Translating the GUE T/1 Deco Curve

[Rainer]

I had the same instructor as the OP, but we learned to shape differently. We first, though, spent several hours comparing RD (various versions to follow) with Buhlmann (+GFs) and VPM (older version). In class, we covered both s-shaping and linear RD. After leaving class, I've done almost all my deeper dives s-shaping (half time from 50' and 40' applied to 70' and 60'). I was never taught, nor have used, a "countdown" schedule (5-4-3-2-1). As rjack noted, I don't see how it scales to two bottle dives where you want a backgas break at 30' before re-spiking PPO2.

Edit: And please, if you're new to T1 dives, consider doing a max of only 25 minutes on an AL40 (50%). I see way too many people (myself included) fresh out of class trying to eek out 30 and going well into what should be a reserve, if not straight up killing the bottle at 20' or 10'. Past 25 minutes of deco, I now take two bottles.

 

[Blackwood]

Richard pretty much covered how the spreadsheet generates that schedule - yes, it's actually generating it (awkwardly) not just saying "if 30 then 4-4-2-2-3-10-5" or some such thing.

The classical reference is the 5thD-x Document. There have likely been some changes since the inception of UTD (also, the linked PDF is missing the last page), but I haven't taken the refresher course.

 

[rjack321]

Edit: And please, if you're new to T1 dives, consider doing a max of only 25 minutes on an AL40 (50%). I see way too many people (myself included) fresh out of class trying to eek out 30 and going well into what should be a reserve, if not straight up killing the bottle at 20' or 10'. Past 25 minutes of deco, I now take two bottles.

I think I stuck to 20mins on an AL40 for quite a few dives. Not so much for the extra reserve, I didn't have much confidence in my capacity at the time and so stayed relatively "close to home" (aka 1 ATA).

 

[Blackwood]

My first 10-15 T1 level dives were planned for 30 minutes. I think I had a cube or two left in the bottle remaining, but we were either lucky with conditions or simply drifted the deco (live boat).

These days when I only have one (deco) bottle I too am likely to plan for 25 minutes with those extra 5 held for contingency.

 

[ScubaInChicago]

Streetdoctor's example is actually pretty close to an inverted VPM profile.

I've lost my identity.....

My first 10-15 T1 level dives were planned for 30 minutes. I think I had a cube or two left in the bottle remaining, but we were either lucky with conditions or simply drifted the deco (live boat).

These days when I only have one (deco) bottle I too am likely to plan for 25 minutes with those extra 5 held for contingency.

Outside of time, how does your deco gas planning relate to the 2/3rd's infornation we recieved?

 

[rjack321]

Outside of time, how does your deco gas planning relate to the 2/3rd's infornation we recieved?

You mean a lost deco gas plan?

 

[ScubaInChicago]

You mean a lost deco gas plan?

It wasn't explained to be exclusively a lost deco plan as much as a reserve for the "just in case".....I'd love to hear how RD plans in lost deco gas though...

 

[rjack321]

It wasn't explained to be exclusively a lost deco plan as much as a reserve for the "just in case".....I'd love to hear how RD plans in lost deco gas though...

K, new thread in a bit...

 

[Rainer]

It wasn't explained to be exclusively a lost deco plan as much as a reserve for the "just in case".....I'd love to hear how RD plans in lost deco gas though...

What's "just in case"?

I was taught to reserve enough gas to cover (most of) a single lost bottle.

As rjack notes, the way GUE and UTD handle the lost gas (one bottle) is really quite different.

I was taught in GUE T1 (and would do):
-For 70-30', switch every stop (1.5 x time) [only reg is passed]
-For 20-10', each diver does half time (1.5 x time) at each stop [only reg is passed]

UTD teaches
-Everyone does O2 window time. Basically each diver does 5 minutes at 70' and 60' (at which point the bottle is toast). Pass the bottle or the reg. Lecture notes then have you doing normal (not 1.5 x time) on backgas for remaining stops. Why you aren't extending the deco times for 50'-surface is beyond me.

The cons for the GUE method are having to constantly pass around this reg. Too many switches to make handing off the bottle practical, and for new T1 divers, not used to juggling multiple bottles, it really doesn't make sense to add this task-loading (which might very well result in a dropped bottle and then no deco gas). It isn't all that difficult in practice, though. We shared gas like this in decent St. Lawrence current while remaining together without issue.

If you wanted to extend the 50'-surface (by 1.5 x time), I'd have less issue with UTD's method. For me, as is, it places too much emphasis on the O2 window (which admittedly, the GUE method under-emphasizes).

In any case, one goal should be to reserve enough gas to make *some* kind of gas sharing possible. Figure this stuff out in the team before diving. I'm more interested in having a reasonable team standard than debating the particulars of 20 slightly different methods.

 

[ScubaInChicago]

What's "just in case"?

Lost deco, bad SAC day....current, stress, ect....