Rock Bottom Spreadsheet

[simbrooks]

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

I know quite a few and they all come from the traditional agencies, diving either single or double E7-130's. I personally dive double HP120's. I have only dove with 70 different folks of SB though.

from were I'm sittin it looks like "rock" would or should be the smallest tank out of the two divers.

This sounds like you are trying to cylinder match or something, am i getting you right here? The rock bottom would be the same in terms of cuft for both tanks, so you work out your ascent pressures from that.

but my training was different

"Different" seems to be an appropriate term here

So how were you taught when to turn the dive?

Its always thirds it seems from every other post i have read, of course allowing for the use of a pony due to the flakey divers that seem to go diving with him that keep being brought up....

 

[roakey]

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

Thanks,
Jason

The numbers track so it looks like you did.

When the reg starts breathing hard.

Works for me in the Aquarium!

Roak

 

[solo_diver]

What program do i need to download other than the file provided above to view this? Yes i am pc illiterate

yea you can use excel, but if you don't have excel you need to buy it, then of course you'll probably want to buy Office...

nah.


just download open office.

http://download.openoffice.org/index.html

that's what I do!

 

[GreenDiverDown]

Jason,

I think that you did a great job with this. It is nice and compact and user friendly. On first look it appears overly conservative but on closer inspection the reasons for this become obvious. If one enters 0 for Deep Stop Duration and 0 for PSI Padding, then the numbers look very much like those more commonly seen.

I do question your default 2 min deep stop. Typically, on a recreational profile the deep stop, if used at all is very brief - described by some as "more of a pause". Two minutes seems long. Again, you allow for this very well by letting the user choose the length and depth of this stop...very nice.

If you don't mind, I'll attach the file that I have been using for the past several years. I designed it as a teaching aid to use when I teach AOW. The charts are made so that they can be selected and then printed. I then trim and laminate them and pass them out to my students.

A few notes:

These are designed for teaching purposes.

They are based on standard recreational depths with standard ascent profiles...ie. 30 ft/min ascent rates and a 3 minute 15 foot stop. Deep stops are not included.

Included, are cylinders that I most often see used for recreational diving. Around here that means Al 80’s (single and twins) or Al 63’s.

Also included is a chart with values expressed in cuft which in turn can be applied to any cylinder size.

Because these are intended for teaching purposes not all depth/cylinder combinations are recommended for actual use...ie. it would not be wise to do a 130 foot dive with an Al 63. Likewise, I don't recommend exceeding 100 ft with any cylinder size when using air.

They are not intended to be used alone but rather in conjunction with other principles of gas management.

User changeable values include each buddy’s SCR working and at rest and length of time at depth between the onset of the OOA condition and the onset of the ascent. Rock bottom figures are rounded to the nearest 100 psi.

 

[ScubaDadMiami]

We are talking about two different concepts here: one is rock bottom, one is reserves. They are not the same thing.

Rock bottom is the amount of gas that you need to bring both you and your team member back to the surface at a given moment including required stops along the way or until your first gas switch. Lop this off from how much gas you have before you move to planning reserves. Reserve is the amount of gas you want to have left over after lopping off rock bottom and after figuring out how much (of what is left after figuring out rock bottom) you want to use for your dive.

So, if you have a 3,000 psi tank, and you need 1,000 psi to take you and your buddy to the surface, that is rock bottom. If you hit 1,000 psi during your dive, there is no decision: you and your buddy surface even if both of your equipment is working fine at that moment. If you stay any longer and there is equipment failure, you would otherwise not have enough gas to get the two of you back to the surface unbent and alive. (At least, that would be the case without luck. You do not want to rely on luck, do you? :06: )

Since you need 1,000 psi for rock bottom and you are using a 3,000 psi tank, that means that you have 2,000 psi of gas available to make your dive. From there, you decide if you want to have reserves or not.

Obviously, on a shallow, easy dive with no current and great conditions, you can decide to pretty much dive all of the 2,000 and leave no reserves if you think it prudent. In that case, dive away until you hit the 1,000 mark. At that point, call the dive and make your way to the surface.

On other types of dives, you can choose to use one third of your available gas (not including rock bottom) for the trip out, one third for the trip back, and one third for reserve. There are other rules you can use besides thirds. That's another story.

 

[vondo]

I'm attaching an update I did of the original XLS at the top of this thread (thanks, BTW, it is great). What I added was a slot to put in your normal SAC and a projected bottom time for each of the tanks listed. I'm only concerned with rec. diving, so no attempt at more complicated approaches.

I also changed the padding to 100 PSI and I probably broke the cell protection... Apologies if Excel has problems with this, it is exported from OpenOffice (which I use). An OO version is also attached in the zip file

 

[plsander]

Open Office is another option for viewing/editing Excel documents.

Open Office is open source, runs on a variety of platforms (Windows, Linux, Mac...) and is free to download from http://www.openoffice.org/.

Excel is part of the Microsoft Office Suite, and, as such, isn't available for free download from any legitimate source.

If you don't have Microsoft Office, you can download a free/low-cost Excel file-viewer from any number of sites (try this one if you can't be bothered to Google for one) and read it that way.

 

[theatis]

I'm attaching an update I did of the original XLS at the top of this thread (thanks, BTW, it is great). What I added was a slot to put in your normal SAC and a projected bottom time for each of the tanks listed. I'm only concerned with rec. diving, so no attempt at more complicated approaches.

I also changed the padding to 100 PSI and I probably broke the cell protection... Apologies if Excel has problems with this, it is exported from OpenOffice (which I use). An OO version is also attached in the zip file

Hi Vondo,

I don't know if this is an incompatibility between OO and XL but there is a redundant parenthesis in your formulas and unlike air supply that's not a desirable thing. (lame joke, i know )

Just to give an example, cell B19=(((Q19)/B$17)*B$18)+$B$10. Instead it should be =((Q19/B$17)*B$18)+$B$10, the parenthesis around Q19 is not needed. Otherwise, it works fine.

 

[vondo]

Hi Vondo,

I don't know if this is an incompatibility between OO and XL but there is a redundant parenthesis in your formulas and unlike air supply that's not a desirable thing. (lame joke, i know )

Just to give an example, cell B19=(((Q19)/B$17)*B$18)+$B$10. Instead it should be =((Q19/B$17)*B$18)+$B$10, the parenthesis around Q19 is not needed. Otherwise, it works fine.

Well, it is there in my OO version too, but I don't have XL to see if it was there initially. Does this cause an issue for you? If so, I can fix up the OO version and re-export it into XL.

Eric

 

[theatis]

OK, weird thing. I went back and downloaded the original version of the spreadsheet and it also has the redundant parenthesis, but in that case it works whereas in yours it doesn't. I don't know why, but in any case, when using your spreadsheet removing it also removes the problem on my computer (otherwise all values are empty).