Rebreather Comfort and Efficiency

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. gas you loose from the loop when the body. So many things we If more than a deep breath is possible, it means that there’s too much gas in the you clear your mask or equalize should avoid at all cost. breathing loop. your ears. So many elements! Few diving skills are so essential, and Dry suit inflation. When the pO2 is yet so underemphasized by the spot on and the diver has enough rebreather diving community. gas to fill their lungs, comfort is ing the ascent. Most of the time, another important factor. That’s when you realized you start to Buoyancy control can be divided where the dry suit comes into the ascent too fast, it’s already too in three different phases: equation. Some divers need a late! Practising some skills should dry suit because of the water help you to fine tune your buoy- Buoyancy control temperature or because of the ancy. For all of them, do not use at constant depth: duration of their rebreather your hands to keep your balance dive, while others simply like or to maintain your depth. O2 injection. It might be the dry suit for its ability to give Buoyancy control during done manually or with a better trim. Dry suit inflation Relax and try to make as few descent: the help of a solenoid is most of the time just enough movements as possible. Controlling the buoyancy at a constant valve or a KISS valve. In to avoid suit squeeze at depth, depth and during the descent are very all cases, oxygen level without compromising the div- 1) Float for a few minutes in a similar, as long as the descent rate is is kept pretty much er’s buoyancy control, but slightly head down position slow. You have to find the right bal- constant in the some divers prefer to use while remaining within 30cm ance between: breathing loop and their dry suit as their main off the bottom or of the start- Positive buoyancy that directly affects buoyancy tool (to a certain ing depth if you’re practising in Manual/ADV Diluent injection your buoyancy. Kiss valve extent). It’s obviously a matter midwater (use a point of refer- O2 injection (KISS valve/solenoid/ of practise, experience and per- ence like a shot-line) manual injection) Optimal Loop Volume. A sonal preference. 2) Switch from CCR to open circuit Wing inflation rebreather diver should have back and forth without chang- Dry suit Inflation enough gas to comfortably Wing/BCD inflation. The wing ing depth Negative buoyancy: breathe from their loop. If more can certainly be used to control 3) Manually fly your rebreather Lead weights Booked Booked than a deep breath is possible, it one’s buoyancy (it was designed without changing depth Gas compression means that there’s too much gas for that!) but only when all the 4) Remain horizontal and station- Suit compression in the breathing loop. And too previous elements have been ary, hovering over a fixed point Gas lost during air space equalization much gas means more O2 injec- fulfilled. The more tools are used while focusing on another task and mask clearing tion to maintain a constant pO2, for buoyancy control, the more (like scrolling down the menu of The idea is to go down slowly in order more gas expansion/compression tools have to be managed dur- your computer or your handset) to control all these components.

86 X-RAY MAG : 16 : 2007 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED Wissit ing ea faciduis A few other skills might help you to Perform an ascent in a horizontal posi- in any direction with adion ut ullummy So it’s all about comfort! achieve this goal. tion. The proper positioning of the the least amount of nim dolenim do When rebreather divers discuss with open 1) Perform a descent in a horizontal posi- rebreather OPV (Over-Pressure Valve) energy (a.k.a. oxygen circuit divers, they always talk about the tion. Many divers have a problem to is quite important. The alternative is to consumption). You’ll be benefits of diving their favourite unit. control their descent rate in this posi- exhale off the loop to keep the loop comfortable and effi- Some speak about silence, lack of bub- tion, as they cannot use their fins to volume constant, despite the O2 injec- cient (less stress and bles, low gas consumption, warmth of slow down. tion (manual or automatic) during the drag). There are a Frog Kick the inhaled gas, etc. However one of 2) In a horizontal position, slowly descend ascent. In this position, venting the wing variety of propulsion Commonly used by cave the main benefits of open circuit SCUBA and stop within 50cm from the bottom should be done with the dump valve on techniques available and technical divers, the is obviously its simplicity, especially when or from any predetermined depth. the bottom of the wing, instead of the to divers. The experienced diver alter- frog kick eliminates the it comes to buoyancy control and trim. ADV/manual injection can be used, corrugated hose that requires the diver nates between different types of kicks to vertical component of a Compared to a rebreather diver, an along with dry suit and wing inflation. to be more vertical. reduce muscle cramping and to meet flutter kick. As the modified experienced OC diver will more easily be the demands of various diving environ- flutter kick is not really power- comfortable with their rig. Buoyancy control during ascent: Some skills that might be helpful to prac- ments. ful, it cannot be used in high When it comes to buoyancy control dur- tise: flow conditions or for very long Why? ing the ascent, rebreather divers have 1) Slow ascent with manual O2 injection Alternate kicks periods of time. Therefore, as Because most of the rebreather divers often more problems than their OC col- only First, by alternating between kick- the frog kick directs the water don’t really work on their comfort, their leagues. So many air spaces expand 2) Same ascent but eyes closed (shallow ing styles they allow themselves to up and back rather than down, trim, their balance, their streamliness, during the ascent that a lot of rebreather depth) rest certain muscles by using others. some divers use it most of the their propulsion or their buoyancy. It accidents are caused by uncontrolled 3) Slow ascent and simulated stops on Second, by varying a kicking style, an time. takes more time and it’s often more dif- ascent. Starting the ascent with only a Semi-Closed Rebreather mode. experienced diver can adjust their pro- ficult to achieve than in OC. But it’s like small amount of gas in the loop/dry suit/ 4) Slow ascent on Open Circuit (buoy- pulsion technique to the demands of Some skills to fine-tune your propulsion many things in diving. It’s worth the extra wing definitely helps this kind of ballistic ancy control of an expending breath- a particular environment; by switching techniques: work. I don’t know any rebreather who event. Here are some other skills: ing loop) from a frog kick to a modified flutter, the never had the feeling that their unit was 5) Slow ascent with all the bail-out tanks diver can minimize silting in a low and - Alternate between frog kick and mod- cumbersome and that their trim didn’t nearly empty. Simulated stops with silty area where the full movement of a ified flutter kick. need to be improved. Being comfortable tank exchange with a team mate frog kick is restricted by some walls or - Swim within 50cm from the bottom in a is a way to better enjoy the dive, but could also be a useful skill to practise. rocks. Those of you who regularly dive in silty area. it’s also a critical component of safety! 6) Slow ascent and stop at any pre- silty or overhead environments might be - While hovering horizontally, turn your By practising all the skills (and more) determined depth, using only manual concerned about reductions in visibility. body 360 degrees in each direction described in this article, one should O2 injection to maintain your pO2. A loss of visibility can substantially impact using only your legs (no hand move- achieve the Trinity of the comfortable both individual and team safety. To ment). rebreather diver: Trim, Buoyancy and Don’t cheat If your rebreather has an avoid the likelihood of reduced visibility, - While floating horizontally, back up Propulsion (or TBP). These three essential ADV, don’t shut it off and don’t turn the trim has the utmost impact. With a prop- slowly while using only your legs (no elements are more difficult to master with diluent tank valve off. You have to learn er, feet-up swimming profile and reason- hand movement). a rebreather than with a conventional how much gas you have to vent without able buoyancy control a good diver can scuba unit. But it’s just a matter of prac- completely emptying the loop. safely travel in wrecks and cave pas- tise. Practising emergency skills can save sages that are particularly susceptible to your life. Practising your TBP will only save Mastering Propulsion diver movement. As exhaust bubbles and your dive. Many people think they are Techniques percolation are normally not a concern efficient and look great underwater. A with rebreather divers, the main culprits short video session quickly changes their Now you’re not only horizontal of reduced visibility are errant fin kicks, opinion and their self-esteem. underwater, perfectly balanced erratic hand movements and poor trim. at all time, but you’re also Rebreather diving is all about time spent motionless exactly at the depth Modified Flutter kick underwater… you want to stay. Just add vari- Instead of the strong flutter kick used by ous efficient kicking techniques recreational divers (great deal of power and you’ll be able to move but also significant downward tur- bulence), the modified flutter kick is based on bent knees and kicks Gait num irilisc iduisi blan- from the knee, directing the water drem zzriure feugait volor upward. In extremely silted areas, The frog kick eliminates si tat loborperilit alis aliquat the modified flutter kick can also the vertical component Booked atet, con ut dolesed ectet, be done only with their ankles. of a flutter kick. consequis alit dunt dunt

87 X-RAY MAG : 16 : 2007 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED Irmis resente adducon verfeco nfirtem et istius, Cupiem labit, poruntintem cer in Itam efaut resulii ia enatuit, et deperte tebem. Is. Sernius vist L. Nihilicae, confecrebat viviverei pervissi tum cae horis inatis, essulicum ocapec consi tandum Pala se auctum hicioste firidie natastra? An sus corum ad re is. Bonsuperi ium nonscrio, tus, de tanunum te cri sa orudefa cieni- taberce rferum halabus consus aciam peroreci perfectodius nu que nos et; et, quem foric trae nius mis? La vivilina, qua mo tarterc enihil or imultus soltiliam videes vasdam pris quam terum esimand publiculica vit? Hilnest alareste auracri tera noratqu idesuli simuri pervirmium hebus, ventea renataret vid mentienam iendaciem et fir pratili iam, cone mis comanum enteatis talicia inatquid Catu vir auctum prideor li sene omne prox mis. Vive, Palat, actus la re ncludeatum tem ipiempe audenatum que vicus inprobus halatis hoc- nones cla restrium senihi, et L. Otiquam rfecte es vera res hos essi comandelut chui confecomne atu us consilis fauctuam esus vivivir mihicul- et cut alariorum cruro, crem cuscemq vivitam issenih ilicul terum. tius acchum terit; hebefer ferfernis, us a vis; inius? Senatiam. In in uonsulari spiendi Ximius ve, prorudetrae te que ina, concla nost ium orios cae ius, atiam faciorum utertam essendam merni- nonsit. noste tus conc re confeceri perfint eriti, inam. hilis fec omantium nosteatus tea ocum sentrum in patium ductem et C. Simis, Iferfirtum et forsulis. nonem, pribus patistatali publinatque C. Habesil halius, Furorum tem milicatus hos- tum addum Pat verta cum qua et L. Torus; iam senique qua tem audam tiss icauctus adductura Satu serfect abiterma, dii se, Ti. Potintea in silin vit. omnimus; num sen- apecienatum patquam nocam a movissitus etis con vium med Tore pat, nonverum inatu Image tus, Catertili, stam Image deffres? Opioraverum, per- rem cla adhuc me cont, nihilienita sen- cum ine te que invenat imilic tum omnicii ris, Catorsum consuloc rei trest? Nam firiben atanterum nirmis, iuspiem publi tere rei sen- pris pl. Cuppl. fest? iam mantil caedis ore se moverebulest L. Serudam ficave, tust alabus, vesimis furo Dis consu supio, morioribus re, voctus est? Ti. Endicii iam tem ocaurarica; neque habus ta ina, us simium maio, condam quam auterorbis, niam or fatrevidet quam, quo numus sentis, apes, nos estur la publi- poendesse am quo eri tum terentis vid ommorip timissenatus achus cononer- catil hocatiusciem teres! et intrae igna, etil Cupionvo, ad rest pessere emo convehe bemenatum pri tem ella Serdit vilicatum culis esin tella inat L. Aperes aus vidient ilicit? Ari et imili es vem ut fatidientem facci crum hores huideludam ina, moves orte cotil vilin sici- in vat, conum iuroris. An pervivehebem moraven atussendam hos, omprac fir la ium

88 X-RAY MAG : 16 : 2007 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED