Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

[Storker]

Seems odd that you would be so worried

Not worried at all. Just trying to get the data.

 

[ChuckP]

• What was your proper min gas reserve?
• At which bottom time did you pass that reserve?
• How did that bottom time square with your NDL?
• Did you overstay your proper min gas time, or did you leave the bottom when you reached your proper min gas reserve?
• If there was a mismatch between your min gas time and your NDL, did you have sufficient reserves and a redundant gas supply in case you had to do deco time?

Curious minds would like to know.

Define min gas reserve as it relates to an open water recreational dive. It's all muddy, does one want to be at a safety stop with 300 or 1000 psi? Your minimum gas reserve may not be my minimum gas reserve.

NDL is quite the same - using Scuba Pro logic, is MB set at 0 or 5? GF hi of 70 or 90? If you can see a surface GF number, how high are you willing to see it?

That dive shows max depth at roughly 6 minutes in with 4 minutes of NDL and 2600 psi - he stayed 2 minutes at depth and had a nice gradual ascent. It would be curious to see NDL graphed for that dive or Surface GF.......

IMO, deep diving with a single source can get ugly when there is an equipment failure - specifically a 1st stage failed shut or low pressure side failure - be painfully aware of those possibilities and ready for that type of failure - unless your buddy is within a few arms length, you should probably consider yourself solo..... Think thru and understand the what ifs while on the boat, not at 100+ feet.

 

[Storker]

It'll take me about 5 minutes to get to 130 ft and 5 minutes NDL bottom time. My SAC would be about 0.5 cfm. So at 5 atmospheres, it would be about 2.5 cfm x 5 minutes = 12.5 cubic feet (cf). Let's triple that volume to account for 5 minutes descending and 5 minutes ascending, 12.5 x 3 = 37.5 cf. So, I would have more than half of air capacity left in the tank when I get back. At that depth, the time to surface is about 10 minutes x 2.5 cfm = 25 cf x 3000 psi / 80 cf = 938 psi. So, when my tank pressure reaches 1500 psi, it's time to get the hell up.

I never passed the bottom time for the reserve pressure of 1500 psi. I started with 3048 psi in the tank and came back with 1696 psi left in the tank at the surface. It looks like my gas planning estimate is conservative.

I still have 2 minute NDL when I ascent from 138 feet depth. I carried a 3cf Spare Air too as a back up.

Pretty good hand-waving there.

Min gas? Psi + water volume, or surface gas volume?
Time at depth, compared to a reckonized NDL?
Remaining reserve? And how does that reserve square with standard min gas?

 

[Storker]

Define min gas reserve as it relates to an open water recreational dive

The gas required to feed two divers with enough gas given an elevated SAC due to stress, until a safe ascent to the surface. Preferably with a safety stop, but not required. It ain't rocket science, there are more than enough posts on the 'net about that

 

[Dan]

Pretty good hand-waving there.

Min gas? Psi + water volume, or surface gas volume?
Time at depth, compared to a reckonized NDL?
Remaining reserve? And how does that reserve square with standard min gas?

Not sure if I understand your questions. Please elaborate.

I use AL80 (Aluminum 80 cubit feet) tank. I try to keep my diving plan simple, i.e., when I reach 1500 psi tank pressure, it's time to ascent as my Teric says it'll take 10 minutes to get back to the surface or about 1000 psi according to "hand-waving" estimate + 500 psi reserve.

I only spent 3 minutes out of 5 minute NDL and not planning to go on DECO.

 

[Dan]

Define min gas reserve as it relates to an open water recreational dive. It's all muddy, does one want to be at a safety stop with 300 or 1000 psi? Your minimum gas reserve may not be my minimum gas reserve.

NDL is quite the same - using Scuba Pro logic, is MB set at 0 or 5? GF hi of 70 or 90? If you can see a surface GF number, how high are you willing to see it?

That dive shows max depth at roughly 6 minutes in with 4 minutes of NDL and 2600 psi - he stayed 2 minutes at depth and had a nice gradual ascent. It would be curious to see NDL graphed for that dive or Surface GF.......

IMO, deep diving with a single source can get ugly when there is an equipment failure - specifically a 1st stage failed shut or low pressure side failure - be painfully aware of those possibilities and ready for that type of failure - unless your buddy is within a few arms length, you should probably consider yourself solo..... Think thru and understand the what ifs while on the boat, not at 100+ feet.

NDL graph is shown in red. I use GF Conservative Medium 40/85.

 

[Storker]

Not sure if I understand your questions. Please elaborate.

When I did my CMAS 3*, I was supposed to be able to estimate my min gas on the fly. Min gas = minimum gas amount to bring both buddies to the surface in a safe way if any of them suffered a catastrophic gas loss. With a given tank, that translates to a given tank pressure.

If you have a proper min gas calculation and a proper min gas plan, you should know when it's time to return to the surface. If you dont understand that concept, you probably shouldn't dive that deep. In case SHTF. In which case you might (or might not, if you're lucky) die. Me, I kinda resent dieing.

 

[Dan]

Define min gas reserve as it relates to an open water recreational dive. It's all muddy, does one want to be at a safety stop with 300 or 1000 psi? Your minimum gas reserve may not be my minimum gas reserve.

NDL is quite the same - using Scuba Pro logic, is MB set at 0 or 5? GF hi of 70 or 90? If you can see a surface GF number, how high are you willing to see it?

That dive shows max depth at roughly 6 minutes in with 4 minutes of NDL and 2600 psi - he stayed 2 minutes at depth and had a nice gradual ascent. It would be curious to see NDL graphed for that dive or Surface GF.......

IMO, deep diving with a single source can get ugly when there is an equipment failure - specifically a 1st stage failed shut or low pressure side failure - be painfully aware of those possibilities and ready for that type of failure - unless your buddy is within a few arms length, you should probably consider yourself solo..... Think thru and understand the what ifs while on the boat, not at 100+ feet.

My buddy is within a few feet away. She is on red fins right in front of me as shown in the video, below. I have 3cf Spare Air to get to her in case my regulator fails.

 

[Storker]

My buddy is within a few feet away. She is on red fins right in front of me as shown in the video, below. I have 3cf Spare Air to get to her in case my regulator fails.

Have you done the math? Is it enough?

 

[Dan]

Have you done the math? Is it enough?

In earlier post I mentioned about consuming 2.5 cfm (cubic feet / min) at 5 atmospheres. With 3 cubic feet Spare Air, that means I have over a minute to get to her.

1000 psi gas usage is estimated based on air consumption at 5 atmospheric pressure and including the 3 minute safety stop, which can be skipped during an emergency. As we ascend, the ambient pressure will decrease and the air consumption rate would decrease.