Question for the masters - TriMix / Manual CCR

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

SW diver here. As the SW uses "dilout" we can't have the the luxury of different bailout and diluent ppo2, so you may get mixed messages without specifying the configuration. For cave I generally run dilout max ppo2 @1.4, with the understanding it can make pulling down an O2 spike difficult. This way the the deco penalty for bailout is minimized. I generally run standard gasses, so 32% up to 110'(30 meters).
This is great feedback thank you. I was thinking the dame thing and you bring up a great point about config. I should have been more specific. Where I live almost all of the cave entrances start at about 40m and then the journey varies. I’m still just building up my diver hours but I would love to hear more about the diving you’re doing. Coincidentally, I used to live in Parker :)
 
I don’t plan my bailout at anything like a PO2 of 1.6
I would look at something closer to 1.0 and be more concerned about the gas density - preferably less than 5g/l
Yeah the 1.6 came from an article I was reading and @Heat Miser I think summed it up perfectly with the 1.6 debate. My inclination is to be more conservative but I don’t really have any experience to back up any opinion.
 
I'm pretty sure he's not coming back...see what I did there?
Ouch lol…. To be clear, it’s not what my instructor suggested, it’s just me (as a CCR noob) trying to logically work out things in my head. I do appreciate the feedback and data though. I have a ways to go before I‘m qualified to even take the course but I can’t help looking at old dive profiles (regular side mount air with a 50 and 100 deco) wondering how I could have done them with a CCR.
 
Yeah the 1.6 came from an article I was reading and @Heat Miser I think summed it up perfectly with the 1.6 debate. My inclination is to be more conservative but I don’t really have any experience to back up any opinion.
Bailing to 1.6 is, in general, a very bad idea. Even moreso in a cave.

You'll find all sorts of nonsense like this in the CCR community, often attributed to "well known names" even.
It's up to you to sort out the "that sounds like a bad idea" from the useful.
 
First and foremost I am not an expert or a ccr instructor so don't take anything I say seriously...

So you plan an emergency bailout using a 1.6 (I get the why) and I see divers planning their dives at a 1.4, but for my CCR which is manual the recommendation is 1.2. Is that because it’s manual vs electronic?

When you plan your dive, and you’re working out your trimix, is there a reason why you would pick an END of say 30 vs 40 or 20?

Who is planning on a po2 1.6 as their bailout? What are you "getting" about the why here? I'm not sure I'd want to be hyperventilating from a co2 hit and then jump on a po2 at the recommended limit. I'd take a high po2 over water anyday but it would not be the plan.

Ouch lol…. To be clear, it’s not what my instructor suggested, it’s just me (as a CCR noob) trying to logically work out things in my head. I do appreciate the feedback and data though. I have a ways to go before I‘m qualified to even take the course but I can’t help looking at old dive profiles (regular side mount air with a 50 and 100 deco) wondering how I could have done them with a CCR.

To clarify, my comment about "not coming back" was about Gus, not you.
 
This is great feedback thank you. I was thinking the dame thing and you bring up a great point about config. I should have been more specific. Where I live almost all of the cave entrances start at about 40m and then the journey varies. I’m still just building up my diver hours but I would love to hear more about the diving you’re doing. Coincidentally, I used to live in Parker :)

Mostly FL caves the last few years with training in local mud holes and at Rock Lake. A buddy and I did a week looking around JB3 back in March. I wouldn't want to take the bailout deco penalty that air dill would give me just because the cave dips down to 100' at one point on the way back there. Especially when most of the time your in the 60/70' range.
 
I see a lot of discussion about ppo2 on bailout for deco purposes. Surely cave and overheads alter that a bit but... With a 2 bottle bail out plan, ie bottom and deco gas; I'm showing within a minute of a 110' dive 1.3 @40mins
20230622_223519.jpg
 
First I miss why most CCR's are dived on 1.3 PO2 if the ccr works. This has to do with CNS that lasts 3 hours to get to 100% and most scrubbers officially last only 3 hours.
1.2 is also used quite a lot. 1.4 in ccr is not used a lot.

First we do open water ocean diving, no cave diving.
There are some advantages and disadvantages on which PO2 you use at depth. Let's say we go to 100m for 20 minutes . If you use a 1.3 or a 1.2, this makes already a difference in the total divetime.
Put it in a diveplanner, diluent 10/70 (DIR-gas with also a lot of disadvantages), it will give you on 1.3 a divetime of145-150 minutes (calculated with Multideco, 40/75). So 59 minutes at 6 m. You stay the whole dive on the loop.
A 1.2 setpoint for this whole dive will give you 70 minutes at 6m. So the 1.2 has for sure disadvantages.
This means, diluent switches can have advantages. All will be learned by your instructor when you do a full trimix course.

On OC I use the 1.4 on deep dives, but that is only at bottom. As soon as you go up, there is no 1.4 anymore. Then you switch to a 1.6 on the first stop where you switch, but the 1.6 will become less than 1.6 on the next stop. So with the gasswitches you go to 1.6 for a while.

A bailout gas means you go up from the deepest point in the dive with oc bailout. Then you choose for the decogases on 1.6. The bottomgas is not that important because you don't dive there anymore as bottomgas, it is just a bailout to breath and you go up.
So if you have 10/70, ean50 and 100% as bailoutgases (ignore icd as 10/70 to ean50 is not the best choice, ignore a travelgas between the bottommix and first decogas to make it easier), you take the 10/70 oc after 20 minutes bottomtime. Then you go up. The PO2 lowers because of the 10% oxygen. But at 21m, you switch to ean50 and at 6m you have 100% at a PO2 of 1.6. Because of the low PO2 of the first bailout, your total divetime will be longer.
But if you use a 12/65 instead of a 10/70 as bailout, the PO2 when breathing the 12/75 will be higher, and the total bailouttime and divetime will be less than using a 10/70.
So a 12/65 is a better bailout gas. But if you take a travelgas, the choice for a 10/70 as bailout can be more valid as a 10/70 also can be used as diluent if the 3 liter cylinder drains for whatever reason.

You can also choose for a poormans mix as diluent, 6/72. This means if there is a high PO2 at bottom, you can lower the PO2 quite fast. And high PO2's at depth are more tricky than in shallow waters. So the 6/72 vs 10/70 discussion is done in a course also.

OC diving, a 12/65 is for sure a better mix at 100m than a 10/70. It gives a lot less deco, the PO2 is still within the 1.4 norm. Some people choose a 13% oxygen also.

In a cave you can use if the tunnels are constant at depth (p)scr bailout. This means the bailoutgas must have a right PO2 to maintain a PO2 in the loop.
So if the cave is only 20m deep, you can take air as bailout gas. No problem, you must calculate how much is needed from the longest penetration distance, and you drain the tanks while breathing it oc.
But if you take an ean32 as bailoutgas, you can use the ccr in some cases as gas extender. This option fails with air as bo gas.
Also if you go deep in a cave and the tunnel is horizontal, a higher PO2 but max 1.4 can have advantages. So a 6/72 at 100m in a cave and 10 minutes swim back at 100m means oc a lower PO2 than a 12/65. The 12/65 will give you less deco. Where the 6/72 a good diluent can be, the 6/72 can be not the best bailout option.

And don't forget to think about safetydivers if you do ocean diving and go to 100m or more, oc and ccr. In a cave you can probably do setupdives, in an ocean it is more difficult.
 
I have advice for you: If your instructor thinks it's a good idea to have deep BO in one of the sidemount tanks and shallow BO in the other, run for the hills.
what's the standard set up for Side winders ?
 
https://www.shearwater.com/products/swift/

Back
Top Bottom