Is a SCR or CCR right for me?

[kwinter]

Ken, only reason I brought up the deco was because he mentioned loathing long deco stops which means he's trying to shorten them not extend them. For hour long dives at 100ft it may be inconsequential compared to OC, but CCR will be much shorter unless you're diving square profiles with your actual "best mix", which almost never happens.

We dive square profiles all the time on Northeast wrecks. So there really isn't a big difference in deco time between the CCR guys and the OC guys. In fact, the OC guys might do a little better since their bottom time is usually at 1.4 compared to my 1.2. But they do have to carry a large amount of gas, which is why the CCR guys are more prevalent on the deeper stuff.

It's not that im trying to shorten them, it's just that in order for me to get the really long stops which I'm not happy with I need huge tanks, which I don't want to carry. I want to be able to do the long dives with the least amount of complexity and as efficiently as possible.

If I can take a 40cf bottle and an 80 bailout and do the dives I wanna do with out the added complexity and risk with a full CCR that to me seems the most efficient but I don't know any better. So that's why I'm asking yall.

You can figure about a triple extension of gas with something like the GEM. So a single aluminum 80 is essentially like diving double 120s. Of course you might want to carry a separate bailout bottle for deeper dives, or a richer deco or travel gas. I've done back to back 90 minute dives to 120 feet on a single LP95 filled with 32% and still had plenty of gas left over.

 

[cidcolada]

My rebreather experience is somewhat limited, and I don't have or dive any of the units mentioned so far in this thread (I dive an old Drager Dolphin). With that said, if you are looking for a unit to dive past 130ft then I would give up on the idea of an SCR.

I'm not really sure how this applies to the GEM, but on more traditional SCR's with the leanest drive gas (32%) and a pretty stable average O2 metabolic rate you would be looking at a loop FO2 of around 28% which gives you a PO2 of around 1.5. If for any reason you purged the loop, for instance your mask got pulled of and when replacing it things didn't go exactly right and you had to give it a second go, you could possibly add a nice fresh burst of 32% to the loop. Always figuring worst case, that would give you an approximate PO2 of around 1.8.

In short SCR's are great for what they are designed to do, but beyond that they require modification to be appropriate for the task, something that is beyond the scope of this discussion,. Once you begin down that path you have abandoned all of the safety benefits (or perceived benefits depending on who you ask) that SCR provides over CCR. For the dives that you discuss in the OP I say CCR all the way.

 

[PfcAJ]

My rebreather experience is somewhat limited, and I don't have or dive any of the units mentioned so far in this thread (I dive an old Drager Dolphin). With that said, if you are looking for a unit to dive past 130ft then I would give up on the idea of an SCR.

I'm not really sure how this applies to the GEM, but on more traditional SCR's with the leanest drive gas (32%) and a pretty stable average O2 metabolic rate you would be looking at a loop FO2 of around 28% which gives you a PO2 of around 1.5. If for any reason you purged the loop, for instance your mask got pulled of and when replacing it things didn't go exactly right and you had to give it a second go, you could possibly add a nice fresh burst of 32% to the loop. Always figuring worst case, that would give you an approximate PO2 of around 1.8.

In short SCR's are great for what they are designed to do, but beyond that they require modification to be appropriate for the task, something that is beyond the scope of this discussion,. Once you begin down that path you have abandoned all of the safety benefits (or perceived benefits depending on who you ask) that SCR provides over CCR. For the dives that you discuss in the OP I say CCR all the way.

Not all SCRs are the same. A Drager works quite a bit different then a rb80, tres presidentes, or even a GEM.

 

[cidcolada]

Not all SCRs are the same. A Drager works quite a bit different then a rb80, tres presidentes, or even a GEM.

This is of course quite true, which is why I made a point of saying that I wasn't sure how it would apply to the GEM. I should have been a bit more specific and said "I'm not really sure how this applies to PSCR's like the GEM, rb80, or Tres Presidentes, but on more traditional active addition SCR's..." Thanks for pointing that out, I wouldn't want to be misinforming anyone.

PSCR's have certainly been dived WAY deeper than I would ever be comfortable taking a Drager or an Explorer (I have heard of at least a few dives on RB80's and Satori's in the 120m range). The reason that I mentioned this potential issue is it is a possibility with the way the Explorer operates, and that was the unit the OP mentioned.

 

[muddiver]

I've trained on the Kiss Sport (manual CCR) and I am certified on the Poseidon Se7en (electronic CCR). All the Kiss CCR's are true CCR's that you can dive pretty deep and well within the range you are talking about. They seem to be the lightest and least complicated, but... you must monitor your PO2 at all times. They are simple in design but not simple in operation.

The Poseidon MK 6 or 7 is a true recreational eCCR that removes a lot of the management that is required by most other rebreathers. It sounds like the Hollis Explorer is also very simple to use as well. I like the Poseidon because the one component that causes the most accidents (besides diver error), the scrubber, comes in a prepackaged cartridge (as does the Hollis). And it is fully upgradable from a simple recreation range (no deeper than 130') to a full trimix unit. All in a package that weighs only 40 lbs.

The Hollis Explorer appears to be a very good unit for the typical sport scuba diver because it removes the issues with oxygen handling and oxygen toxicity by using nitrox, but that limits the unit to what it is intended for, shallow to mid range recreational limits. I do wish my Poseidon came with a CO2 monitor, that is a really cool and desirable feature.

If, like all purchase decisions, it comes down to price. The Jetsem Kiss units are the least expensive and least costly to operate. The Poseidon is at the other end of the price range (though the MK 6 is going for about the price of a Kiss Orca right now from the factory). I think the Hollis and the other SCRs are in between. good post Muzikbiz22, good info.

 

[abscuba]

I am going to agree with kwinter and SCR like a GEM might fit what you are looking for. CCRs are great, I personally dive a rEvo, but to a recreational dive add complexity making it closer to what you would see on a technical dive. If you are just looking to extend bottom time with out carrying extra bottles then I would look at the SCRs out there. The down side to RBs is it is almost impossible to get an unbias opinion. If you have the chance to try one out in the water see how it feels that will help alot in making your choice. If you don't have the chance for that call up AH they sell many of the mainstream brands out there and will be your best chance at getting something that fits your diving and not something thats ment to go down to the doria.

 

[ffdiver]

I think I'm turned off enough from the explorer for it not to be in the running anymore. I've been doing some diving in the 130 -140 range this year and it wouldn't work with the explorer even though I can get one cheap enough.

I don't want to have to keep switching between closed and open circuit weekly just to do certain dives, seems counterproductive.

I'll be looking around for a used Revo or KISS and just start simple and effective in CCR

 

[abscuba]

I dive a rEvo III mini and I love it. I use it for diving mostly from 100-200ft range. It will work great at any depth and is an all around great unit. The draw back is you have alot more to maintain and keep up with. 4 to 5 O2 cells, multiple computers, its built with the technical diver in mind. The kiss on the other hand it what you make it. It can be as simple or as complex as you want it to be and is very expandable. You can get a KISS in a basic configuration that would work great for the diving you are doing now, and if you decided to start doing deeper longer dives it can be expanded to do what ever you need it to. It will also be cheaper. I love the rEvo 100% but its not a cheap unit by any means and if you dont need its redundancy then the KISS would make more sense money wise.

 

[ffdiver]

I think that's pretty much where I'm at now. Honestly even the best wreck divers I know and dive with now are only doing the 150 -300 ft dives once or twice a year if that. It just seems silly now to get a unit geared for that when I won't be doing those dives regularly or if at all.

My next goal is a wreck at 170ft. I think I want to do it on CCR though. I was frustrated on a 140ft wreck dive with my short bottom times.

 

[abscuba]

CCR is def the way to go for 170ft wreck. I did truk last year OC and we did the San Fransisco Maru and I was wishing the whole time I had a RB down there. CCR is really best for deep wrecks. I CCR every where now and I have my sidemount kit as both back up and if I find a place that is to tight for a RB then ill do an OC sidemount to get in there, but that doesnt happen often the rEvo is pretty low profile.