Is a SCR or CCR right for me?

[kensuf]

I just rebuilt a KISS last weekend, and will be diving it this weekend. It's a ridiculously simple design, and with the exception of the head, the majority of the parts can be found at REI or Home Depot. That makes maintaining it pretty straightforward and simple. Plus, you can find a used one pretty cheap right now.

 

[ffdiver]

I've been eying all the forums for one. I'm trying to keep things under 4k with training. Nice thing is I'm in no rush whatsoever so I can just wait for a good deal to pop up

 

[kwinter]

I love CCR. I've had an Optima, a rEvo, and now I'm diving a JJ. But SCR is a viable alternative that I have no problem using at 130 or even 170 feet. It is simpler than CCR, requires less cost to buy and train, and travels easier too. Let's look at the numbers for something like the GEM. Deeper than 100 feet you can practically ignore any drop in pO2 from the drive gas. So at 165 feet (50 meters) you are at 6 ATA. Even if you used plain air or a normoxic mix like 21/25, you would be at pO2 of about 1.3 at the bottom. But at the surface your pO2 would drop about 5 points, so it would be 0.16. All that is necessary is to use what is called open loop breathing where you inhale from the loop and exhale through the nose so you are getting fresh 21% gas each breath until you descend a few feet. Please note that this is NOT a recommended strategy and would not be covered during training. I am only putting this out there so you understand the numbers. An alternative is to use 23% gas which would give you a pO2 of 1.4 at the bottom and about 0.18 at the surface. Or to use a travel gas for the initial descent since you would probably want a bailout gas with you for such a dive.
SCR is a viable alternative. It may not be as good as CCR for 200 foot plus dives, but it's cheaper and less complex to buy, learn and maintain.


iPhone. iTypo. iApologize.

 

[abscuba]

I have to again agree with kwinter if your end game is to be able to have long time at 130ft and your budget is 4k then SCR would be the way to go. If you plan to continue deeper and do very long dives or push to 200ft and below then CCR. It will be hard to find a rEvo for 4k, most 2nd hand are around 6k and your not going to find parts for it at home depot. Its really deciding what endgame you are looking for just longer bottom times at 130 to 140 ft then go SCR. If you are only going to do 170ft once in a blue moon that is an easy OC dive and no sense to spend the money unless you are going down there regularly. There are many options out there and if you get the chance to get your hands on one try it see what you like and what will suit you as ever diver is different.

 

[Dr. Lecter]

It will be hard to find a rEvo for 4k, most 2nd hand are around 6k and your not going to find parts for it at home depot.

That depends on what you're looking for. I had a stainless mini II hCCR rEvo ready to go for about $4500, and a buddy snagged a standard size of the same unit for $3000 that was just immaculate. If you want a rEvo III hCCR, yeah, $6k is more realistic.

 

[ffdiver]

I should have been more specific that I was looking at the revo II.

after some conversations with other about different units and whatnot, they kinda convinced me that whatever unit I choose, I'm going to out grow or decide I don't like anymore and get a new one eventually. WOB will suck and I will be overwhelmed. Just grab a unit in it's basic form, as cheap as you can and get diving and the experience to figure out what you like.

 

[Doppler]

If your reason for switching to a RB is to avoid weight, I think you're going to be a bit disappointed. Now you've got the unit, a bottom bailout tank, and the same deco bottle you had before.

If you are diving doubles (sounds like you are in the form of SM), you're just trading in one of those tanks for a rebreather and all its associated accoutrements, while adding risk (hypercapnia, hypoxia, maybe hyperoxia depending on the unit) and complexity.

TO the OP... sounds to me as though you are NOT a candidate for a CCR. And I say this as a factory sanctioned instructor-trainer for a brand of European CCR... and an avid CCR diver. Nothing in what you mentioned, points to the need for a CCR. As quoted above, the considerations/reasons for switching from OC should not include wanting a lighter dive package... not really the case.

However, sounds like you are wanting to justify getting into rebreather diving. More power to you. But be aware that things on this side of the loop are not all rose-tinted and kumbayah. Rebreathers (SCR and CCR) are a useful tool, and I love 'em, but getting straight information about them, their pros and cons, which one suits your style of diving, your goals, and budget is not an exercise to be completed online. If you wanna talk, drop me a message. I'll call.

 

[ffdiver]

Thanks Steve, I'll probably get in touch sometime next week.

I think my original post is getting misconstrued. This is an example of what I'm looking to do.

Last weekend we dove the Arundo. It's listed at 140 but in reality it's a 130ft depth wreck. My biggest tanks (that I choose to dive) are HP100s, I had a 40 with 100% for deco. With my SAC (real and emergency) and planning on losing my deco bottle the longest bottom time I can do with the 100s is 35 - 40 mins give or take. Everything went to plan and I was back on board with 1900 in each tank. Enough for a second dive with a bottom time of 20 mins. I enjoyed my dives, but I was sad when I had to ascend after 20 mins. (I had a full set of LP50s that were pumped up and gave me 4cf extra over the 100s, I chose to just breathe down the 100s instead)

We had 2 rebreather divers on board too. Both had a bottom time of 67 mins. Just playing around with numbers and v-planner, in order for me to do a 67 min bt I would have to carry up to 2 130s and 2 al 80 stages (assuming a loss of all my deco gas) or make a direct assent depending on the contingency plan and what not. On a rebreather, with a direct assent its a 40 of 100% and a 40 of bottom mix to do the same dive or an 80 to return to the anchor line.

That's the point i'm making. Can I SM 130s and drop stages as I go, sure. But there seems to me a more efficient way of doing the dive I want. HP 100s are the perfect SM tank for me. They are really the biggest I want to go.

So my next immediate goal is 170ft. I need to be trimix certified for that dive. The chances of actually making it out on the wreck on the day planned is 50/50 (as always). On OC that means I have a very expensive mix in my tanks that will probably not get used on the right wreck or I'll be diving a $300 mix on a 100ft dive, which just pisses me off. With a rebreather (SCR or CCR) it doesn't matter.

Does this make sense? Are my numbers totally off or is my bailout plans too conservative or not enough?

---------- Post added July 24th, 2015 at 08:48 AM ----------

I should also add, I'm not 100% sold on doing two very long divesand that's why I usually don't just bring an extra set of 100s with me.

 

[Doppler]

Thanks Steve, I'll probably get in touch sometime next week.

Look forward to hearing from you... will PM a phone number

I think my original post is getting misconstrued. This is an example of what I'm looking to do.

...


So my next immediate goal is 170ft. I need to be trimix certified for that dive. The chances of actually making it out on the wreck on the day planned is 50/50 (as always). On OC that means I have a very expensive mix in my tanks that will probably not get used on the right wreck or I'll be diving a $300 mix on a 100ft dive, which just pisses me off. With a rebreather (SCR or CCR) it doesn't matter.

Yep, likely it is.

Gas costs and logistics, especially deepish trimix stuff, do bring into focus a whole raft of considerations many of which weight the argument supporting rebreathers.

Anyhow, hope I can help you make a sane equipment choice...

 

[kwinter]

You have my number too. Feel free to call.


iPhone. iTypo. iApologize.