Redundancy Required for Decompression Diving?

[CptTightPants21]

And even if they say that, what does it mean for someone with a pony bottle? If someone comes back with a full 40 plus 200 psi on their back, are they in violation of the rules?

If the point is to ensure people don't drop below a safe margin for error, doesn't a full 40 do that? Would they have been "okay" if they switched to their pony at 500 psi, but otherwise done the exact same dive?

If the point is to limit people's time, then if the boat didn't have to wait on them, isn't that okay, too?

Do not attempt to use logic on a boat operator.

These aren't the droids you are looking for...........

 

[KeithG]

And even if they say that, what does it mean for someone with a pony bottle? If someone comes back with a full 40 plus 200 psi on their back, are they in violation of the rules?

If the point is to ensure people don't drop below a safe margin for error, doesn't a full 40 do that? Would they have been "okay" if they switched to their pony at 500 psi, but otherwise done the exact same dive?

If the point is to limit people's time, then if the boat didn't have to wait on them, isn't that okay, too?

You will need to ask the operators why they make their rules. My belief is that the 500 psi rule is to make sure people do not suck the operators tank dry. 500psi minimum in any tank provided by the operator. But I do not make the rules. i just choose dive operators whose rules i agree with.

I have witnessed people surface with more than 500 psi and then suck the tank down way past 500psi on the hang line as they struggled in current and waves and boat swing to reboard the boat. More than once i have seen divers miss the ladder on a liveaboard swing and they ended up waiting another 5 minutes for the boat to come back to them. the divers surfacing with 500psi all had enough air to miss the boat and survive without too much trauma.

 

[lermontov]

Lots of people have the capacity to learn things without formal instruction. Some people can probably pick up mathematics textbooks and go from algebra through advanced calculus on their own. Similarly, according to Edgar Rice Burroughs in the novel Tarzan of the Apes, after being raised by apes, Tarzan found a trunk full of books left in the jungle by some careless explorer and not only understood what they were for, he learned to read them and speak the words with a perfect Oxford accent. (That may have been fiction, though.)

If you are such a person, congratulations. Others are more likely to need some help.

Tarzans not real ?

 

[Storker]

There is only so far that youTube and forums will get you, at some point someone who knows more than you needs to show you where you need to be and help you get there.

Anecdote time: I struggled to crack the code with backfinning. No matter how may YouTube videos I watched, no matter how much I read on the 'net, I wasn't able to make it work underwater. It took me exactly one dive with another club member, with good mentoring, to find out how to do it. I still don't know what I did wrong, though (as if that matters at all...).

And no, he wasn't an instructor.

 

[Storker]

Even decompression diving doesn't require anything tougher than basic arithmetic.

Yes, it does. It requires a basic grasp of physics and physiology. Which far from every person - even if they're born and raised in a 1st world country - has.

 

[Storker]

Being able to hold a mid water stop to a degree of accuracy, while being task loaded, and priortising the order of the tasks, are some that spring to mind.

It's not rocket science, though. Last summer, my youngest son - with less than ten post-cert dives - was able to hold a safety stop in mid water, only with me with my dSMB as a visual reference.

I won't claim that I'd be able to do the same when I was at his level, though...

 

[jseyfert3]

Did the boat operator mandate that? The poster I quoted never said that.

No, they never did give a min pressure to be back on the boat, just to signal the DM at half (1500) and low air (1000), and that they didn't want to see the out of air signal.

PADI seems to emphasize being back on the boat with 500, and perhaps I incorrectly assumed that everybody tried to have that much or more left. My point wasn't on the specifics of the pressure so much as the two guys with the tech training who openly said they were carrying pony bottles for redundancy and safety, not for extending their dives, seemed to use them to extend their dives by using air normally left in reserve. Perhaps they planned to surface with 250 PSI though, I didn't ask.

And even if they say that, what does it mean for someone with a pony bottle? If someone comes back with a full 40 plus 200 psi on their back, are they in violation of the rules?

If the point is to ensure people don't drop below a safe margin for error, doesn't a full 40 do that? Would they have been "okay" if they switched to their pony at 500 psi, but otherwise done the exact same dive?

I haven't seen many tanks in person yet but if I had to guess I'd say one guy had a 13 and the other a 19.

 

[stuartv]

The theory for sure,

But the practice skills are somewhat different. Being able to hold a mid water stop to a degree of accuracy, while being task loaded, and priortising the order of the tasks, are some that spring to mind.

These are best practiced and perfected with the assistance of an instructor. Of course some people believe that their skills are good enough, and they may very well be so, while everything is going to plan.

Throw in a few issues and suddenly the flaws in those suppose skills come to light.

My experience is that once you know what the skills are (whether from an instructor, a non-instructor diver, or a video) the practice part is something an instructor might spend some time facilitating, but otherwise, you are expected to practice on your. I don't see an instructor as a person that I expect to be there every single moment that I am ever practicing a valve drill - even if I'm practicing it sometime between the 1st day and the last day of my training with that instructor for that class.

If my buddy and I go get in a pool and take turns practicing holding a stop, while air sharing, and shooting a bag, that is not something that I would feel like my instructor had to be there for. In general, the instructor is there to teach me what to do and make sure I've understood the instructions, and then to assess me at the end and (hopefully) certify that I have met the agency's standards and the instructor's own standards. Usually, classes work out that there is adequate time in the schedule for the instructor to direct the students to practice while the instructor watches and gives feedback. And even enough time that that is all the practice required to pass the class. But, I don't see that as a requirement. And I DO see it as exemplified by people I know who have taken Fundies. From what I can tell it's pretty normal to start Fundies and be taught what you need to do, but not to get a pass. Then you go away and practice the skills until you think you've got them to the required level of proficiency. Then come back to finish the course (i.e. be assessed).

Now, obviously, this process is not the case for basic OW certification. And I also think it's not necessarily the case for some advanced technical disciplines (e.g. cave diving).

Do not attempt to use logic on a boat operator.

These aren't the droids you are looking for...........

I was explaining myself to giffenk, not a boat operator.

As for boat operators, I haven't been on that many boats, but I have yet to see a boat staffer check my tanks for remaining pressure when I got out.

And the real point is, even IF they say to get out with 500 psi left (and no further clarification), how could anyone say it's wrong to get out with a full pony and 200psi on their back?

Yes, it does. It requires a basic grasp of physics and physiology. Which far from every person - even if they're born and raised in a 1st world country - has.

I would say that the basic physics and physiology that is REQUIRED is not more difficult than the basic arithmetic (e.g. for manually calculating gas requirements on a multi-gas deco dive) - which is exactly what I said before (that the hardest thing is the arithmetic required). But, that is certainly subjective.

 

[stuartv]

No, they never did give a min pressure to be back on the boat, just to signal the DM at half (1500) and low air (1000), and that they didn't want to see the out of air signal.

PADI seems to emphasize being back on the boat with 500, and perhaps I incorrectly assumed that everybody tried to have that much or more left. My point wasn't on the specifics of the pressure so much as the two guys with the tech training who openly said they were carrying pony bottles for redundancy and safety, not for extending their dives, seemed to use them to extend their dives by using air normally left in reserve. Perhaps they planned to surface with 250 PSI though, I didn't ask.


I haven't seen many tanks in person yet but if I had to guess I'd say one guy had a 13 and the other a 19.

They were diving with singles, not doubles? Were they doing deco dives or NDL dives?

Do you know how much gas they had left when they got to their safety stop? And to the surface (not back on the boat)?

I've seen divers who clearly expected to be the most bad-ass divers on the boat get to their safety stop and then hang there until everyone else had gone past them and gotten on the boat. Whether that was simply to increase their safety margin with an extra long safety stop, or whether it was so they could say "we were the first ones off and the last ones on" is hard to say. But, they were the first ones off. And they were overheard (by me) to say "last ones back, baby" quietly to each other as they bumped fists.

I would not judge another diver one way or another if all I knew about them was that they got back on the boat carrying a pony and 200psi on their back.

 

[stuartv]

PADI seems to emphasize being back on the boat with 500, and perhaps I incorrectly assumed that everybody tried to have that much or more left.

ps. I have never taken any kind of PADI training. And I haven't done that many boat dives. Maybe 40- or 50-something?

I have been out on some boats where they made some statement regarding tank pressure. Sometimes, it is "be back on the boat with 500psi." Sometimes, it is "be on the surface with 500." Sometimes is is "start your ascent with 700" or whatever.

But, I have been out on more boats that said nothing about tank pressure at all. Mostly, they just make a point of emphasizing that everyone should ascend on the anchor line versus a free ascent away from the anchor line. On the few drift dives I've done, I don't remember them saying anything about either.