First dive at 40 meters - Newbies recreational

[KenGordon]

This one for example. But you should read the full study not the summary. There are many more if this too old.
Memory and metacognition in dangerous situations: investigating cognitive impairment from gas narcosis in undersea divers
Malcolm Hobbs et al. Hum Factors. 2014 Jun.

That paper asks the question, can people tell they are narced? Interestingly it uses the same depth range you were in as the deep side.

It says that the people who claim not no be narced are actually lying, not just mistaken, because they can tell they are narced. It is not about being narced but being aware you are narced.

 

[yle]

I seriously hope that you don't hurt yourself and that I won't be reading about you in A&I. But given what you've demonstrated here, I won't hold my breath about that. Dive safe. Please.

I will pass. Thank you.

I think this sums up the entire thread nicely. Our work here is done.

 

[EFX]

I really dislike the rule of thirds. For open water diving, it's seldom a good rule. It's either too conservative (in the shallows) or too liberal (at depth). Do a proper min gas calculation and compare the output to the rule of thirds. The former depend heavily on depth, the latter not at all. Which makes no sense, since depth is one of the only two factors determining what your reserve should be.

It depends on what you do with it. I would not use the rule of thirds, halves, etc to calculate a reserve but for turning pressure it is useful depending on the context.

The purpose for rule of thirds is to get yourself and your buddy safely out of an overhead environment to open water. A third of the gas to go in, a third to come out, and a third left in reserve. As @Storker quoted above it's use is rather restrictive for open water except for one condition: where you descend, swim out, and absolutely must return to the entry point (i.e. descent or anchor line). Some plausible scenarios might be situations where one could pop up in heavy boat traffic, or on a night dive in heavy seas, or in high surface currents.

The rationale for the rule of thirds is based on a worst-case scenario where one of the divers has a catastrophic gas loss at the furthest point in the overhead, and both divers must share gas to exit safely. For those of you who are unfamiliar with how to calculate rule of thirds, here is an example:

Diver 1 uses an AL80. Tank factor = 3000 psi / 80 ft3 = 37.5 psi/ft3.
Diver 2 uses a steel 95. Tank factor = 2400 psi / 95 ft3 = 25.3 psi/ft3.

Tank factor is rated pressure divided by rated volume. Base the turn pressures on the lowest volume of the two divers which is Diver 1. To surface with a reserve pressure of 400 psi the turn pressure of Diver 1 is 3000 - ((3000 - 400) / 3) = 3000 - 867 = 2133 psi. The volume of this gas is 867 / Diver 1's tank factor = 867 / 37.5 ~ 23 ft3.

To calculate Diver 2's turn pressure multiply Diver 1's usable 1/3 volume with Diver 2's tank factor and subtract from full pressure which equals 2400 - 23 x 25.3 = 1818 psi.

Whichever diver hits their turn pressure first, turns the dive and both divers head back to the starting point.

 

[KenGordon]

To be honest I think you lot are being a bit mean. He clearly has gaps in his knowledge and has lots to learn but a bit more counting to 10 before posting might be in order.

 

[Storker]

I think this sums up the entire thread nicely. Our work here is done.

Kinda depressing, isn't it?

Mit der Dummheit kämpfen Götter selbst vergebens

 

[Dody]

To be honest I think you lot are being a bit mean. He clearly has gaps in his knowledge and has lots to learn but a bit more counting to 10 before posting might be in order.

I know I have gaps in my knowledge and that's why I posted in the first place. I doesn't mean that I am a masochist. No wonder why so many newbies posted just once on SB and never came back.

 

[David Novo]

Mit der Dummheit kämpfen Götter selbst vergebens

Now you are just giving me the trouble of going to google translate

 

[David Novo]

No wonder why so many newbies posted just once on SB and never came back.

I would not do that. I learn daily from SB as I am sure a lot of less experience divers (as you and me) do.
It may require a bit of tough skin from time to time but so is life.

 

[KenGordon]

Once, I ascended at 13m/min from 25 meters to 5 without finning too hard and stopping finning at 12. That’s when I decided to never inflate my BCD while ascending, fearing that I would go too fast. I don’t master it yet.

Here is why I say this. I teach a course where the divers have to arrive at various depths exactly on time. They get to choose the time and always start by assuming 9 or 10 m/minute. I always ask whether they are sure, they always say they are and the always miss and arrive late. On the next dive they decide to plan on a slower ascent and arrive on time.

Sometimes I am the student and the purpose is to go up as fast as is safe and I am astounded when I manage 10m/minute.

Free ascents are quite hard, being in a rush doesn’t help.

 

[Storker]

To be honest I think you lot are being a bit mean. He clearly has gaps in his knowledge and has lots to learn but a bit more counting to 10 before posting might be in order.

We've all been there. Problem is, the OP has resorted to snark instead of learning from what has been said by very competent divers and instructors (me not included)