Rock Bottom Spreadsheet

[JeffG]

no MF I'm talking about an event that happens after an ascent starts.say your coming up and after your first deep stop, your buddy flakes and does the crash and burn. are you telling me that RESERVE stays in the tank untill your feet dry on the boat?

Thats just being silly....The reserve is there to be used to get you to the surface...in a nice slow safe manner.

Its just a way to plan a dive so that if your buddy does do the crash and burn...your not sitting there with your 500 psi in your tank.

 

[JasonH20]

are you telling me that RESERVE stays in the tank untill your feet dry on the boat?

The reserve changes as you get shallower. As you come up your reserve will become less.

The spreadsheet is just a guide to help you plan your dive. If you're not interested in having reserve gas for a buddy, then change the cell for your buddy's SAC to 0. If you don't want reserve gas for safety stops, change the cells for their duration to 0. If you don't want a 200psi padding, change that to 0. These aren't "rules", just guidlines to help plan.

HTH,
Jason

 

[novadiver]

You could always just bring small doubles or a single tank that has enough gas to let you safely do the dive you want.

I'd much rather have one 130 that will let me bust any NDL out there than an Al 80 plus a second pony bottle to deal with.

a single 130 doesn't have the redundancy that "I " require for deep diving. OUT OF THOUSANDS of divers I've met, only 4 dove with 130s , from were I'm sittin it looks like "rock" would or should be the smallest tank out of the two divers.

 

[lamont]

I've got a CGI rock-bottom calculator i wrote here:

http://www.scriptkiddie.org/air.html

I used that to generate all-of-usable bottom time graphs along with deco graphs which are
here:

http://www.scriptkiddie.org/airplot.html

The CGI is optimized for the fact that I know that 1 @ 30, 1 @ 20, 1 @ 10 is equivalent to 3 @ 20, so I didn't include options for sticking in a bunch of different stop levels. It doesn't compute things like GUEs 1/2 min at X, 1/2 min moving up to X - 10 stop practice, which actually makes the CGI more conservative.

If you change the SAC rate from 2.0 to 1.0 you can get cu ft requirements for a pony bailout.

It also gives you "tank SAC" rates which are how many psi/min/ata you'll be expecting to burn for a given 'normal' SAC rate.

Also, i wrote this up:

http://www.scubaboard.com/showpost.php?p=735077&postcount=33
http://www.scubaboard.com/showpost.php?p=735077&postcount=34

I think the only major "bug" I've found in those posts is I calculate out a deep dive on an AL80 which would be better done on a much larger tank.

 

[novadiver]

Thats just being silly....The reserve is there to be used to get you to the surface...in a nice slow safe manner.

Its just a way to plan a dive so that if your buddy does do the crash and burn...your not sitting there with your 500 psi in your tank.

well that's what the ponies for also. but my training was different.good luck to you

 

[JasonH20]

like you posted in that " other" site , this has become a pro DIR clique and is no longer open for debate, just one way. THAT"S SBs bad

Read Roakey's post I linked above. It's not so much a DIR thing as a general planning thing.

As a new diver I don't have much feeling for how much air I might use in what situations. I think as you become more experienced this stuff becomes automatic, but for me I put the spreadsheet together so I could see in hard numbers what was going on. I have both LP 80's and HP 130's. Now I can look at my spreadsheet and decide which tanks I want to use depending on the dive profile I want. As you noticed, for dives to 100+ feet you're kind of limited with 80's if you want sufficient reserve for you and a buddy to get back topside in a safe manner. If I'm doing a dive to 50 feet, the 80's will be just fine.

Thanks,
Jason

 

[jonnythan]

a single 130 doesn't have the redundancy that "I " require for deep diving. OUT OF THOUSANDS of divers I've met, only 4 dove with 130s , from were I'm sittin it looks like "rock" would or should be the smallest tank out of the two divers.

If "rock" is the smallest tank, then what happens when you're both at 500 psi and hit the upline.. then one of you is suddenly OOA? You deploy the pony... and the diaphragm is busted, so you can't even breathe through it.

Oh well.. your buddy doesn't have enough gas to get you up. You're screwed.

 

[roakey]

well that's what the ponies for also. but my training was different.good luck to you

So how were you taught when to turn the dive?

Roak

 

[JeffG]

So how were you taught when to turn the dive?

Roak

When the reg starts breathing hard.

 

[JasonH20]

Hey Roakey! So did I understand your post I linked above correctly? Thanks for laying the groundwork for my spreadsheet!

Thanks,
Jason