Stage Dive Planning

[ianr33]

I am planning a dive I hope to do later this month. Profile is 110 max for 40 minutes then 80 feet for 10 minutes. Using 32%. From V-Planner:

Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 110ft (2) Nitrox 32 50ft/min descent.
Level 110ft 37:48 (40) Nitrox 32 1.38 ppO2, 90ft ead
Asc to 80ft (41) Nitrox 32 -30ft/min ascent.
Level 80ft 10:00 (51) Nitrox 32 1.09 ppO2, 64ft ead
Asc to 20ft (53) Nitrox 32 -30ft/min ascent.
Stop at 20ft 6:00 (59) Nitrox 32 0.51 ppO2, 13ft ead
Stop at 10ft 11:00 (70) Nitrox 32 0.42 ppO2, 4ft ead
Surface (70) Nitrox 32 -30ft/min ascent.

OTU's this dive: 77
CNS Total: 30.8%

142.1 cu ft Nitrox 32
142.1 cu ft TOTAL

This is an open water,wall dive.

Going to be using double Al 80's. Looking at the above it is obvious that to allow a safe reserve we will need to carry an extra 80 stage.

Am planning on breathing the stage first , taking it down to 1000 psi then switching to backgas.

The thinking behind this is that 1000 psi in the stage would be enough gas (just) to ascend and do deco in the rather unlikely combination of losing all backgas and my buddy as we end our bottom time.

Does this sound reasonable or is it certain death

 

[limeyx]

I am planning a dive I hope to do later this month. Profile is 110 max for 40 minutes then 80 feet for 10 minutes. Using 32%. From V-Planner:

Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 110ft (2) Nitrox 32 50ft/min descent.
Level 110ft 37:48 (40) Nitrox 32 1.38 ppO2, 90ft ead
Asc to 80ft (41) Nitrox 32 -30ft/min ascent.
Level 80ft 10:00 (51) Nitrox 32 1.09 ppO2, 64ft ead
Asc to 20ft (53) Nitrox 32 -30ft/min ascent.
Stop at 20ft 6:00 (59) Nitrox 32 0.51 ppO2, 13ft ead
Stop at 10ft 11:00 (70) Nitrox 32 0.42 ppO2, 4ft ead
Surface (70) Nitrox 32 -30ft/min ascent.

OTU's this dive: 77
CNS Total: 30.8%

142.1 cu ft Nitrox 32
142.1 cu ft TOTAL

This is an open water,wall dive.

Going to be using double Al 80's. Looking at the above it is obvious that to allow a safe reserve we will need to carry an extra 80 stage.

Am planning on breathing the stage first , taking it down to 1000 psi then switching to backgas.

The thinking behind this is that 1000 psi in the stage would be enough gas (just) to ascend and do deco in the rather unlikely combination of losing all backgas and my buddy as we end our bottom time.

Does this sound reasonable or is it certain death

I'd say take a deco class and find out

If I were considering that dive, I'd certainly consider using 30/30 instead of 32%.

I'm not really trained in planning dives with a bottom stage, but I'd say breathe the stage dry, and make sure you plan enough bailout gas in your back gas for two OOA divers to complete all deco from the "worse case scenario" point (i.e. where you need the most gas to safely surface from)

Planning enough gas for those 17 mins of deco is going to require a lot of gas (assuming you provide for one diver OOA).


Choices:
1) do 2 shorter dives
2) Or, if you have the training, consider taking a deco bottle of 50% Nitrox or 100% O2 and see if you can do away with the bottom stage.

 

[karstdvr]

Personally I don't find 110 too bad on a non-trimix dive,but I agree with dropping down to 30% to lower the ppo2,and add O2 for deco.

Maybe I am old school,but I am not too fond of sucking a stage dry,then going to backgas. In an OOA situation I would much rather hand off a stage to the OOA diver than be umbilically connected to them by a 7' hose.

 

[JeffG]

I'm not really trained in planning dives with a bottom stage, but I'd say breathe the stage dry, and make sure you plan enough bailout gas in your back gas for two OOA divers to complete all deco from the "worse case scenario" point (i.e. where you need the most gas to safely surface from)

We have concaved stages, but we are thinking about backing away from that. OOG situations are usually around transitions and if you are breathing the tanks right down to the bottom you could be passing a reg to a buddy thats about to quit. So we were thinking about going back to backgas at 400-300 psi.

 

[theskull]

I'm with Karstdvr,

I would save the stage. Switch to it only when you are down to enough backgas that you could complete an ascent and deco on your remaining backgas with some reserve. Then if your buddy had a problem you could pass your stage to him and complete the dive on your backgas. BTW, it would be best if your buddy used the same procedure.

There is a lot of peace of mind in knowing that you could complete the dive just on your backgas OR just on your stage at any point.

theskull

 

[boomx5]

We have concaved stages.

Lol...I sucked one dry @ 200' one time. Normally, we try and leave a couple hundred psi in them when we call the switch.

 

[JeffG]

Lol...I sucked one dry @ 200' one time. Normally, we try and leave a couple hundred psi in them when we call the switch.

When your mask is leaking because your face is so puckered trying to get the last bit of gas out of the stage is a good sign that I should go to my backgas

 

[boomx5]

When your mask is leaking because your face is so puckered trying to get the last bit of gas out of the stage is a good sign that I should go to my backgas

Lol...and that's when I'm usually saying to myself, " I payed good money for this !@#$% stuff, and I'm going to take every last hit!

 

[ianr33]

I'd say take a deco class and find out

If I were considering that dive, I'd certainly consider using 30/30 instead of 32%.

I'm not really trained in planning dives with a bottom stage, but I'd say breathe the stage dry, and make sure you plan enough bailout gas in your back gas for two OOA divers to complete all deco from the "worse case scenario" point (i.e. where you need the most gas to safely surface from)

Planning enough gas for those 17 mins of deco is going to require a lot of gas (assuming you provide for one diver OOA).


Choices:
1) do 2 shorter dives
2) Or, if you have the training, consider taking a deco bottle of 50% Nitrox or 100% O2 and see if you can do away with the bottom stage.

I have done the deco class as clearly stated in my profile. I guess some people dont read them ?
Maybe I need to do a deco Proceedures Stage Diver Class???

Taking a tank of O2 only reduces the deco by 7 minutes,which seems more trouble than it is worth

I hear you about using 30% O2. Although I would plan the dive with a maximum depth of 110 I would probably actually do most of it at around 100 to back of the O2 exposure a bit. I am happy with 32% for that.

Dive is going to be on Grand Cayman,dont feel the need for He in 100 foot vis and 80+ degree water.

My question really boils down to the stage. Am I best to.
1) Suck it dry or
2)Leave a usable amount of gas in it

 

[theskull]

. . . My question really boils down to the stage. Am I best to.
1) Suck it dry or
2)Leave a usable amount of gas in it

Personally, I always like to leave at least a few hundred psi in the stage. In a pinch I could breathe from it for a few minutes while getting things sorted out, or could hand it off to a buddy so that we could make our ascent to the surface without being tethered to each other in the event we had been sharing air through the deco.

theskull