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How many bailout tanks?



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Old 19th May 2005, 15:40   #1 (permalink)
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How many bailout tanks?

There have been a few threads on bailout already here, but I have a new thought, and wondered peoples opinion.

Currently I dive with 2x 7L ally bailout tanks for my deeper dives (one with 18/35 and one with 60%), if I want to go deeper, I will need more bailout. I see that I have 2 options (sticking with ally tanks for now):
1. Get another ally 7
2. Get 2x Ally 80s

Both these options will give me about 21-22 litres total volume of gas, but with 3 tanks I can have more efficient deco gasses than with 2 tanks. I also have 3 first and second stages so a single failure is less catastrophic, losing 1/3 instead of 1/2 my gas....

Apart from the logistics of carrying 3s stages, does anyone see a downside?
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Old 19th May 2005, 15:43   #2 (permalink)
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What max depth are we speaking about with this config. I am very interested in theis topic as I am in the process to buy some sort of bailout cylinders! Also Padown what RMV ?

Quote: (Originally Posted by Padowan)
There have been a few threads on bailout already here, but I have a new thought, and wondered peoples opinion.

Currently I dive with 2x 7L ally bailout tanks for my deeper dives (one with 18/35 and one with 60%), if I want to go deeper, I will need more bailout. I see that I have 2 options (sticking with ally tanks for now):
1. Get another ally 7
2. Get 2x Ally 80s

Both these options will give me about 21-22 litres total volume of gas, but with 3 tanks I can have more efficient deco gasses than with 2 tanks. I also have 3 first and second stages so a single failure is less catastrophic, losing 1/3 instead of 1/2 my gas....

Apart from the logistics of carrying 3s stages, does anyone see a downside?
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Old 19th May 2005, 16:42   #3 (permalink)
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Thing to watch out for with 80's. They go significantly positively bouyant if you breathe them down. It's noticeable from about 100 bar.

Not a problem if you're happy with sending them up the line if you use a significant ammount of the gas in them.

/Zak
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Old 19th May 2005, 17:53   #4 (permalink)
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I recently used Faber ultralight 10ls in the Red Sea and they were pretty easy to handle. Is there any specific reason you have discounted steel stages?
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Old 19th May 2005, 18:00   #5 (permalink)
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Quote: (Originally Posted by Pierre Farrugia)
What max depth are we speaking about with this config. I am very interested in theis topic as I am in the process to buy some sort of bailout cylinders! Also Padown what RMV ?
At the moment I'm confident in the gas carried in 2x 7's for a full, efficient deco OC ascent from a dive to about 60-65m for a 30-35min bottom time. Another tank, or the twin 80's I'm looking at for dives in the 70-80m range, as I don't think there's enough deep gas in a single 7 to get you to a decent depth for your deco mix.

Anything deeper than this, and I'm pretty sure that a team bailout strategy is required if you want a self/team carried (ie. not staged) full OC ascent bailout option. Some may disagree on this, but I reckon they're relying on things like SCR mode or drop tanks (which you can't rely on) - SCR mode for example is no good if you have a total loop failure or a CO2 hit, and for me, they're the only 2 scenarios which necessitate an OC bailout anyway.

I base my calcs on my OC RMV which was 15-17 slm average back in my OC days.
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Old 19th May 2005, 18:01   #6 (permalink)
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Quote: (Originally Posted by Padowan)
There have been a few threads on bailout already here, but I have a new thought, and wondered peoples opinion.

Currently I dive with 2x 7L ally bailout tanks for my deeper dives (one with 18/35 and one with 60%), if I want to go deeper, I will need more bailout. I see that I have 2 options (sticking with ally tanks for now):
1. Get another ally 7
2. Get 2x Ally 80s

Both these options will give me about 21-22 litres total volume of gas, but with 3 tanks I can have more efficient deco gasses than with 2 tanks. I also have 3 first and second stages so a single failure is less catastrophic, losing 1/3 instead of 1/2 my gas....

Apart from the logistics of carrying 3s stages, does anyone see a downside?
Disclaimer - I was writing this while you posted your reply above

Hi Padowan,

As you go deeper, as you know, you need to develop a sound bailout strategy.

This can mean carrying gas as a team, or, staging cylinders at the bottom of the shot, at the tie-off for the lazy, on the trapeze etc.

To this I add a 'drop' independent twin set. I find that this works for me and doesn't need me to carry too many cylinders. Ali 40s to 90 metres and 80s after that.

For seriously deep diving, we have used a standby CCR diver ready to descend to a diver ascending off the shot, in fact on the trip to the Solomons for USS Atlanta we had 4 bottom divers and four standby divers (nearest chamber Oz!!).

The other approach is to count on anything going catastrophically wrong at the beginning of the dive and at worst you having to go SCR or M-CCR to exit any other scenarios safely.

I know you have given the bailout issue some thought, personally I feel that more than 2 stages on CCR starts to kind of counteract one of the reasons I went CCR in the first place.

Cheers,

Dave Cooper.
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Old 19th May 2005, 18:06   #7 (permalink)
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Quote: (Originally Posted by Padowan)
I base my calcs on my OC RMV which was 15-17 slm average back in my OC days.
When the shit hits the fan you might find yourself nearer 40!!

Just a thought.

Cheers,

Dave Cooper.
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Old 19th May 2005, 19:24   #8 (permalink)
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Quote: (Originally Posted by wreckweasel)
Thing to watch out for with 80's. They go significantly positively bouyant if you breathe them down. It's noticeable from about 100 bar.

Not a problem if you're happy with sending them up the line if you use a significant ammount of the gas in them.

/Zak
I add a two pound weight to the tank band strap- problem solved. I float test tanks in the pool with 250psi and regulators attached.

Also the tank band is a great place to stick a pocket for goodies- drinks, food, things we can drop early in systems. In the ocean goodies get hung on the down line.

In certain cave systems- high flow steel tanks are a help.

Hope this helps- offered as a suggestion.

Regards, Andrew
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Old 19th May 2005, 21:23   #9 (permalink)
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Padowan,

Your question is a good one and one that really needs a bit better look. Hopefully I’m reading you incorrectly but I’m gleaning from your posts that you feel that two 7 litre tanks with 18/35 and EAN 60 is an adequate amount of gas to do a safe OC ascent when diving to 65m.

I may be unfortunately going down the wrong path but if you are using 18/35 as your dil and diving a pO2 of 1.4 (has to be at least 1.35 at that depth) then I think you don’t have any where near enough bailout gas.

Here is why;

I will use V Planner for our tables as it gives a very nice OC bailout gas requirement output. The algorithm isn’t all that important as they will all have a similar ratio of CC to OC requirements. I have the descent rate set at 25m/min, ascent is 9m/min. RMV is set to 20 lpm. Many would argue that this isn’t anywhere near high enough. OK let’s get tedious and cut some tables. These are cut using VPM/B on the most aggressive setting so the OC requirement is as low as one could get. These tables would bend a good many of us.

DIVE PLAN

Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = Nominal

Dec to 65m (2) Diluent 18/35 0.70 SetPoint, 25m/min descent.
Level 65m 32:24 (35) Diluent 18/35 1.40 SetPoint, 34m ead, 39m end
Asc to 42m (37) Diluent 18/35 1.40 SetPoint, -9m/min ascent.
Stop at 42m 0:27 (38) Diluent 18/35 1.40 SetPoint, 17m ead, 26m end
Stop at 36m 2:00 (40) Diluent 18/35 1.40 SetPoint, 13m ead, 22m end
Stop at 30m 2:00 (42) Diluent 18/35 1.40 SetPoint, 9m ead, 19m end
Stop at 27m 2:00 (44) Diluent 18/35 1.40 SetPoint, 7m ead, 17m end
Stop at 24m 2:00 (46) Diluent 18/35 1.40 SetPoint, 4m ead, 15m end
Stop at 21m 3:00 (49) Diluent 18/35 1.40 SetPoint, 2m ead, 14m end
Stop at 18m 3:00 (52) Diluent 18/35 1.40 SetPoint, 0m ead, 12m end
Stop at 15m 5:00 (57) Diluent 18/35 1.40 SetPoint, 0m ead, 10m end
Stop at 12m 5:00 (62) Diluent 18/35 1.40 SetPoint, 0m ead, 9m end
Stop at 9m 7:00 (69) Diluent 18/35 1.40 SetPoint, 0m ead, 7m end
Stop at 6m 10:00 (79) Diluent 18/35 1.40 SetPoint, 0m ead, 5m end
Stop at 3m 15:00 (94) Diluent 18/35 1.30 (1.40), 0m ead

Surface (94) Diluent 18/35 -9m/min ascent.
Off gassing starts at 48.5m
OTU's this dive: 148
CNS Total: 58.6%



DIVE PLAN OC BAILOUT

Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = Nominal

Dec to 65m (2) Diluent 18/35 0.70 SetPoint, 25m/min descent.
Level 65m 32:24 (35) Diluent 18/35 1.40 SetPoint, 34m ead, 39m end
Asc to 42m (37) Trimix 18/35 -9m/min ascent.
Stop at 42m 0:27 (38) Trimix 18/35 0.93 ppO2, 21m ead, 24m end
Stop at 36m 4:00 (42) Trimix 18/35 0.82 ppO2, 17m ead, 20m end
Stop at 30m 2:00 (44) Trimix 18/35 0.72 ppO2, 14m ead, 16m end
Stop at 27m 3:00 (47) Trimix 18/35 0.66 ppO2, 12m ead, 14m end
Stop at 24m 4:00 (51) Trimix 18/35 0.61 ppO2, 10m ead, 12m end
Stop at 21m 5:00 (56) Trimix 18/35 0.56 ppO2, 8m ead, 10m end
Stop at 18m 7:00 (63) Trimix 18/35 0.50 ppO2, 7m ead, 8m end
Stop at 15m 4:00 (67) Nitrox 60 1.49 ppO2, 3m ead
Stop at 12m 6:00 (73) Nitrox 60 1.31 ppO2, 1m ead
Stop at 9m 8:00 (81) Nitrox 60 1.14 ppO2, 0m ead
Stop at 6m 13:00 (94) Nitrox 60 0.96 ppO2, 0m ead
Stop at 3m 23:00 (117) Nitrox 60 0.78 ppO2, 0m ead
Surface (117) Nitrox 60 -9m/min ascent.


Off gassing starts at 49.6m
OTU's this dive: 117
CNS Total: 45.2%

2112.4 ltr Trimix 18/35
1771.6 ltr Nitrox 60
3884 ltr OC TOTAL

A 7 litre tank pumped to 207 bar holds 1449 litres and a 232 bar tank holds 1624 litres, and those figures have no reserve built in.

Sorry about the long post but what am I missing?

Cheers

Steve
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Old 19th May 2005, 21:24   #10 (permalink)
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Hey Steve that font and size is a bit tough on the eyes ;-)

For your bail out tables- I can not tell but it looks to me like it might be calculating using your OC for descent and actual bottom time - rather than the ascent only(eg when you bail out)...I shall go play with some tables too!

Stuart

Ps did you make that bigger or am I imagining things?
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