Faith diving and magic?

[Charlie99]

I often hear people say that "Weight yourself to be neutral at 15ft and 500 psi in the tank". It seems like such a bad idea! It effectively mean that you forfeit that last 500 psi because if you start breathing it you'll go positive. Seems to me, that like TS&M is saying, a diver should aim for neutral at 15ft with 0 PSI in the tank. .

That's splitting hairs that have no meaning compared to at what point in the breathing cycle you are considering your neutral point. In an AL80 500psi is 1 pound.

I describe the ideal weighting as one which you can do a controlled ascent to the surface with a near empty tank. That means you should be able to still hover at 5'. Your lungs might be skewed towards empty to stay there, but you should be able to control your ascent, and stop if desired, at any depth right up to the surface.

If you have double 7mm wetsuit, then being neutral at 15' and an empty tank you still might have a hard time overcoming the extra buoyancy of the expanding wetsuit as you go up into 8-10' range. If so, then you need a bit more weight.

 

[aquaregia]

I recently increased my weighting because I found I had trouble on my 10' stops. Also, to compensate for not wearing a ridiculous knife.

 

[Atom]

That's splitting hairs that have no meaning compared to at what point in the breathing cycle you are considering your neutral point. In an AL80 500psi is 1 pound.

I describe the ideal weighting as one which you can do a controlled ascent to the surface with a near empty tank. That means you should be able to still hover at 5'. Your lungs might be skewed towards empty to stay there, but you should be able to control your ascent, and stop if desired, at any depth right up to the surface.

If you have double 7mm wetsuit, then being neutral at 15' and an empty tank you still might have a hard time overcoming the extra buoyancy of the expanding wetsuit as you go up into 8-10' range. If so, then you need a bit more weight.

I know you can adjust for that with your breathing, but it still feels to me that if you're going to adjust your weight precisely you might as well take everything into account, and adjust yourself so that you can breath normally. But then again, we should probably adjust for 2ft or something ; )

And it's true if you're diving a thick wetsuit, you should probably be negative at 15 ft because it'll expand.

 

[DwayneJ]

I recently increased my weighting because I found I had trouble on my 10' stops. Also, to compensate for not wearing a ridiculous knife.

... But wearing a knife is the coolest part of scuba diving!

 

[DwayneJ]

Are you a thrill seeker and occasionally put your watch into Deco...

I hope this will stimulate some adult conversation and not a bunch of pointing out my mistakes.

In my humble diving experience, I have never performed unplanned deco. I have some great buddies and irrespective of our experience we actively monitor our NDL time and remaining gas.

There's plenty of "tests" which show considerable difference in NDL limits with Rec computers.

I use a full deco computer (currently VR3) and am familiar with it's algorithm. My next computer will likely be a Liquid Vision with VPlanner software which will closely match VPlanner I use of my laptop. Only planned deco diving for me (and my buddies).

 

[SailNaked]

Thank you all for discussing this with me.

I am Deco trained, not that it would have made any difference in this situation if anything it made it worse.

bottom line is as soon as i knew we might have a deco obligation on a non deco dive I should have immediately rescued my wife and ended our dive to satisfy or avoid the pending obligation.

Some background.

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.

What made this dive special was the medium loading of the longer compartments, I had not accounted for it in my thinking and was complacent with the shorter stuff burning off a few minutes after leaving depth.

I accept my mistakes, I made a decision for my buddy, not knowing what her computer was saying about her profile and we were outside the yellow band safety.

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

we use tables based on algorithms, we use computers based on the same algorithms, all of these algorithms are based on guesswork and experimental evidence that the guesses are mostly right for most people. there is nothing specific about any table or computer that will keep you personally safe on any one dive.
we teach that if you exceed a limit by 1-4 minutes that you do an 8 minute safety stop, we did over a 20 minute safety stop and still had 5 minutes on one of the computers.

my wifes air consumption was much better than mine that trip because I had a chest cold normally it is the same. I assumed she had much more air than me. had we not had the medium loading and this had been the first or second dive of the day we probably would have been back on the boat with ~500# making the same decisions I made that dive.

I had 3 watches two on one arm all by the same manufacturer there is no good reason for them to be significantly different, yet there was some variation.


it is faith and magic we put into these devices (a table is a device too). we bet our lives on them, we take it as Gospel that if you exceed a limit by this much you do this, and if by that much you do that. only because it has worked in the past most of the time even if not always.

healing with leaches worked for a long time, and if you need a blood thinner it would still work, but we have moved on. when are we going to get computers that actually take into consideration the person actually diving.

I really do appreciate the comments and I have been here too long to care that some of you are willing to call me stupid. I read past that to see if the comments are useful to others. Bash me all you like, I still love to dive and teach safe divers all that they need to know. including the mistakes that can be made.

my wife learned from this experience also she was embarrassed to be sucking O2 at the back of the boat, she hates to be embarrassed and she will not do it again.

The weighting issue was only hers, I gave her some weight and she was fine at 10ft, but we do not usually get our weight set to have empty tanks and do a stop at 10ft. that is in the realm of 2 mistakes/failures.


I believe it may have been possible that we were a little narced but that would be an poor reason and not an excuse for our actions. by the way one of the divers on our boat that had about the same profile mentioned later when we were explaining why we were down there so long, said "oh I never looked at my computer" BANG!!!!

Put that comment in the "strangest things I heard on a dive boat" thread.

 

[Blackwood]

bottom line is as soon as i knew we might have a deco obligation on a non deco dive I should have immediately rescued my wife and ended our dive to satisfy or avoid the pending obligation.

Bingo. Lesson learned. Perfect.

BTW, if it's and consolation to your wife, most of my dive buddies have sucked surface O2 multiple times. Nothing to be embarrassed about. Just being cautious.

 

[DandyDon]

Bingo. Lesson learned. Perfect.

BTW, if it's and consolation to your wife, most of my dive buddies have sucked surface O2 multiple times. Nothing to be embarrassed about. Just being cautious.

Really?! I've only seen that a couple of times, before shipping them to the chambers. Ran out both times too.

...one of the divers on our boat that had about the same profile mentioned later when we were explaining why we were down there so long, said "oh I never looked at my computer" BANG!!!!

Ok I had that that you were wrong in your calls, not stupid, but that is!

 

[Blackwood]

Really?! I've only seen that a couple of times, before shipping them to the chambers. Ran out both times too.

Really. We've never broken out the boat's supply, though. As often as not, we have our own handy. Not feeling 100%? Suck some down. Cheap and perhaps effective.

 

[DandyDon]

Really. We've never broken out the boat's supply, though. As often as not, we have our own handy. Not feeling 100%? Suck some down. Cheap and perhaps effective.

Not worried about masking symptoms?