Semi-closed circuit rebreathers are a cheaper and more accessible alternative to closed circuit. New boy John Liddiard is happy to dispense with most of his bubbles in Bonaire but finds he could do with an extra hand.
Like most UK divers, I have been thinking about rebreathers for quite a while, but never got round to doing anything about it. As a photographer, I like the idea of emitting fewer bubbles and the prospect of getting closer to big fish is attractive. Other rebreather benefits such as lighter equipment, nitrox, extended duration and warm gas would be nice, but in many ways offer me little more than convenience over open-circuit scuba and a thicker diving suit.
With fish pictures in mind, I was really looking at overseas use. I already carry more than enough camera and diving gear on foreign trips without having to ship a rebreather as well, so having the equipment available for rental locally is a prerequisite if I hope to put any training to good use in the future.
In this respect one type of unit dominates, and that's the semi-closed circuit rebreather (SCR) in the shape of the Dräger Dolphin and earlier Atlantis. Dräger rebreathers are available for rental at various dive resorts, and even on liveaboard boats.
Back off or breathe
Having analysed my objectives, I ventured to Captain Don's Habitat on Bonaire and TDI rebreather instructor Jack Chalk. Jack is Diving Operations Manager at the Habitat and has been using rebreathers since his US Army days in the early 1970s.
To warm up for the course, I started with a few days of open-circuit diving. Bonaire has many visiting divers and one would expect the fish to be used to us, but feeding them is illegal and they are certainly not tame.
Large fish such as groupers are still quite nervous about a diver approaching closer than within 2m or so. It is not our size that bothers them, but the noise of our exhaust bubbles.
On open-circuit I applied my usual fish-stalking technique. By holding my breath and sneaking in with a long lens, I was able to get close enough to take one picture at a time before having to back off or breathe and scare the fish away. Things were going well, and by the start of the rebreather course I was feeling a little sceptical. Would a rebreather really make any difference?
The course started with classroom work: a mixture of theory and practice assembling and testing the equipment.
I was amazed at just how simple the whole thing was. A hard shell protects exhale and inhale breathing bags connected via a scrubber canister. The inhale bag is fed with nitrox from what is effectively a second-stage demand valve with a controlled leak. A standard first stage fits on a cylinder of nitrox that lies across the diver's back.
The scrubber removes carbon dioxide from exhaled gas, as fresh nitrox is trickled into the system to make up for consumed oxygen. An exhaust valve similar to that fitted to a drysuit automatically vents excess gas from the breathing loop.
In practice, the amount of oxygen in the bag is less than that supplied from the cylinder. For example, with 50 per cent nitrox in the cylinder, a diver making a relaxed swim would end up breathing a mix of about 40 per cent.
With appropriate nitrox mixes, the Dolphin can be used to a maximum depth of 40m. Compared to a fully closed-circuit rebreather, on which maximum depth is not such a consideration, this is simplicity itself. There are no separate cylinders of oxygen and diluent, no electronic control systems needed to monitor oxygen levels and inject fresh gas, and no redundant electronics to watch the first set in case it malfunctions.
The only electronic feature of the Dolphin SCR I was using was an optional oxygen monitor to warn of high or low oxygen levels.
Divers have been using SCRs for years without these gadgets, but it seemed an attractive idea to have something to reassure me that the mix I was breathing was within safe parameters.
Keep it simple
We started in the shallows and sorted out neutral buoyancy. Next came practice at removing and refitting the mouthpiece, which is more complicated than with open-circuit scuba because it has to be closed before removal to stop water getting into the system.
The only normal reason for this would be to bail out to a pony cylinder, the standard solution to all underwater problems with these rebreathers.
Simple exercises out of the way, we set off to the reef so that I could get used to the system and take some photographs. As this was my first dive on a rebreather, I had decided to keep the photographic side simple. I had a very wide-angle lens on my camera to get some basic diver shots.
Ups and downs
Lining up for a picture by a clean dome of brain coral, I breathed in to rise up slightly - and nothing happened. I had forgotten about the quirks of buoyancy control with a rebreather. With the breathing loop holding exhaled air, such control has to be achieved by fine-tuning the air in the BC.
I scrabbled to get some air into my jacket and avoid denting the reef. Coming round again, I could have done with a third hand to control my buoyancy while the other two were busy with the camera. I guess experienced rebreather-using photographers develop techniques to get round this problem.
I was just lined up for the shot when the audible alarm in the oxygen monitor went off. At just 15m, the oxygen partial pressure had risen above 1.3 bar. I ascended a couple of metres to reduce the PPO2 and clear the alarm before repeating the attempt - with the same results.
It was OK while I was swimming along and metabolising oxygen, but as soon as I simply floated to take a picture, the oxygen percentage I was breathing crept closer to that of the supply cylinder. These monitor and alarm accessories can be set for less frustrating levels, but this relatively new piece of kit had yet to be reprogrammed.
I was soon feeling confident enough with the rebreather to practise some fish-stalking. I found a large grouper resting in the shade of a soft coral and crept towards it.
Expecting it to bolt at any second, I got close enough for a photo through my 14mm lens, one not designed for fish portraits of anything smaller than a whale shark. The grouper flinched at the flash but stayed put.
Just a day before I had been congratulating myself on getting within a metre of similar groupers on this stretch of reef, perhaps this same specimen, and grabbing a single shot before scaring them away. Yet here I was less than half that distance from my subject, and staying there.
Jack approached the grouper from the other side. The only thing more likely to scare a fish than one diver getting too close is a second one boxing it in.
Now there were two divers on rebreathers much closer than a single diver could have got with open-circuit scuba, and the fish was just floating there, not seeming to mind the occasional trickle from the rebreather's exhaust port.
The next day, fate played a nasty trick. Bonaire was hit by big waves thrown off by Hurricane Lenny. Most dive centres were damaged and had to halt diving for several days. Jack apologised, but there was no way we could complete the course. He had a pier and dock to rebuild.
Never one to miss a diving opportunity, I rented a car and headed for the undamaged east coast. At Lac Cai I found a sandbowl full of enormous tarpon. Just relaxing and letting them get used to me enabled me to get in close, but they were still obviously nervous about my open-circuit bubbles. A photographer's dream, but also a bit frustrating now that I knew I could have got even closer with a rebreather.
By the time you read this I should have finished my SCR training with Current State Diving in a nice UK quarry. At least there is no chance of a hurricane getting in the way, and perhaps I'll get to stalk a pike or two.
GETTING THERE: American Airlines to Miami, then ALM to Curaçao and Bonaire. Other options include a direct flight from Amsterdam with KLM.
DIVING: The rebreather course was with Captain Don's Habitat Resort, www.habitatdiveresorts.com, and includes four dives and classroom teaching over a total of 2-3 days, at a cost of $400. Other diving was with Dive-Inn, www.diveinn-bonaire.com.
WHEN TO GO: Bonaire is normally good for diving at any time of year. Even with an unexpected storm, it was possible to dive on the opposite coast.
ACCOMMODATION: The Habitat, but there are plenty of hotels with friendly dive operations from which to choose.
QUALIFICATIONS: Bonaire diving is all fairly easy. Minimum entry requirement for the Dräger Dolphin rebreather course is a basic nitrox qualification.
FURTHER INFORMATION: Most resorts and operators on Bonaire have websites. Bonaire Marine Park at www.bmp.org has information on the park and links to other sites. For information on the Dräger Dolphin rebreather, try www.draeger.com (note the different spelling). Training in the UK with Current State Diving, 0117 9247030.
Appeared in DIVER - March 2000