laikabear
Contributor
Hi guys,
I am going to be taking GUE Fundamentals in 2 months (so excited!) and am currently reading the materials they provide once you register for the class. The materials include several different PDFs and this topic is covered in a few different places. For those interested, the materials are about 1000 pages long in total.
Here's the question:
In one area, it is stated that for divers with dissimilar tanks, usable gas must be calculated for EACH diver individually, and then use the diver with the smallest amount of usable gas to calculate the turn pressure for each diver. (Say Diver 2 has the least usable gas, you then use that number for Diver 1 also). There are a couple of examples done in this style (I will call it Method #1).
In another place (2 places actually), each diver gets their own usable gas calculation, and then their individual usable gas is used to calculate a turn pressure (Method #2).
Here is an example I just made up. Minimum gas is 20 cu ft. Diver 1 has 120 cu ft of gas total, Diver 2 has 220 cu ft of gas total. It's an out and back, rule of halves dive. Diver 1 turn volume would be at 120 - (120-20)/2. Do we say Diver 2 would turn at 220 - (120-20)/2 also, or would it be 220 - (220-20)/2? I think it's the 2nd one.
Now that's all in cu ft and I did not include converting to PSI but that should not matter. It's the basic assumption that is confusing me since it's stated both ways, not the math. I can do math (usually).
If we do it Way #1, Diver 1 turn volume is at 70 cu ft and Diver 2 has to turn at 170 cu ft. Way #2 Diver 1 still turns at 70 cu ft, Diver 2 turns at 120 cu ft. Obviously whichever diver reaches their turn volume first would call the dive, the question is just WHAT is the turn volume for Diver 2?
I figured this should go in Basic Scuba since calculating turn pressure should be pretty basic, right? I wish we had gone into more depth about it in my PADI OW and AOW classes. We did not. We did not cover converting between PSI and cu ft. or really do anything other than say that starting with 3000 psi, you want to ascend at 800 (reserve of 300 for ascent and 500 for emergencies). That is also what is printed in the OW Diver manual (pgs 92-93).
*If you have the GUE Fundies materials and want to look at what I am talking about, there is a PDF called Gas Management which calculates turn pressures on Page 4 via method #2. There is another PDF called Gas Planning Concerns which calculates turn pressures on Pages 1 and 2 via method #1. This type of calculation is also mentioned in the Powerpoint notes, on a slide called Gas Strategies, where method #2 is used. Another mention is in the PDF Beginning With The End in Mind, but I did not see where it explicitly stated either way.
I have mentioned this question to my instructor but haven't heard back from him yet. I am just trying to understand all the classroom material PRIOR to the class, because I know that just trying to learn the physical skills is going to have me well-taxed during the class. Hopefully some of you (GUE or not) will be able to give some advice.
I am going to be taking GUE Fundamentals in 2 months (so excited!) and am currently reading the materials they provide once you register for the class. The materials include several different PDFs and this topic is covered in a few different places. For those interested, the materials are about 1000 pages long in total.
Here's the question:
In one area, it is stated that for divers with dissimilar tanks, usable gas must be calculated for EACH diver individually, and then use the diver with the smallest amount of usable gas to calculate the turn pressure for each diver. (Say Diver 2 has the least usable gas, you then use that number for Diver 1 also). There are a couple of examples done in this style (I will call it Method #1).
In another place (2 places actually), each diver gets their own usable gas calculation, and then their individual usable gas is used to calculate a turn pressure (Method #2).
Here is an example I just made up. Minimum gas is 20 cu ft. Diver 1 has 120 cu ft of gas total, Diver 2 has 220 cu ft of gas total. It's an out and back, rule of halves dive. Diver 1 turn volume would be at 120 - (120-20)/2. Do we say Diver 2 would turn at 220 - (120-20)/2 also, or would it be 220 - (220-20)/2? I think it's the 2nd one.
Now that's all in cu ft and I did not include converting to PSI but that should not matter. It's the basic assumption that is confusing me since it's stated both ways, not the math. I can do math (usually).
If we do it Way #1, Diver 1 turn volume is at 70 cu ft and Diver 2 has to turn at 170 cu ft. Way #2 Diver 1 still turns at 70 cu ft, Diver 2 turns at 120 cu ft. Obviously whichever diver reaches their turn volume first would call the dive, the question is just WHAT is the turn volume for Diver 2?
I figured this should go in Basic Scuba since calculating turn pressure should be pretty basic, right? I wish we had gone into more depth about it in my PADI OW and AOW classes. We did not. We did not cover converting between PSI and cu ft. or really do anything other than say that starting with 3000 psi, you want to ascend at 800 (reserve of 300 for ascent and 500 for emergencies). That is also what is printed in the OW Diver manual (pgs 92-93).
*If you have the GUE Fundies materials and want to look at what I am talking about, there is a PDF called Gas Management which calculates turn pressures on Page 4 via method #2. There is another PDF called Gas Planning Concerns which calculates turn pressures on Pages 1 and 2 via method #1. This type of calculation is also mentioned in the Powerpoint notes, on a slide called Gas Strategies, where method #2 is used. Another mention is in the PDF Beginning With The End in Mind, but I did not see where it explicitly stated either way.
I have mentioned this question to my instructor but haven't heard back from him yet. I am just trying to understand all the classroom material PRIOR to the class, because I know that just trying to learn the physical skills is going to have me well-taxed during the class. Hopefully some of you (GUE or not) will be able to give some advice.
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