CNS/OTU`S

[Paul Dowling]

Hi lads just out of curiousness whats the highest % ye have being on CNS and OTU on a long deep dive 

[Stephen McMullan]

None of my dives have been very long. The longest was three and a half hours or thereabouts - somewhere between 110-115% CNS as far as I remember

[Alan Price.]

Mine has been something the same as Stephens, Paul.

[Ken Hawk]

3 and a half hours would be a bloody long time for me, longest RT I have done is about 90 mins and that was in Bonaire with the camera, longest deco dive would be no more than 70 mins

[Stephen McMullan]

Its all relative Ken. I bet you spent 90mins in Bonaire looking at the reef and the fish. In my case it was 10mins looking at a wreck and something like 3hrs looking at Pricey & co. on the deco bar. 

I'm waiting for Stewie's, Baza's, PT's or Artur's stats 

[Ken Hawk]

I think 3 hours deco would do my head in, with noting to look at.
Is 10mins bottom time worth the deco, take it, was the Amazon dive.
I may push it too 40 mins next year

[Peter McCamley]

It’s my belief and again what I was taught. After questioning the explanation I am content and subseqeunlty this is a personal choice. I would try and keep my CNS levels no higher than 80%. If I was doing a deep dive long dive, in order to avoid air breaks, it is best to keep the set point to around 1.0 or 1.1. Granted, you will be in the water longer, however you can avoid the air breaks and a possible O2 hit.

In relation to OUT’s, apparently it would be almost impossible to get into trouble on this side as you would need to do repetitive diving for a week at depths in excess of 100 mtrs every day for 5 to 6 hours daily, so not really relavant to my type of diving, however it is very relevant in the event that you had to be go to a recompression facility, as the OTU level may in fact save you having to go straight to level 6, which I believe is the level that a patient automatically goes to. I would welcome information on this.  

[Stephen McMullan]

Run the numbers Peter. If you lower the set point, you'll be longer in the water on deco and you'll end up with a high CNS anyway. I ran a few numbers (see here: http://forum.technicaldiving.ie/index.php/topic,2074.0.html) and found that it makes no practical (*) difference one way or the other. Best advice from the lads was to make sure you're very comfortable on deco, minimize CO2 production and hang in there 

* note for Matthieu 

[Paul Dowling]

Ok so far I have my longest is 61 min bottom at 70m cns 165% and otu 125 this was second dive of two day diving

[Stephen McMullan]

  That's impressive, I'd say you were cooked somewhere between medium and well done. G'wan, spill - when did you get out of the water 

[Paul Dowling]

3 long hours of deco, boredom nearly killed me 

[Capt Morgan]

I think 3 hours deco would do my head in, with noting to look at.

You could always review the smashing photos that you have just taken 

[Colin Parle]

3 long hours of deco, boredom nearly killed me  

Well if the boredom don't kill you the CNS or OTU'S will

[baza]

Is that CNS thing not what holding the right button down on the vision to mask the alarm?!

CNS% is a big factor in planning any long dives. You will be very limited when you do any dives deeper than 90 m or if your run times run over 4 hrs. Dropping the set point is one way to go, but has limited benefits and in reality isn't the most practical option. Looking at any group doing long dives, you really have to face the fact, there is no real way to avoid CNS% of over 80%.... You just need to mitigate the risks and adding air breaks etc. This all depends on what sort of CNS% you are going to end up at the end of your dive.... If you are running 100% to 120% you will have one set of rules to follow, running CNS% of >150% needs to be treated different.

Like Stephen said, dropping set points doesn't sort the problem as the run time just increases. Using the oxygen window is critical and quality deco is a must... Burning you lungs isn't the goal either...

Saying that, lots of o2 is always good for healing up cuts during a week of gas diving

[Stewart Andrews]

Even on single deep dives (no recent previous dive), I have run over 180% CNS and over 150% OTU's (many, many times). It is also worth noting that, in the last three years, I have not done any 'air' breaks - fashions change! (though the human body remains the same!!). There are other things that I have done underwater which I can not allude to here cos I would be put into the Artur category (ie. M*D).

I use 1.3 bar ppO2 on the decent and on the bottom and, generally, 1.5bar as soon as I get back to the shot or at the first Pyle / deep stop, but only when the world starts to relax and the big muscle groups are put away.

To do this a lot of things have to be in place - in respect of your physiology... you have no business being in the water at these depths for those run times if all is not well sorted before-hand anyway. Obviously, I refer to 24 hour pre-hydration, fitness, not tired, not hungry (a good meal the night before), keep moving on deco (circulation), good exposure protection, etc. etc.
Edit: Meant to say that cave divers are now doing around 800% CNS without hits, though the latter half is up in a half-dry habitat.

I certainly do not intend to force this type of diving down anyones throat (nor would I), nor should this forum be scathing about what other people do - it is you choice to push out the boundaries at your own pace (or not). It is worth looking back on your own career and seeing the 'advances' that you have made - perhaps at one time you would have thought these things 'impossible' or M*D! That's why I believe that the M*D word should be banned from this forum. We could replace it with BARKING (just a suggestion!!!!)