Solo diving

[swimlikethefish]

If you had a sac anything above a 0.4 and did a 60 minute dive to 60 feet you would run out of gas on an Al80. Using an 130 you would run out of ndl before gas with that consumption rate.

Inversely if your sac was 0.7 or higher you would run out of air before hitting the ndl even on a 130. That is why knowing your sac rate is important. With that you can calculate your rmv and truly figure out what your usage will be.

 

[scubadada]

If you had a sac anything above a 0.4 and did a 60 minute dive to 60 feet you would run out of gas on an Al80. Using an 130 you would run out of ndl before gas with that consumption rate.

Inversely if your sac was 0.7 or higher you would run out of air before hitting the ndl even on a 130. That is why knowing your sac rate is important. With that you can calculate your rmv and truly figure out what your usage will be.

Over the last 1100 dives, my average RMV is 0.36 cf/min. Of course these calculations depend on EAN% and depth. Repetitive dives and SIs also play into the calculations. I often approach, or slightly exceed my NDLs doing multiple dives using AL 80s, it's not that hard

 

[swimlikethefish]

Quick math for you.

With a sac of 0.36 as you stated. Doing a 60ft dive for 60 minutes. Assuming a descent rate of 60ft a min and an ascent rate of 30ft a min. With a 3 min safety at 15ft. Then the same 30ft/min ascent to surface. Using an Al80 filled to 3000psi with a volume of 77.6 cu/ft. You would consume 65.58 cu/ft of air. Leaving you with 466 psi in your tank at the surface. This assumes a square profile. And also assumes no safety margin and also assumes you utilize no gas for your buoyancy compensator.

Same dive same characteristics, same assumptions but this time your sac is 0.4 as I stated above. You would consume 72.12 cu/ft and surface with 212psi.

That is without using any air for anything other than breathing. We all know now that with a sac of 0.4 or higher you can not do a 60ft dive for 60 minutes using an Al80.

Edit: this is calculated using air. If you were on Ean with a shallower ead you would most certainly run out of nitrox before you ever hit your ndl. All while diving a square profile. You must also remember we are in the new member forum, so if you'd like to start another thread in the advanced forum I will gladly break down the numbers for any interested.

 

[tursiops]

If you had a sac anything above a 0.4 and did a 60 minute dive to 60 feet you would run out of gas on an Al80.

You can't do a 60-minute air dive to 60 ft unless you are on the Navy tables.
And, if you are using Nitrox, your "rule" about running out of gas before you run out of NDL is not valid.

 

[tursiops]

You must also remember we are in the new member forum

"New Member" is not the same as "Basic Scuba."

 

[scubadada]

Quick math for you.

With a sac of 0.36 as you stated. Doing a 60ft dive for 60 minutes. Assuming a descent rate of 60ft a min and an ascent rate of 30ft a min. With a 3 min safety at 15ft. Then the same 30ft/min ascent to surface. Using an Al80 filled to 3000psi with a volume of 77.6 cu/ft. You would consume 65.58 cu/ft of air. Leaving you with 466 psi in your tank at the surface. This assumes a square profile. And also assumes no safety margin and also assumes you utilize no gas for your buoyancy compensator.

Same dive same characteristics, same assumptions but this time your sac is 0.4 as I stated above. You would consume 72.12 cu/ft and surface with 212psi.

That is without using any air for anything other than breathing. We all know now that with a sac of 0.4 or higher you can not do a 60ft dive for 60 minutes using an Al80.

Edit: this is calculated using air. If you were on Ean with a shallower ead you would most certainly run out of nitrox before you ever hit your ndl. All while diving a square profile. You must also remember we are in the new member forum, so if you'd like to start another thread in the advanced forum I will gladly break down the numbers for any interested.

So now do a 2nd, 3rd , and 4th dive of the day, usually with shorter SIs. Max depths often greater than 60 ft, etc, etc. You need to spend less time calculating and more time diving. Believe me, I don't need you to run calculations for me,

 

[swimlikethefish]

That is correct I used the navy tables. Your ead for 32% at 60ft is 47 ft. Rounded to 50ft. Gives you an ndl of 92 minutes. So therefore you would have to extend your 60 minute dive by 32 more minutes to hit ndl. Which you can't do on your remaking 466psi you have in your Al80. So it looks to me like you would run out of gas before you hit your ndl on nitrox.

 

[swimlikethefish]

"New Member" is not the same as "Basic Scuba."

I didn't even look to be honest. I just knew it wasn't where it should be.

 

[swimlikethefish]

So now do a 2nd, 3rd , and 4th dive of the day, usually with shorter SIs. Max depths often greater than 60 ft, etc, etc. You need to spend less time calculating and more time diving. Believe me, I don't need you to run calculations for me,

So you are trying to say my calculations are wrong? I do not think there was an error made. I did it on paper with a calculator using the data above. The numbers usually do not lie, I use the same math planning my dives. It wouldn't matter of you had 40 or 4000 logged dives. If your sac was 0.36 doing that dive on nitrox with an Al80 you would run out far before you reached your actual ndl.

 

[scubadada]

So you are trying to say my calculations are wrong? I do not think there was an error made. I did it on paper with a calculator using the data above. The numbers usually do not lie, I use the same math planning my dives. It wouldn't matter of you had 40 or 4000 logged dives. If your sac was 0.36 doing that dive on nitrox with an Al80 you would run out far before you reached your actual ndl.

Single dive, square profile, get real, out behind the calculator and into the water. I dive nitrox all the time in Boynton Beach, Jupiter, and West Palm. Dives are frequently limited by NDL and not gas, even with an AL80.