Deco Bottles- 30cf vs 40cf?

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

[FONT=&amp]Loss of Decompression gas[/FONT]
[FONT=&amp]If a loss of one or more decompression-gasses should occur, the diver has several options:[/FONT]
·[FONT=&amp]Switch to backup gas and run a contingency schedule[/FONT]
·[FONT=&amp]The diver may wait until a team member has completed their decompression and if sufficient deco gas remains, breathe from the team member's decompression cylinder.[/FONT]
·[FONT=&amp]Buddy breathe deco gas with a team member (site conditions permitting)[/FONT]
·[FONT=&amp]In the case of a regulator malfunction, feather the deco cylinder valve while breathing from the malfunctioning regulator.[/FONT]
[FONT=&amp]

Also taken from the TDI/SDI Decompression procedures manual concerning lost gas options.
[/FONT]
 
You share the bottle. You can alternate times on the bottle for short stops (like 5mins) or split up longer stops. When you or your buddy isn't on the deco bottle, hang out on either back gas or (hopefully) another deco gas. Repeat for 1.5x the deco time, then up you go to the next stop.

So a 30min obligation on 50% now becomes a 45min obligation. Half the time you're on the gas, half the time you're not. You're still decompressing when you aren't on the gas, just not as quickly.

You're not going to double the stop times because someone's deco bottle crapped out (what's the point if you have a working bottle to share?), and 1.2x doesn't really cut it.

There is a school of thought out there for multiple deco gas dives that suggests NOT extending the intermediate gas stops (time on 50%,35%, etc) but extending the o2 stop by 1.5x. I think this is ok, especially for shorter bottom times.
 
PfcAJ, I'll agree that sharing the bottle, whether it's 10 minutes on it, 10 minutes off or some other magic number, it is the correct approach, but on a dive with, say a total deco obligation of 20 minutes, with divers that typically solo dive anyway... people will complete their deco and leave the water; giving the bottle of O2 to their buddy who remains behind.

It's not what I would do on a dive to say Eagle's Nest. It's certainly not what I teach, but it is real world and I've seen it at least a half dozen times.

There is of course the best answer, which is what we teach, and then there's what happens in the real world.
 
Yeah leaving a buddy behind isn't something I'd ever recommend or even do.

Why is what you teach different than what you do? Why is your protocol for Eagle's Nest different then at another site?
 
...people will complete their deco and leave the water; giving the bottle of O2 to their buddy who remains behind

So much for team diving

To be fair, I used to do that, but not any more
 
Yeah leaving a buddy behind isn't something I'd ever recommend or even do.

Why is what you teach different than what you do? Why is your protocol for Eagle's Nest different then at another site?

Guys, you can look for a witch hunt if you want. You can have instructors who tell you everything they should in class, and tell you they never do anything in a grey area. They never dive solo, leave a buddy at 10' to complete deco, never omit a primary reel or omit putting in a jump in a cave. You can have instructors who have told you they've never dove X amount of feet on air, or any number of things that are considered taboo.

And then you have people like me. Guys, the real world is that we are only human. Even instructors. I'm not going to blow smoke up your ass. I'll teach you what you should do. But have I broken thirds on a dive before? Yes. Do I put primary reels in every time? No. Have I left buddy's at 10' to finish their deco because they won't buy a better computer? You betcha. Am I going to lie about it? Nope. I am who I am.

If it makes you feel all warm and fuzzy to be around people who lie to you, then you should probably find another instructor. You know, it's interesting, two years ago I took a class from an instructor I barely knew, and he beat into my head this one particular concept. "Make sure you do ABCD every single time, never skip, don't omit, do it, do it, do it, or you'll die. Then in 5 dives, he broke that rule every single time. Wtf? I was pissed. How dare you make this sound so friggin important, tell me it's imperative, then neglect to do it every single dive. What a hippocrite. It still makes me mad thinking about it.

So my approach is this.
Student, I believe there are 5 rules to cave diving. I believe that if you obey all 5 of those rules, you virtually have a 100% chance at survival. Look, I don't obey all 5 of those rules every single dive. Does that mean if the math is right I'm risking 20% of my survival? Quite possibly. But it's my decision to make. I'm telling you that if you obey all 5 of those rules you get to survive. I'm also telling you that on occasion I take the calculated risk of not obeying one of those rules.

PfcAJ, I wouldn't expect you to leave a buddy behind. If I recall correctly, you're a DIR/GUE diver and not diving with a buddy is pretty much completely opposite of your agency's entire training philosophy.

The reason my protocol is different with EN is based on my own assumptions. I believe that the chance of issue from an EN dive is greater than say issues arriving at Ginnie. How about 12 minutes of deco at 10' versus 45 minutes at 10'. At EN, we're probably looking at an CNS% well over 100. Do we need to worry about an O2 hit? Yes. At ginnie, we're probably looking at a CNS of less than 40%. Is there a difference in the risk? I think so. Is it a big difference? Yes, I believe it is.

I can be real, or I can lie to you. I know lots of people who spout off on boards like these that they never break any rules, and then I see them in the caves the following weekend breaking those very same rules. Can you imagine how much my word would be worth to students the first time they caught me in a lie? Would they discount everything I taught them? Would they discount something incredibly valuable that might save their lives? I prefer to just be honest. Perhaps I've got the wrong approach. Only time will tell. But for now, I'm going to keep being honest.

---------- Post added August 3rd, 2013 at 02:32 PM ----------

Coldwaterhusky: I'm sorry your thread got derailed. Buy an AL40.

Mod's can you fix this thread to be fair to Coldwater. Maybe split it to another thread or something.
 
Honesty is great. I no longer leave people deco'ing on their own. It's a great theory until something goes wrong.Your computer says you have X mins more time than me? No problem, I have the gas to do it. Let's play noughts & crosses on wetnotes, I came here to get wet not sit on a boat waiting for you to (hopefully) surface later
 
Actually, I wouldn't do it from a boat. For a few reasons. The one of which is that in the water, even on deco, is better than sitting on boat. I've gotten sea sick a few times lately, not sure what's that's about. But, too much unpredictable stuff in the ocean.

You know, I'm all for team diving. If my buddy requires it, fine I'm happy to stay. If he wants to leave me on deco, that's fine too. Don't really care one way or the other. But what you have to understand is that most of my buddies have more big solo dives in caves than most people have dives.... period. They really don't care if you leave them at 10'.

Now the flipside of the coin... this isn't my philosophy with all divers, just some divers. Hell, even just a select few divers. I know a girl who has spent the last 20 minutes of a cave exit throwing up over and over again. There's no way I'm going to leave a weak diver in the water, even if they think their okay with it.
 
40 are the standard, but 30s seem to be common as well. I'm just starting my venture into tec diving and am setting up my first deco bottle. I'd like to go with a 40, but no dive shop in my area has any in stock. Is it worth it to order one in, or go with the 30s avalible around here? What's your view on 30s vs 40s? When is one prefferable to the other?

You need a tank that's big enough to handle the needs of your dive plan.

This might sound like "Mr. Obvious" but on some dives a 30 is way more than you'll need and on others a 40 isn't close to enough. To figure out what tank you need, first you need to plan your expected dives, then calculate your consumption and deco stop depths/times/mixes (and possibly that of your buddy depending on your philosophy) and then you'll know what size deco tank you need.

vPlanner is very helpful for this.

It might be a 40. It might be an 80. It might be something else. This is something you need to calculate for yourself.

flots
 
http://cavediveflorida.com/Rum_House.htm

Back
Top Bottom