technical Most of the articles one can find about rebreath- matters ers deal with potential problems and limits of these wonderful pieces of kit. They give extensive infor- mation about oxygen sensors, scrubber duration, electronics and any of the risks associated with this kind of equipment. Becoming proficient with the emergency procedures is a very important component of training and experience. Cedric Verdier But an aspect that is sometimes a little bit over- looked is how to properly dive with a rebreather. Text and photos: Cedric Verdier Additional photos: Peter Symes Rebreather Comfort And Efficiency 83 X-RAY MAG : 16 : 2007 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED They swim as gracefully as a grasshopper with a portable fridge strapped on its back and a vacuum cleaner around its head. Each rebreather diver adapt and to improve their units and how more O2 to to safely deal with all these modifi- move underwa- should have someone cations that they forget the most ter means having else taking pictures important skills any diver with any a shorter dive time and or video of their con- figuration to see how poorly kind of equipment should master. a higher CO2 production. Words like simplicity and ease disap- Both factors are counterpro- streamlined these handsets are. A peared from their vocabulary. ductive for a rebreather diver better routing and maybe a chock cord who wants to get all the benefits of using loop at the appropriate location should Being Streamlined such a complex piece of equipment. help to keep the cables close to the With A Rebreather body in any position (not only in a verti- Configuration and danglies cal position in front of a mirror!). Booked Very often, one can see a lot of rebreath- Most of the time, er divers who don’t move in a very rebreathers look SPG and LP hoses: in a similar way, a efficient way. They swim in a strange very bulky and rebreather is full of hoses pointing down- position, closer to the sea horse messy. The ward or bulging out when the diver swims than to the manta ray. They technical horizontally. Shortening the hoses is of spend a lot of energy fight- rebreather prime importance if you want to have Counterlung placement: OTS (Over-The- ing against the increased diver has a better configuration. And of course, Shoulder) counter-lungs often look very density of water, adding lots of hose unnecessary hoses and components are cumbersome compared to the back- drag and turbulence to and cable like pimples on a fashion-model’s face: mounted counterlungs where the chest the necessary energy one on their chest they should be immediately removed! area is clear. Nevertheless even OTS CLs has to spend for their pro- and their arms. rebreathers can be configured properly pulsion. Additional sling to diminish the cumbersomeness some- In one of his articles, tanks and poor how. CLs can be adjusted very close to Jarrod Jablonski states: configuration don’t the body, almost under the armpits, with- “Resistance increases as help to avoid the now out compromising the Work of Breathing the square of velocity. The popular astronaut-like image and the diver’s comfort. Quite the energy required to overcome this of the rebreather diver. It’s maybe opposite; when the diver has nothing resistance increases approximately as the satisfying to show that we can manage on their chest, they can move more cube of the initial energy required. What to dive with heavy and obviously very easily, closer to the obstacles or the Unfortunately even some experienced this means is that if one doubles the sur- complicated equipment, but it’s definite- bottom, with less drag and effort. rebreather divers are not comfortable face area of something, this results in a ly not streamlined and efficient. and efficient with their rig. resistance that is four times the original Balance and trim resistance; in turn, this requires an increase Handsets: most of the CCRs have one or Being able to achieve a horizon- Their equipment is a mess and you hardly in energy nearly sixteen times as great to two handsets that are attached to the tal position at all time (slightly see their face underneath 200 hoses, offset the increase in resistance.” diver’s forearm. A highly inelegant cable head down, feet up) is not one straps and D-rings. It simply means that a rebreather diver is connected to the electronics, most the cave/wreck diver’s dream. They swim as gracefully as a grasshop- (and all divers in general) should work to of the time on top of the canister or the It should be the main goal for per with a portable fridge strapped on reduce their surface area. An article pub- housing on the back of the rebreather. everyone but it’s definitely not its back and a vacuum cleaner around lished in DIVE Magazine a few years ago the case for a vast majority of the its head. When asked the reason why shown that lots of drag were simply cre- rebreather divers. A balanced rig they struggle for most of time they spent ated by hoses and danglies not as close A rebreather diver (and all would avoid the so common “butt- underwater, most of them finally agree as they should be to the diver’s body. The heavy” position. The ideal horizontal that their trim sucks! Rebreather divers are gas consumption of a CCR diver is directly divers in general) should work position mainly helps when you don’t most of the time so focused on how to proportional to their level of exertion. Using to reduce their surface area want to silt up a place. Many divers think they are horizontal underwater: it’s most 84 X-RAY MAG : 16 : 2007 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED The first step is to work on the rebreather Dry or wet suit: a dry suit generally gives back to land, have some fun discover- configuration: a better trim as it provides the diver with ing what you actually look like. Spot all some additional buoyancy on the legs. the danglies. Check what could be more Cylinder and regs: Some rebreathers It’s most of the time not the case with streamlined. Go back diving and repeat have the option to de-invert the tanks in a wetsuit (specially at depth with the the process till you become frozen. To order to shift some weight on top of the suit compression). Other equipments speed up this process, a friend of mine unit. like pockets or heavy fins (ie even uses a big mirror in his pool. You JetFins) have also to be directly see what could be adjusted and The sling tank is clearly too low!!! Trim weight: The rebreathers with a case considered. immediately try! Like a dancer in a ball- don’t have a lot of flexibility for their room. configuration. A trim weight can then be of the time not true. They are maybe added on top of the unit to offset the Mastering Buoyancy Control horizontal when they swim but slowly (or unbalance. Scubapro’s quickly!) come back to a more vertical Jetfin is a With A Rebreather position as soon as they stop swimming. Wing and backplate: A short wing with classic favoured So let’s assume that the trim is now a With a balanced rig you can stop close more lift on the bottom than on the top is by many, but it is problem of the past. The next step is to the bottom and stay horizontal even clearly a useful tool for a better trim. weighy Buoyancy. while doing a specific and difficult task Counterlungs: the position of the CLs is (tying some knots on a guideline, adjust- obviously important but their size is also Additional equipment: Most of the time, Buoyancy control is an essential element ing some settings on a camera/dive another factor to consider. A smaller vol- a rebreather diver will carry other pieces of diving proficiency; it is also one of the computer, helping another diver, etc). A ume and less gas (optimal loop volume) of gear like sling tanks and canister lights. hardest skills to master, especially with balanced rebreather is sometimes quite help to reduce the uplift component of The buoyancy characteristics of the tanks a rebreather. You have to control the difficult to achieve because most of the the vertical vector. (full or empty) and the lights have to be gas in the wing, the dry suit, the breath- units have the heavy components on the thoroughly checked as they can easily ing loop. You have to take into account bottom (valves, regs, etc) and the buoy- Then the second step is to see how the ruin a good trim so difficult to achieve! the suit compression at depth, the buoy- ant components on the top (counter- rest of the dive gear will interact with the Ask a friend who has a camera to spend ancy characteristics of the tanks when lungs, wings, etc). rebreather. some time with you underwater. Then, empty at the end of the dive, the effect Spot all the danglies. Check what could be more streamlined. Booked 85 X-RAY MAG : 16 : 2007 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED of oxygen automatic injection when the depth changes, more A rebreather diver should just have enough when you’re in the shallows, the buoyancy on the upper part of gas to comfortably breathe from their loop.