Small intermediate stage cylinder

**Ian_6301** · 25-07-2018, 05:14 PM

Erm. Sort of.

If you use 18/45, 50 and 100, you'll find the deco gas volumes work out about even for that dive, around 1100L, or about perfect in a 232bar 7L, with 50% reserve.

**Kermit** · 25-07-2018, 05:24 PM

Discounting the use of a 3l p*ny clamped to a back mounted cylinder (we do want to go THERE, do we). A 3l stage is no easier to handle than a 7l. A 7l has much more gas and is more versatile.

**Paulo** · 25-07-2018, 07:21 PM

There are not many examples I can think of where you could not use your onboard 3L of o2 back at 6m as an o2 CCR or o2 SCR.

Unless you ran out of o2 or had a caustic flood of the scrubber

**Mark Chase** · 25-07-2018, 08:09 PM

I used to use inboard 3ltr dill as bottom bailout for immediate ascent dives the switch to 21/35 & 50%

I binned the idea for obvious reasons

On V deep dives (like 90-100m) Id use a 7ltr. SO deep bailout AL80 intermediate switch 7ltr 21/35 @ 60m then on to 50 at 21m and the drop tank

This works well with no deep stop deco

OC diving week trimix I often used 32% in a 7 and a 3ltr of 02 for final deco

A 3ltr is always a challenge on gas consumption v hassle of having a third tank but many of my friends who were taught by Andy Abery ended up using 3 X 5ltrs on 60-80m dives?

But as I always say

Calculate the gas required ten calculate how big a tank you need to hold that volume.

If that's a 3?

cool go for a 3

**gobfish1** · 25-07-2018, 09:02 PM

7l 15/55
7l 64nitrox
and ye pony of o2 ,

id not use a small cylinder on the move , or deeper than 12m

a 7l of 57 or 64 gives a better spread of your two main cylinders , you can sit on the 64 till you hit a number/time that your o2 will last you
dont know what sac your on at 6m resting , you can always move up save / make the gas last you a bit longer , a pony would do me , plus iv inboard if needed ,

**AxeMan** · 25-07-2018, 09:14 PM

Originally posted by Kermit

. A 3l stage is no easier to handle than a 7l. A 7l has much more gas and is more versatile.

It's a lot lighter and smaller on the surface. I wouldn't switch to one at 21m though. At 9m or shallower, you can easily get 20 mins out of one as long as you're also able to get out of the water on your backgas in case you lose it.

**Paulo** · 25-07-2018, 09:26 PM

I think a Ali40 should last around 45 mins at 6m from memory. 45mins of o2 deco is a lot of deco.

I still would not bother with carrying OC o2 and would rely on inboard o2 as SCR or o2 CCR if I needed it. Dropset of an Ali 80 or 12L of 80% would cover a lot too. In Malta I was carrying an ali80 of bottom BO of 16/55, Ali 7 of 32% nose clipped behind me and an Ali 80 of 50% and can't say the extra 7L was in the way.

For the safe effort as carrying a 3L, an Ali40 gives you almost twice the bang for the buck

**gobfish1** · 25-07-2018, 09:37 PM

Originally posted by Paulo

I think a Ali40 should last around 45 mins at 6m from memory. 45mins of o2 deco is a lot of deco.

I still would not bother with carrying OC o2 and would rely on inboard o2 as SCR or o2 CCR if I needed it. Dropset of an Ali 80 or 12L of 80% would cover a lot too. In Malta I was carrying an ali80 of bottom BO of 16/55, Ali 7 of 32% nose clipped behind me and an Ali 80 of 80% and can't say the extra 7L was in the way.

For the safe effort as carrying a 3L, an Ali40 gives you almost twice the bang for the buck

id not do a 55m deco dive with out a 2nd cylinder of o2 , 45mins out of a pony , more if i move ,

ps what was the cost to learn to take the wrong gas diving .

**Paulo** · 25-07-2018, 09:55 PM

Whats wrong with the gas choices?

**gobfish1** · 25-07-2018, 10:37 PM

Originally posted by Paulo

Whats wrong with the gas choices?

16/55 would be a 50ish meter gas choice , so your humping a ali 80 to move 10m to your 32% thats a shite gas once you move to a real deco stop, round 21m, the 80s way to big , you could have spread to gas choice/use much better
and also prob covered a lost gas better , shit load 0f 16/55 is not much use on your deco stops , your humping 3 gas cylinders and none are going to work at there full potential.

on a 3 gas dive last gas should be o2 , keeps the po2 spread working for you, ie max it out
plus whats the point of 55he in bottom gas then ten meters up your moving to a 40m end from a 18m end on bail out ,

just my 1000 quids worth ,

**JonG** · 26-07-2018, 05:12 AM

Why not use it on the 21m stop and then up to 10m Steve, it's the shortest portion of the ascent, if you switch the cylinders around and use the 3l for 100% after the 7 of 60% it doesn't give me the same BT:

DIVE PLAN - BailOut
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 80/80

Dec to 55m (3) Diluent 15/55 0.70 SetPoint, 15m/min descent.
Level 55m 24:20 (28) Diluent 15/55 1.20 SetPoint, 14m ead, 21m end
Level 55m 2:00 (30) Trimix 15/55 0.97 ppO2, 15m ead, 19m end
Asc to 30m (33) Trimix 15/55 -7m/min ascent.
Asc to 21m (34) Trimix 15/55 -7m/min ascent.
Stop at 21m 1:09 (36) Trimix 15/55 0.46 ppO2, 2m ead, 4m end
Stop at 18m 4:00 (40) Trimix 15/55 0.42 ppO2, 1m ead, 3m end
Stop at 15m 4:00 (44) Nitrox 60 1.49 ppO2, 3m ead
Stop at 12m 5:00 (49) Nitrox 60 1.31 ppO2, 1m ead
Stop at 9m 7:00 (56) Nitrox 60 1.14 ppO2, 0m ead
Stop at 6m 29:00 (85) Oxygen 1.60 ppO2, 0m ead
Surface (91) Oxygen -1m/min ascent.

WARNING: Dive bottom time reduced due to limited OC gas supply volume.

OTU's this dive: 124
CNS Total: 76.9%
Gas density: 4.3g/l

1157.4 ltr Trimix 15/55
404.5 ltr Nitrox 60
629.5 ltr Oxygen
2191.4 ltr OC TOTAL

I have MD set up with deco at 12lpm, 25lpm from bailout to first stop. I realise a third 7 would pad the gas better but was just looking for a stop gap before moving to 3 decent sized cylinders because I think there would be a big difference in and out of the water between a 7 and a 3 on an open water/wreck dive.

**Paulo** · 26-07-2018, 06:26 AM

Originally posted by gobfish1

16/55 would be a 50ish meter gas choice , so your humping a ali 80 to move 10m to your 32% thats a shite gas once you move to a real deco stop, round 21m, the 80s way to big , you could have spread to gas choice/use much better
and also prob covered a lost gas better , shit load 0f 16/55 is not much use on your deco stops , your humping 3 gas cylinders and none are going to work at there full potential.

on a 3 gas dive last gas should be o2 , keeps the po2 spread working for you, ie max it out
plus whats the point of 55he in bottom gas then ten meters up your moving to a 40m end from a 18m end on bail out ,

just my 1000 quids worth ,

Mod 2 has a min o2 level of 16%. I made a mistake last night, the deco gas was your favourite gas ...50%

So what would be your preferred gas choices in any size cylinders for a 50m dive & 60m dive and a 70m dive?

People are not going to have a whole host of BO cylinders so they will always be a best compromise

**jturner** · 26-07-2018, 09:19 AM

Originally posted by JonG

Just wondering why the use of a small 3 litre as a travel intermediate stage isn't more popular, just running through some scenarios and it appears to make sense.

At the level I'm diving at (Mod 2), why bother with it? 2 bailout cylinders are enough, one each side, one with a deep bailout gas (16/50 or something like that) and one with a rich one (for me, Nx68-72). If I'm bailing out, I want to get shallow and get gone, not muck around with multiple gas switches unless I need to. There might be a few moments saved on a deco stop somewhere maybe but instead time is wasted switching stages, and the inconvenience of carrying 3 instead of two, I can do without!

**gobfish1** · 26-07-2018, 10:09 AM

Originally posted by JonG

Why not use it on the 21m stop and then up to 10m Steve, it's the shortest portion of the ascent, if you switch the cylinders around and use the 3l for 100% after the 7 of 60% it doesn't give me the same BT:

DIVE PLAN - BailOut
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 80/80

Dec to 55m (3) Diluent 15/55 0.70 SetPoint, 15m/min descent.
Level 55m 24:20 (28) Diluent 15/55 1.20 SetPoint, 14m ead, 21m end
Level 55m 2:00 (30) Trimix 15/55 0.97 ppO2, 15m ead, 19m end
Asc to 30m (33) Trimix 15/55 -7m/min ascent.
Asc to 21m (34) Trimix 15/55 -7m/min ascent.
Stop at 21m 1:09 (36) Trimix 15/55 0.46 ppO2, 2m ead, 4m end
Stop at 18m 4:00 (40) Trimix 15/55 0.42 ppO2, 1m ead, 3m end
Stop at 15m 4:00 (44) Nitrox 60 1.49 ppO2, 3m ead
Stop at 12m 5:00 (49) Nitrox 60 1.31 ppO2, 1m ead
Stop at 9m 7:00 (56) Nitrox 60 1.14 ppO2, 0m ead
Stop at 6m 29:00 (85) Oxygen 1.60 ppO2, 0m ead
Surface (91) Oxygen -1m/min ascent.

WARNING: Dive bottom time reduced due to limited OC gas supply volume.

OTU's this dive: 124
CNS Total: 76.9%
Gas density: 4.3g/l

1157.4 ltr Trimix 15/55
404.5 ltr Nitrox 60
629.5 ltr Oxygen
2191.4 ltr OC TOTAL

I have MD set up with deco at 12lpm, 25lpm from bailout to first stop. I realise a third 7 would pad the gas better but was just looking for a stop gap before moving to 3 decent sized cylinders because I think there would be a big difference in and out of the water between a 7 and a 3 on an open water/wreck dive.

main problem for me with the 50% pony swap at 21m is co2 , id rather have two large cylinders to give me time to get breathing under control

ps why cant you get the 45mins bottom time on your planner ,

just add 10mins or more at 6m on your 60% , ie sit on the 60% till your o2 stop time match,s your cylinder size ,

ps dont be so hard on your self when planning , i almost never use max depth , if a wreck dive is 55m id be putting in 2 or 3m less your not sat in the mud for all the dive ,

edit
for all the arsing about with the pony at 21m i could prob get the same advantage buy using a avg depth and running a bigger po2 at depth , then wacking the arse out of my o2 later , its just what ifs jon.
and if your going to pick a deco gas ie your 60% try to at least pick a number that hits 1.6 at first use , its only going to drop as you move up, so start with the max you can get /have

your going to end up like MC on the pure o2 at 6m lol 105%

Small intermediate stage cylinder

Small intermediate stage cylinder

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