Ratio Deco Lost Gas Planning

[SillyQuestions]

Little question on lost gas planning for ratio deco. I'm fluent in metric but not so much in imperial, I'll try my best for you all, but I do not understand how american cylinders work.

I dive to 45m (150ft) for 30mins. I now have 30mins deco to do.

I ascend to 30m (100ft) and do 30second stop, 30seconds movement every 3m (10ft) to 21m (70ft)
21-6m (70-20ft) I spend 15mins.
6m-Surface (20ft to surface) I spend 15mins.

My gas requirement on 15l/min (0.5 cu/ft per min) is:
3359L (119cuft) 21/35 including buddy bailout so I'd use twin 12L cylinders which hold 4800L (169.7 cuft)
1140L (40cuft) 50% including reserve so I'd use an AL40.

If I lose my 50% I suddenly need an extra 2280L (80cuft) of 21/35 to double my 50% times. So to cover this I'd have to jump up to twin 15s/16s (212/226cuft).

Wouldn't it make more sense to just take my twin 12s and two Al40s of 50%?

 

[PfcAJ]

share deco gas with your buddy

 

[SillyQuestions]

So obvious its brutal.

 

[rjack321]

IMHO 30mins is too tight for your consumption and an AL40. You need an al80 of EAN50 for this dive. Past 30mins of deco you should be bringing O2 instead of 2x al40s of EAN50.

AL80s for 30mins of bottom time at 150ft with rock bottom is doable but tight.

And yes if one of you loses EAN50 you share. Exactly how depends on your training/agency/and how much else is going upside down on the dive.

 

[Kevrumbo]

Little question on lost gas planning for ratio deco. I'm fluent in metric but not so much in imperial, I'll try my best for you all, but I do not understand how american cylinders work.

I dive to 45m (150ft) for 30mins. I now have 30mins deco to do.

I ascend to 30m (100ft) and do 30second stop, 30seconds movement every 3m (10ft) to 21m (70ft)
21-6m (70-20ft) I spend 15mins.
6m-Surface (20ft to surface) I spend 15mins.

My gas requirement on 15l/min (0.5 cu/ft per min) is:
3359L (119cuft) 21/35 including buddy bailout so I'd use twin 12L cylinders which hold 4800L (169.7 cuft)
1140L (40cuft) 50% including reserve so I'd use an AL40.

If I lose my 50% I suddenly need an extra 2280L (80cuft) of 21/35 to double my 50% times. So to cover this I'd have to jump up to twin 15s/16s (212/226cuft).

Wouldn't it make more sense to just take my twin 12s and two Al40s of 50%?

That's a typical gas management planning profile for the 45m wrecks and deeper (San Francisco Maru, Aikoku Maru etc) at the Fourth Fleet Anchorage at Truk Lagoon (I'm leaving tomorrow from LA for another three week trip).

I use a 11l Alu twinset and three 11l Alu stages with bottom mix, nitrox50 and Oxygen respectively, so I've got plenty to share with the Dive Guide if he loses deco gas (or if either of us has to do IWR on O2 at 9m). The dive guides have a phenomenal SCR of better than 5l/min so they can share their 5.5l deco bottle of Nitrox50 with me no problem if I should lose my Nitrox50 deco bottle. We've also got an additional contingency 11l cylinder of O2 hanging from the dive skiff at 6m as well.

 

[ajduplessis]

share deco gas with your buddy

So obvious its brutal.

....seperation from your buddy would be brutal, just saying. Plan for worst case.

 

[SillyQuestions]

To be honest the majority of diving I do is entirely solo with 100% reserves in gas. That's why the buddy option didn't occur to me and the extra Al40 of deco gas did.


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[PfcAJ]

I'm inclined to contend that sharing with a buddy is a poor strategy if you're solo diving.

 

[SillyQuestions]

I'm inclined to contend that sharing with a buddy is a poor strategy if you're solo diving.

Ha I'd agree. Just trying to increase my understanding of gooers planning. Not try and actually dive like them.


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