Reflections of a Rebreather Rookie

Rebreather scuba diver

This series of articles will talk about why I chose to go down the closed-circuit path, why I chose the rebreather I did, my experience training on the unit and then diving it the past few years. Please note my use of the first person; “why I chose …” not “why you should choose …” I’m not trying to convince anyone of anything.  I’m merely explaining why I made the choices I made. My choices apply to me and are not the best choices for everyone. I have been a certified CCR diver for 3 years and have about 150 hours on my rebreather. That puts me in a good position to offer a few thoughts on my journey thus far. I am still new enough to remember what it was like to take that initial leap into the great unknown but experienced enough to have gained some perspective.

First, a bit of my background to help you understand my transition from open circuit to closed circuit rebreather diving. I have been diving for over 40 years. I became an Open Water Scuba Instructor over 30 years ago and a technical diving instructor 20 years ago. You can certainly call me an experienced diver. I am certified as an Advanced Trimix Instructor. Living in the Great Lakes region of the US, wreck diving has become my obsession. I have done lots of very deep dives in very cold water, all on open circuit. When one of my friends heard I bought a rebreather, his reaction was, “Rick? I thought he would be the last open circuit diver on earth!” It is in this context you should consider my observations.

Even though many of my friends and dive buddies thought my CCR purchase came out of the blue, such was not the case. I had been contemplating the move for quite some time, years in fact. Before I talk about how I came to choose the rebreather I did, I should explain why I decided to switch to a CCR in the first place.

Why I chose to pursue closed circuit diving

You will hear about all sorts of reasons to switch to CCR: longer bottom times, you can see more marine life because your bubbles don’t scare them away, cost savings on trimix fills, warmer, moister breathing gas, and lots of others. I dive in the cold waters of the Great Lakes. Longer bottom times do not interest me. I am also not concerned with marine life. There isn’t much marine life on Great Lakes wrecks (except for quagga mussels).

Logistics Advantage

A few things did catch my interest though. The ease of travel due to increased gas efficiency was one. My wreck diving expeditions are usually 4 or 5 days long in remote areas. That means taking 4 sets of doubles and 8 deco bottles per person. My dive buddy bought an enclosed trailer just for diving. We routinely hauled 8 dets of doubles, 16 deco bottles, gear bags, dry suits, and other sundry items. On one of our trips, we were diving with two CCR divers. We roll into the motel parking lot with our dive shop on wheels. They had a pickup truck. We were doing the same number of dives, same depth, same bottom times, yet all their equipment fit in the back of a pickup with enough room left over for a barbecue grill. They obviously knew something we did not.

Decompression Advantage

Another thing that drew me to rebreather diving was the optimized decompression brought about by diving a constant PO2. On open circuit, the partial pressures of the gasses in your breathing mix vary with ambient pressure (depth). As you ascend, the partial pressure of oxygen decreases. Technical divers adjust the PO2 by switching gasses. Once you ascend far enough that the PO2 of your current gas is low, you switch to a different mix that will give you a higher PO2. When you ascend farther and that gas is no longer beneficial, you switch to yet a different mix, and so on. That is why you see technical divers carrying several tanks in addition to primary double cylinders.

A rebreather is basically a gas mixing machine. A rebreather has two tanks: oxygen and diluent (air or trimix). You program the computer on the rebreather with the PO2 you desire, and it adds oxygen to the diluent to yield the PO2 you want, regardless of depth. Maintaining a constant PO2 optimizes on-gassing and off-gassing. This is an oversimplification, but you get the point.

Gas Efficiency and Cost Savings

One reason I kept hearing repeatedly was that I would save so much money on helium. I admit I didn’t give that one much credence. You can spend between $10,000 and $15,000 on a new rebreather plus training. I can buy a lot of helium for $10,000. I must admit though, now that I’ve been diving my CCR a few years and have started doing trimix dives on closed-circuit, those helium saving are nice.

Bear with me while I walk you through a math story problem (as my third-grade math teacher called them). I’m doing a four-day trip to dive some wrecks around 200’ deep. Let us consider open circuit diving first.  I’ll spare you all the detailed math. Suffice to say I’ll use about 50 cubic feet of helium per dive. If I do four dives, that is 200 cubic feet of helium. At $3 per cubic foot, that comes to $600 just for helium. It also doesn’t include cost of deco gasses.

Let’s look at the same scenario on closed circuit. Again, I won’t bore you with all the math, but I calculate I would use about 25 cubic feet of helium. Let’s round it up to 30 cubic feet. That comes to $90 dollars’ worth of helium. That is quite a savings! And on my CCR, I am not carrying multiple deco gasses, further reducing my gas costs. Multiply this savings over multiple trips per season and the savings add up.

And then I had a list of what I considered minor advantages like warm, moist breathing gas, ease of breathing, and weight reduction (double tanks are heavy!). None of these individually could justify switching to a rebreather. But when taken all together, all the advantages combined made a compelling argument. It was time to transition to the silent side.

In the next article, I will describe my search for the rebreather that best fit my needs.