwater with a variety of tools; an HSE Full face mask, open circuit, CCR and sidemount. I try to use the best tool for the dive. Sometimes its Sidemount sometimes itʼs not.

What can be improved in sidemount in general?

Sidemount equipment has had many and significantly good changes over the years. Itʼs also had many equipment and training disasters, but thatʼs another story! If we take the sidemount community as a complete package, the one thing I would like to see improved is less of the self righteousness from some parts of the social media world. We all need to learn that shouting down at divers who are not in perfect spirit-level trim needs to stop. Sidemount has many varied skill sets and equipment and if itʼs not what you learnt on your course, itʼs not always wrong.

Was there an epiphany moment for you with sidemount?

The magic moment for me was not the ability to transport equipment easily underground or being able to move easily in low cave passage. These things just happened naturally as sidemount was what we used to cave dive. However, the first time I used a xDeep Classic harness with the ability to place weights down the spine of the harness rather than around the waist like a classic CDG harness, it was the game changer for me. No more back ache from pressure on the lower spine and better trim overnight. Iʼm not sponsored by xDeep or have any financial involvement with the company, but they have changed the game in my opinion.  I still use my xDeep harness today.

Whatʼs the main difference between an early day British sidemount diver and a modern one?

Traditional sidemount divers in the UK such as CDG members are actually not much different from CDG divers active today. Our system and harness is designed with dry caving in mind and passing through sumps (flooded cave passage ) to reach the next dry section. Our sidemount systems are designed to drop cylinders along the way or use any cylinder needed. Also we carry equipment used for dry caving beyond the flooded section. Ropes, drilling equipment and camping gear if required. All of this goes on the harness. 

Traditional UK CDG divers are commonly diving wetsuits and not much interested in a perfectly organized and trimmed out cylinder configuration. We have a job of exploration to do and take what is required. Steel cylinders are common, aluminum are easily damaged transporting through the dry sections. We also use karabiners instead of bolt-snaps for attaching the cylinders. Karabiners still work when covered in mud and you should not use a bolt-snap as a weight loading device when lowering cylinders in vertical dry cave.

What has gotten better with sidemount and what got worse ?

The choice of good sidemount harnesses for the various different styles is now excellent. Regulator setups with the correct length LP and HP hoses also makes diving life so much more streamlined. 

Whatʼs gotten worse? Too many manufacturers offer poorly designed harnesses because they think they must add sidemount to their product line.

So you have to tell the unwitting student that bought one, they have a suboptimal harness that wonʼt work the way they think it will.

What makes a good sidemount diver?

Making good sidemount divers is very subjective and each diver will have strong opinions. In my world, having a sidemount diver that can use and work the traditional CDG system for cave exploration and travel, and also have the technical skill set of a modern day sidemount diver with great trim and buoyancy is the best. In addition to floating around looking at nice stuff, they need to be able to work and explore.

Return to: The Who’s Who of Sidemount


Speaking Sidemount: Episode #25 – British Cave Diving & the CDG with Michael Thomas

InDEPTH:Meet The British Underground By Michael Thomas

InDEPTH: Dem Bones, Dem Bones, Dem Wookey Bones By Michael Thomas

The Big Scuba: Fathers Day Scuba Special with Michael & Robert Thomas diving team -Father and Son make great team

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GUE 25 Anniversary Conference Round Up




Global Underwater Explorers held a conference to commemorate the organization’s 25th anniversary. Held at GUE headquarters in High Springs, Florida, where it was founded by a group of cave divers founded in 1998, the organization convened instructors and divers from all over the world to recall the people and diving technologies that shaped GUE, how they’ve changed over time, and how they’ll evolve in the future.

In addition to celebrating the occasion, GUE convened speakers to present on topics related to its three biggest priorities: Exploration, Education, Conservation.

Shipwreck explorer Mario Arena, for example, gave a presentation on the “Battle of Convoys in the Mediterranean,” his 16-year project discovering and documenting dozens of shipwrecks left behind by the three-year-long battle during World War II and how his team is bringing the wrecks back to life using new technologies.

Cave explorers Fred Devos, Julien Fortin, and Sam Meacham gave a presentation on their efforts to document Ox Bel Ha, the largest underwater cave system in Mexico, a project which is concurrently celebrating its 25th anniversary. The project started out with, as Meacham called it, “two chainsaws, a compressor, and a horse,” and has begun to resurvey 144 square miles of caves with advances in diving equipment. Advances as simple as upgrades to lightbulbs and batteries, for example, enable the explorers to see through new passages.

Bill Stone, a cave explorer and head of Stone Aerospace, discussed “Recent Advances in Machine Exploration,” chronically how he’s used machines to explore underwater caves farther than any human. Stone’s autonomous drone, called Sunfish, uses sonar mapping to produce 3D maps and models deeper than photogrammetry divers can dive.

Ulrik Juul Christensen, a founder and chairman of Bonaire’s Area9 Mastery Diving Research Center, is developing an adaptive learning education platform for GUE and has spent about as much time as the organization has been in existence building education technologies. Christensen’s talk, “Learning That Matters,” focused on how to create new systems to help educate learners at their own pace so that knowledge, and not speed, is the priority.

In a complementary presentation, Sean Talamas, a managing partner and executive coach at leadership development consulting firm, discussed “The Depth of Character: Cultivating Grit, and a Growth Mindset.” The presentation focused on research by Angela Duckworth suggesting success is not achieved through talent, but a combination of passion and persistence she called “grit.” 

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GUE Instructor Trainer Andrea Marassich gave a presentation on “Building Capacity for Extreme Explorations” about the Sa Conca e Locoli Cave Project in Sardinia, Italy. Learning, he suggested, happens when you go out of your comfort zone, but not all the way to what he called the “panic zone,” where you are overwhelmed to the point that you don’t learn but instead shut down and it becomes extremely dangerous.” “You need a mentor,” Marassich said. “Someone who knows you enough to push you when you need to be pushed and pull back when you need to pull back.” 

These were just a few of the education- and exploration-focused presentations. Speakers also included Blue Green Expeditions Managing Partner Faith Ortins on how divers can support environmentally conscious destinations, Peter Gaertner on citizen science conducted in the Caves of Gulf of Orosei project, Daniel Ortego on the Marine Genome Project, and Neal W. Pollock on the physiological limitations of technology in diving. 

Max Deco & Bubble Trouble entertained conference attendees at the Friday night social with a pre-dive playlist of classic rock. Band members: John Kendall vocals, Gary Franklin vocals, Bill Stone lead guitar, Andrew Dow guitar, Francesco Cameli bass, Michael Menduno bass, Jason Cook drums.


You can find the full conference photo album here

InDEPTH: GUE’s 25th Anniversary Timeline-Picturing 25 years of Global Underwater Explorers.

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

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