10 replies to this topic

[PerroneFord]

For those of you who can manipulate your EAD (trimix/RB divers) I have a question.

Do you find that you limit your gas choices based on EAD or helium costs? What brings me to this question was my attending the big WKPP dive a couple of weeks ago. As the stage tanks were being preped, I happened to sneak a look at the tanks.

All were Heliox. With O2 content between 9 and 11.5%. Now I don't have to tell the mixed gas divers what that means in terms of costs, but for those who may read this and don't know what helium costs are I'll provide a bit of math.

Referencing Fill Express:

http://www.fillexpress.com/fills.shtml

Helium is going for $.75 per cubic foot retail.
Oxygen $0.30 per cubic foot

The tanks (about a dozen - 20 on estimate) were AL80s.

So 80cuft * 10% = ~8 cubic feet of that tank was oxygen
The remainnig 72cuft was helium.

8cuft of oxygen at .30 per cubic foot = $2.40
72cuft of Helium at .75 per cubic foot = $54.00

So each tank (at retail) would have cost $56.40

Assume 15 tanks, so that $846 for just the stages. That says nothing of the decompression tanks at 240, 200, 130, 70, and 30ft gasses.

Of course the RB divers here will laugh because this dive could have been completed with FAR less Deco time on CCR, with probably two sidemount 80s filled with 9/80. Probably the way to do it is to ride CCR down to 320, then pick up OC on best mix and explore, then come home on CCR towing the empty OC cylinder back into reach of the support guys. That way you don't burn through the canister. The question is do you TRUST the loop not to flood? I don't know enough about CCR diving to know whether this is an acceptable or unacceptable risk. Or how you'd clear the loop after abandonding the unit for 3 hours at 300+ feet.

Thanks in advance for your thoughts


(Sorry these are the things that tickle my brain at midnight on a Sunday!)

[6Gill]

So each tank (at retail) would have cost $56.40

When you pump helium on a regular basis or in volume,retail is not an option.The shop needs to pay someone plus overhead so by filling our own we save.Example this weekend a set of twin 130s from empty cost CAN$78 which equals 3AL80s.The only thing not included here is time....

[scubafanatic]

.....boy, that's the kind of 'economics' that has me contemplating bypassing the whole OC scuba training program ( involving massive doubles/stages/etc.) and saving up my pennies for a rebreather/training instead........... it's just insane to burn through that kind of money for assorted gasses, especially considering the helium prices quoted are US prices, which are the cheapest in the world (helium is produced here in Texas as a byproduct of oil/gas production) ...I can only imagine what the price/availability of helium in the remote third-world dive locations would be!

I know ScubaDadMiami recently ditched all his OC gear and migrated to a rebreather....... I'm almost considering getting a 'deep-air' cert, good down to 165-180 ft. , depending on the agency, and leapfrogging to a rebreather once I'm ready to expand my dive envelope further..........moreover, it is probably more practical to lug along a rebreather on an overseas dive trip than to expect to have access to doubles/stages/large volumes of gasses on site.

I'm still in the preliminary stages of reviewing all this, and I know the entry price of rebreathers isn't cheap, but given the cost/availability issues with helium, I'm beginning to think skipping the whole 'natural' progression through 'tech OC' is misguided/wasteful and it might be wiser to go ahead a jump to 21st century dive technology.

Karl

[Diverbrian]

The politically correct answer is that cost is never an issue.

Realistically, I have no problem diving a deeper dive with a little less work involved on less helium if making a mix with a shallower END involves me having to vent my tanks and reload 20-35 percent helium into the mix. For most any profile that I do, I am happy with 15-35 pecent helium (one fill to 35 percent Helium and one nitox top-off). And as was so astutely noted, I blend my own for economic reasons. It's still quite a bit less expensive to blend my own than to pay for a blender's time to do it and I KNOW what is in that mix as well.

When I start getting into the hypoxic profiles that you refer to, I will be on a rebreather of some nameplate. I have a feeling that cost will be much less of an issue when you aren't talking about double 130's (my tank of choice) than on the smaller diluent bottles that a CCR uses.

As to the arguement that one's bailout is OC if something happens, that is true. But I dive pretty deep on OC now. I think that I could handle OC bailout with a little bit of practice.

[PerroneFord]

Ok,

So apparently, people aren't worring about EAD as a fixed point. Fair enough.

It's also interesting to hear people talk about rebreathers in such definitive terms. I am thinking of offering (through my shop and instructor), a rebreather comparison checkout sometime this fall or next spring. We are going to do a trial run of this at the NACD conference, but I want to run it privately.

We have in stock, the Inspiration, the Megalodon (2), KISS (2), Ouroboros (2), and are working or the Optima (order has been placed for months). We are in a very unique position to allow prospective buyers the opportunity to swim them all, and can offer sales and training on these units.

For those of you who are interested, would this appeal to you? Or do you already have firm ideas on what you want?

As to skipping OC mixed gas diving, I can certainly see the appeal in that. FIlling 2 14cuft or 2 19cuft tanks certainly makes more sense. It's one of the few ways you can dive Heliox or helitrox economically. Essentially using 16/84 or 18/82 as diluent, along with your normal OC bailout.

It seems that the Megalodon is getting the most attention from home-brew folk right now, and I know for a fact there are two MAJOR changes coming on the Meg in the next few weeks/months that are going to make people stand up and take note.

I got a chance to poke around with the Evolution this past Saturday. It's a nice, small unit, but I REALLY doubt that I'd spend that kind of money on it for the limited time it offers. The KISS is just a better deal overall even if you have to fly it manually. I'd make an exception for someone doing film or video though.

I am debating whether to go to a rebreather myself before I go trimix. Just do it as an air/nitrox unit. And take advantage of the piddly decomprssion times I'd generate.

Best mix, all the time. Gotta love that!

[TekDiveGirl]

I am debating whether to go to a rebreather myself before I go trimix. Just do it as an air/nitrox unit. And take advantage of the piddly decomprssion times I'd generate.

Best mix, all the time. Gotta love that!

There are advantages and disadvantages of the RB route for sure.

I saw divers miss dives on a very expensive trip due to having issues with the electronics -- and other parts.

Being OC any issues we had were pretty easily fixed -- and we were diving -- then drinking and having a great time while the RB Boys were still messing with their gear.

Yes at night we took a bit longer filling all the doubles/deco bottles etc with trimix and deco gasses -- but we didn't miss any dives nor much playtime.

[PerroneFord]

Kimber makes a VERY valid point. In fact, just last night I was reading a story about a cave explortion expedition where one of the divers intended to do a long push on a RB, only to see that they'd dropped the loop into the water with the loop open. Dive over before it started.

That said, the RB has some HUGE advantages over open circuit. As far as electronics, that is one of the reasons I am looking HARD at the KISS and the Meg, both of which can be flown manually if desired or required. Of course the KISS has no electronics in the first place other than the oxygen sensor display.

I don't think I'd do an expensive trip where I couldn't have redundant gear or a backup solution. This is where sidemount really comes in handy. If your rebreather isn't usable, clip on some sylinders, and get going. Lots of ways to get the job done.

[ScubaDadMiami]

Excellent discussion. Good and true points raised all around. So, let me comment on a few of them based on the real world experience of our Bahamas live aboard trip. http://www.singlediv...mas live aboard

After a four day live aboard trip, my gas bill for fills came to $8.40. I could have not gotten a bill for this at all. However, rather than enter the water with a partially filled tank (but probably enough gas to still do another six or so dives), I opted to be conservative, getting a couple of top offs. (You never know when an emergency will happen warranting having the extra gas.) Ask everyone else on the trip how much they paid for their fills. I suspect their gas bills came to a tad higher (and then some ).

Bottomtimewise, I could have elected bottom times for up to four hours on any dive we did on the trip had there been another CCR diver aboard. However, I kept my bottom times conservative since my buddy was on open circuit. If you like to go deep and still have long bottom times, CCR is the way to go.

Workwise, there is no question about it. I spent an extra hour or so at night working on my gear before the next day. One night, people went into town for a bit while I elected to work on gear for an hour or so, and then I got a good night's sleep. My choice, my preference, and my happiness. I love every minute of it.

I also elected (and so did my buddy) to log every dive that we did, and to spend endless hours running dive profiles considering the contingencies and emergencies. We discussed our previous and next dives while we were between dives, too. This ended out taking way more time than I ever spent working on my rebreather. I guess that I just trying to say that I am diligent a/k/a anal about all but the most recreational dives anyway. So, if you are the "I'll just do whatever the computer says" kind of diver, CCR is not for you. I love all of it, and so it is not work to me.

Failurewise, I did miss a half hour of diving when an oxygen sensor went out on my rebreather right before I hit the water. I had to undress (I was not going to stand around in 90+ heat in my drysuit) and change it before entering the water. I made up for it by staying longer on the dive after most of the others ascended. No big deal.

So, everything that has been said here is true: the good and the not so good. It is more work. It costs more up front. If it breaks, you need to have spare parts (is that so different?). It costs way less operationally especially on technical dives (though it can cost more on shallow, occasional recreational dives).

I find CCR to be highly reliable. In technical diving (see my signature line), I actually find it more conservative and safer than open circuit. I'll never go back.

[Diverbrian]

It's funny that one thing gets mentioned. Divers looking at doing long decompressions and deep diving (aka OC Deep divers) or overheads had better be at least a bit anal or they are looking at a bad day coming their near future.

An Inspiration instructor whom I know mentioned that to me. You have to be just as diligent, just on different things.

[BlckShadow]

I fill my own HE to save on costs. I have an account at the local welding supply and keep argon, O2, and uhp HE in my garage. Since I am a contractor I get a pretty good discount so it does not cost too much for fills. I then take it to the LDS and have them top it off with air and analyze the HE.

When it comes to END I am a deep air diver. Generally I will dive air to about 160' - 180' unless it is a difficult dive and will use trimix deeper than that. When I dive mix I base the END on the dive difficulty. I will generally use about 120' END unless there are strong currents, overhead, or other factors then I will use 100'.

[webhead]

I think you will find that dive plans change to the circumstances. For example, I prefer a low END or EAD - around 80-90 feet. Why, because I've done a deep air dives and deeper trimix dives and I tend to remember the deeper trimix dives better. :-) But when I went on a recent dive trip, the gases for the dives were pretty much pre blended. The store made it clear that they could and would blend any mix I wanted but what they offered fit my requirements so there was no need to change. So I'm breathing 60% helium on my dives versus 40%. It does affect your deco some but again, not to the point that it is outside of a dive plan that I'm comfortable with. And I apply this to OC as well as CCR.

Another comment. There was mention that the Meg can be flown manually if the electronics fail. This is true but it is for use only during an aborted dive. You would never start a dive on a Meg with failed electronics. If you get a Meg or an Inspi/Evo, you will learn to fly the unit manually and be confident that you can maintain a PO2 without the aide of the computer. But that training is to give you an option to use the rebreather to get to the surface, not to start a dive with bad electronics.

And yes, you can clear a flooded loop on most rebreathers while underwater.... some easier than others. And if you are at 300 feet for 3 hours, do expect me to wait underwater with you to complete all that deco. ;-)