Faith diving and magic?

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Thank you again, SailNaked, for your post.

As an instructor there is a larger issue than the mistakes I made on that dive.

As a fellow Instructor, I would make this plea. Take the experience as a motive to make sure that you teach your students on how to be comfortable in using tables. If a recreational diver is dependent on computers, then that is what he will rely on.

we use tables based on algorithms, we use computers based on the same algorithms, . . . .

Are you sure about that? Recreational Tables are conservative.
 
halemanō;5713000:
If a diver is calculating "rock bottom" I would contend that "kind" of diver is very unlikely to "push NDL's" and "accidentally run out of gas." Are we not mostly talking about "catastrophic failure" with this type of planning?

I am still confused as to how an experienced, knowledgeable diver "accidently" runs out of gas, necessitating the emergency use of "rock bottom." :dontknow:

I think you don't understand what "rock bottom" means.

The definition of rock bottom is having adequate gas reserves to get you and your dive buddy to the surface while making an orderly ascent ... with appropriate stops ... from a given depth.

So any diver who's using rock bottom is ... by definition ... diving appropriately with a dive buddy AND maintaining appropriate gas reserves for both of you. Therefore if there's a catastrophic failure, they aren't going to "blow and go" ... they're going to share air and make a controlled ascent. There isn't a need to exceed recommended limits ... or to blow off a safety stop ... because if you're using rock bottom you have adequate air to make the ascent within the accepted safety standards.

That's the whole point of rock bottom ... to always make sure you have adequate gas reserves to avoid the need for an emergency ascent.

Therefore I fail to see your point. Making a 60 fpm ascent and blowing off your safety stop when you don't need to would be a stupid thing to do ... you're just increasing your risks unnecessarily ...

... Bob (Grateful Diver)

Yes, I agree, in my other post you quoted previously; my statement about blowing off the SS was wrong when discussing Rock Bottom. If I could type that post over I would have contended that if we make it to 15 feet with "some" air in the tank, a combined 2.0 SAC seems pretty high. :)

Yes, I agree that I did not include words that the OP also did not include; on an 80cft and typical recreational Cozumel diver.

My statement was working off the premise that the OP said this;

all the diving in Coz is deep followed by multi levels up. so it is typical for a computer to show deco at depth then clear 1/2 way through the dive.

Since the OP implied that this was typical in Coz, I assumed we were talking about dives made with the typical tanks found in Coz, again assuming 80's.

If we "humor me" by allowing the assumption that we are discussing typical warm water 80 cft diving, and looking at the RB tables James posted he seems to have also made that assumption; starting with 3000 psi we really only have 77 cf so we are only allowed to use 40 cf to get to "that" posted RB for Recreational 110 feet deep.

With a typical SAC and typical descent, are we typically "pushing" NDL's at 1421 psi? My understanding of the science of ascent speeds is that 30 feet per minute is "really" conservative for the first 50 feet of that ascent. Is there really only one recommended ascent speed for the entire alternate ascent on the typical rock bottom warm water dive we are discussing?

How often are typical warm water divers doing 110 foot deep boat dives as second dives? Maybe after lunch on the second boat trip of the day?

Also, other than dip tube blockage, for typical warm water diving, wouldn't there be some ascent time on the "failing" gas supply? A few breaths from the bottom ascending at 60 feet per minute sounds nice. At another end of the warm water problem spectrum, perhaps some breathable air "at the stop" in the "empty at depth" tank. :dontknow:

James typed "the most common definition of rock bottom" in his post. That led me to believe there were other possible definitions of rock bottom. :coffee:
 
halemanō;5715306:
Yes, I agree, in my other post you quoted previously; my statement about blowing off the SS was wrong when discussing Rock Bottom. If I could type that post over I would have contended that if we make it to 15 feet with "some" air in the tank, a combined 2.0 SAC seems pretty high. :)

Yes, I agree that I did not include words that the OP also did not include; on an 80cft and typical recreational Cozumel diver.

My statement was working off the premise that the OP said this;



Since the OP implied that this was typical in Coz, I assumed we were talking about dives made with the typical tanks found in Coz, again assuming 80's.

If we "humor me" by allowing the assumption that we are discussing typical warm water 80 cft diving, and looking at the RB tables James posted he seems to have also made that assumption; starting with 3000 psi we really only have 77 cf so we are only allowed to use 40 cf to get to "that" posted RB for Recreational 110 feet deep.

With a typical SAC and typical descent, are we typically "pushing" NDL's at 1421 psi? My understanding of the science of ascent speeds is that 30 feet per minute is "really" conservative for the first 50 feet of that ascent. Is there really only one recommended ascent speed for the entire alternate ascent on the typical rock bottom warm water dive we are discussing?

How often are typical warm water divers doing 110 foot deep boat dives as second dives? Maybe after lunch on the second boat trip of the day?

Also, other than dip tube blockage, for typical warm water diving, wouldn't there be some ascent time on the "failing" gas supply? A few breaths from the bottom ascending at 60 feet per minute sounds nice. At another end of the warm water problem spectrum, perhaps some breathable air "at the stop" in the "empty at depth" tank. :dontknow:

James typed "the most common definition of rock bottom" in his post. That led me to believe there were other possible definitions of rock bottom. :coffee:

You are getting lost into the weeds of trying to tweak and tune and argue with the assumptions that go into rock bottom calculations.

By far, one of the worst problems is actually that recreational divers at 100 feet are narc'd and will mentally vapor-lock on problems and the usual input assumption into the rock bottom calculations is likely to be underestimating the amount of time that may be necessary before the divers manage to get moving.

And the kind of problem that is more likely to occur is a free-flow that drains the tank of one of the divers. Quite a bit of time can be burned trying to solve problems like that before ever attempting to ascend. Divers also will often try to swim back to the upline at depth instead of ascending midwater to swim to the upline and slow down the gas and deco clocks.

Many mistakes like that can be made, and the average recreational diver assuming that they'll solving a problem instantaneously and ascend at 60 fpm and not need stops so they only need a few sips of gas for rockbottom is missing the bigger picture in that they're vastly overconfident in their ability to simply end the dive and ascend when they are placed under stress.

And trust me, I've swum behind many recreational divers at 100 feet who would swear they weren't narc'd who were completely mentally vapor locked and out of it. I'm sure that I've done it before as well, and could easily do it if I undergo some stress and take up a bit of CO2 loading at depth, which is why I don't try to short change my rock bottom.
 
And the kind of problem that is more likely to occur is a free-flow that drains the tank of one of the divers. Quite a bit of time can be burned trying to solve problems like that before ever attempting to ascend. Divers also will often try to swim back to the upline at depth instead of ascending midwater to swim to the upline and slow down the gas and deco clocks.

How common is free-flow that drains one divers tank in warm water recreational diving?
 
also:

halemanō;5715306:
typical typical typical typical typical typical typically typical typical typical

the dive where you really need rock bottom isn't going to be "typical", its going to be high stress with problems.
 
halemanō;5715403:
How common is free-flow that drains one divers tank in warm water recreational diving?

I dunno, how commonly are the rental regulators serviced, and what kinds of IP ranges do you think you'd find if you threw a gauge on them?
 
Could anyone link a thread here on SB where a typical recreational warm water dive had a free-flow that drained a divers tank; preferably deeper than 100 feet?
 
Fascinating "assumptions" by many about what is "average", "typical" and who has learned, not learned, accepted or not accepted responsibility for mistakes made.

I admit to being human enough and making enough mistakes not to qualify to cast that stone!

People tend to accept opinions when they are delivered without condescending/condemning undertones!

I think DB said it best

Originally Posted by D_B
You can comment, and instruct those that have made mistakes, without making them feel like a fool, even if what they did was foolish ... you DO want others to post their mistakes so we, and they, can learn from them, don't you?


 
Fascinating "assumptions" by many about what is "average", "typical" and who has learned, not learned, accepted or not accepted..........................

Thanks for the intro, I share the feeling.



halemanō;5715431:
Could anyone link a thread here on SB where a typical recreational warm water dive had a free-flow that drained a divers tank; preferably deeper than 100 feet?
I seriously doubt it. Unless it is a mechanical problem, why couldn't you resolve a secondary free-flow in warm water?


This is an interesting thread and most are trying to be understanding of surprisingly (to me) differing views. The real problem, as I see it, is http://www.scubaboard.com/forums/ac...cidents.html?highlight=dan+triggers+accidents.

Either of the two triggers can be reduced by an increased level of personal discipline. The OP doesn't formally plan dives, I do. However, I'm sure that the OP has seen his particular dive repeated without incident many times over. This is a form of dive planning, I just don't buy into it. It has served him up to now, and now after a thrill, he is intending to fine tune it to add an extra measure of safety. Cheers!

As far as NDL multi-level dives go, I do them all the time. I also like to plan them. Not at all hard, first I try to make the dive an RGBM ascent, if that fails I approximate the dive by starting my approximation 10' lower in depth and progressing in time to where I want to be with respect to the NDL then jumping up 20' at which point I continue until again 10’ below. I continue to squarewave it to the exit depth. I don’t even know if this is an accepted procedure, just mine at the moment and open to change. This will only make sense to half of the divers on this thread. No matter, there are other ways to calculate and ride the NDL curve. BTW, you can ride the curve without being on the extreme edge of it.

We were all told that reverse profile dives are inherently bad. That seems to have changed also. Always Do Your Deep Dive First?: Undercurrent 05/2000 .

Things change. Peaceful coexistence does not mean capitulation from either side.

Stay safe.
 
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I missed the change along the way here...?? :confused:

You went into deco because you ignored your high priced computers.

Well Don it makes no difference on the point of the post, and since I believe you are of an age that you will understand the difference between memory and looking at the log on your computer you will forgive my memory differences. the last numbers were from the actual log of the dive, the original numbers from memory. :D

yes I made a choice to go into deco, it was a bad one and as I have said it was based on thinking the deco was the same as if it were acquired deep. Shallow deco must be worked out at a sufficient delta of depth, so 10ft. not 15 and definitely not 20 and it builds fast. we would have hit deco even if we had immediately gone to the surface, but it would have been manageable and if I had understood the reason for it I would have known to immediately go to 10ft to work it off and not try to do it at 20 and 15ft first. maybe we were at risk and maybe we were not, no way to know, all I can say is the watch said to do it, so we did the best we could.

And for the record, we were out of air at 10ft, having been there a long time. not really a deadly risk. however I have said many times to my students that there is no reason to be out of air. and this one is not an exception.
 

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