Can someone look over my numbers for cost of consumables on KISS mCCR and SCR?

[fuzzybabybunny]

KISS rebreathers have piqued my interest because they make several models that are very light and compact. Can someone check my calculations on price of consumables and weight?

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KISS Spirit LTE mCCR:

BOV, Harness, Wing: 21 lb
Sorb: 6.2 lb
14 cuft tank: 6lb

Total Weight without Diluent / Bailout: 33.2 lb

6.2lb of sorb can do about 2 hours @ 45F water (KISS Rebreathers Syntactic Foam Insulation | KISS Rebreather) or 3.5 hours @ 75F.

44lb sorb is $160 + $40 shipping = $200 (Dive Gear Express) = $4.55 / lb, or $28.21 for 6.2lb.

Oxygen is $0.40 / cuft, so $5.60 for the 14 cuft tank. A person metabolizes about 19 cuft of pure oxygen per day, so 0.75 cuft per hour, so a 14 cuft tank would last 18.67 hours, or $0.30 / hour of oxygen use. (How much oxygen does a person consume in a day?)

So it appears that sorb is the most expensive consumable on a rebreather dive.

Sorb is about $10 / hour dive time and oxygen is $0.30 / hour of dive time. Plus there's diluent usage, but I'm not sure how long, say, an 80 cuft tank of air can last @ $8 per tank fill when used as diluent.

Let's just say that CCR diving costs $15 per hour for consumable usage? Seems quite high, but the economics pay off if you're doing deep dives. I've done shallow dives catching crabs that amount to $4 / hour on OC.

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KISS Gem SCR:

Entire SCR loop assembly – hoses, scrubber, DSV, counterlungs - 13 lb
Sorb: 5.2 lb

Total Weight without main tank: 18.2 lb, 15 lb lighter than the Spirit LTE mCCR

Total Weight with filled AL80 Nitrox: 18.2 lb + 40 lb AL80 tank = 58.2 lb

Let's say that the gas extension is a factor of 2.5.

AL80 Nitrox is $12 and say that does 0.75 hr on OC for a certain dive, so 1.88 hr on SCR for the same dive and tank size, and $6.38 / hour.

Sorb usage is still $10 / hour of dive time?

So total is $16.38 / hour of dive time on SCR, and you're limited to the MOD of your Nitrox mix.

But does gas usage change drastically with depth on a SCR as it does on OC? Or does a tank @ 100ft last just as long @ 40ft on a SCR?

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Open Circuit:

Total weight of BC and regulators and computer: 10 lb

Cost of consumables: $11 / hour air or $16 / hour nitrox (0.75 hour / fill @ $8 air and $12 nitrox), but varies greatly with depth

 

[Superlyte27]

I did this math last year. Full Retail was under $10/hour

This includes maintenance, mushroom valves, sensors, sorb, etc.

 

[Superlyte27]

I wouldn't consider SCR in any situation. If you're going to do it, go all the way.

 

[rddvet]

Holy cow. Way to take all of the fun out of deciding to buy a rebreather.

 

[kelemvor]

Wow, the more I see what some people pay for oxygen the more I realize I've got a good thing going at my LDS . I wind up paying about $0.16/cuft, although I'm paying a flat rate per fill with a card.

No helium in your calculations? In my mind, CCR only starts to make good sense when you are doing dives that require helium.

 

[Superlyte27]

It's under $10/hour regardless of depth.

 

[broncobowsher]

Errors...
You will NOT use 100% of the scrubber capacity. That would be taking it to the edge of breakthrough every dive. For the math you are trying to do, double the amount of scrubber material.
There are better deals for scrubber. $200 would be on the high side. $150 on the low.
You will waste a fair bit of O2 as well. Just doing the loop flush as part of the predive eats a fair bit of O2. A sawtooth dive profile will eat it up as well. But a square profile it will last nearly forever.
Check your local shops for O2 fills. Where I am at there are only 2 places in town that can actually fill (have a booster that will pump O2). That adds a little to the cost.
There is even the cost of driving to that shop that will pump O2, and since only one guy does it and I never catch when he is there that means leaving the bottle and picking it up again. Another drive across town. The gasoline costs can be as much as the gas costs.

It is not the cheapest way to dive, especially shallow. The economy comes deeper. And you stay longer if you want. More of an apples/oranges comparison. My math came out closer to $20/hr considering actual materials consumed/wasted instead of theoretical using everything to 100%.

I can't really comment on the SCR. I know of it. Learned about it. Never spent that much time with the math side of it.

 

[fuzzybabybunny]

If you're getting less than $10 per hour on CCR does that mean you're getting your sorb for way cheaper than what I calculated from dive express?

 

[fuzzybabybunny]

And does SCR gas usage vary a lot with depth like it does on OC?

 

[Superlyte27]

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'llget about an hour per pound. My two rebreathers hold just under 6lbs and are good for about 6 hours without pushing it. So45hours 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 asneeded, 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 okayreplenishing 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.