RB v. OC comparisons

[O2BBubbleFree]

Hi all,

On another thread GoProHonduras mentioned:

I've been executing OC Trimix dive profiles for the last few years to depths of 90mt/300ft for times of approximately 15 minutes bottom with about 80 min deco obligation plus considerable expenses in gases...

And I started wondering what that dive will look like now that he’s on his RB...

I think most of us who are considering (longing for, dreaming about) RB diving understand that the RB dive takes a lot less gas, gives more bottom time, less deco, etc. but we may not have a real appreciation for the differences.

So, I thought it might be fun and enlightening if some of you experienced RB divers could list profile, equipment, and cost details for a dive that you do on your RB, then list profile, equipment, and cost details that would be necessary if you were doing the dive OC. If you could give planning/set-up/cleaning time comparisons, that would be good, too.

Are there dives that you did OC that you will not do RB? Or vice versa? Why?

I recognize that there are different approaches, theories, and practices. Let’s try to keep this thread from becoming a discussion (war) on what’s right or wrong. While I would like to see as much detail as I can, feel free to leave out details that you feel may be controversial or improperly used by other divers.

On the other side of the coin, for those of us not yet as trained and/or experienced, let’s remember that this thread is not meant to be training and/or advice on rebreather diving practices or procedures.

 

[wedivebc]

Hi all,

On another thread GoProHonduras mentioned:



And I started wondering what that dive will look like now that he’s on his RB...

I think most of us who are considering (longing for, dreaming about) RB diving understand that the RB dive takes a lot less gas, gives more bottom time, less deco, etc. but we may not have a real appreciation for the differences.

So, I thought it might be fun and enlightening if some of you experienced RB divers could list profile, equipment, and cost details for a dive that you do on your RB, then list profile, equipment, and cost details that would be necessary if you were doing the dive OC. If you could give planning/set-up/cleaning time comparisons, that would be good, too.

Are there dives that you did OC that you will not do RB? Or vice versa? Why?

I recognize that there are different approaches, theories, and practices. Let’s try to keep this thread from becoming a discussion (war) on what’s right or wrong. While I would like to see as much detail as I can, feel free to leave out details that you feel may be controversial or improperly used by other divers.

On the other side of the coin, for those of us not yet as trained and/or experienced, let’s remember that this thread is not meant to be training and/or advice on rebreather diving practices or procedures.

That's a very interesting question and let me see if I can shed some light.
First of all I have been diving beyond rec limits for about 5 years now (properly trained and equipped) but only diving CCR for about a year and SCR for a year before that.
The reason that time is imorptant is that although I considered myself a fairly experienced diver when I started on RBs I felt like a rank beginner again. My bouyancy, trim and faliliarity went out the window and it has taken many dives to get it back to where I consider myself fairly competent on CCR.
One of the main reasons I switched was my helium habit. Yes, my name is Dave and I am a trimix user. I mostly only use it on weekends but I sometimes use it for several days at a time and this habit can get a little costly.
By switching to CCR I have reduced the cost of my helium to about 1/10 of OC costs. Now I don't feel I need to add helium until about 130ft or so and if diving OC I wouldn't but it is so easy and cheap to splash a few cf of helium in my 20cuft dil tank that I just do it for most dives.
It cost me about $15 to fill my scubber and about $5 worth of helium for a trimix diluent fill and about $1 worth of O2. That I could use down to about 250ft. At that depth I could theoretcally get about 3hrs duration of course I can't get away from the inert gas issues just like OC but from an economic standpoint that is my cost of operation.
From a deco perspective the CCR is a great help on multilevel dives where I can optimize my po2 at every depth I am at the moment. It show less advantage over OC on square profile because the OC diver will usually plan the best mix for the dive so that their bottom po2 is 1.4 or so. The CCR wins out during ascent because the po2 setpoint, usually 1.3 is constant all the way to the surface so it would be like an OC diver carrying a multitude of deco cylinders like one for every stop.
I have about $6000 invested in my CCR as opposed to about $4000 for my OC gear. That includes 2 sets of doubles, 2 main regs and 2 deco regs. I have not factored in my backplate, wings etc since I use the same with my RB as with my doubles.
Like I mentioned before I still feel like a noob on CCR so my deepest dive on CCR is about 170ft and usually no deeper than 150. The one issue with deep CCR is there is still a requirement to carry OC bailout gas. Some strategies require the buddy to carry half the bailout gas which prevents me from solo diving which I often enjoy on OC. I am not comfortable on RB as a solo diver nor am I comfortable not carrying all my own gas as I was taught the principals of self reliance right from my very first tech training.
Hope that helps.

 

[caveseeker7]

Hi 3dent,

since I make up the "bottom end" of CCR diving, recreational dives, I might as well go first.
(at least I'm starting to type when no reply is posted )

I don't trimix, don't dive deep, and pretty much stay within no deco, recreational profiles in regards to time and depth.

So why CCR in the first place? Because I enjoy it.
That's the only reason to dive OC, and that's the main reason to dive CC.

My OC setup is a 72 cuft Scubapro shorty, Atomic B1, either Zeagle Ranger or DiveRite bp with Oxycheq wing.
Weight: 47.5 lbs with ss bp/w or 51 lbs with Ranger
Duration: averages around 40 mins (drysuit)
Cost: I can get air fills free, but nitrox (much preferred) costs $10/tank
Pre-dive: About 15 minutes, gotta bolt it all together and check pressure, mix and valves. Between dives less than that, just checking.

On occasion I rent or borrow larger tanks to actually stay in the water for an hour.
I only do single tank dives, if I use twins there better be a rebreather in between.


The CC setup: PRISM Topaz (rented or borrowed at this time)
Weight: 47 lbs with full tanks and cannister
Duration: 300 mins (factory rating at 60 ft. generating 1.35 lpm CO2 - realistically more) scrubber, gas longer
Cost: O2 - $10
diluent - free (air)
absorbant 6 lbs of Sodasorb - $16
Pre-dive: About 45 mins, immediate pre-dive about 10 mins (valve, pressure checks, breathing)

Now consider the duration, and cost looks different:
Five hours, so gas $2/hr, absorbant $3.20/hr, throw in other stuff like cells, lube, batteries etc and it's still not more than $9/hr.

On OC I usually can't do an hour, with a larger tank costs go to $15/gas fill.

The dive boats here in SoCal either do 3 - 4 one hour dives dives per day on a recreational charter.
OC that means 3-4 40-minute dives costing $30-$40
or 3-4 1hr dives lightening my wallet anywhere between $45 and $60.

CC gas will last all day, though dil gets topped off So add a few $. Absorbant lasts all day.
With enough left for quite some beach/shore diving.

 

[wedivebc]

Hi 3dent,

since I make up the "bottom end" of CCR diving, recreational dives, i might as weel go first.
(at least I'm starting to type when no reply is posted )

Ha ha I beat you to it for once...

 

[caveseeker7]

All that math before my 2nd cup of coffee slowed me down. :bluthinki
Enjoy while it lasts.

 

[cameron]

CCR is nice. It is quiet, it is warm, its fun being first off and last on the boat. I havnt dove OC since I purchased the unit a year ago but borrowed my girls kit and did two dives this weekend on on a single. OC is nice too. Its easy and its also fun leaving the boat with buddies and climbing the ladder with buddies. As there are no other CCR divers that I would be willing to dive with in my area (that I know of), I find most of my CCR dives solo and pretty long. I guess its just a different dive, no better or worse but just different....

 

[DrMike]

A few weeks ago I was asked to help survey a huge wreck that a company was thinking of salvaging.

A remote site, the other survey divers all dove air OC and did 3 dives each of 30mins on the wreck.

As we were gearing up they asked me what I was going to do and I said, I would maybe do a single 2 or 3 hour long dive and survey the whole wreck in one shot. They thought I was kidding.

I spent over 2 hours at depth (max depth 40m - deck at 20m) videoing and surveying the wreck (it was a huge wreck) - silent, peaceful, beautiful. Best thing was no deco despite spending a lot of that time sub 30m. The time spent surveying the deck and house was my deco! Inside the wreck in silence I swam over a huge nurse shark without realizing it until it was maybe half a meter below me! Scared the crap out of me.

So its not just all about deep deco tech dives - On days like this that RBs really do make a lot of sense to me.

 

[teksimple]

So its not just all about deep deco tech dives - On days like this that RBs really do make a lot of sense to me.

I will have to agree, and I have almost no rebreather experience. On one of my last Mk 15.5 training dives 6 months ago, I stood on the forecastle of the Sea Tiger ship wreck off Oahu and basically hung like a statue. Everyone else was up on the superstructure. A pair of eagle rays circled the wreck and then came in for a pass. They slowed down and swam inches from my mask. They made another pass a few minutes later and this time they came even closer, slowing down to almost zero relative to me in the current, as if they were checking me out. They must have spent a full minute within an arms reach of me. Having done thousands of OC dives in Hawaii, I have had plenty of encounters with eagle rays, but nothing that close!

I can't imagine what it will be like in the Galapagos with a rebreather! Howard Hall may write about the "myth of invisibility" with a rebreather, but I am pretty convinced otherwise, at least for some animals. It seems to me, if you want to see normally skittish animals, stop and stay absolutely put for a while, and use a rebreather.

Er, I guess you could hold your breath for about 10 minutes on OC. ;-)