First dive at 40 meters - Newbies recreational

[Dody]

I may have made a mistake this was a training dive as you kept writing about your instructor who you now write did not attend the dive on the the DM.

You wrote "It’s been a wonderful 50 days journey from the day we visited a dive shop for the first time to now AOW with 37 dives" Enjoy.

With inflating a BCD you have 3 places to purge air normally both shoulders and back right rear. So you won't inflate BCD to max and have a rapid ascent. Also dive computers can show you your ascent rate so you can manage an ascent watching your DC.
You can see here where I practice an ascent using BCD and of course lungs don't forget to continually breath out and you can slow your ascent doing that. Never fully breath in when ascending.

I took this video as my son wanted to do his OW. So I could explain he could see the ascent range on the right and also the NDL change as you ascend. You can practice this a lot on your dives with your wife so you can get a feeling of what a nice steady ascent is. When you are finning against a current and trying to ascend you burn a lot of air and you can get tired if prolonged, or suffer leg cramp as I have seen many divers get. Some of my friends who are instructors have this video to show their students.

I wear my dive computer on my right hand. I can see it if using the left inflator hose or using my right shoulder purge valve. I am giving another diver an assisted ascent I use my left hand to hold that diver and my right hand where I can see my computer while holding my purge handle in case I need to prevent rapid ascent as you can also get up currents as well.

Narcosis? Not necessarily. Inexperienced in this situation, yes. Both Narcosis and inexperience possible. The two can be deadly. Your certifications mean nothing underwater.

Thanks. Very useful. I now understand that I should have inflated our BCDs and not think about it as last resort.

 

[Blackcrusader]

Well. I am not sure I agree on that one. From my calculation at 40 meters and with our SAC in the last 10 dives, we still had 30 minutes of air. Let's say 15 minutes in case of buddy breathing. We were not in a deco dive. So all we had to do was to ascent 40 meters which is 5 minutes at 9 m/ min plus 5 minutes safety stop at 5 meters and 2 minutes at 20 meters. Without panicking, it is enough. And the DM was around. But I agree, not so much safety margin. Pony with a regulator will be a must in my next dives.

Your calculation was wrong. Your assumption of 11l/min is incorrect.

 

[Blackcrusader]

Thanks. Very useful. I now understand that I should have inflated our BCDs and not think about it as last resort.

BCD Buoyancy Control Device. Not Last Resort Device that I can talk about in this thread.

BCD's are used at all points of the dive

 

[Blackcrusader]

This relates to a point someone raised on a different thread of yours: you are doing trust me dives. And this: if you had a catastrophic loss of air, you would not reach the tank at 5m (even if buddy breathing or with gas donation).

Should we say over confident in ones ability until **** really hits the fan?

 

[David Novo]

Obviously . I started nov 3rd, 2020 and fin pivot is now a ritual for me when I can.
From 20 m, I either ascend vertically with my left hand holding the LPI extended and protecting my head or I do it horizontally like a base jumper.

This was not a deco dive. But I agree that it could have been if everything had gone wrong. What do you mean by BASICS?

It was a deco dive as your computer indicated stops at 12m and 20m. It could have not been if everything had gone well.
I would drop the fin pivot ritual and train buoyancy control in trim. And gas planning.

Let's do the math, based on the limited data we have.


210 to 160 bar is 50 bar. Times 12 L is 600 surface liters.

The PADI RDP says that NDL @40m is 9 min. 1 min left, that's 8 min. 600 by 8 is 75, divide by 5 bar is 15 surface liters per minute. Perhaps on the slightly high side for a wetsuit dive in warm water, but not bad at all for a drysuit dive in cold water. Particularly since the OP has <50 dives under his weight belt; most n00bs that I've dived with use quite a bit more (generally closer to 20 than to 15 SLM. Or even >20)

Now, what would a proper reserve be here? 1 min @40m, that's 75 L. Ascent at 10 m/min, average depth 20m, that's 4 (min) x 3 (bar) x 15 (SLM) = 180 L. 3 minutes safety stop @5m, that's 3 (min) x 1.5 (bar) x 15 (SLM) = 67.5 L. Total 322.5 L. Times two for increased consumption due to stress, times another two to account for donating to your buddy and we get a minimum reserve of 1290 L. In a 12 L tank, that's close to 110 bar. Plus some 20 or so bar to account for SPG error and to be certain to be able to inflate their BCD at the surface.

So the only two things the OP did right was to leave before they went into deco, and to have a fairly decent reserve. Me, I'd be more conservative than that, especially considering that everyone is narked at 40m, no matter whether or not they notice it. I definitely would allow for a more time than one minute at 40m, on air, to sort things out and start a controlled ascent. And 10 m/min is pretty fast. Lot of n00bs would probably struggle with their buoyancy control at that ascent rate, and corking is a definite risk.

You are underestimating either the gas consumption or the time it took them to ascend.
With a 10 m/min ascent rate, it would mean their consumption during ascent was around 45 l/min.

 

[David Novo]

Should we say over confident in ones ability until **** really hits the fan?

The problem is compounded if he is overconfident on someone elses ability.

 

[UCFKnightDiver]

Well. I am not sure I agree on that one. From my calculation at 40 meters and with our SAC in the last 10 dives, we still had 30 minutes of air. Let's say 15 minutes in case of buddy breathing. We were not in a deco dive. So all we had to do was to ascent 40 meters which is 5 minutes at 9 m/ min plus 5 minutes safety stop at 5 meters and 2 minutes at 20 meters. Without panicking, it is enough. And the DM was around. But I agree, not so much safety margin. Pony with a regulator will be a must in my next dives.

Please re-read, this was kinda a work in progress. Was on my cell phone so had to save post, got back to your original post for the details, and then edit/continue with mine.

 

[Dody]

So this wasn’t actually a deep dive for a PADI course correct, just one you planned and wanted to do on your own?

No. It was the last SSI deep dive before certification. But I have the tendancy to never fully trust anyone with my safety so I even plan my training dives and cross check with the instructors.

 

[Storker]

But I am interested in what you think I did wrong for continuous improvement and I am not sure that I understand. Can you please explain further?

Most obvious: Narc. Narc sets in already above 30m, but most of us don't notice it before we pass 30. Just as you can train yourself to drive drunk, you can train yourself to dive narced. However, if SHTF and you're in a situation which requires other actions than those you regularly encounter, you may very well be majorly shafted. Because your brain will be as slow as cold molasses.

Second point: assuming that the one-point gas consumption of 11 SLM is typical for you. Your gas consumption is what it is (IOW, don't try to brag about low numbers, not even to yourself), and planning for a best-case scenario is iffy at best. More specifically, it's bad practice. Plan for average or worse, and then pad your numbers.

Third point: no proper gas planning. Read the post you quoted, and familiarize yourself with how to calculate a proper minimum reserve.

Fourth point: breaking the 40m "barrier" just to have been there. Especially since you have <50 dives under your weight belt. Depth is just a number, and if you want big numbers set your 'puter to Imperial units.

 

[Dody]

Do yourself a favour. Go to www.divinglong.com and download the software. Scan in your dives and then go to your 40m dive. Put in your AL80 tank with 200 bar and end 40 bar. Then save the dive log. Then you can go to the profile save your data and you will see your sac rate. You can then see your air consumption on the right. My 45m dive not much different to your 40m dive except I did not exceed NDL and I did a 70 minute dive time and had 60 bar at end of the dive.

OK so on this profile, you can see at left my current depth at 11.33m time 30.03 mins average depth for dive 14.2m and my sac rate for the total dive time. You can see even at 30 mins I still have 120 bar left. Second half of the dive I was swimming against a slight current to get to the boat pickup area.

What you think your sac rate of 11l/min is not going to be what you get on your dive. It may well shock you how much you miscalculated.

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I did it using my software. SAC was actually 14 l/ min during the 40 min dive. Yours was less than 10. Impressive. The cylinder was 12 liters not 80 cu ft, 5% more, not much and we did not exceed NDL, far from it. I agree that I could have done better and I will use this experience to dive safer in the future.