Hollis Prism II CCR

PRISM Enter the

The Hollis Prism II closed-circuit rebreather has gained CE approval, and as it goes on sale across the UK, Mark Evans headed to NDAC for a trydive on the unit

PHOTOGRAPHS BY JAMES NEAL AND PAT HOLLIDAY

Closed circuit rebreathers, or CCRs. These are undoubtedly cool pieces of kit. Maybe you dive one yourself already, but if not, most of us will have seen divers on CCRs at our local sites or on dive boats with us. They look daunting, complicated pieces of kit, and they do require a particular mindset to dive them safely – but are they as dangerous as some people make out? I am always a bit dubious when a piece of diving equipment warns you, in no uncertain terms, that diving it without the proper training will lead to your death, but that is what you find emblazoned across most closed-circuit rebreathers, some in a more in-your-face fashion than others. Add to this the sad fact that many of the diving fatalities I have had to write about over the years have involved CCRs, including longtime Scuba Diver contributor and friend Gavin Anderson, who tragically died while diving his rebreather off Scotland.

Combined, this was enough to have me steer clear of CCRs. I may have been diving for over 35 years and have thousands of dives, but I just didn’t feel that going the CCR route was right for me, although I could see several massive advantages when it came to underwater photography in particular – no noise, no bubbles, and extended dive times.

However, over the years, technology has been steadily advancing and there are more and more CCRs coming on to the market. And I finally succumbed when so-called ‘recreational rebreathers’ were released, qualifying first on the Poseidon MK6 CCR, and then the Hollis Explorer eSCR. Both units had their plus points, but both also had their negatives. I got on better with the Explorer, taking it on trips to the Red Sea and up to the Orkney Islands, where it held its own on a boat full of technical CCRs, as well as diving it around England. It was easy to set up, felt quite small and compact on your back, and it looked cool, with its Stormtrooper-esque backplate. However, I had nothing but issues with the electronics, both the main ‘brain’ and the handset, and this seriously knocked by confidence in the unit. Suffice to say, neither the MK6 or the Explorer had enough allure to draw me away from my trusty open circuit rigs. When I had qualified on the Explorer, my instructors were trying to tempt me on to its technical sibling, the fully closed circuit Prism II, but at the time it was not CE-approved and I was not ready to take that step.

Fast forward several years and it’s all change. Hollis – along with Oceanic – is now owned by Huish Outdoors and sits alongside brands like Zeagle, Atomic Aquatics and BARE. The Explorer is no more, having been discontinued, and the Prism II is the flagship CCR – and it has just recently received CE approval. The COVID-19 pandemic delayed the Hollis Prism II trydive event, but in early July, I made my way down to NDAC in Chepstow ready to give this CCR a run in the quarry waters.

The other nifty thing about the Prism II is the fact that it can be configured with front-mounted counterlungs or back-mounted counterlungs

I have always liked the look of the Prism II ever since I first saw it at the DEMA trade event in the USA. It is quite compact, and with the clip-on cover, looks rather sleek, and I was looking forward to learning more about it and actually getting it in the water.

Trevor Leyland from Rebreathers UK (distributors for the Prism II in the UK, Ireland and the EU) was heading up the team, and he’d drafted in various instructors from around the country to assist with taking myself and other members of the diving press for our trydives. Lucky for John Crawshaw from Dive Manchester – he had the privilege of taking me in!

The Hollis Prism II is a fully closed-circuit rebreather, which can be electronically or manually controlled, which means you, the user, can choose how you want the loop PPO2 maintained. I know that many CCR divers like to ‘fly’ their units manually, and not rely on electronics, and given some of my past experiences of rebreather electronics, that doesn’t surprise me, but the Prism II uses a tried-and-tested Shearwater Petrel as its handset, which filled me with a lot of confidence. Kudos to Hollis – they could have spent thousands developing their own handset, but at the end of the day, when someone else has made a very well-regarded unit, why not make full use of it?

The other nifty thing about the Prism II is the fact that it can be configured with front-mounted counterlungs or back-mounted counterlungs. I usually dive in a travel wing, and don’t like having a lot of clutter around the front of me. The MK6 I dived had front-mounted counterlungs, whereas the Explorer had back-mounted counterlungs, which probably explains one of the reasons I preferred the latter. For the Prism II trydive, I was using a unit fitted with back-mounted counterlungs. Both examples were on display, and personally, I would definitely go for back-mounted over front-mounted every day of the week.

Whichever version you go for, you will be astounded by the ease of the breathe – the Hollis Prism II has got the lowest work-of-breathing of any mixed-gas CCR on the market. I hadn’t dived a CCR for over three-and-a-half years, yet this smooth breathe, with seemingly little resistance, instantly became familiar and was an extremely pleasant experience.

During the day, Trevor took us through a short presentation detailing the history of the unit, and some of its USPs. As well as the aforementioned Shearwater handset and the option of front and back mounted counterlungs, the Prism II also uses standard hoses throughout, so no special fittings required, and it also uses standard, easily obtainable batteries. Another neat feature is the clear ‘bucket’ that mounts the radial scrubber. This is clear, so you can easily see that one, there is a scrubber actually in there, and two, whether there are any issues, such as water ingress, etc.

The oxygen regulator

Conducting a pressure test

All smiles before going into the water

The Prism II ships with a DSV (dive surface value) as standard, but you can get a BOV (ballout value) featuring a high-performance regulator as an option. I had a version of this BOV on the Explorer I used and it was an impressive little unit. Our trydive units were already built up, but Trevor stripped down one of his units so we could see how it goes together. Everything seems to be robust and well-made, and you can tell that a lot of thought has gone into its construction. Just little things, like the fact that the metal clips that hold the top on the scrubber ‘bucket’ cannot be opened once the diluent and oxygen cylinders are in-situ, and that the first stages have been specifically designed to aid hoserouting into the CCR.

Statistics show that the vast majority of CCR deaths are down to human error, not a problem with the rebreather itself. Take check-lists, for example. On both my rebreather courses, we referred to a checklist every time we built up the unit to ensure that everything had been correctly configured and confirmed. When I did the trydive on the Prism 2, John and I ran through a check list step-by-step – and even Trevor, who has been diving the unit for more than eight years, said he still uses the check list during preparation. It is better to be safe than sorry – you only need to miss one single thing and it could be potentially fatal – yet I have witnessed people prepping their CCRs and going diving without a check list in sight. At the end of the day, it is all down to personal choice – but given many deaths are down to the oxygen cylinder not being turned on, the scrubber not being correctly fitted and other elementary mistakes that would have been picked up and dealt with when using a check list, is it worth the risk?

Back to the actual trydive. Remember I said I got used to the breathing action of a CCR quickly thanks to the low WOB of the Prism II? The same couldn’t be said for my buoyancy! You really are back to being a beginner again when you move on to a CCR, regardless of how many recreational and technical open circuit dives you have done. As an open circuit diver, once we are neutrally buoyant, we can go up and down by breathing in and out. After years of open circuit diving, this becomes a very natural thing to do. However, this all goes completely out of the window once you move on to a CCR. Breathing in and out makes absolutely zero difference to your buoyancy, as the gas in the breathing loop is either in the counterlungs or in your lungs.

Cue lots of swearing when you first start diving on a CCR as you crash into the bottom, or swim into a rock, as your ingrained habit of breathing in to arrest your descent, or to rise up over an obstacle, makes no difference. You soon start to get to grips with remembering to use your wing and/or drysuit to control your buoyancy, but as soon as you begin to relax a bit, that muscle memory comes back into play and the swearing starts all over again. Suffice to say that John had to patiently hover while I swore and cursed as I got used to diving a CCR once again.

When you are diving a CCR, you have to be bang on your game monitoring what gas mix is in your breathing loop. CCRs like the Prism II have oxygen sensors, but you still need to be monitoring what the handset is showing you on its display. When diving a CCR, the gas you are breathing can kill you if the partial pressure of oxygen in the gas is too high, or too low, or if the partial pressure of carbon dioxide is too high. Your CCR should give you a warning on the computer screen and on the heads up display, but you also have to notice and react to these warnings. Thankfully, the screen on the Shearwater is extremely clear, and I just got into the habit of glancing at it every minute or so to check all was well, but it is comforting to have the HUD right there in front of your face showing that nothing is amiss. When there is an issue, it is blindingly obvious, and the displays on the handset and the HUD leave you in no uncertain terms that there is something that needs your attention.

WHY DIVE A CCR? So if CCRs are this complicated and require this much effort and concentration to dive them, why would you go down that route? Well, there are many reasons people opt to dive CCRs. Photographers and videographers love the fact that CCRs are completely silent, so you can closely approach your marine life subjects without spooking them, and the vastly extended bottom time means you can spend longer getting those perfect shots or footage. However, the big winners with CCRs are technical divers. Closed-circuit rebreathers allow tech divers to make deep, complex dives in open water, and in overhead environments like caves and wrecks, which would just not be logistically possible on open circuit due to gas demands. And with the ever-rising costs of mixed gases, a CCR can essentially pay for itself within the space of a dozen or so dives, as you use a fraction of the gas you would on open circuit, so that initial purchase price – the Hollis Prism II is £8,449 without cylinders / £8,798 with - does not seem so out of this world.

Silent diving on the Prism II Mark soon got to grips with the unit

Checklists are vital on a CCR

CONCLUSION So, has this changed my mind on CCRs? Well, yes and no. Learning to safely dive CCRs needs extensive training, and while you are diving on one you need to be constantly vigilant, monitoring the gas in your breathing loop. More so, you need to be prepared for the more-intensive regime of cleaning and preparation that is needed both before and after a dive on a CCR. If you have the right mindset, and commit to the strict routines required to dive them safely, CCRs can open up a whole new world to you. If you are not the sort of person to be absolutely fastidious in your preparations and cleaning regimes, or willing to accept that you are going to be essentially a beginner again when you first start out, I’d suggest that CCRs are not for you and to stick with open circuit.

I would say, if you are tempted to go down the closedcircuit rebreather route, take your time and look at all of the different units on the market. Talk to instructors on the different models, get their take on things, and then once you have narrowed down your selection somewhat, go for trydives to see what they are like in the water for yourself. If may well be at this point you decide that a rebreather is not for you, or you may just be bitten by the bug. I was certainly impressed by the Hollis Prism II – the work of breathing is phenomenal, the build quality is first rate, and it doesn’t feel cumbersome on your back (I’d equate it to twin 10s). So, who knows what the future might hold… n