Deco gas choice for 30m dive?

anders · June 20th, 2007, 01:31 PM

Hi,

We want to do a wreck dive to 30m for 45-50 mins.
That implies a deco of about 15-20mins if I'm correct.

The question is:
If we bring 50%, there won't be much gradient at the gasswitch - could we move the extended stop from 21m to 15m to increase gradient?

Or would O2 be a better decogas for this dive?

Best,
Anders

NickB · June 20th, 2007, 01:42 PM

Quote: (Originally Posted by anders)

Or would O2 be a better decogas for this dive?

Yes, O2 would be the best choice for a dive like this.

Gareth Burrows · June 20th, 2007, 01:43 PM

O2. No point mincing about at 21M with 50% and a 3 minute stop as you will still be ongassing.

so put the bag up at about 15 metres and switch to O2 at 6.

*Clare Gledhill* · June 20th, 2007, 01:44 PM

Quote: (Originally Posted by anders)

Hi,

We want to do a wreck dive to 30m for 45-50 mins.
That implies a deco of about 15-20mins if I'm correct.

The question is:
If we bring 50%, there won't be much gradient at the gasswitch - could we move the extended stop from 21m to 15m to increase gradient?

Or would O2 be a better decogas for this dive?

Best,
Anders

Look at your profile - where do the stops start lengthening. What impact would taking O2 have on your minimum gas requirements? If you take that amount of gas off available will you have sufficent to do your intended bottom time - or will that have to change?

Answering these questions will answer the deco gas question for you.

Gareth Burrows · June 20th, 2007, 01:47 PM

Quote: (Originally Posted by Clare Gledhill)

Look at your profile - where do the stops start lengthening. What impact would taking O2 have on your minimum gas requirements? If you take that amount of gas off available will you have sufficent to do your uintended bottom time - or will that have to change?

Answering these questions will answer the deco gas question for you.

bloody instructors. Always answering a question with another question.

coops · June 20th, 2007, 04:16 PM

Hi

May I ask what your bottom gas mix is going to be?

Tnx

NickB · June 20th, 2007, 04:39 PM

Quote: (Originally Posted by coops)

May I ask what your bottom gas mix is going to be?

32% is my guess

GLOC · June 20th, 2007, 04:48 PM

Quote: (Originally Posted by NickB)

32% is my guess

Or could be 30/30 if you have lots of money

Deco obligation is about the same for 30m and 50mins.

coops · June 20th, 2007, 04:53 PM

Nick

I agree, but he may want to do 21/35 to increase his safety; not knowing his full bottom time or worst case scenario depth. Dont know, but I am just curious to play around with different tables and see where I would go for my own education.

cheers

coops

NickB · June 20th, 2007, 05:31 PM

Quote: (Originally Posted by coops)

I agree, but he may want to do 21/35 to increase his safety; not knowing his full bottom time or worst case scenario depth. Dont know, but I am just curious to play around with different tables and see where I would go for my own education.

Well, due to having a last minute change of plan, my buddy & I ended up diving 21/35 on the Maine (30m) a couple of weeks ago. 58 minutes bottom time gave us 20 minutes on O2. This is around double what we'd have had to do if we'd used 32%. So there's a compromise. I don't see 21/35 as being a 'safer' gas for this dive.

June 20th, 2007, 01:31 PM	#1 (permalink)
anders(Offline) andersbomholdt.dk Join Date: Dec 2005 Location: Copenhagen, Denmark Posts: 156	Deco gas choice for 30m dive? Hi, We want to do a wreck dive to 30m for 45-50 mins. That implies a deco of about 15-20mins if I'm correct. The question is: If we bring 50%, there won't be much gradient at the gasswitch - could we move the extended stop from 21m to 15m to increase gradient? Or would O2 be a better decogas for this dive? Best, Anders

June 20th, 2007, 01:42 PM	#2 (permalink)
NickB(Offline) Always lowering the tone Join Date: Dec 2005 Location: Cardiff, UK Posts: 340	Quote: (Originally Posted by anders) Or would O2 be a better decogas for this dive? Yes, O2 would be the best choice for a dive like this. __________________ SnowHeads / BreastFriends / Free Money!

June 20th, 2007, 01:43 PM	#3 (permalink)
Gareth Burrows(Offline) Chimp 2 Join Date: Nov 2005 Location: Horsham, West Sussex Posts: 365	O2. No point mincing about at 21M with 50% and a 3 minute stop as you will still be ongassing. so put the bag up at about 15 metres and switch to O2 at 6. __________________ Garf Amusing and Clever Signature under construction.

June 20th, 2007, 01:44 PM	#4 (permalink)
Clare Gledhill (Online) GUE Instructor Site Admin Join Date: Nov 2005 Location: UK Posts: 1,540	Quote: (Originally Posted by anders) Hi, We want to do a wreck dive to 30m for 45-50 mins. That implies a deco of about 15-20mins if I'm correct. The question is: If we bring 50%, there won't be much gradient at the gasswitch - could we move the extended stop from 21m to 15m to increase gradient? Or would O2 be a better decogas for this dive? Best, Anders Look at your profile - where do the stops start lengthening. What impact would taking O2 have on your minimum gas requirements? If you take that amount of gas off available will you have sufficent to do your intended bottom time - or will that have to change? Answering these questions will answer the deco gas question for you. __________________ Clare . "Keep away from people who try to belittle your ambitions....Small people always do that, but the really great make you feel that you too can become great." Interested in DIR dive training? Always happy to chat/answer questions so get in touch via PM or visit www.dirdiver.co.uk Last edited by Clare Gledhill; June 20th, 2007 at 01:51 PM.

June 20th, 2007, 01:47 PM	#5 (permalink)
Gareth Burrows(Offline) Chimp 2 Join Date: Nov 2005 Location: Horsham, West Sussex Posts: 365	Quote: (Originally Posted by Clare Gledhill) Look at your profile - where do the stops start lengthening. What impact would taking O2 have on your minimum gas requirements? If you take that amount of gas off available will you have sufficent to do your uintended bottom time - or will that have to change? Answering these questions will answer the deco gas question for you. bloody instructors. Always answering a question with another question. __________________ Garf Amusing and Clever Signature under construction.

June 20th, 2007, 04:16 PM	#6 (permalink)
coops(Offline) New Member Join Date: Oct 2006 Location: Oman Posts: 62	Gas Hi May I ask what your bottom gas mix is going to be? Tnx

June 20th, 2007, 04:39 PM	#7 (permalink)
NickB(Offline) Always lowering the tone Join Date: Dec 2005 Location: Cardiff, UK Posts: 340	Quote: (Originally Posted by coops) May I ask what your bottom gas mix is going to be? 32% is my guess __________________ SnowHeads / BreastFriends / Free Money!

June 20th, 2007, 04:48 PM	#8 (permalink)
GLOC(Offline) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,949	Quote: (Originally Posted by NickB) 32% is my guess Or could be 30/30 if you have lots of money Deco obligation is about the same for 30m and 50mins. __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King

June 20th, 2007, 04:53 PM	#9 (permalink)
coops(Offline) New Member Join Date: Oct 2006 Location: Oman Posts: 62	Bottom Gas Nick I agree, but he may want to do 21/35 to increase his safety; not knowing his full bottom time or worst case scenario depth. Dont know, but I am just curious to play around with different tables and see where I would go for my own education. cheers coops

June 20th, 2007, 05:31 PM	#10 (permalink)
NickB(Offline) Always lowering the tone Join Date: Dec 2005 Location: Cardiff, UK Posts: 340	Quote: (Originally Posted by coops) I agree, but he may want to do 21/35 to increase his safety; not knowing his full bottom time or worst case scenario depth. Dont know, but I am just curious to play around with different tables and see where I would go for my own education. Well, due to having a last minute change of plan, my buddy & I ended up diving 21/35 on the Maine (30m) a couple of weeks ago. 58 minutes bottom time gave us 20 minutes on O2. This is around double what we'd have had to do if we'd used 32%. So there's a compromise. I don't see 21/35 as being a 'safer' gas for this dive. __________________ SnowHeads / BreastFriends / Free Money!