Stage planning in caves

[rjack321]

Fair enough, do you happen to know of a thread that covers that incident? Being in Ontario, I've heard about it, but always through second hand information.

Thanks,
Jim

The Deco Stop

 

[Steve R]

You have misread

1/2+200 psi = dropping a 3000psi stage at 1700.
On the exit you have ~100 for the switch (1600 in there now)
As you reach the next stage there's 300 remaining
100 more to switch to the next stage out
200 psi remains in the bottle effectively unusable.

Unless I have misread or misunderstood, I was thinking the same thing

 

[DeepSeaExplorer]

You have misread

1/2+200 psi = dropping a 3000psi stage at 1700.
On the exit you have ~100 for the switch (1600 in there now)
As you reach the next stage there's 300 remaining
100 more to switch to the next stage out
200 psi remains in the bottle effectively unusable.

I dunno...

Twice now I've heard things like, "I only use my stages", "1/2+200 isn't safe" and "Thirds on stages is stupid."

So I guess I really have no clue what he's talking about. I'm going to bow out of this conversation.

 

[limeyx]

I dunno...

Twice now I've heard things like, "I only use my stages", "1/2+200 isn't safe" and "Thirds on stages is stupid."

So I guess I really have no clue what he's talking about. I'm going to bow out of this conversation.

I *think* RTodd said that 1/2+200 isn't safe if you don't reduce your usable back gas by a certain amount to reflect that you now dove more than 1/3 on the stage.

diving 1/3 on a stage could be irritating because then as he said, would you rather have
- 3 stages at 1000 psi (all needed for the exit)
- 1 stage and the gas that would be in those other 2 stages in your back gas where it is easier to carry and easier to share ...

Now, I am far (far) from a gas planning expert for cave (only have cave1), but that seems to make some sense to me ...

 

[Jason B]

I dunno...

Twice now I've heard things like, "I only use my stages", "1/2+200 isn't safe" and "Thirds on stages is stupid."

So I guess I really have no clue what he's talking about. I'm going to bow out of this conversation.

You are talking about diving your stage to 1/2 + 200 then continuing the dive using thirds on back gas, correct?

The issue is you are only allowed to dive thirds of your total gas supply and you are violating that.

You need to pull about 30cu/ft of gas ( for each stage) out of your starting pressure before you calculate your thirds.

You can sit down with a calculator and do the math, but the short dirty way, when using Al80's for stage (filled to 3000-3400psi) and 95 -104's as backgas, what we do is for each stage we deduct 100psi from our back gas thirds.

So if we started a dive with a single stage (diving it to 1/2 + 200), and our back gas thirds is 1100psi, we would subrtract 100psi and make our back gas thirds 1000psi. For a double stage, we would subract 200psi from the 1100psi for a back gas turn pressure of 900psi. I have yet to do a triple stage.

You also mentioned earlier that you never go back on your stage on exit. I'd suggest getting off back gas as soon as you get to the stage and reserve the back gas. Now if the **** hits the fan, you can ditch the stages and make a more expedient exit if needed.

 

[Steve R]

You also mentioned earlier that you never go back on your stage on exit. I'd suggest getting on back gas as soon as you get to the stage and reserve the back gas. Now if the **** hits the fan, you can ditch the stages and make a more expedient exit if needed.

edit alert.

 

[rjack321]

So for the 1/3rds portion backgas planning you assume every stage bottle is non-functional upon pickup/return (i.e. you save enough backgas to compensate for every one)??

 

[limeyx]

You need to pull about 30cu/ft of gas ( for each stage) out of your starting pressure before you calculate your thirds.

You can sit down with a calculator and do the math, but the short dirty way, when using Al80's for stage (filled to 3000-3400psi) and 95 -104's as backgas, what we do is for each stage we deduct 100psi from our back gas thirds.

So if we started a dive with a single stage (diving it to 1/2 + 200), and our back gas thirds is 1100psi, we would subrtract 100psi and make our back gas thirds 1000psi. For a double stage, we would subract 200psi from the 1100psi for a back gas turn pressure of 900psi. I have yet to do a triple stage.

So when you say "take out 100 psi" you mean calc 1/3 and then reduce the "penetration" (1/3) by 100

so then you reduce the gas by a total of 300 psi (1/3 in, 1/3 out, 1/3 from reserve)
and then 300 * TF of 8 = 24 cft which is close (enough) to 1/3 of an AL80 (alebeit an AL80 filled to 3000 not really 3400

with AL80's as BG, you would take 30 / 5 = total of 600 psi = 200 psi off of 1/3's for each stage, right ?

 

[amascuba]

Fair enough, do you happen to know of a thread that covers that incident? Being in Ontario, I've heard about it, but always through second hand information.

Thanks,
Jim

PM Sent

 

[Jason B]

edit alert.

Huh? What I do?