How major of NDL benefits?

[aue-mike]

Maintaining a 1.2 while slowly working up a wall is where the real benifits of constant PO2 diving are seen.

For long/deco dives, the constant PO2 advantage is irrelevant and actually a fallacy IMHO. Yes, there are many other advantages of CCR, but I personally don't buy the whole "constant PO2 is more efficient for deco dives" line for a variety of reasons. YMMV...

 

[Mr.X]

Been watching this thread a bit. When it comes to the deeper stuff, with extended bottom times & long hangs the idea of having portable chamber on site makes sooo much sense for OC or CCR. Having had these on a few job made me feel secure + physically fit and ready to work the next day.

Also, a nice pastrami sandwich in the afternoon is said to cure any longish- dive after-effects.
I just made that up because I'm hungry and don't want to eat my Subway vegan sandwich.

 

[cameron]

For long/deco dives, the constant PO2 advantage is irrelevant and actually a fallacy IMHO. Yes, there are many other advantages of CCR, but I personally don't buy the whole "constant PO2 is more efficient for deco dives" line for a variety of reasons. YMMV...

Why don't you share your reasons.

As I stated before, I don't think it makes much difference on square profiles, but when you take into account a multi level profile, then it is just plain physics. There is less inert uptake when maintaining a constant ppo2 as you ascend.

Remember we are talking about NDL Diving here, not decompression diving; deco diving is a totally different beast.

 

[silent running]

For long/deco dives, the constant PO2 advantage is irrelevant and actually a fallacy IMHO. Yes, there are many other advantages of CCR, but I personally don't buy the whole "constant PO2 is more efficient for deco dives" line for a variety of reasons. YMMV...

Hello aue-mike, how did you form such an opinion?

It's pretty simple, less inert gas uptake, longer time in water before deco obligation. Assuming you've picked a good, high set point, a CCR with air dil is essentially a nitrox mixing machine and will give the optimal mix for your depth, especially and including your ascent. The % of O2 will increase in a smooth curve and provide you with the quickest inert off gassing possible during ascent as the increasing O2 % washes out the inert gas. Are you prepared to take 10 different gas mixes with you on an NDL dive to try and imitate the same inert gas uptake? It still wouldn't be a nice smooth curve and you'd still rack up some deco while I on the CCR won't.

For deco dives, the same is true only more so. I have had 25 minute deco times upon starting ascent which vanish by the time I get to my shallow stops, simply from making a long, slow ascent on CCR. The benefits of constant PO2 diving are well known, like the physics on which they rely. -Andy

 

[silent running]

As I stated before, I don't think it makes much difference on square profiles, but when you take into account a multi level profile, then it is just plain physics. There is less inert uptake when maintaining a constant ppo2 as you ascend.

Remember we are talking about NDL Diving here, not decompression diving; deco diving is a totally different beast.

Hello cameron, the principles involved in constant PO2 diving apply for any dive, deco or not. And anyway, all scuba dives are deco dives.

Whether you ascend from a square profile or a multi level, one of the benefits of constant PO2 diving is a smooth increasing % O2 on ascent, no gas switching, no part of the dive where you are breathing a mix that was better for the deco stop you did 20ft below, but not the next one. Another huge benefit is the very small amounts of gas needed at depth. On a square profile/wreck dive, you only need very small amounts of O2 once at depth, to maintain the PO2 as you are rebreathing the gas. And because you are not metabolizing the inert gas in the dil, which is there merely to give you enough volume to expand your lungs and breathe, you will need no additional dil gas once at depth, or for the rest of the dive.

On square dives in particular, you will use very little gas, until you begin your ascent, when you begin to use your more of your O2 supply, but again, you're rebreathing the O2 and only metabolizing a small amount. My CCR instructor routinely gets 10+ hrs out of his 19cuft cylinders doing square profile dives on the Andrea Doria. NE wreck divers were the earliest civilian pioneers of CCR, diving used military gear, like the Mk 15.5. A yo yo profile will cause you to use more gas, but you'd have to do an awful lot of yo yoing to use up the same gas as on OC, you'd probably get bent first.

There is no way to improve on the gas economy of a CCR, unless you come up with human usable gills... -Andy

 

[Mr.X]

Hello cameron, the principles involved in constant PO2 diving apply for any dive, deco or not. And anyway, all scuba dives are deco dives.

Whether you ascend from a square profile or a multi level, one of the benefits of constant PO2 diving is a smooth increasing % O2 on ascent, no gas switching, no part of the dive where you are breathing a mix that was better for the deco stop you did 20ft below, but not the next one. Another huge benefit is the very small amounts of gas needed at depth. On a square profile/wreck dive, you only need very small amounts of O2 once at depth, to maintain the PO2 as you are rebreathing the gas. And because you are not metabolizing the inert gas in the dil, which is there merely to give you enough volume to expand your lungs and breathe, you will need no additional dil gas once at depth, or for the rest of the dive.

On square dives in particular, you will use very little gas, until you begin your ascent, when you begin to use your more of your O2 supply, but again, you're rebreathing the O2 and only metabolizing a small amount. My CCR instructor routinely gets 10+ hrs out of his 19cuft cylinders doing square profile dives on the Andrea Doria. NE wreck divers were the earliest civilian pioneers of CCR, diving used military gear, like the Mk 15.5. A yo yo profile will cause you to use more gas, but you'd have to do an awful lot of yo yoing to use up the same gas as on OC, you'd probably get bent first.

There is no way to improve on the gas economy of a CCR, unless you come up with human usable gills... -Andy

A CCR is certainly a terrific nitrox mixing machine. Having a steady PO2 is a real blessing. Not having to dive the Doria with so many stages/bailouts is so welcome...although I do miss the "macho effect" when posing for the cameras!

The Doria can be a tricky madame. Curious...is your instructor taking pluggable gas for his unit? 10 hours is a long stretch of time for a set of 19's. I personally like knowing I have a bare minimum of thirds in the bottles. I developed this practice many years ago when I read in an early Insp. list of someone in the UK thinking he would make the dive on 50 bar. He finished the dive, but in the end got into some humorous difficulty.

...some historical reference off the top of my head. The NE USA tech crowd of the early 90's were predominantly bottle users. The CCR's I saw coming aboard the premier tech boats (late 90's) were Mk's, Cis and some hot-rodded Atlantis units. The Inspirations, home-builts, PRISM's made it during 1998-9's. Again, this is my best recollection. Nowadays, every one and their uncle uses one of these dang things.

 

[wedivebc]

never mind

 

[o2deep4o2long]

Wow,faster than your rebreather profile!

I am sure rebreathers have many advantages,but greatly reduced deco times on 200 foot dives is not one of them !

The big advantage of a ECCR is that it removes a great deal of time pressure from divers (deep and shallow).

There is a huge difference in "having 10 breaths to solve a problem" and "having 1-2 hours to solve a problem" when diving deep.

 

[caveseeker7]

There is a huge difference in "having 10 breaths to solve a problem" and "having 1-2 hours to solve a problem" when diving deep.

That largely depends on the problem now, doesn't it.
And after how many breath you realize you have it.

Not having to dive the Doria with so many stages/bailouts is so welcome...although I do miss the "macho effect" when posing for the cameras!

One of the big Kahunas, a MK16, MK-5p or Ouroboros should do the trick.
And you can always mount 20 ltr bailout tanks on the side like the xKPP divers. :14:

 

[Mr.X]

That largely depends on the problem now, doesn't it.
And after how many breath you realize you have it.


One of the big Kahunas, a MK16, MK-5p or Ouroboros should do the trick.
And you can always mount 20 ltr bailout tanks on the side like the xKPP divers. :14:

LOL. I think the big prize winner of the bunch was the Halcyon PVR with twin 80's. It was a monster. The one pictured is without the shroud and smaller steels bottles.

http://www.therebreathersite.nl/Presentatie2002/1990-2000/halcyon_pvr-basc.htm

Back to NDL's...while a CCR is nice in the shallows I see almost no point in it unless you are doing work with shy animals, or some stealth stuff. OC is far easier to manage...and cheaper!!!