deco mix & travel gas for hypoxic dives; thoughts

[Kern]

You use 21% at 100m????????????? That is one hell of a PO2!

I am glad someone else made that comment - looked mind blowing to me, but no one else had commented on it... 2.31 ATA? Even at 70m it would be 1.68 ATA.

The context is for deco & travel gas for those that missed it.

 

[Kern]

55m (180') = 18/45, 50% and O2
75m (246') = 15/55, 50% and O2 and sometimes 35/25 but mostly just a bottom stage of 15/55. I would not bring 21/35 for a 75m dive.

Basically if there is <13mins or less between the bottom and the first deco gas I'm fine with that. 15+ mins of ascent time I add another (deeper) deco gas (at whatever deep stop ascent rate you desire - no need to get into that here). The rock bottom for 15+mins is just rediculous. Adding a deeper gas for only a 220ft dive (eg 35/25) doesn't really do much as far as deco goes it just reduces the rock bottom YMMV.

>75m I'm not doing, its too damn cold around here. The CCR guys are breathing warmer gas and this is pretty much seem to be the CCR-OC breakpoint. There are only a couple guys around here doing >75m on OC.

I would not do a 3 bottle dive in current without a scooter (regardless of mix). The granny line to pull yourself to the anchor line in any kind of current is silly 1990s stuff. With any kind of water movement at all, scooters become required equipment once you add the 3rd bottle IMHO whether its a deco gas or bottom stage doesn't matter much.

Interesting stuff, you run dives quite differently to the way I'v been trained. I just don't see too many scoters, that's a sum total of 2 on 1 dive, around here. I do see what you mean with the last century comment though. It's one of the reasons I started the thread.

I know, my bad learning how to dive on the internet. But when you live in the middle of nowhere country Oz, & the only people you encounter have similar training & use similar procedures, I thought I'd see whats happening in the wider world.

 

[limeyx]

Someone nearly killed themselves doing that at a large cave exploration project, when they got tangled on descent.

Wasn't he also on a rebreather which has a PO2 drop in the shallows ?

 

[limeyx]

With a scooter, we hit 240 fsw in about 2 minutes. No travel gas needed. Even without a scooter, I've been just dropping like a rock in the ocean and not using a travel gas.

Ken, thats a pretty fast descent rate. Have you had any issues keeping the team together especially in low-vis at those rates ?

We usually average 70-80fpm on descent and thats usually enough for my ears.

12/65 and reasonable surface conditions, I dont use a travel gas. If it was lumpy, I might consider it especially since on a couple of dives we spent a while on the surface fixing argon bottles etc.

 

[MXGratefulDiver]

I'm not using travel mixes for mildly hypoxic gases like 15/55.

For even deeper dives (12/65 or less that I'm not doing around her cause its too damn cold) I would almost for sure have a 3rd deco gas along which I would use before EAN50 if it was absolutely required. But even 12/65 I'd probably just deal with the surface on the surface breathing air, then pop the reg in and drop. We don't screw around at ~8ft, we hit the trigger and go down down.

That's generally our strategy, and it works pretty well ... except for that one time on the Al-Ind-Esk-A-Sea when there was a strong surface current pulling us away from the downline. At full throttle it took a couple minutes to make it from splash to the buoy, and even on 15/55 I was a bit breathless by the time I got there. Knowing what I know now if I had to deal with that kind of current again I'd probably start on my EAN50 bottle and make the switch on the way down ...

... Bob (Grateful Diver)

 

[rjack321]

Interesting stuff, you run dives quite differently to the way I'v been trained. I just don't see too many scoters, that's a sum total of 2 on 1 dive, around here. I do see what you mean with the last century comment though. It's one of the reasons I started the thread.

I know, my bad learning how to dive on the internet. But when you live in the middle of nowhere country Oz, & the only people you encounter have similar training & use similar procedures, I thought I'd see whats happening in the wider world.

I don't know anyone around here doing serious (> about 160ft IMO) wreck diving who doesn't own a scooter. Its not just a function of our area, they are everywhere nowadays. There are 100x the scooter dives here now compared to just 4 or 5 yrs ago.

I almost never see a tag line from the anchor to the 60m past the stern or whatever. Maybe on a recreational boat but never on a serious wreck/deco boat which is generally done live around here. So our lack of travel gases is shaped by what we do (don't) do on the surface.

 

[rjack321]

That's generally our strategy, and it works pretty well ... except for that one time on the Al-Ind-Esk-A-Sea when there was a strong surface current pulling us away from the downline. At full throttle it took a couple minutes to make it from splash to the buoy, and even on 15/55 I was a bit breathless by the time I got there. Knowing what I know now if I had to deal with that kind of current again I'd probably start on my EAN50 bottle and make the switch on the way down ...

... Bob (Grateful Diver)

I did that once. Agree, won't do it again. Not going to pass out but feeling winded is annoying. I can drive with my head sideways if need be or get picked up to re-splash.

But that wreck is so nasty I won't be doing it again anyway.

 

[liuk3]

Ken, thats a pretty fast descent rate. Have you had any issues keeping the team together especially in low-vis at those rates ?

We usually average 70-80fpm on descent and thats usually enough for my ears.

12/65 and reasonable surface conditions, I dont use a travel gas. If it was lumpy, I might consider it especially since on a couple of dives we spent a while on the surface fixing argon bottles etc.

We were shooting down to 240 ft on a series of 5 dives over 2 days to execute a search. Trying to maximize bottom time at depth. Two-man team in decent viz, so it wasn't a problem keeping together. You're right though that you can only shoot down that quickly if you know for a fact that your buddy can clear that quickly. I wouldn't try dropping like that with a new buddy.

 

[PfcAJ]

Wasn't he also on a rebreather which has a PO2 drop in the shallows ?

Yeah, theres an article about it outlining the incident over on Rb world. His buddy saved his life.

 

[boydski]

I don't know anyone around here doing serious (> about 160ft IMO) wreck diving who doesn't own a scooter.

Yes you do!

Scooters and Deathstar-like cameras just don't work very well together.

Like Richard, I don't use travel mix unless I'm getting down in the 300' range and then we just use our deep deco mix. It has been handy a few times when we've had to stop just below the surface and re-attach inflator hoses or fix something on the camera (aka The Beast).