Kevrumbo
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Finally as a fun aside, I've been trying for some time to convince my dive buddies here in the States using D15 Tanks (i.e. double backmount manifolded Faber steel 15L cylinders for 30 liters/bar total, same rating as both the double Faber HP117's and HP120's ), to at least use a BAR SPG as a volume "Cubic Feet Remaining Gauge" so they won't have to figure with cumbersome PSI units -and also as sneaky pretext to ultimately convert them to Metric too!
The BAR SPG to Cubic Foot Volume Gauge transformation goes like this:
There are 28.3 liters in 1 cubic foot, and the D15 cylinders have 30 liters/bar total tank factor.
So in order to read the BAR SPG in Volume Cubic Feet, divide the tank factor by the liters-to-cubic foot conversion:
30liters/bar divided-by 28.3 liters/cubic foot equals 1.06 cubic foot per bar.
In other words 1 bar unit on the BAR SPG also represents 1.06 cubic feet, roundable to nearly a one-to-one correspondence. So a full 230 bar reading also translates as 230 cubic feet full volume capacity; 150 bar reading translates as 150 cuft remaining; 90 bar means 90 cf remaining, and so on. . .
-->Remember, this only works with D15 Steel HP Cylinders for a total of 30 liters/bar.
To see how much easier figuring out gas calculations on-the-fly is using the BAR SPG as a Cubic Feet Remaining Gauge, here's an example:
Suppose you originally planned a wreck penetration with Double HP117's, same Sac Rate and twinset as your Buddy, starting with a full 230 "bar" (same as cubic feet) reading on the SPG at the entrance, with an openwater Rock Bottom minimum gas reserve of 50 "bar" (same as cf). So 230 minus 50 equals 180 "bar" (cf) usable for the penetration --Rule of Third's of this value is 60 "bar" (one-third of 180 equals 60), so you would turn-around for egress when you consume 60 "bar" of gas with an actual SPG reading of 170 "bar" (230 minus 60 consumed is 170 "bar"). If you needed to do a gas-sharing emergency egress with your buddy at this point, you would together need 120 "bar" to get out of the wreck, with 50 "bar" actual SPG reading Rock Bottom remaining to get both of you to the surface (or your deco stop bottle switch).
Lets say you used up 20 "bar" (cf) already working against a current getting to the entrance of the wreck for a total of 210 "bar" (cf) reading on the SPG available --can you quickly recalculate Third's?
No problem: 210 minus 50 Rock Bottom yields 160 usable for the penentration; One-Third of 160 is 53 which is your new Thirds turn value. Therefore you would turn the dive when you consume 53 for an actual turn SPG reading of 157 "bar" (210 minus 53 equals the actual turn SPG reading of 157 "bar").
What if you lose your buddy at this instance, at the farthest distance inside the overhead your Thirds turn value allows? How do you calculate the amount of gas to do a Lost Buddy Search?
Easy! At your turn around reading of 157 bar on the SPG, simply add your Rock Bottom value to your Third's turn value (50 bar Rock Bottom plus 53 bar Third's turn value equals 103 bar); Put a line-arrow pointing the way out on your Primary Reel line that you've been laying, and take reference note of where you are inside the overhead at that exact point as well. Now go and search for your buddy with the understanding that you must be back at this line-arrow marker by the time your SPG reads this actual value (103 bar). So you would have from 157 bar down to 103 bar reading on your SPG, or 54 bar delta of gas to search for your buddy --if you were to do a straight line search down a long corridor inside the wreck for example, tactically you should use 27 bar out and 27 bar back to your line-arrow marker for a delta of 54 bar, and an actual end of search SPG reading of 103 bar-- you must start your egress whether you found your buddy or not when you use up this 54 bar delta of gas, at the line arrow marker, with the actual 103 bar final reading on your SPG.
Now could you honestly do all the above maths quickly in your head and on-the-fly using a SPG with actual PSI units?
Use a unit transformed BAR SPG in this instance as described above . . .better yet, just convert over & go Metric
!
(Note: Remember that on a lost buddy search, you will deliberately encroach and use up the Third's Reserve Value needed for an emergency gas-sharing egress contingency (and possibly use up some amount of Rock Bottom as well) --in other words, if you do find your lost buddy and worst of all worst scenarios he happens to be out-of-gas in a silt-out . . .well dea ex machina. I hope you're in a 3-person Team, somehow make it out and run into other divers on the outside who can donate gas & assist. . .)
The BAR SPG to Cubic Foot Volume Gauge transformation goes like this:
There are 28.3 liters in 1 cubic foot, and the D15 cylinders have 30 liters/bar total tank factor.
So in order to read the BAR SPG in Volume Cubic Feet, divide the tank factor by the liters-to-cubic foot conversion:
30
In other words 1 bar unit on the BAR SPG also represents 1.06 cubic feet, roundable to nearly a one-to-one correspondence. So a full 230 bar reading also translates as 230 cubic feet full volume capacity; 150 bar reading translates as 150 cuft remaining; 90 bar means 90 cf remaining, and so on. . .
-->Remember, this only works with D15 Steel HP Cylinders for a total of 30 liters/bar.
To see how much easier figuring out gas calculations on-the-fly is using the BAR SPG as a Cubic Feet Remaining Gauge, here's an example:
Suppose you originally planned a wreck penetration with Double HP117's, same Sac Rate and twinset as your Buddy, starting with a full 230 "bar" (same as cubic feet) reading on the SPG at the entrance, with an openwater Rock Bottom minimum gas reserve of 50 "bar" (same as cf). So 230 minus 50 equals 180 "bar" (cf) usable for the penetration --Rule of Third's of this value is 60 "bar" (one-third of 180 equals 60), so you would turn-around for egress when you consume 60 "bar" of gas with an actual SPG reading of 170 "bar" (230 minus 60 consumed is 170 "bar"). If you needed to do a gas-sharing emergency egress with your buddy at this point, you would together need 120 "bar" to get out of the wreck, with 50 "bar" actual SPG reading Rock Bottom remaining to get both of you to the surface (or your deco stop bottle switch).
Lets say you used up 20 "bar" (cf) already working against a current getting to the entrance of the wreck for a total of 210 "bar" (cf) reading on the SPG available --can you quickly recalculate Third's?
No problem: 210 minus 50 Rock Bottom yields 160 usable for the penentration; One-Third of 160 is 53 which is your new Thirds turn value. Therefore you would turn the dive when you consume 53 for an actual turn SPG reading of 157 "bar" (210 minus 53 equals the actual turn SPG reading of 157 "bar").
What if you lose your buddy at this instance, at the farthest distance inside the overhead your Thirds turn value allows? How do you calculate the amount of gas to do a Lost Buddy Search?
Easy! At your turn around reading of 157 bar on the SPG, simply add your Rock Bottom value to your Third's turn value (50 bar Rock Bottom plus 53 bar Third's turn value equals 103 bar); Put a line-arrow pointing the way out on your Primary Reel line that you've been laying, and take reference note of where you are inside the overhead at that exact point as well. Now go and search for your buddy with the understanding that you must be back at this line-arrow marker by the time your SPG reads this actual value (103 bar). So you would have from 157 bar down to 103 bar reading on your SPG, or 54 bar delta of gas to search for your buddy --if you were to do a straight line search down a long corridor inside the wreck for example, tactically you should use 27 bar out and 27 bar back to your line-arrow marker for a delta of 54 bar, and an actual end of search SPG reading of 103 bar-- you must start your egress whether you found your buddy or not when you use up this 54 bar delta of gas, at the line arrow marker, with the actual 103 bar final reading on your SPG.
Now could you honestly do all the above maths quickly in your head and on-the-fly using a SPG with actual PSI units?
Use a unit transformed BAR SPG in this instance as described above . . .better yet, just convert over & go Metric
!(Note: Remember that on a lost buddy search, you will deliberately encroach and use up the Third's Reserve Value needed for an emergency gas-sharing egress contingency (and possibly use up some amount of Rock Bottom as well) --in other words, if you do find your lost buddy and worst of all worst scenarios he happens to be out-of-gas in a silt-out . . .well dea ex machina. I hope you're in a 3-person Team, somehow make it out and run into other divers on the outside who can donate gas & assist. . .)
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