After a long wait, our regular deep wreck correspondent Leigh Bishop finally gets his hands on the latest CE-approved closed-circuit rebreather. The Ouroboros may be difficult to pronounce, but it's British and purpose-designed for the sort of diving Leigh does. So he headed for Egypt to undergo the gruelling training course.
IT WAS FRUSTRATING when the new Ouroboros closed-circuit rebreather arrived, I hardly had time to lift the lid off the carbon-Kevlar case before having to catch a flight to Sharm el Sheikh. Along with other divers from around the world, I was heading to the Egyptian Red Sea to train on what promised to be the most sophisticated piece of diving equipment I had ever laid my hands on. I was full of expectation, but hardly prepared for the intensity of the training to come, including in-water skills I now feel I should have had under my belt years before. Our instructors were Kevin Gurr and Phill Short, both of whom had been instrumental in the design and development of this rebreather, as well as the popular VR3 dive computer on which its software is based. According to the manufacturer, 'the control-system setup, decompression modelling and alarm systems have been evolved from a system that incorporates a knowledge base and proven design for diver interaction with underwater computer systems. In addition, the modularity and reprogram-ability of the software systems provides a future-proofing of the system design'. Time will tell, I thought! If this all sounded very futuristic, the unit certainly looked the part. All I hoped was that it wasn't over-engineered, not to mention over-complicated. By the time the sun was setting on the first day, our group had become familiar with the basics of preparation and software operation and, with time left for a quick dive, the first production units entered the water. The Ouroboros rebreather features a completely back-mounted system, similar to the US military Mk15.5/16, and boasts improvements over other commercial units. The first of these is mechanical, in that it combines a more robust breathing loop (due to the internal counter-lungs) with armoured breathing hoses. Everything is protected within a carbon-Kevlar shell. The second is in the electronic computer systems for control, logging and decompression requirement analysis. The unit adopts a no-tools ethos, and has been designed with easy user preparation in mind. A self-packing scrubber means not having to tap the side of the canister for 10 minutes, so dives could be turned round very quickly indeed. Having said that, the fast turnround time is stolen back from you during pre-dive checks which at first seem to take an age. For safety, the solenoid, controllers and software power systems are independent of the breathing loop. Without metal components within the loop, internal condensation is also reduced to a minimum. Oxygen cells are positioned to avoid water contact, no matter what position the diver is in, thus reducing problems of water across the cell membrane. Moisture variations can reduce the life of cells, so if you are in a hot country you can simply unscrew the connecting jack plugs, remove the small bracket that holds the three cells at the heart of the unit, and slip them into your pocket to take back to your hotel. No special tools are required. The software is designed to draw minimal power from the batteries, and these are said to give at least 40 dive hours, depending on backlight use. All on-board electronics systems are powered by the sort of ordinary batteries you can buy anywhere. The unit incorporates a pair of 2 litre cylinders. You can specify larger ones but, as Kevin Gurr pointed out, the low-volume 3.2mm stainless pneumatics of the systems are designed for minimal gas usage, and the counterlungs also run on minimal volume. Two litre cylinders may be enough for most dives, but deep wreck divers and serious cave divers can supplement this simply by plugging in off-board gas supplies when required. I always liked the idea of a completely back-mounted rebreather that would relieve my chest and shoulders of all those counterlungs and pipework. How nice to wear a simple harness, as in the good old open-circuit days! But back-mounted rebreathers are renowned for having poorer hydrostatic breathing characteristics - that is, they make it easier to breathe out than in. An original factory-development Ouroboros I dived a year before had had uncomfortable breathing characteristics in some orientations, and I feared that this might not have been rectified in the new production unit. However, I have to admit that over the 15 hours I spent on the unit under water in Egypt, neither I nor the other divers noticed any problems of this sort. When the point was put, Kevin Gurr showed us the extensive work he had done on the design of the flow dynamics and work of breathing to compensate for any hydrostatic imbalance. I wasn't keen on the larger size of the breathing hoses and mouthpiece, perhaps because I'm accustomed to units with smaller hoses. The hoses, similar to those used in the pilot breathing systems, are protected by ballistic nylon and an internal stainless steel spring, designed to be crushproof and very durable. The automatic diluent valve kicked in nicely on descents and could be isolated when not required. Interesting also was the fact that off-board gas plugged into the unit is, like on-board gas, directed dynamically through the ADV or the solenoid, depending on whether it is diluent or oxygen. Another nice feature is the oxygen shut-off valve, which isolates the solenoid in the event of a failure and allows manual gas injection. In keeping with a philosophy of reliability, safety and recognition of variations in diving style, the Ouroboros can also function fully without the main electronics computer system. The unit incorporates an independent back-up ppO2 display system that shows both the milli-volts and normalised ppO2 reading for each cell. This alternative and/or backup system gives the diver adequate information on which to perform or complete a dive, manually controlling the setpoint through the manual O2 addition valve. A breathing circuit with a low-resistance work of breathing, dual back-mounted counterlungs, partial flood recovery and an efficient radial canister complete the system. The scrubber is of a radial doughnut design with a patented system inside to assist dwell time and molecular collision, which CE testing has indicated is 40% more efficient than on other tested scrubbers. Set high in the top of the unit, the positioning of the 2.7kg of lime seemed to make my in-water trim just right. I found myself using far less weight than usual. As the week passed, I became more familiar with the electronics. They had come far from the old development unit, especially the pre-dive check screens. On entering the water, a wet-contact activation system maintains a life-sustaining ppO2 if pre-dive checks have been missed, and there are also alarms to warn of the situation. There are 20 pre-dive check screens, and I did think this was a little over the top. But Kevin Gurr told me that he had designed at least 16 of these functions after studying serious rebreather incidents, in the hope that Ouroboros users wouldn't make the same mistakes. After you have made your way through all the checks, and done a five-minute pre-breathe to activate the chemical reaction and check for CO2 breakthrough, the systems divert to operational mode. If I was dissatisfied, it was at the point when I was warned not to dive because of a system operation fault, and told to check the alarm screen status. On doing so, the system appeared operational, and it cleared as I entered the water. Two days after I returned home, Kevin had posted on the Ouroboros users forum that a new upgrade had identified the software bug I had encountered. All I would have to do was drop into the factory in Dorset for my upgrade - a slight inconvenience but, I guess, one advantage of buying a British product! Each training dive began with an open-circuit bail-out test on a wreck before the instructors familiarised us with the main skills. One morning, for example, our Emperor Divers liveaboard moored over the Thistlegorm, and we were able to assemble on the topgallant forecastle for a skill session before exploring the rest of this famous wreck. The first skill would be a hypoxic drill simulating the ppO2 in the loop dropping below a sustainable level, assuming that the solenoid or manual injection had failed and that visual and tactile alarms had activated. The alarms are incorporated into a heads-up display (HUD) as well as the primary electronics, and vibration in the mouthpiece is activated. As my experience grew over the week, so did my confidence in what I originally perceived to be a complicated device. If an alarm went off during a dive, instead of falling into an alert state of panic, I would simply check the alarm status screen, and deal with the situation as the unit maintained function. For example, the stack countdown timer alarm would go off to remind me that I was nearing the end of my scrubber life. The HUD light would remain in alarm status, though the vibrating alarm could be deactivated. All alarms relating to serious issues would re-activate after a predetermined time, or if the status changed. High-pressure rubber contents hoses, especially oxygen ones, are regarded as a weak point on rebreathers and have been known to cause serious fires if they burst. Ouroboros electronics incorporate high-pressure transducers accurately monitoring cylinder contents on the wrist computer - so no hoses! Of course, the disadvantage of this is that, in the unlikely event that you should lose your electronics, you would also lose awareness of your cylindercontents. In theory, if this happened a qualified diver would abort the dive, and have enough gas left to complete it. When I deliberately purged the manual diluent add button to simulate a high rate of diluent usage, another alarm gave me a warning. A neat little alarm, I thought, especially if you should be unaware of a loss of gas from the unit because it is out of sight on your back, or if a leak should develop during pre-dive checks. All alarms are recorded, and the system's memory can be downloaded from the electronics pod to the diver's laptop computer for analysis. The software details the entire dive, from stack temperature and usage to ppO2 levels and even whether you aborted the five-minute stack pre-breathe. Beware, big brother is watching! There were numerous electronic features I continued to discover as the week passed, and when a period of time went by under water without any menus being activated, the average ppO2 reading from the cells was enabled as a full-screen screensaver. Another screen I discovered gave me an abundance of information about what was going on, including what the ppO2 of the programmed diluent should be at my current depth! I could use this facility should I need to identify a problematic cell reading - should the system's intelligent computer not already have sorted it out and disabled any 'rogue' oxygen cells. A skill incorporated into the Ouroboros module one course is flying the unit on the HUD without using the primary electronic controller or back-up passive O2 display. A neat arrangement of LEDs mounted on the diver's mouthpiece behind obvious marked displays shows alarm status, decompression and both solenoid and oxygen information. As we gained experience, we got used to flying the unit by the HUD alone. On what were truly silent night dives along the reefs, the brightness could simply be adjusted during the dive. Rebreathers come into their own on the reefs, giving wildlife photographers a serious advantage. We were able to interact endlessly with turtles and all manner of interested creatures. Over the week, the primary diving skills required to use the Ouroboros were accompanied by some testing in-water survival skills. My first closed-circuit dives were made in the early '90s using the Prism, then on the Inspiration and also the Cis-Lunar MK4. I've done a lot of CCR dives - so what, I asked myself, was left for me to learn in the water? Well, I'll admit it - quite a lot. These guys really put me through my paces, and if I thought at any time that I wasn't being watched, I was wrong. Phill Short even had a mirror to spy on his students as he led them round those Red Sea wrecks, I later discovered! Kevin had chosen Egypt for the first Ouroboros course because the environment and predictable weather allows more in-water time (precisely why DIVER tends to test gear in such locations). This raises the question of taking your unit on a plane. The weight of it in its case is 32kg, right on the limit of baggage-handling but not too big to send you to Oversize Baggage. The Ouroboros costs a hefty£8000, but this is no entry-level rebreather but one that is attracting the attention of serious technical divers. Its detailed failure mode analysis gives it multiple redundancy paths. Canister design, gas-handling and decompression are optimised for deeper diving, so overall are suitable for all levels of diving. The build quality and functionality would seem to justify the price tag. 'I wanted a unit where I could concentrate on deep cave penetration, navigation and scootering,' French cave-diver Jerome Meynie told me. 'The Ouroboros is an interactive rebreather I would not have to monitor continuously with my hands, but would still be redundant with information which the HUD and vibrating mouthpiece would give me.' Carl Spencer, who led the Britannic 2003 expedition, was also on the course. 'I wanted a life-support system that was specifically designed for depth as well as shallow water,' he told me. 'Its scrubber duration will give me confidence in performance at depth, something I value when diving deep wrecks.' The course costs£600, and you have to complete 50 hours on the unit before you can access the trimix codes to allow it to compute with mixed gas, This is to ensure that users familiarise themselves with the unit in an air depth range. My own initial concerns over weight, size and ease of use of the earlier test units subsided as the week's training progressed and I grew accustomed to the final product. And I do like the fact that is British!