I did this back when I first got a rebreather. I just did the math again... It costs me about $6/hour to dive a CCR, pretty much regardless of depth. Here's my numbers... You can do the math...please correct me if I'm wrong. I did this while watching a movie with the wife and kids, patiently awaiting a hurricane.
First, the retail cost of several popular rebreathers including instruction is about $9500.
I used 300 hours, as that's the most diving I did when I was very active doing a lot of 300' dives
Sorb costs me $115 per keg. A keg of sorb weighs 45lbs (especially if you weigh the kegs at the shop and pick the heaviest ones, they fluctuate by as much as 5lbs) Assume you'll get about an hour per pound. My two rebreathers hold just under 6lbs and are good for about 6 hours without pushing it. So 45hours per keg requires 6.66 kegs @ $115/keg is $767.
I also on a bad year buy 4 oxygen sensors. Retail is about $80/sensor. Thankfully, I don't pay retail. But we'll use that number. So $280 annually on sensors.
I used to spend a fortune on mushroom valves for the rEvo. Thankfully, my current rebreathers have good mushroom valves. So on a bad year, I might spend $20 on mushroom valves (retail) but I haven't replaced a mushroom valve in two years and I don't pay retail. But assume I'll have a bad year eventually.
If you rebuild your first stage regulators annually (I don't rebuild until IP creeps) then plan on $25 in parts, and $30 in labor. I rebuild my own, and I don't pay retail for parts.
Also, you can plan on replacing o-rings as needed, or during an annual service. That's up to you. I replace as needed, but an annual services would remove the above cost and replace it with $250 annually for new orings, hoses, mushroom valves and 1st stage rebuilds, etc. Let's use that number for easy math.
Now, this is where it will get a bit tricky...
I don't pay for gas fills because I'm affiliated with a few shops and a few shops are just really good to me, but my students do. They're charged $6 for a minimum fill of O2 or Trimix. Let's plan on all 300' dives. My rebreather has 4liter bottles. 4 liters at 200 bar is 800. 800 / 1 liter per minute (what a male person consumes on average at any depth in oxygen) is 13 hours. And frankly, a good rebreather diver will consume even less diluent, and typically, diluent bottles are filled to a much higher pressure than 200bar. But we'll use 13 hours for this math. Because I have big bottles and a lot of time on CCR, I might dive all week on a single fill of O2 and Dil. We're trying to get the cost for 300 hours on the loop. If we just assumed 10 hours per fill (and frankly, we exceed this often) we're looking at 30 fills at $12. $360 in Gas fills for the rebreather. I'm not going to add in bailout, because frankly, it's not consumed unless you need it, and if you need it, I'm pretty sure you're okay replenishing it, since it likely saved your life.
So what's the math? $767+$280+$250+$360 = $1657/300hours = $5.52/hour. And here's the kicker... want to go to 400'? That cost doesn't change significantly.
Well, what would 300 hours at 300' cost on OC? I haven't given it much thought... But let's see if I can figure it out.
Plan on a .5 SAC.
300' / 33 +1 = 10ata x .5 = 5cu' per minute. But, I'd guess than only 25% of that dive is actually on bottom mix. The majority of that dive is deco gas. So 300 hours x 60(minutes) x 5cu'/min x .25 = 22,500cu'.
Now, I haven't added up the cost of Deco gases like Oxygen and 50%. They are not insignificant. But if you take EE's cost of $.67/cu' for 10/70, you'll see that 22,500cu' for 300 hours of diving at Eagle's Nest will cost you about $15,075. Of course this is assuming all 300' dives. What if we were talking about 300 hours at Ginnie? Well, let's see... We replace 10ata with 4ata and we get 4ata x .5 = 2cu' per minute, except that all of that dive is on 32%. 300hours x 60(minutes) x 2cu'/min = 36000cu' x $.11/cu = $3960. Don't forget to add in annual service, o-rings, etc.
So, I guess break even really depends on where you are diving. Diving shallow? CCR is 3x cheaper than OC. Diving deep? CCR is 20x cheaper than diving OC.
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