Using an SCR range for gas planning

[Sloth]

You miss my point Sloth and unfortunately don't follow--accuracy & precision is not the aim, but rather a simple arithmetic process demonstrated to estimate gas consumption that you can do both pre-dive as well as on-the-fly, in your head, and after some practice --without whipping out your wetnotes anymore for reference.

You are good at math, I suck at math. Math on the fly for me is a disaster waiting to happen. Trust me, its safer for me to memorize a simple range then do math underwater no matter how easy it is.

On the fly can get some people into trouble. Id rather do all the heavy lifting before the dive instead of during.

 

[Kevrumbo]

You are good at math, I suck at math. Math on the fly for me is a disaster waiting to happen. Trust me, its safer for me to memorize a simple range then do math underwater no matter how easy it is.

On the fly can get some people into trouble. Id rather do all the heavy lifting before the dive instead of during.

Fair enough, that's okay! (Our numbers do kind of jibe anyway. . .)

 

[Trace Malinowski]

I find that 1 cubic foot per minute SCR solves all my math and gas management problems.

Experience has taught me extra gas left at the end of a dive - good. Three OOG situations during a single dive - bad.

 

[Kevrumbo]

I know with your experience Trace, you're "A-okay" in planning with SCR 1 cf/min and bringing the requisite amount of gas for the dive at hand.

But the neat thing about double AL80's together with that SCR of 0.75 cf/min, it just happens there is a one-to-one correspondence between depth in ATA and instantly knowing your DCR (refer back to the example in post#2) --albeit in metric terms . . .unfortunately that's where my Imperial Brethren get lost in translation, and don't know what to do with this seemingly "metric numerology".

 

[Trace Malinowski]

I know with your experience Trace, you're "A-okay" in planning with SCR 1 cf/min and bringing the requisite amount of gas for the dive at hand.

But the neat thing about double AL80's together with that SCR of 0.75 cf/min, it just happens there is a one-to-one correspondence between depth in ATA and instantly knowing your DCR (refer back to the example in post#2) --albeit in metric terms . . .unfortunately that's where my Imperial Brethren get lost in translation, and don't know what to do with this seemingly "metric numerology".

Yeah, Kevin, it is amazing what happens to the math when you dive with GUE instuctors who base SCR on JJ's RMV and forget that the scooters aren't on the D-rings of the Tech 1 divers with the single deco bottle AL40's when swimming them into a current during deco.

Two of us were probably sure we wouldn't have enough gas in the planning phase. One of those two definitely was sure we wouldn't! And, one of us had 3 bottles - wonder who that was? Probably not a Tech 1 diver!

 

[vioch]

What factors DIR divers take into account for planning minimum gas reserve (rock bottom) for deco dives?

 

[Rainer]

What factors DIR divers take into account for planning minimum gas reserve (rock bottom) for deco dives?

Enough gas to get two divers from max depth to the bottle switch (70' or 20') doing all deep stops along the way OR lost deco gas. These actually tend to be very similar gas reserves. If anything, planning for the former tends to cover the needs of the latter.

 

[limeyx]

What factors DIR divers take into account for planning minimum gas reserve (rock bottom) for deco dives?

RB or min gas is enough gas to get 2 stressed/working divers to the next gas supply (either next shallower deco bottle or surface) OR the amount of gas needed to compensate for 1 lost deco bottle (whichever is greater)

"Stressed" SAC is something open to interpretation, and based on experience and rule of thumb. Of course, this is the minimum (hence the name) and can be padded for all kinds of reasons

- cold water
- possible currents
- remote locations
- new team/gear

etc

This is for open water. for caves it gets a little more involved.


RB/Min gas is in backgas, not stages wherever possible -- then you can ditch the stages for greater efficiency of swimming) and BG you have 2 2nd stages to share

 

[Sloth]

What factors DIR divers take into account for planning minimum gas reserve (rock bottom) for deco dives?

Not sure what Kev's RB calculation is based on but the GUE standard for deco dives is as follows:

Old Tech 1 and current Tech 2:

Assumed SAC rate of 1cft per min (up for tweaking based on team makeup)
1 minute at depth for emergency
30ft/min to first deep stop at 75% of depth
10ft/min to gas switch
1min allocated for gas switch


New Tech 1 standard:

Assumed SAC rate of 1cft per min
2 minutes at depth for emergency
30ft/min (10m/min) to first deep stop at 75% of depth
20ft/min to gas switch (or 50% of depth, 10ft/min if you still have stops before gas switch)
2 minutes allocated for gas switch

 

[Bob Sherwood]

Trace, You had more than enough gas!!!! Remember gas is a TEAM resorce.

Yeah, Kevin, it is amazing what happens to the math when you dive with GUE instuctors who base SCR on JJ's RMV and forget that the scooters aren't on the D-rings of the Tech 1 divers with the single deco bottle AL40's when swimming them into a current during deco.

Two of us were probably sure we wouldn't have enough gas in the planning phase. One of those two definitely was sure we wouldn't! And, one of us had 3 bottles - wonder who that was? Probably not a Tech 1 diver!