New to this board

[trimixer860]

Im new to this board so please be nice I been reading a bunch of post on this board and have spent a few hours reading post on rebreathers. I was wondering is any one on the board would give me an exaple of a dive profile using ccr. Ill take one of my dives 160' 30 minutes on the bottom. My Mix 24/30 with two deco bottles nitrox 60 and O2. Total run time 55 minutes. Making the deco 22 minutes. If you where using a ccr for 160' for 30 minutes what would your profile be and what would you carry for a bail out bottle.Thanks

 

[Mark Milburn]

To be honest the difference in dive profiles will be negligable. You're running a PPO of 1.39 we would calculate on 1.25 though we would be running a set point of 1.3.

Even the deco wouldn't be much different. As we would have the similar loadings if we were using the same diluent as your bottom gas. The deco would also be similar, the main difference is that our PPO will be constant for the whole ascent.

For this kind of dive, bailout would probably be 2 bottles, 1 of bottom gas and 1 of 80%.

The big difference is the running cost, I may never use my bailout and I would only have used 30bar of my Dil and O2. I'm ready to go in again a few times without refilling my cylinders.

CCR users tend to run the same Dil for all dives, I have 2 cylinders one has 18/30 the other has 10/50. So 18/30 for this dive, using the 10/50 would increase the deco obligation which is why I have options.

But I am currently thinking about changing the way I dive deep. Keeping air as my Dil and manually adding my bottom gas from my bailout into my 2nd manual add on the counter lungs. This way I only need to keep my bailout of trimix and not have to worry about my unit. This is the way APD designed the unit to be used and it makes sense in a lot of ways. I will always have access to my air dil to bail-out too if need be and I also have a reg on my O2 which I can bail to at 6m.

 

[trimixer860]

To be honest the difference in dive profiles will be negligable. You're running a PPO of 1.39 we would calculate on 1.25 though we would be running a set point of 1.3.

Even the deco wouldn't be much different. As we would have the similar loadings if we were using the same diluent as your bottom gas. The deco would also be similar, the main difference is that our PPO will be constant for the whole ascent.

For this kind of dive, bailout would probably be 2 bottles, 1 of bottom gas and 1 of 80%.

The big difference is the running cost, I may never use my bailout and I would only have used 30bar of my Dil and O2. I'm ready to go in again a few times without refilling my cylinders.

CCR users tend to run the same Dil for all dives, I have 2 cylinders one has 18/30 the other has 10/50. So 18/30 for this dive, using the 10/50 would increase the deco obligation which is why I have options.

But I am currently thinking about changing the way I dive deep. Keeping air as my Dil and manually adding my bottom gas from my bailout into my 2nd manual add on the counter lungs. This way I only need to keep my bailout of trimix and not have to worry about my unit. This is the way APD designed the unit to be used and it makes sense in a lot of ways. I will always have access to my air dil to bail-out too if need be and I also have a reg on my O2 which I can bail to at 6m.

Mark thanks for the reply. so what size bail out bottles do you normaly use on such a dive? I normaly carry two 40cf bottle for any thing over 150 one would be o2 and the other 60 nitrox. I plan my bottom time by how much back gass i carry, needing enough in case of lossed deco gas. Are you planing your bottom time for a dive base on how much bail out gas you what to carry?

 

[padiscubapro]

Im new to this board so please be nice I been reading a bunch of post on this board and have spent a few hours reading post on rebreathers. I was wondering is any one on the board would give me an exaple of a dive profile using ccr. Ill take one of my dives 160' 30 minutes on the bottom. My Mix 24/30 with two deco bottles nitrox 60 and O2. Total run time 55 minutes. Making the deco 22 minutes. If you where using a ccr for 160' for 30 minutes what would your profile be and what would you carry for a bail out bottle.Thanks

running a conservative profile with a 1.3 setpoint runtime would be about 58 minutes with a dil containing 30% Helium..

Bumping the deco up to 1.45 will cut about 4 minutes off the deco, doing to OC oxygen would bump another 2 or 3 minutes off..


My personal preference for a dive this short is to runmy bottom setpoint around a 1.3 and use this all the way to 20 fsw where I'll periodically flush with oxygen maintaining a minimum po2 of 1.45

For adive this shallow, I would normall do at least 60 minutes on bottom, with a total runtime of 2 hours.. If this was a big wreck or reef where you could multi level it Itd add in a 30 minute leg at 100ish and only add 22 minutes to the run time.. If I swapped out the 100fsw leg with a 60ft leg it would have only added 12 minues to the original run time..

This is a dive I have done many times in grand cayman..
130fsw for 60, 100 for 30, and 60 for 90 minutes.. If Im using air as a dil I have no required deco, if I uses 20% he, I have under 10 minutes of deco at 10fsw

This way I get my 3 hours of bottom time in on a single dive... If you wanted to do this OC you would need ALOT of Gas..


My worse case deco if I didnt get to do the shallow 60ft leg would be 40 minutes (if I did the entire 100ft leg), deco after the 160fsw stop is about 36minutes, so the 30mins at 100fsw is almost "free" (a 25 minute leg instead of 30 would have the same required deco time as not doing the leg at all)

This is the beauty of a CCR you can multi level the dive and since the loop gets richer as you ascend. you can deco while enjoying yourself..

 

[Mark Milburn]

Mark thanks for the reply. so what size bail out bottles do you normaly use on such a dive? I normaly carry two 40cf bottle for any thing over 150 one would be o2 and the other 60 nitrox. I plan my bottom time by how much back gass i carry, needing enough in case of lossed deco gas. Are you planing your bottom time for a dive base on how much bail out gas you what to carry?

My usual bailouts are 2 x 7L 232bar cylinders, just a little bigger than a 40cf with a little more pressure gives me about 20% more gas. I would plan my dive according to how long my bailout of 80% would last. Working a SAC of 15LPM I can do about 67 minutes at 6m on my 7L 80% (emptying it, my SAC is actually as low as 8.5LPM), and I would still have my 7L of bottom gas as well as my 3L of dil and 3L of O2. So I would calculate my bottom time based on a max of 60 minutes of deco at 6m on 80%.

What you have to remember is that only a complete loop flood or a CO2 breakthrough would stop the rebreather from working. Completing your pre-dive checks should make the likelihood of a complete flood very unlikely, proper packing and usage of the scrubber should stop a CO2 breakthrough.

Sorry for all the metric stuff, I am in the UK.

p.s. I also fill my own cylinders, usually to 250bar.

edit: I forgot to say I know people who do not take bailout on 100m dives, I may be a little crazy but I'm not completely bananas.