Remaining air

oscar_2424 · Jun 6, 2005

hi i just got my AOW want really enjoy the deep dive, my question is whit how much remaining air should i start surfacing from 100 ft. so i dont push my limits considering i just have done one deep dive (100 ft.) thanks for the help

jonnythan · Jun 6, 2005

Do a search for "Rock Bottom" and read this page: http://jonnythan.com/rockbottom.html

The link is my own goofy and wordy explanation of the concept.. you'll find lots of info on the boards here if you search for that. Short answer is 1200-1500 psi for an Al 80...

lamont · Jun 6, 2005

Al80/LP72:

30 fsw: 700 psi
60 fsw: 1000 psi
100 fsw: 1300 psi
130 fsw: 1700 psi

HP120/HP130/LP104/LP95/LP96:

30 fsw: 500 psi
60 fsw: 700 psi
100 fsw: 1000 psi
130 fsw: 1300 psi

HP100/LP80/AL95 are in the middle of those ranges. and take half of those values or 500 psi (whichever is greater) for doubles.

EDIT: those are the numbers that I use, there's multiple different ways to arrive at similar numbers that will differ slightly in how liberal or conservative the assumptions are.

H2Andy · Jun 6, 2005

Oscar, along Lamont's answer, my rock bottoms are as follows (in psi):

DEPTH............AL80.......ST95/104......HP80........HP100
0-60 feet........700...........500............800...........600
60-100 feet.....1000..........700...........1100.........900

that should get you and your buddy safely to the surface, including safety
stop, from the depths indicated.

oscar_2424 · Jun 6, 2005

H2Andy:
Oscar, along Lamont's answer, my rock bottoms are as follows (in psi):

DEPTH............AL80.......ST95/104......HP80........HP100
0-60 feet........700...........500............800...........600
60-100 feet.....1000..........700...........1100.........900

that should get you and your buddy safely to the surface, including safety
stop, from the depths indicated.

thanks for the inputs i usually dive with AL 80

RedCash02 · Jun 6, 2005

I received my AOW last summer in the Florida Keys and I used a steel tank for the first time. It was so nice to not have lead in my vest (although, I've read some other posts where others argued that was a problem). I would suggest you atleast give it a try sometime.

Charlie99 · Jun 6, 2005

One thing to watch out for in these rock bottoms is that, if you have a higher than normal air consumption rate, then you should be using a more conservative rock bottom.

Lamont's numbers for an AL80 are a good set to start with.

A popular, and easy-to-remember, rule of thumb for AL80 rock bottom is 100 psi per every 10' of depth (or 500psi, whichever is greater). This really is a minimum rock bottom, and is cutting it close for someone with high air consumption.

lamont · Jun 6, 2005

Charlie99:
One thing to watch out for in these rock bottoms is that, if you have a higher than normal air consumption rate, then you should be using a more conservative rock bottom.

Lamont's numbers for an AL80 are a good set to start with.

A popular, and easy-to-remember, rule of thumb for AL80 rock bottom is 100 psi per every 10' of depth (or 500psi, whichever is greater). This really is a minimum rock bottom, and is cutting it close for someone with high air consumption.

100 psi per every 10' of depth plus 300 psi pretty much duplicates my numbers.

my numbers are based on an OOA scenario with a combined SAC of 2.0 for both divers (your buddy who is fearing for his life may have a consumption above 1.0) and 1 min at depth, 30 fpm ascent to the surface and 1 min @ 30, 1 min @ 20, 1 min @ 10 for stops.

in terms of cu ft the table looks like:

30 fsw - 16 cu ft
60 fsw - 24 cu ft
100 fsw - 36 cu ft
130 fsw - 48 cu ft

matt_unique · Jun 7, 2005

oscar_2424:
hi i just got my AOW want really enjoy the deep dive, my question is whit how much remaining air should i start surfacing from 100 ft. so i dont push my limits considering i just have done one deep dive (100 ft.) thanks for the help

There are lot's of personal preferences on this topic. For recreational purposes an easy guideline is the rule of thirds. Use 2/3 of your gas for the dive and surface with 1/3 as a safety margin. So for a 3000psi tank - you would surface with 1000psi remaining. This method does not require consideration for varying air consumption rates or tank sizes. (Those with a higher air consumption rate will be ending their dives in less total time to remain on target).

To more directly answer your question - it depends upon how much air you've used to reach the time (or depth) at which you would like to begin the return to the surface/mooring/anchor/beach/etc.

--Matt

artw · Jun 7, 2005

so on an open water recreational numpty dive to what, 75-100 feet, you want me to thumb the dive when my SPG reads 2000psi? screw that.

Remaining air

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