Translating the GUE T/1 Deco Curve

[Rainer]

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

I try to plan that even with current, stress, "bad SAC day", etc that I'd still have enough gas to cover lost deco. Best way to get a sense of this is to be conservative with your planned bottle time after class. Plan for 20 minutes only and see how you do. Then up to 25 and see if that works. I really don't think 30 minutes on a single AL40 is reasonable for most in moderately challenging conditions (cold water, currents, mid-water, etc) if you hope to reserve enough gas to cover a lost bottle. Doing 2x deco on back gas is not exactly fun or efficient.

 

[Blackwood]

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

I don't understand your question.

 

[ScubaInChicago]

I don't understand your question.

I'm asking; if your SAC & deco call for using more than 2/3rd's the volume of a tank, are you bringing a bigger tank based on you training/experience? Or do you plan on going to backgas in case of a lost deco tank or higher than usual SAC rate?

 

[rjack321]

I'm asking; if your SAC & deco call for using more than 2/3rd's the volume of a tank, are you bringing a bigger tank based on you training/experience? Or do you plan on going to backgas in case of a lost deco tank or higher than usual SAC rate?

Within reason I'll just go to backgas.

30mins on only an AL40 of EAN50 in cold current is not reasonable to begin with, I would bring O2 for this dive as well. At this point in my career I am very unlikely to bring an Al80 of EAN50 for 30mins of deco.

I will do 25mins of deco on an Al40 and will typically get out with ~750psi remaining. Less than your course guidelines but not totally bogus.

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.

If you are totally draining an AL40 in 20mins (total) at 70ft something is wrong. 0.5cf/min * 1 diver * 10mins of ~65ft time * 3 ATA = 15cf per diver. 30cf used, should have about 700psi remaining once both divers are ready to leave the 60ft stop. The good news is that you have done the equivalent of 15mins of EAN50 deco once you are ready to leave 60ft. Between 5 and 10mins left if you stuck to reasonable max deco for a single 40 (25mins max IMO)

 

[Rainer]

Was using 0.6 (mildly stressful situation, that, and plenty of guys I dive with are 0.6 on deco anyway; 0.5 for me is a good deco, too). That's basically the entire bottle after 60'. In any case, I'm not against the idea of making use of it "deep"; I just don't get not padding the time shallower once back on back gas. While this might work for AG (super deco man), it just seems aggressive to me.

If you are totally draining an AL40 in 20mins (total) at 70ft something is wrong. 0.5cf/min * 1 diver * 10mins of ~65ft time * 3 ATA = 15cf per diver. 30cf used, should have about 700psi remaining once both divers are ready to leave the 60ft stop. The good news is that you have done the equivalent of 15mins of EAN50 deco once you are ready to leave 60ft. Between 5 and 10mins left if you stuck to reasonable max deco for a single 40 (25mins max IMO)

 

[Rainer]

Plan for less time on the bottle. It's really that simple. Taking an AL80 around for simple T1 deco is overkill (the extra mass is a pain and will affect your SCR). Planning dives so you have to finish deco on backgas is pretty much the antithesis of DIR. If you want more bottom time: plan shallower dives, take T2, or hit the gym.

I'm asking; if your SAC & deco call for using more than 2/3rd's the volume of a tank, are you bringing a bigger tank based on you training/experience? Or do you plan on going to backgas in case of a lost deco tank or higher than usual SAC rate?

 

[rjack321]

The UK GUE Tech1 guys seem fine doing 30 or even more mins of deco on only EAN50 - right after class with barely any experience or even on class experience dives. They use larger 7L bottles that we don't have over here, or frequently 80s. That kind of plan is so foreign to me, it seems like they were trained with a different agency.

 

[Rainer]

It was awhile till I realized they use 7L bottles instead of AL40s for 50%. Makes the difference. I'd rather not have to bother with an AL80 when I don't have to (*especially* if I'm already bringing one for a bottom stage).

The UK GUE Tech1 guys seem fine doing 30 or even more mins of deco on only EAN50 - right after class with barely any experience or even on class experience dives. They use larger 7L bottles that we don't have over here, or frequently 80s. That kind of plan is so foreign to me, it seems like they were trained with a different agency.

 

[Blackwood]

I'm asking; if your SAC & deco call for using more than 2/3rd's the volume of a tank, are you bringing a bigger tank based on you training/experience? Or do you plan on going to backgas in case of a lost deco tank or higher than usual SAC rate?

Oh, no. I was not trained to go to a bigger bottle if the plan calls for more than some percentage of a 40, nor have I ever carried an 80 of deco gas.

The plan for a lost bottle is to share team resources in an efficient manner and go to backgas subsequently. The plan for a higher than normal SAC rate is to go to backgas subsequently.

For reference, the spreadsheet doubles all the stops.

The UK GUE Tech1 guys seem fine doing 30 or even more mins of deco on only EAN50 - right after class with barely any experience or even on class experience dives.

That (30 minutes of 50% on a 40) is what we did during our experience dives and immediately after. However, I'm not likely to plan for it these days. On repet dives I like to have oxygen (too) anyway.

 

[limeyx]

Plan for less time on the bottle. It's really that simple. Taking an AL80 around for simple T1 deco is overkill (the extra mass is a pain and will affect your SCR). Planning dives so you have to finish deco on backgas is pretty much the antithesis of DIR. If you want more bottom time: plan shallower dives, take T2, or hit the gym.

I consider a 40 a 30 min bottle and will plan a dive that way. Generally on a reef ascent ending up with 800+ psi and on an ascent up an anchor maybe down to 500.