This time last year I started my adventure as a KISS GEM rebreather diver. For those not in the know, the GEM is a Semi Closed Rebreather. This rebreather recycles two thirds of every breath you take, and one third gets expelled just like a regular Open Circuit diver.
I switched to this rebreather primarily for its buoyancy characteristics; the extended bottom time ’as you only use a third of your gas compared to your OC system’ is a nice bonus. Being motionless in the water is the goal every underwater videographer tries to achieve. It will improve your footage because your camera will be more stable. With an open circuit system your breathing will constantly change your buoyancy resulting in up and down movement in the water column. A rebreather captures your exhaled breathe in counter lungs thus not affecting your buoyancy. This feature is also the reason is why diving a rebreather is so hard to master. Looking back I can say that all the trouble and tribulation I went through to learn how to dive this system is worth it. With every dive I do, I am getting better, resulting in steadier camera work.
To learn how to control your buoyancy with the GEM rebreather you need to forget many lessons you learned as an Open Circuit diver. The biggest issue with the GEM is the placement of the counter lungs. Because the system can be attached to almost any BCD the placement of the counter lungs is somewhat of a trial and error approach. The placement of the counter lungs is going to determine how easy it is to dive the system. In the beginning your buoyancy is going to be the same as a diver who just got OpenWater certified. It is going to take perseverance to get both your buoyancy and counter lung placement sorted.
The manufacturer has guidelines for the placement of the counter lungs, but because everybody is built slightly different this can take some time. It took me a while before I could say that I had my buoyancy under control and my counter lungs in the spot where they should be. You also need to figure out where you are going to clip off things like lights or cameras as the two chest d rings are covered by your counter lungs.
To get certified on the GEM you need a nitrox certification and 50 dives under your belt. As any diving course it teaches you the basics. It would be a great idea to find a local GEM diver with experience to help you further after your certification. There are so many little things you need to know that would make your learning curve a lot easier. Somebody that has gone through the process and has solved all these issues can help you along much faster. I had to find out the hard way, as my instructor was in Seattle WA and I live in Vancouver BC. Rebreather World is a great site to get more information, but having somebody close to help makes things a lot easier.
Everything else is much the same as diving a normal OC system. The GEM uses a nitrox mixture of somewhere between 32% and 40%. It can be connected to almost any wing and harness style BCD, and you can use a normal scuba tank. Nothing special about the regulator required to supply the gas to your breathing loop. The two biggest differences between OC diving and the GEM are your buoyancy and the monitoring of your PO2.
Setting up the system takes a little longer and requires more attention to detail. I can set up my system in about 20 minutes with all required tests and checks. Breaking down the GEM takes about the same as a normal scuba unit. It is disinfecting and drying of the breathing loop that takes a little longer. I use a boot dryer to dry the loop and counter lungs. This all takes about 4 hours. But I normally don’t stand there and watch my gear dry.
After a year and about 60 dives I finally have the system dialed in. I dive a 120 cft tank and can do 5 to 6 one hour long dives on a single tank. I would not want to switch back to open circuit diving. The benefits that I have with the system out way all the issues I had to overcome. This system is perfect for recreational divers that want to take up photography or videography and anybody who has issues with their air consumption. In my opinion if you thinking about doing technical dives with deco or would like to go deeper than recreational limits this system is not for you.