AL100 for deco bottle and/or sidemount?

[kensuf]

I'm a weenie in the open ocean and shoot for run-times less than 2 hours whenever there's going to be blue water / drifting deco.

 

[stuartv]

I'm looking at a plan that's 25 - 30 minutes of bottom time and about 60 minutes total run time. With 70% for deco gas, that is still putting me over 20 cu-ft required.

Also, for the Oriskany, I believe the deco will be hanging on (or near) the anchor line.

 

[kensuf]

You might be planning on staying on the anchor line for all of your deco, but unexpected stuff can happen in the ocean that alters your plan. That's one of the reasons I limit my total runtimes in the open ocean.

Regardless, 30 minutes on 18/45 will give you a run-time of less than 90 minutes with 50% as a deco gas.

 

[stuartv]

Right. Like I said, my plans that I'm considering are all right around a total run time of 60 to maybe 70 minutes. The most recent plan I ran is 58 minutes, total, using 24/20 (my highest cert is for Helitrox) and EAN70 for deco. But, that results in a requirement for 24 cu-ft of deco gas. Not acceptable for only carrying 1 AL40 for deco.

I need to either get an 80 for my deco gas, or get trained to carry 2 deco bottles before then.

 

[kensuf]

An AL80 will do it for deco. Helitrox probably won't.

The flight deck is at 150'. Personally, I'd probably run something more like 21/35 or 18/45 so I could have a gas that gives me the flexibility to go a bit deeper than the flight deck.

Oriskany Reef Dive Safety Considerations

 

[BRT]

I think you will find that those Luxfer cylinders are more buoyant than an AL80. They are a lot heavier.

 

[stuartv]

I understand that the certification limits of Helitrox are 150'. My current level of experience is a max of 160' on EAN23. My goal for this trip is to look in on the hangar deck, by going to 165 - 170 feet. That will extend my depth experience a little further. As my highest cert is (and will be, when I do this dive trip) Helitrox, I won't be able to get a fill with more than 20% He or less than 21% O2. If I do settle on a plan with a max of 170', I will revise my bottom gas selection to reduce my max ppO2. Since my current deep experience is on (basically) air, on wrecks in the Saint Lawrence River, I feel pretty good about using Helitrox and (possibly) extending the depth of my experience a little bit on the Oriskany, where I'm expecting much warmer water and much better viz.

I'm hoping to do full normoxic trimix training later this year. But, in the meantime, I want to do the dives I can and enjoy them as much as I can without pushing my limits other than in a very cautious way, taking baby steps.

 

[stuartv]

I think you will find that those Luxfer cylinders are more buoyant than an AL80. They are a lot heavier.

The specs say an 80 is +4.4 when empty and a 100 is +2.8 when empty.

Regardless, I decided not to buy them.

 

[sea_ledford]

The dive you are proposing is basically what our deco divers do for working dives; 160' for about 60 min total run time. We use O2 for deco, so that is the primary difference, but we can get several dives off of a single O2 40 filled to about 2000 psi (no booster). We are happy to run them down to dregs for one reason - we limit our dive time based on being able to deco out on back gas solo (not within 1/3s though). I figure if the currents are strong enough to get blown off the rig, they are also strong enough to purge away our O2 if we forgot to shut off the valve. Unplanned hour long solo blue water drifting deco would totally suck, but we wouldn't drown. And we would have plenty of time to contemplate the multiple mistakes we made to get in that situation

Just something else to throw into your planning matrix.

-Chris

 

[stuartv]

Yes, I am discussing this very subject with my dive buddy now. I have been running plans based on being able to deco out on back gas alone, if necessary.