Deco gas choice for this dive?

[tomfcrist]

Doing both dives on the same deco bottle?

Thus adding the O2. Both dives end up shorter(thermal stress is less), and less than half a 40 of each is used between both dives.

 

[Kyle0692]

Will be topping the 40 off after the first dive to make sure ample supply for dive 2.

 

[tomfcrist]

Will be topping the 40 off after the first dive to make sure ample supply for dive 2.

I would certainly hope so based of that plan and your gas calculations.

Have a good dive.

 

[tomfcrist]

Here is what I would do... running 50/80.

adding O2 for the first dive seems a little overkill, but this gives you an idea of how much deco time you are saving...and you won’t have to get fills for your deco bottles.

for what it’s worth, I’d probably take the 50% on the first dive and not use it. I’d just backgas deco that dive. It’s shallow, and short.

Dive #1
Dive: 100ft for 30 [ 30 ] on Air
Asc.: 70ft for 1 [ 31 ] on EAN50
Asc.: 40ft for 1 [ 32 ] on EAN50
Deco: 30ft for 1 [ 33 ] on EAN50
Deco: 20ft for 5 [ 38 ] on 100% O²

Gas Consumption:
Air 84.6 cuft
EAN50 5.1 cuft
100% O² 5.6 cuft

24hr surface.

Dive #2
Dive: 150ft for 22 [ 22 ] on Air
Asc.: 120ft for 1 [ 23 ] on Air
Asc.: 90ft for 1 [ 24 ] on Air
Deco: 60ft for 1 [ 25 ] on EAN50
Deco: 50ft for 1 [ 26 ] on EAN50
Deco: 40ft for 1 [ 27 ] on EAN50
Deco: 30ft for 3 [ 30 ] on EAN50
Deco: 20ft for 9 [ 39 ] on 100% O²

Gas Consumption:
Air 91.3 cuft
EAN50 9.3 cuft
100% O² 10.1 cuft

 

[RyanT]

50%. It is also useful mix when you add a second deco gas (100%). I don't like the idea of changing my deco mixes between dives; changing your gas switch depths just adds another variable to keep track of. For me, gas switches happen at 70' and 20' every time.

 

[CptTightPants21]

Adding a 2nd deco bottle is overkill on this dive.

Assuming that the 150ft dive must be after the 110' (why). I would either top up the 50% or use an al40 of O2 on the 110' and save the full al80 of 50% for the 150' dive.

 

[barth]

Here is what I would do... running 50/80.

adding O2 for the first dive seems a little overkill, but this gives you an idea of how much deco time you are saving...and you won’t have to get fills for your deco bottles.

for what it’s worth, I’d probably take the 50% on the first dive and not use it. I’d just backgas deco that dive. It’s shallow, and short.

Dive #1
Dive: 100ft for 30 [ 30 ] on Air
Asc.: 70ft for 1 [ 31 ] on EAN50
Asc.: 40ft for 1 [ 32 ] on EAN50
Deco: 30ft for 1 [ 33 ] on EAN50
Deco: 20ft for 5 [ 38 ] on 100% O²

Gas Consumption:
Air 84.6 cuft
EAN50 5.1 cuft
100% O² 5.6 cuft

24hr surface.

Dive #2
Dive: 150ft for 22 [ 22 ] on Air
Asc.: 120ft for 1 [ 23 ] on Air
Asc.: 90ft for 1 [ 24 ] on Air
Deco: 60ft for 1 [ 25 ] on EAN50
Deco: 50ft for 1 [ 26 ] on EAN50
Deco: 40ft for 1 [ 27 ] on EAN50
Deco: 30ft for 3 [ 30 ] on EAN50
Deco: 20ft for 9 [ 39 ] on 100% O²

Gas Consumption:
Air 91.3 cuft
EAN50 9.3 cuft
100% O² 10.1 cuft

For the first dive I would use ean32 as backgas and use oxygen for safety stop. But it’s not even a deco dive for me.

Or I would bring doubles ean32, bottomstage ean32 and a decostage filled with oxygen and do longer bottomtime.

Using air as backgas and bringing 2 stages for deco doesn’t make sense for me for a 30 meter or 100 feet dive.

 

[tomfcrist]

Barth and tight pants, I agree in general. I wouldn’t choose those runtimes or that backgas on dive 1.

Mostly just trying to show that if those are the desired bottom times, you can get out of the water a hell of a lot quicker while using significantly less gas. It eases up the logistics, and for an open ocean dive in the winter(albeit Florida) doing less deco time isn’t a bad thing.

 

[Kyle0692]

Adding a 2nd deco bottle is overkill on this dive.

Assuming that the 150ft dive must be after the 110' (why). I would either top up the 50% or use an al40 of O2 on the 110' and save the full al80 of 50% for the 150' dive.

Cpt,

Lady Luck is on Friday AM and Hydro Sat AM. If I could have them swap the days I would!

Initially for dive 1 I proposed 28% back gas to shave 5 mins deco. Deck is at 110 and we wanted to go down to see the props in the sand hence the 28 vs 32. Others in the group decided against the nitrox because we would have to drain the tanks for dive 2 and fill with air, bit waste of $ but I was willing to get the nitrox to save deco time, personally. One of the divers is taking their AN/DP course so we did want to do some deco on this dive and carry a deco bottle for gas switch training. The limiting factor for dive 1 is back gas due to one diver having an SCR of 1.0... I typically run 0.6-0.7 and would have plenty to stay longer but it is what it is!

 

[RyanT]

If you use 28% on the Lady Luck, you wouldn't really have that much to drain. The tanks will be fairly low after the dive anyway, so just finish bleeding them down low. If you top up from 300 to 500 psi or so, you might end up around 22-23%, which would still be fine for the Hydro. I wouldn't dive the Hydro on air, but that's just me.