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The Who’s Who of Sidemount

Published

1 year ago

June 16, 2023

InDEPTH

Aleš Procháska

Aleš Procháska is the co-founder and chief technology officer (CTO) of Divesoft and was responsible for developing the Liberty Sidemount rebreather and CCR Bailout mode software.

What is sidemount to you?

If I’m completely honest, I was a bit shy about sidemount at first, because the profiles of the caves we were diving, didn’t really require sidemount. We got the strongest impetus to start developing sidemount from our friends who had gone very far into remote caves and needed to go further. Eventually I was convinced to get involved with my sidemount friend Tonda Ptáček who made a rough prototype, which he put together from a cut off waste pipe. He called it a “trough.”

What was it like?

When Jakub Šimánek and I tried it out, we had to admit that the proposed component layout was close to ideal. We wanted to maintain the presence of both cylinders to make the device completely self-sufficient. The placement of the counter lung above the cylinders compensates for the weight of the cylinders in front, plus it is in an ideal position relative to the centroid of the lungs, giving us a great work of breathing. This is aided by the fact that the counter lungs are not restricted by being enclosed in a tube. We let them “breathe freely”.

What were your considerations in developing the Liberty Sidemount?

Sidemount devices should be as compact as possible, and that always entails a degree of compromise. You’re dealing with a dilemma, whether to put cylinders on the device or replace one or both with off-board gasses. The cylinders are two liters instead of the usual three liters. That’s a limitation, but not that big, because it’s still enough gas even for challenging dives. For the most extreme dives there is the off-board option, and you still have the two-liter cylinder to spare.

For compactness, we also cut down on the water trap volume from the standard unit and redesigned the scrubber, saving a full 8 centimeters in length and getting us down to almost the size of an Al80 bottle. We wanted a completely self-contained unit from the beginning for many reasons, the unit can be completely handed over to your buddy or used as a bailout. Overall, in the area of miniaturization, and in general there are improvements to be made on all devices, but until a miraculous technology gets discovered, sidemounting will always be about balancing costs and benefits.

Was there an epiphany moment for you with sidemount?

When you develop a device from scratch, you have the disadvantage of doing the first experiments on yourself and your friends. When we held a Liberty Sidemount prototype test week in Croatia, none of us had our “Whoo” moment! We had some minor flaws in the design and were still looking for the best way to use the device. Every second dive ended with one or more units flooding. After that week, I sat back down at the computer with my collected notes and fine-tuned the design. In the meantime, I was diving on the back mounted unit and leaving further testing of the sidemount to Jakub, who fine-tuned the ideal way to wear and use the device. When I tried the device again after some time with the new setup, I felt incredibly free, gliding through the water with each flip of the fins. That’s when I fell in love with the sidemount.

What are the real challenges in sidemount rebreathers both in terms of manufacturing and user experience?

From a development point of view, the hardest part was working out the original concept and all the ideas we had so that everything was as compact as possible, everything fit together, it was easy to make and it was functional. I like clean and elegant solutions. I like to go down a path that no one has tried before to find a better and more efficient solution. I’ve always liked solving puzzles, and the harder the better. In the end, I think it worked, and I hope it shows on our unit.

From a user point of view, the attachment of the sidemount to the body is absolutely crucial. Its position affects the work of breathing and the comfort of the diver. This in turn determines many other factors such as gas consumption or the risk of flooding the device. When you clip it on correctly, you don’t even know you’re wearing it and that you’re breathing underwater.

Twin sidemount rebreathers—your thoughts?

That’s the way some divers have gone. The popularity of bailout rebreathers has grown incredibly over the last five years. Prior to that, only a few individuals around the world were diving with a double rebreather in any combination. Whereas today I would estimate it’s more in the hundreds of divers, and given its benefits, it’s no wonder. I dare say that this is also our contribution, as the Liberty Sidemount is ideal for this purpose.

In addition to the design itself, we have a software solution for the Bailout CCR mode, which idles the unit in terms of oxygen injection while in backup mode, and then switches automatically to standard mode the moment you start breathing from it. It also monitors your profile and calculates decompression based on the fixed set point method. This allows it to take into account the tissue saturation to date and calculate the decompression for follow-up even if you switch from one device to another.

And the double sidemount? Why not? The important thing is to always carry a sufficient supply of gas in the open circuit as a first response to an emergency, from which you will only subsequently switch to a second rebreather. You also need to clip those on somewhere too. This can be done either by clipping a small bottle, say Al 40, to each side, or by carrying a small twin, say 2×7 liters, on your back. Granted, this kind of defeats the purpose of a sidemount, but a small twin on the back isn’t that much of a burden and it simplifies a lot of things like immediate gas availability in an emergency and no collision with the perfect position of sidemount rebreathers. That’s up to everyone’s choice though. Anyway, two sidemount rebreathers are ideal in that all their controls are easily in your reach.

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