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seafox · 8th March 2007, 19:56

I suggest that you calculate your B/O requirements for every dive.
After a while you can standardize with a certain amount of gas on dive with similar profiles..
ie: for dive to 60' for 60 minutes I need X cuft of gas, for 90' for 45 mins, I need X cuft of gas, ect......
I am sure your instructor has covered this.
Refresher: to calculate B/O: RMVxATAxTIME
ie: dive 70' for 45 mins
70"=3.12 ATA
B/O Calculation:
3 mins to sort out the reason you're B/O .7x3.1x3 (I am using .7 for RMV, you're mileage may vary)
Ascent .7x3.1x2
Safety Stop .7x1.6x3
To surface .7x1.6x2

That's adds up to 16.45 cuft, ADD 33% reserve =21.88 cuft.

So for your dive 45 mins @ 70' you will need to carry a minimum of 22 cuft of B/O.
Oviously on dives where you have a deco obligation, you will have to add that!
So an AL 40 under your arm will do just fine for this dive.

I connect my BOV to my outboard bottle with a QD.
On my B/O bottle I have 2 hoses each with a QD.
One for the BOV and one for the CL should I need to connect.
I also have reg on a 5' hose.
I use either the 27 or the AL 13 cuft depending whether I am home or travelling.
However, and this is my choice: I don't rely on my onboard gas for B/O, so I ALWAYS carry a B/O bottle.
BTW 60 dives since last June is very good. You are well on your way.
Please don't get complacent, use checklists, and practice drills.

Take care,

Cornel

8th March 2007, 19:56	#7 (permalink)
seafox 02ptima Instructor Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Join Date: Mar 2005 Location: TORONTO, CANADA -Have "02ptima" will travel! Posts: 172	Re: what FFM should I get for my new optima? I suggest that you calculate your B/O requirements for every dive. After a while you can standardize with a certain amount of gas on dive with similar profiles.. ie: for dive to 60' for 60 minutes I need X cuft of gas, for 90' for 45 mins, I need X cuft of gas, ect...... I am sure your instructor has covered this. Refresher: to calculate B/O: RMVxATAxTIME ie: dive 70' for 45 mins 70"=3.12 ATA B/O Calculation: 3 mins to sort out the reason you're B/O .7x3.1x3 (I am using .7 for RMV, you're mileage may vary) Ascent .7x3.1x2 Safety Stop .7x1.6x3 To surface .7x1.6x2 That's adds up to 16.45 cuft, ADD 33% reserve =21.88 cuft. So for your dive 45 mins @ 70' you will need to carry a minimum of 22 cuft of B/O. Oviously on dives where you have a deco obligation, you will have to add that! So an AL 40 under your arm will do just fine for this dive. I connect my BOV to my outboard bottle with a QD. On my B/O bottle I have 2 hoses each with a QD. One for the BOV and one for the CL should I need to connect. I also have reg on a 5' hose. I use either the 27 or the AL 13 cuft depending whether I am home or travelling. However, and this is my choice: I don't rely on my onboard gas for B/O, so I ALWAYS carry a B/O bottle. BTW 60 dives since last June is very good. You are well on your way. Please don't get complacent, use checklists, and practice drills. Take care, Cornel __________________ Protect the SHARKS! Excellence is never an accident; it is always the result of high intention, sincere effort, intelligent direction, skillful execution and the vision to see obstacles as opportunities. Experience is a hard teacher because she gives the test first, the lesson afterwards! Last edited by seafox : 8th March 2007 at 20:01.
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