Rainer
Contributor
1) Extending the shallow time by 1.5x on backgas is now assuming that you were getting a 50% time advantage from the EAN50 up there (shallow). The time advantage is derived from the average over all stops the gas is used for. EAN50 is only "used for" the 70-30ft segment - Tech1 level EAN50 dives are actually the exception. You've taken the exception and made it the rule that the 50% time advantage is derived from the entire 70-surface segment while that is not assumed for deeper dives.
I understand perfectly well how the 50% advantage works. In any case, since I *am* doing T1ish dives only, of course I'm most concerned with lost deco gas to cover such dives!
The point is, once both are on backgas (i.e. after 60'), it really seems you ought to be extending shallow stops. The 50% is still advantageous over the backgas even at 50'. I do agree with Nick, though, that over-staying 50-30' isn't doing much. Personally, however, I can't see any reason not to camp out at 20' for awhile (assuming no O2). If not 2x, then at least 1.5x. I'm already planning gas reserves for this, so that's not an issue.
I just don't see doing 1.5 x time at 70' and 60', then treating the rest of the deco as normal (where 50'-surface is all on a high helium back gas). I do see the point, though, of trying to squeek some greater use of the bottle by emphasizing the 70' and 60' stops.
Thanks for the discussion!
2) Streetdoctor's profile has more "O2 window" emphasis than I've ever seen. Limey and I did a profile like that once and I felt like crap. He thinks he was fine but was asleep on the couch so I don't know how he knows Maybe is was because of the shape, maybe because it was the 2nd dive of the day. In any case, I don't think its fair to say UTD emphasizes the O2 window more or less than GUE anymore, it depends on the circumstances now.
Yeah, we never even discussed such a profile. I will say, though, that the BAUE people I've done dives with do a similar profile. Our dives were all 25 minutes (on a single 50% bottle) and they all shape 5-2-2-2-2 for the 70-30'. 20-10' is "normal" (e.g. 8-4). I can't remember feeling any different.