Deco Bottles- 30cf vs 40cf?

[PfcAJ]

Weird. Thanks.

 

[TSandM]

There's some literature out there stating to plan 1.2 instead of 1.5, because your sac rate decreases significantly during deco,

But I plan the amount of deco gas I need with my deco SAC rate in mind . . . The reserve I carry is for my buddy's lost deco gas. 1.2 won't cover that.

 

[Tortuga68]

IMO 40 > 30 and Luxfer > Catalina

If you're planning to use 50% and O2 for deco, 2 x 40s are pretty versatile. If you just use O2 for deco, an 80 might be better for more advanced dives (deeper/longer)

 

[Rich Keller]

I'd get the AL40 between those two...or even better a Lp45 or Lp50 steel cylinder.

I would second that if you do not need a full size bottle. They are also useful as a primary for shallow shore dives or any short dive where a full size bottle would be a waste.

 

[MalibuJerry]

2x is equally new.

Really? Seriously?

So you and your buddy are diving and he loses his deco gas. What is your plan with 1.2? You both blow off 40% of your deco? The rule of 2's is one so that both of you can complete your deco. The same is true for the rule of 1/3rds. 1/3 in, 1/3 out and 1/3 if your buddy needs your gas so that both of you can get out.

I suppose if you are doing technical diving solo it does not matter as you are not going to share with anyone, but then you have to figure your gases so that you have enough to complete your deco if you lose one of them. Or you can just take your chances. And if there is someone else in the water at the same time who needs your help, oh well, too bad for them.

As for the slower sac rate on deco, that is true, but you should not use an internet formula, you need to find out how much more relaxed you are empirically as it differs between divers.

 

[TSandM]

We don't carry 2x. We carry 1.5, and if there is complete loss of deco gas, some of the deco ends up getting done on backgas.

 

[Superlyte27]

But I plan the amount of deco gas I need with my deco SAC rate in mind . . . The reserve I carry is for my buddy's lost deco gas. 1.2 won't cover that.

I didn't say it's what I practiced. I said it's what an agency's literature said. But, on a typical dive, I'm also not planning extra deco gas for my buddy. In the event that he loses his AL40, he can deco on back gas.

Are you really going to buddy breathe on your deco stop? Or do you have two 2nd stages? Here's what's more likely, and what I've seen happen on more than a few occasions.

I do my dive, buddy came back to find his AL40 bled down to nothing. He starts his 20 minutes of deco (now 40 minutes because he's deco'ing on backgas) and I do my deco on 100%. When my deco is over, he can have my AL40 with the remaining gas. Sure he's not going to get out of the water in 20 minutes, but he might get out of it in 30 minutes. That's one reason for the 1.5x. Do I need double the gas? No, because he's deco'ing on back gas while I'm using the O2. Who's teaching double the gas? I've never seen that. I've also never seen a deco bottle with two 2nd stages on it, and I've never seen anyone buddy breathing a deco bottle when both divers still had back gas they could breathe.

---------- Post added August 3rd, 2013 at 11:19 AM ----------

Really? Seriously?

So you and your buddy are diving and he loses his deco gas. What is your plan with 1.2? You both blow off 40% of your deco? The rule of 2's is one so that both of you can complete your deco. The same is true for the rule of 1/3rds. 1/3 in, 1/3 out and 1/3 if your buddy needs your gas so that both of you can get out.

I suppose if you are doing technical diving solo it does not matter as you are not going to share with anyone, but then you have to figure your gases so that you have enough to complete your deco if you lose one of them. Or you can just take your chances. And if there is someone else in the water at the same time who needs your help, oh well, too bad for them.

As for the slower sac rate on deco, that is true, but you should not use an internet formula, you need to find out how much more relaxed you are empirically as it differs between divers.

Ok, like I said above...
How do you accomplish this? Are you guys buddy breathing the Oxygen or is there two regulators? As far as I know, no one is teaching this. Use your backgas while I'm using the O2. When my deco is finished, you can have my Oxygen bottle.

 

[ucfdiver]

I do my dive, buddy came back to find his AL40 bled down to nothing. He starts his 20 minutes of deco (now 40 minutes because he's deco'ing on backgas) and I do my deco on 100%. When my deco is over, he can have my AL40 with the remaining gas. Sure he's not going to get out of the water in 20 minutes, but he might get out of it in 30 minutes. That's one reason for the 1.5x. Do I need double the gas? No, because he's deco'ing on back gas while I'm using the O2. Who's teaching double the gas? I've never seen that. I've also never seen a deco bottle with two 2nd stages on it, and I've never seen anyone buddy breathing a deco bottle when both divers still had back gas they could breathe.

argh, nononono. That is NOT how it works

Really? Seriously?

So you and your buddy are diving and he loses his deco gas. What is your plan with 1.2? You both blow off 40% of your deco? The rule of 2's is one so that both of you can complete your deco. The same is true for the rule of 1/3rds. 1/3 in, 1/3 out and 1/3 if your buddy needs your gas so that both of you can get out.

I suppose if you are doing technical diving solo it does not matter as you are not going to share with anyone, but then you have to figure your gases so that you have enough to complete your deco if you lose one of them. Or you can just take your chances. And if there is someone else in the water at the same time who needs your help, oh well, too bad for them.

As for the slower sac rate on deco, that is true, but you should not use an internet formula, you need to find out how much more relaxed you are empirically as it differs between divers.

Just curious-- do you have any tech training? From your post, I'm assuming the answer is no.

Carrying 2x makes no sense. If you have 20min of deco, are you really going to do 20min on your bottle, and pass it to a buddy who's already done 20min of backgas deco and wait for him to do 20 minutes on the deco gas ignoring what he has already done? Or are you going to buddy breathe off a 40in hose the whole deco while managing a SMB and possibly a tied off scooter? There's just no logical reason to carry 2x.

If you need 20min of deco gas, you carry 30. If you lose your deco bottle, you extend the deco by 50% (now 30min deco), split the remaining bottle in half, and when you don't have the shared bottle, you're breathing the next deepest gas. So for 20min @ 20ft on o2 where you lose a bottle, you make that 30min, each doing 15min on o2, and 15min on backgas (or 50% if you have it).

 

[Knackas]

[FONT=&quot]Fortunately, there is a simple and very conservative method of reserve gas planning that takes into account multiple failures and typically produces adequate reserves to cover most contingency plans. The following method assumes that divers are not in an overhead environment and it produces a reserve gas amount that will theoretically allow two divers to reach the surface (while performing all decompression stops along the way) on one diver's bottom gas supply.[/FONT]

[FONT=&quot]1) Begin by planning a dive to the desired depth for the desired time using only bottom gas.[/FONT]
[FONT=&quot]2) Calculate the amount of bottom gas needed.[/FONT]
[FONT=&quot]3) Calculate the amount of transitional and decompression-gas consumed.[/FONT]
[FONT=&quot]4) Multiply the transitional and decompression-gas consumed by two and add it to the bottom gas. The sum represents the total amount of bottom gas that must be carried for the dive. Note: A diver's breathing rate should not vary on ascent if he properly monitors and maintains his buoyancy. However, just as with other phases of the dive, it is possible for a diver's breathing rate to increase on ascent if he works harder or experiences anxiety.[/FONT]
[FONT=&quot]5) Ensure that the total bottom gas carried is also adequate for all contingency schedules assuming no gas failures.

The above is taken from the TDI/SDI training manual for Decompression procedures.
[/FONT]

 

[ucfdiver]

[FONT=&amp]Fortunately, there is a simple and very conservative method of reserve gas planning that takes into account multiple failures and typically produces adequate reserves to cover most contingency plans. The following method assumes that divers are not in an overhead environment and it produces a reserve gas amount that will theoretically allow two divers to reach the surface (while performing all decompression stops along the way) on one diver's bottom gas supply.[/FONT]

[FONT=&amp]1) Begin by planning a dive to the desired depth for the desired time using only bottom gas.[/FONT]
[FONT=&amp]2) Calculate the amount of bottom gas needed.[/FONT]
[FONT=&amp]3) Calculate the amount of transitional and decompression-gas consumed.[/FONT]
[FONT=&amp]4) Multiply the transitional and decompression-gas consumed by two and add it to the bottom gas. The sum represents the total amount of bottom gas that must be carried for the dive. Note: A diver's breathing rate should not vary on ascent if he properly monitors and maintains his buoyancy. However, just as with other phases of the dive, it is possible for a diver's breathing rate to increase on ascent if he works harder or experiences anxiety.[/FONT]
[FONT=&amp]5) Ensure that the total bottom gas carried is also adequate for all contingency schedules assuming no gas failures.

The above is taken from the TDI/SDI training manual for Decompression procedures.
[/FONT]

I guess that works, but I don't know that I would want to be using 15/55 to recover from a lost o2 bottle. Me, personally, I always have enough left over from the previous deepest gas (be it a deco gas or bottom mix) to recover from losing the next bottle up. This way if you lost o2 on a 15/55 dive you would use a gas with 50% o2 instead of 15% o2.