Maximizing depth AND time under

[DwayneJ]

Air Integrated Computers such as the Galileo monitor remaining bottom time based on NDL and actual gas usage for the current dive.
So while it's true they don't use SAC, they go one better.

Given we have clarified hitting NDL at depth guarantees you will have gas left at the end of the dive, AI is completely irrelevant. My computer of choice is a Shearwater Predator.

Dwayne

 

[Codiak]

True if he keeps pushing deeper... however, it should be possible to go shallower and thus burn air faster than NDL

 

[Codiak]

No TDI deco instructors on Maui... Any preference of TDI over IANTD?

No preference to the agency, just the proper course.... looks like IANTD Technical Diver Course is what you'd want.

 

[TSandM]

Are you using tables, or diving a computer?

A lot of computers will recognize that you are offgassing in the shallows -- I generally figure that any time I spend at or above 30 feet is "free" (in essence, it's doing backgas deco). So I will do a dive like you describe, going deep at the beginning, multi-leveling up, and then burning off the last of the tank in the shallows, at or above 30 feet. If you get Mark Powell's book, Deco for Divers, you'll get a lot of information on how decompression programs calculate nitrogen loading and offloading -- once you reach a certain depth, you are offgassing, and as you move up, the controlling compartment changes, becoming a slower compartment as you approach the surface. Since you don't load much nitrogen into slow compartments during NDL dives to deeper depths, you're eventually going to reach a point where you will be within no deco limits, essentially no matter how long you stay (given that we aren't diving rebreathers).

 

[DwayneJ]

True if he keeps pushing deeper... however, it should be possible to go shallower and thus burn air faster than NDL

If my dive average depth is less than 60', gas is my limit. If my dive average depth is greater than 60' NDL is my limit - Its not rocket science. My first and last AI computer failed high reading 5000psi which was a good reason for me to switch over to a wrist mounted computer running a well proven algorithm - Buhlmann ZH-L16 using levels of conservatism which I set and understand.

That AI computer you mentioned only uses 8 compartments.

 

[selytch]

Are you using tables, or diving a computer?

A lot of computers will recognize that you are offgassing in the shallows -- I generally figure that any time I spend at or above 30 feet is "free" (in essence, it's doing backgas deco). So I will do a dive like you describe, going deep at the beginning, multi-leveling up, and then burning off the last of the tank in the shallows, at or above 30 feet. If you get Mark Powell's book, Deco for Divers, you'll get a lot of information on how decompression programs calculate nitrogen loading and offloading -- once you reach a certain depth, you are offgassing, and as you move up, the controlling compartment changes, becoming a slower compartment as you approach the surface. Since you don't load much nitrogen into slow compartments during NDL dives to deeper depths, you're eventually going to reach a point where you will be within no deco limits, essentially no matter how long you stay (given that we aren't diving rebreathers).

Will check out the book with the courses. I used computer but willing to do paper calculations as well.

 

[DiveNav]

1) I would NOT recommend to plan to finish the dive with an almost empty tank. At all!

2) Use Trimix for the deep portion and bring a stage bottle for the shallow decompression ... or ... get a rebreather

Alberto (aka eDiver)

 

[DuboisP]

how to go deep and use all the air at the same time.

no way
saturation is physic, depending of depth and time
more depth, less time
less depth, more time
if you want to stay within NDL, no way to extend depth AND time.

go nitrox, go advanced nitrox, go decompression, go trimix

 

[surfinusa555]

I'm 99% certain B&B on Maui can blend you any % of nitrox you want. I'm pretty sure I even saw that they do trimix when I was there. Since you will obviously know your dive plan, just get a blend that works with your dive(s) for that day.

 

[gsk3]

Read up on Rock Bottom (NWGratefulDiver has a great article online) and you will very quickly see that when you end the dive with an empty tank as you are trying to do, your safety margin is not nearly high enough.

Know your rock bottom number for 120ft (calculated using the sum of yours and your buddy's SAC since they'll be breathing off your octo). I suspect you're finishing the dive with about the right amount of air to get you and your buddy up safely in case of total gas loss.

If you still have extra air that you want to use, options include nitrox, dive computers, or getting a recreational deco cert.