Wanna stay down longgerrr

[Blackcrusader]

Eh, what?
My last dive was to 57m on OC, why would you doubt that he went down to 45m on OC...?
But yeah, rational people wouldn't do a dive like that on a single tank.

Doubters are everywhere That was a planned dive so seemed rational to me and the instructor who came with me. lol

Video or it never happened right? By the time we got back to around 6m I still had plenty of air left to stay at around 5m for another 15 minutes doing the slow off gassing and taking some photos on the reef.

 

[Blackcrusader]

well at least not on a "normal" tank. never heard of a rational person going to almost 150ft w/o a twinset or something else like stage bottles... ,tg.

Well I guess you weren't around in the 1980's. BSAC Sports Diving on air is to 50m and we did this on single tanks often Steel 120 with 230 bar. My SAC rate back then was much higher than it is now as was not as good a diver in my first few years of diving. Mainly going too fast on dives lol. We did have tanks on the anchor line at different depths as most of the dives were also multilevel deco dives with planned deco stops. The 45m dive is a short bounce dive and no deco was incurred. Dives to 40m on air on a single tank staying within NDL limits are normal for recreational divers. You wrote that your 70 foot deep dives are not deco dives and you did not exceed NDL. Now you say the dive depth average is 70 feet which could be done for nearly an hour. How about you post your dive log where you say you are showing very high CNS levels for others to look at?

OK on this dive to 25m which is staying at 25m - 26m which is around 80 plus feet even on this dive which was a second dive my CNS never got above 10% My PO2 max was point 74 as can be seen on the display. This on an AL80 with 200 bar start. Maybe you think I should be using twins on these dives but I don't as most recreational dives are around 60 - 70 minutes with a lot of dive centers.

 

[Angelo Farina]

@tursiops many thanks of the detailed explanation of oxygen limit management.
I see that on this point the knowledge advanced significantly beyond what I was taught in 1975-77.
At the time we did use mostly CC pure oxygen rebreathers (ARO), so hyperoxia was a serious problem.
But we did not have such a knowledge. We just had a "safety curve" giving max time at each depth. And it was considered safe to dive for a couple hours at ppO2=2bar, which is far beyond current recommendations.
I am learning a lot in this thread. Thanks again!

 

[Swedinsidemount]

I did that 45m dive on an AL 100 single tank on air. Started dive with 200 bar ended dive with 60 bar. SAC rate for the dive was 9.85L/min due to swimming back against current for last half of the dive. It was as I said just to retrieve a dropped camera rig and I wasn't exceeding NDL. I still had 180 bar left by the time I retrieved the camera rig and had a pleasant dive after that.

My CNS never got above 8% and this is the second dive of the morning.

View attachment 631456

Sorry if my comments came across as rude or anything. But you have answered my question. You use a single AL100 and you dove to 45m safely. SO my twin 63s should be ample to get me to deep MODs safely, that was what i wanted answered, thanks. A lot of people in this thread have gone to those depths, if anyone could please comment what they use gear wise that would end this mayhem.

 

[Blackcrusader]

@tursiops many thanks of the detailed explanation of oxygen limit management.
I see that on this point the knowledge advanced significantly beyond what I was taught in 1975-77.
At the time we did use mostly CC pure oxygen rebreathers (ARO), so hyperoxia was a serious problem.
But we did not have such a knowledge. We just had a "safety curve" giving max time at each depth. And it was considered safe to dive for a couple hours at ppO2=2bar, which is far beyond current recommendations.
I am learning a lot in this thread. Thanks again!

Yup good learning can be done in these threads and the oxygen management great information. Thanks @tursiops

 

[Blackcrusader]

Sorry if my comments came across as rude or anything. But you have answered my question. You use a single AL100 and you dove to 45m safely. SO my twin 63s should be ample to get me to deep MODs safely, that was what i wanted answered, thanks. A lot of people in this thread have gone to those depths, if anyone could please comment what they use gear wise that would end this mayhem.

I do not take your comments as rude. You asked to verify what I used on that dive. If say I was using an AL 120 I would match your twin 63's just about. Now the other thing to consider is your sac rate / RMV on your dives. If I had a scooter I bet my SAC rate would increase from all the excitement of being able to have fun with one.

This issue of MOD is what you can do on air, do you need to do planned deco? Do you plan to dive on Nitrox and stay shallow.
Even on Shearwater for any diver using the AIR mode they can see the MOD on air is 57m. You cannot do that on nitrox. Very few of my dives do I use nitrox.

 

[Alekseolsen]

I dont quite folllow the MOD "obsession".

From PO2 standpoint you could do ~55 meters on air with a PO2 limit if 1.4

Narcosis is a different animal, and different divers with different training would give you very different depth limits on air, ranging from (probably numbers even higher and lower than what I know) 30 meters (GUE) to 50 meters (old IANDT manuals).

What Ive never heard of is the computer telling you this, and giving high CNS values based on it. Is it possible that your computer calculates and gives you "OTU's"?

Edit: (lots of) typos

 

[100days-a-year]

@57m 24% nitrox is 1.6 P02, so doable but probably not a great idea for a square profile dive of any duration.
I have no idea how many single tank dives have been bone to 45m on 72s and Al80s but it has to be an astronomical number over time. I preferred 100s or better as almost all my dives were working and involved some current.
A lot to be said about the conditions the dive is done in as far as feasibility of any given gear.
I used an #18 to #24 bladder and minimalist BP and harness to streamline my profile and did thousands of said 45m dives. As have a couple dozen friends. Some even bypassed any bladder and dove hard backpacks.

 

[tursiops]

Sorry if my comments came across as rude or anything. But you have answered my question. You use a single AL100 and you dove to 45m safely. SO my twin 63s should be ample to get me to deep MODs safely, that was what i wanted answered, thanks. A lot of people in this thread have gone to those depths, if anyone could please comment what they use gear wise that would end this mayhem.

You are asking a different question here than you did before, so you will get a different answer.
Before your issue was CNS buildup, which is NOT really possible given the dives you describe.
If the ONLY issue is getting to 45m "safely" using twin 63s, IF YOU USE AIR the only question is your breathing rate.
Do not try and emulate Black Crusader's dives; he has strange physiology and uses very little gas.
What is YOUR breathing rate?
To go to 45m "safely" you need to account for one of your 63s or the regulator on it failing, because you will need gas to get to the surface and that is in the other 63 you carry. So you need to plan your dive for descending, spending time at 45m, and ascending, all on one 63. . You will find that this is NOT a no-decompression dive...even if you only spend 1 minute on the bottom. So you are talking about a deco dive without enough gas.
You need Deco training, you need to know your breathing rate, you need to do this dive on air, you need to stop worrying about CNS, and after all that you'll find you are probably narced out of your gourd at 45m. Some agencies won't even let you go past 30m without some of the nitrogen in your air being replaced by helium.
You are on a bad path, and staying on it while calling yourself a safe and cautious diver is delusional.

 

[Angelo Farina]

A already say, I like too keep it simple. For a 45m dive with some light deco I would use my standard 15 liters tank. Filled at standard 232 bars it gives me almost 3500 liters of plain air, which are enough.
If going deeper (my recreational cert is for 50m with deco) I would prefer to switch to a 9+9 or 10+10 liters twin.
My SAC rate is around 13 liters/minute.
As others already pointed out, the SAC rate commands the tank size...
I do not worry at all about CNS% (still learning the concept). I do not worry too much about NDL, as I always assume I will need some deco.
I will look at deco only when I am back under the boat (or the buoy), at 9m, and I check the computer for seeing if I need a stop there or I can go to the upper stop at 6m.
I am very concerned, instead, on the amount of gas remaining. I usually start coming back to the boat when I consumed 1/3 of the available gas. If planned deco is not just minimal, I reduce this to 1/4.