Question Question for Experienced O2ptima CM Divers

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Quick question. (This is a thought exercise. I am attempting to understand how one dives a Cho2ptima.) Suppose you are solo diving your Cho2ptima using full, back-mounted, isolation-manifolded doubles containing an "appropriate" Tri-Mix (say, 1/4 He + 3/4 EAN32) for a 150 fsw deco dive in open water.

I am thinking that you should plan your dive so that you can bail out ("dil out") to open circuit, and return to the surface from depth, using at most 1/2 of the contents in your doubles + EAN50 (which you are slinging) + 02 (which you are slinging).

In addition, your bail out plan should allow for the loss of either your EAN50 or your 02.

Is this a reasonable plan?

EDIT: Corrected "2/3" to "1/2", and added "solo."

TIA,

rx7diver
So, the dive you are thinking of is somewhat similar to a dive I did last weekend. I was up at the Thousand Islands planning to do some solo shore diving with my Chop and a set of LP46s filled with good old fashioned breathing air (why pay for nitrox when the Chop is mixing it for me on the fly, right. So right when I get there Friday afternoon, I stop by my friend's dive trailer parked outside the local shop to grab my scooter that he had borrowed the previous week for one of his students to use when the shop owner asks me what my plans are for the weekend. I tell him my meager plans and he says they have room on the boat in the morning and they're going to the Jodrey.

So, now I'm in! Oh, wait... I wanna be in but I came up here with just the mini doubles (with air) and an AL40 of O2. That will technically work, but is far from ideal (I could breathe air at 150 to 170 ft, but it's not the best idea. I would be limited on time based having only 100 cf of bailout that I would have to breathe up to 20 ft). So the shop owner and I did a little calculating on the bailout requirements for the dive I wanted to do the way it really should be done (18/45 dil, AL40 of 50%, and my O2).

So he let me borrow a full 70 ft bottle (with the promise that I would pay for any gas I used if I had to bail out), borrowed a stage reg out of my buddy's trailer, and then dumped all my air and filled the mini doubles with 18/45. That last part was emotionally the hardest, knowing I had 2 twinsets and 3 bottom stages at home already half full of 18/45, until it occurred to me that the $200 I just spent to to fill the 46s with mix would last me a good long time as long as I did not need to actually use them to bail out.

Anyway, we calculated that for a 30 minute bottom time at 170 ft I would need about 12cf to 100 ft, 8 cf to 70 ft, and then the same amounts of 50% and O2 as I would normally use for this dive profile on OC (a 40 of each is plenty). So, in this scenario, I could even get away with losing my 50%, as doubling the stops for being on back gas would mean the 80 cf left in the doubles would get me to 20 ft. So, if I had that much excess BO gas, why did I only plan a 30 min bottom time? Well, I was tempted to stay longer, but the rest of the boat was on OC with just double AL80s and their deco gas, so I didn't want to leave them sitting on the boat waiting for me for too long. I did stay about 5 minutes longer than they on the wreck, and I took my time getting up to 100 ft. I thought I'd end up catching them at the 20 ft stop, but they ended up back on the boat about the time I got there, so I was about 15 minutes behind them surfacing.

Diving the RB on this dive was like a dream. I was so much more relaxed knowing I had all the time in the world if I needed it for any reason, not seeing dollar signs floating up with my bubbles every time I exhaled, and still being clear-headed on a nice gas mix. As it turns out, the mini doubles are even enough gas for a 10 min scooter back to the up line even if I have to bail out further back the wreck (though if I plan to go to the stern I'll take the AL80s or maybe even the LP108s - but at least the days of 1 or 2 bottom stages for this are gone).

The cost of the mix was minimal considering I still have most of it in the tanks. I started with 3000 psi and ended with about 2900, so this fill should last me about a dozen more dives before it's too low to be enough bailout for this type of dive. That's pretty nice considering how much these dives would cost on OC. (Yes, I know it still takes a lot more than that to amortize the cost of the RB, cells, scrubbers, etc. but I count it as a win)
 
No…most people sit them upright. Why would someone would lay a unit down on a boat unless you’re in a small RIB with no other choice?
I know of quite a few that lay them down for the four or five hour car trip to the dive boat.
 
I know of quite a few that lay them down for the four or five hour car trip to the dive boat.
While there are people that do it, and while the risk of channeling a modern, very tightly packed scrubber isn’t very high, it is generally discouraged to leave scrubbers horizontal for bumpy car rides.
 
While there are people that do it, and while the risk of channeling a modern, very tightly packed scrubber isn’t very high, it is generally discouraged to leave scrubbers horizontal for bumpy car
I agree, but that does not mean it isn’t being done (a lot). But I’m side tracking the thread now.
 
Most of the time, no, because most of the time you'll want to use an ExtendAir cartridge rather than pack it yourself with granular sorb. However, if you do pack it with sorb (properly as with any other RB), it should be no more likely to channel than any other scrubber. Think about it... with a "typical" back mount RB with vertical scrubber, isn't the RB typically laying on its side for the car and boat ride anyway? How is that any different to the CM? If you pack it right (tight), it'll be alright. Or just use the cartridge and don't worry about it.
I never ever use the cartridge because while I’m rich, I am also cheap and the cartridge costs 6-8x what sorb costs.

I have also never packed a bad scrubber in over 2000 hours of CCR time.
 
I know of quite a few that lay them down for the four or five hour car trip to the dive boat.
Never have I ever driven mine by boat, car or plane, upright. The risk of something falling and breaking is greater than the risk of channeling. This weeks dives were 12 hours of driving with three Optimas. No channeling.
 
I never ever use the cartridge because while I’m rich, I am also cheap and the cartridge costs 6-8x what sorb costs.

I have also never packed a bad scrubber in over 2000 hours of CCR time.


I have some EAC cartridges to sell you; will do so for 2-3X the cost of sorb, especially at current prices for sorb

sorry can't help but troll a little :wink:
 
I never ever use the cartridge because while I’m rich, I am also cheap and the cartridge costs 6-8x what sorb costs.

I have also never packed a bad scrubber in over 2000 hours of CCR time.
Recently it seems cartridge is "only" 2 to 3 times the cost of sorb, and with the recent rise on shipping cost of Sofnolime from the UK to the US (see thread where DGX has quoted their new price is $209 a jug, but it is in stock and shipping now) it's now closer to 1.5x (8 cartridges - equivalent scrubber time to 20kg of granules - is $300).

I'm not rich, but I am cheap. However, I'm also a bit lazy so (for me) it's worth the 50% overhead to not have to pack a scrubber, clean up the mess I made, dump the used sorb, and then clean up the other mess I made. I prefer pull out cartridge, insert cartridge, dive. Also, I can still be a cheapskate by taking out a partially used cartridge, using a new one for a big dive , then put the partially used one back in later for a shorter shallower dive. This would be 3 scrubber re-packs with sorb, but I only use 2 cartridges. That sort of thing can bring the cost close to even in the long haul.

But I see and fully agree with your point that if you are packing the scrubber properly there should not be a problem with the orientation in which it travels. To that point, even if you keep the scrubber vertical in the car and on the boat, it's always horizontal at some point (like while you're diving and breathing it) so it better be packed tight every time. Shouldn't matter what brand or design; that's just a basic requirement.
 
S
Recently it seems cartridge is "only" 2 to 3 times the cost of sorb, and with the recent rise on shipping cost of Sofnolime from the UK to the US (see thread where DGX has quoted their new price is $209 a jug, but it is in stock and shipping now) it's now closer to 1.5x (8 cartridges - equivalent scrubber time to 20kg of granules - is $300).

I'm not rich, but I am cheap. However, I'm also a bit lazy so (for me) it's worth the 50% overhead to not have to pack a scrubber, clean up the mess I made, dump the used sorb, and then clean up the other mess I made. I prefer pull out cartridge, insert cartridge, dive. Also, I can still be a cheapskate by taking out a partially used cartridge, using a new one for a big dive , then put the partially used one back in later for a shorter shallower dive. This would be 3 scrubber re-packs with sorb, but I only use 2 cartridges. That sort of thing can bring the cost close to even in the long haul.

But I see and fully agree with your point that if you are packing the scrubber properly there should not be a problem with the orientation in which it travels. To that point, even if you keep the scrubber vertical in the car and on the boat, it's always horizontal at some point (like while you're diving and breathing it) so it better be packed tight every time. Shouldn't matter what brand or design; that's just a basic requirement.
So I get sorb SUBSTANTIALLY cheaper than that. The cost difference is very big.

But I get your perspective.

I also have a bunch of rebreathers. Only the optima will take a cartridge. So, what’s good for the goose is good for the gander.
 

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