The Editor says: Sidemount and cave diving hold an irresistible fascination for divers, yet they remain an uncharted territory — one that demands not only a considerable financial investment, but also a level of technical skill and mental fortitude far beyond what recreational diving requires. Detailed sharing about cave diving and technical diving is scarce online, which only deepens the mystique surrounding the technical diving world. We'd like to thank Coach Ryan Chan of 百鬼夜行 TEK Dive Team for sharing his insights and helping us better understand the world of cave diving.
A Personal Take on the Toddy Style Sidemount System!
"It doesn't matter where Turks & Caicos is. What matters is that the ocean there marks the end of one wish and the beginning of another story." —R.C.
In the summer of 2014, I earned my Open Water Scuba Diver certification. On the boat heading back after my final ocean checkout dive, I chatted with my Canadian instructor, who mentioned casually going down to 52m on a single air cylinder with a friend. I told him: that's way too dangerous — I should just be a recreational diver and leave it at that. Then, when I started doing decompression dives, I told myself again: this is far enough. Just push my open-water depth limit a little and call it good. Cave diving, wreck diving — all that stuff is too dangerous. Better leave it to those lunatics who've lost their minds and don't value their own lives!
Later, in Mexico, I completed a full cave diving course with my French instructor. I let out a quiet sigh, thinking: I've come so far, and I've finally reached the finish line... Then, somehow, I became a Hypoxic Trimix Diver and a Cave Surveying Diver. I started detaching cylinders to squeeze through impossibly tight passages. A 100m dive became just another fun dive. These days, I no longer say there are types of diving I'll never do — because you never know where fate will lead a diver.
Toddy Style Sidemount Equipment
What I actually want to talk about today is gear selection, because the path I've walked as a diver — including a few costly detours — has taught me a great deal. Looking back, if someone had stopped me from buying equipment I'd only end up using for a short while, I can't imagine how much time and money I could have saved, and how much faster I might have progressed. That said, having hands-on experience with so many different setups is precisely what allows me, when teaching, to speak from personal experience to my students — the ones I'm enthusiastically steering toward technical diving — and give them a concrete, well-rounded picture of the pros and cons of various gear configurations.
Over the years of diving, I've come to know a great many outstanding technical divers around the world. Because of my own love for cave diving, a significant portion of my circle consists of cave divers, cave explorers, and cave instructor trainers. Around April of this year, I had a conversation with four well-known cave instructor trainers from different countries, regions, and training philosophies, and the topic turned to one specific piece of equipment: Toddy Style Sidemount.
Let me give a brief introduction to Toddy Style Sidemount (TS) using my limited knowledge. This isn't an entirely new concept — OMS had made something similar, the so-called "sandwich" sidemount system, much earlier. But it was the renowned cave explorer Thorsten Waelde (Toddy) who, in the late 1990s, returned to Europe after completing his cave instructor training in Mexico and found that the Mexican-style sidemount setup had certain limitations in the cold-water, drysuit-required environments of Europe. So in the 2000s, he began refining this sandwich-style sidemount — a design where two metal backplates clamp around a bladder. The metal plates serve two purposes: to add the extra ballast needed for drysuit diving, and to constrain the bladder's longitudinal expansion when inflated in confined spaces. Beyond the harness configuration, Thorsten Waelde also developed his own distinctive ideas about hose routing — for example, running all second stage regulator hoses at 1m length with 90-degree elbow fittings. I won't go into further detail here, but if you're interested, I'd recommend listening to Episode 24 of Steve Davis's Speaking Sidemount podcast, which features an in-depth interview with Thorsten Waelde.
Alright, back to my discussion with four cave explorer friends about the Toddy Style. First, the advantages. For those of us who dive sidemount in caves, switching between different gas source configurations always requires some adjustments. For example, the setup for OC (open circuit) with S80 cylinders is quite different from a sidemount CCR configuration. As one of my friends explained, the Toddy Style is primarily designed to work with the T-REB sidemount CCR, and when switching between OC and CC, the equipment adjustments required are apparently not too extensive or complicated. And the dual-backplate sandwich design does genuinely allow divers diving in cold water with drysuits to integrate the necessary ballast into the main rig rather than adding extra weight externally.
Image from the TOBBY STYLE official website
The advantages of the TS sound pretty compelling — so I kept thinking it through. The first question I asked myself: how many dives a year do I actually do in a drysuit? This might be something worth reflecting on when you're choosing your gear too. If you dive primarily in a wetsuit — or don't own a drysuit at all — do you really need to be carrying two metal backplates that cannot be removed underwater? And suppose your bladder leaks and fails, and you need to use a surface marker buoy (SMB) as a backup buoyancy device — can your SMB generate enough lift to overcome the negative buoyancy of two metal backplates? If so, how fully inflated does it need to be? How much drag does that create in a current? And how much extra gas — and energy — does all that drag cost you?
The second question: when I'm diving in R4/R5-rated (Note 1 / Figure 2) extremely tight, confined passages, a soft bladder offers the flexibility to compress and expand with the space. Would rigid metal backplates create a risk of getting wedged and stuck? In a space that small, you have almost no room to move your limbs at all — forget about self-rescue. You might be able to use one hand, barely, to pull yourself along the rock face; you can't kick your fins, and you'd better not, or you'll kick up silt and endanger your dive buddy. Of course, Thorsten Waelde is a far more experienced cave explorer than I am, and he mentioned in the interview that he's never had a problem getting stuck. I believe him. But I'm not him — I don't have his experience, and I certainly don't have his mastery of the TS system. What about you? For wide-open confined spaces, my first choice would be a Mexican-style sidemount setup, and my second choice would probably be back-mount doubles.
R4-rated tight passage
Don't think this has nothing to do with you because you'd never dive in tight caves. Trust me — if you've read this far, you know I used to think exactly the same thing.
Speaking of experience, that brings me to my next concern: training quality. If I were ever committed to using the TS sidemount system, I would go directly to the inventor himself for instruction. For one thing, I simply haven't seen anyone in the areas where I regularly dive using this system. Even if I happened to dive alongside someone who uses it, I wouldn't understand their emergency procedures — so if something went wrong underwater, what would I do? For the sake of my own life, I would never seek instruction from someone nearby who claims to be an instructor but has insufficient experience with this specific system. Such individuals may be far more passionate about selling the equipment for profit than they are skilled or experienced. But I believe the inventor himself could answer my questions and offer concrete solutions and recommendations.
One specific technical detail that concerns me: the cylinder bungee attachment configuration relative to the waist band and the height of the hip D-rings. That setup would be perfectly fine when using steel tanks — as is common in Europe or Florida — but when using aluminum tanks that become positively buoyant as gas is consumed, I imagine it would be quite difficult to maintain the cylinders in a horizontal trim. (I have official photos — if you're curious, feel free to message me privately; I won't post them publicly.) And if you're diving in a cave or any other confined space, and your technical diving instructor tells you that sidemount cylinder trim doesn't matter — I can say with near-certainty that either they don't know how to teach it properly, don't understand it themselves, or are simply not being straight with you.
Logically speaking, the TS system isn't a new sidemount concept that emerged in the last couple of years. Given its adoption rate over the years, it can hardly be called a new trend either. So why has the vast majority of the world's cave diving community not chosen it? For those who want to explore this further, I'd suggest looking up discussions about the TS sidemount system on the international Scubaboard forum — the consensus is fairly one-sided. Then again, maybe people simply don't understand its merits yet. On that point, I don't know enough about it to offer much of an opinion.
On the subject of adoption rates, here's a comparison worth making. By contrast, the British-style sidemount, the Mexican-style sidemount, and the Florida-style sidemount have all been tested, refined, and proven through years of hands-on experience by countless cave explorers across a vast range of cave conditions. They have significantly higher usage rates, more systematized training frameworks, and a more established instructor pool. Practically speaking, which system — from the perspective of after-sales support, training availability, and overall accessibility — represents the safest and most convenient choice for me right now?
And more importantly, I'd encourage everyone to invest in gear you won't need to replace — money is hard to earn.
I genuinely believe no cave diving equipment inventor would create something pointless. I'm certain the TS is capable, well-designed gear. There may also be advantages to it that I haven't yet come to appreciate. But right now — whether for recreational or technical diving — I have too many other equipment options that are safer, more convenient, and easier to understand. Perhaps one day, if the TS undergoes a truly breakthrough development that solves a critical problem no existing system can address, I'll consider getting to know it more seriously. Although all four of my cave diving explorer friends from around the world don't use TS and aren't considering it either — who knows? Even though the TS hasn't become the choice of the majority of cave divers in over a decade, what might change in the future with aggressive marketing and promotion from retailers? We'll just have to keep watching.
Note 1: R = Restriction (confined/narrow space) R1 = Passable — barely — with back-mount doubles R2 = Back-mount doubles cannot pass; only sidemount divers can get through R3 = Sidemount diver can just barely pass without detaching cylinders R4 = Sidemount diver must detach some cylinders to pass R5 = Sidemount diver must remove all cylinders (No Mount) to pass
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