Just got my AOW and might plan a deep dive. Things to make sure I cover off?

[xdjio]

Good advice and thank you guys:

1) I like the notion of rule of thirds and can't see any particular reason to not practice it in my recreational diving.
2) We'll only hit 100 feet if we all plan to. I suspect that - more likely than not - we'll decide NOT to plan our dive that way, and consequently not do it.
3) If we do do it - it would be a straight shot down to 100 feet. I had thought that it might be beneficial to stop a minute at 30 ft, and another minute at 60 ft just for everyone to check in, but is that an excessive amount of time?
4) That is good to keep in mind about rock bottom on 100s. I think I am going to be focussing more on developing an awareness of my SAC
5) You are probably right that my definition of "plenty" needs to be revised!
6) And no, no experience with DSMBs although one day I would like to learn the proper technique.

No way would any of I or my buddies practice skills down there before having everything nailed shallow first!!

 

[Bubbletrubble]

If you don't know your SAC/RMV rate, then you can't do proper gas planning.
If you aren't capable of proper gas planning, you really shouldn't be conducting any "deep" dives.
That's just my opinion on the matter. A compelling case can be made that proper gas planning is the sine qua non of safe diving at any depth.

I'd recommend building up your resume of dive experience at more moderate depths first.
I'm sure there's plenty to see and do at 60 fsw in your locale.
With more experience, you'll have a better handle on your gas needs, you'll have more mental bandwidth to manage any unforeseen challenges, and you can gradually expand your dive comfort range.

Another thing to consider is a rescue class. Nowadays it's possible to graduate from OW and AOW scuba classes yet still not be CPR-certified or have a strong sense of what to do in common emergency scenarios. Those are things I'd like to have if I were contemplating any aggressive diving in the near future.

 

[xdjio]

The more I read about it, and the more I think about RMV and SAC - the more I think you guys are right! Also I am a bit of a stats and maths nerd so the notion of tracking consumption rate over many shallower dives has some intrinsic appeal for me too.

I think that is what we'll do. There is indeed a TON of stuff to see here are < 60ft depths.

However, a point of advice? What's the best way to collect meaningful consumption rates, if I am diving rather multilevel? Should I just be scribbling down depths and time and psi on my slate as I go? Is there a better way? My computer isn't air integrated (which I am sure would make all this calculation much easier).

 

[nimoh]

Good advice and thank you guys:

1) I like the notion of rule of thirds and can't see any particular reason to not practice it in my recreational diving.
2) We'll only hit 100 feet if we all plan to. I suspect that - more likely than not - we'll decide NOT to plan our dive that way, and consequently not do it.
3) If we do do it - it would be a straight shot down to 100 feet. I had thought that it might be beneficial to stop a minute at 30 ft, and another minute at 60 ft just for everyone to check in, but is that an excessive amount of time?
4) That is good to keep in mind about rock bottom on 100s. I think I am going to be focussing more on developing an awareness of my SAC
5) You are probably right that my definition of "plenty" needs to be revised!
6) And no, no experience with DSMBs although one day I would like to learn the proper technique.

No way would any of I or my buddies practice skills down there before having everything nailed shallow first!!

in regards to point #3, the straight shot is a better idea, but during descent, you should all be facing each other and descend as a group, then there is no need to stop and check in, since if someone has a problem, he will just signal the problem and stop the whole group.

 

[Jim Lapenta]

You should use the Rule of Thirds.

1st 1000 PSI down, so do NOT continue down with less than 2000 PSI. Start going up!

2nd 1000 PSI to come up.

3rd 1000 PSI to do your safety stops and reserve on the surface.

Actually if he is diving a tank with 3000 psi to start that is not the rule of thirds. He would first need to subtract the 300-500 psi he wants to keep in the tank. I'm ok with 300 but know my gauges. A new diver 500 is a better choice. So he would have 2500 to start with. If you were referring to the fact that he is using an hp100 and assuming he gets a 3442 psi fill then 3000 would be correct. But the final 1000psi for a newer aow diver on a deep dive who does not know his SAC and what the effects of narcosis may be on him and his teammates, as well as the effects of being in cold water, the second third should be planned for the return including his stop or stops. If he were my student planning this first deep dive on his own I'd want to see him at the surface with 1300-1500. As he gains experience he can see if cutting it a bit closer is ok. He should also have a couple of contingency profiles including an emergency deco schedule should he run over. The 8-10 minute stop instead of three or even a 15 minute one is a bs method if he does not have the gas to do it.
Personally my feeling is if he does not know his SAC he should not be planning a 100 ft dive. That should have been covered in class and then determined on at least one of his dives. I like to do it on the uw nav dive. Rule of thirds and be back with 500 psi is fine for 60 ft reef dives. Woefully inadequate for deep diving, especially in challenging conditions.
Sent from my DROID X2 using Tapat

 

[xdjio]

Actually if he is diving a tank with 3000 psi to start that is not the rule of thirds. He would first need to subtract the 300-500 psi he wants to keep in the tank. I'm ok with 300 but know my gauges. A new diver 500 is a better choice. So he would have 2500 to start with. If you were referring to the fact that he is using an hp100 and assuming he gets a 3442 psi fill then 3000 would be correct. But the final 1000psi for a newer aow diver on a deep dive who does not know his SAC and what the effects of narcosis may be on him and his teammates, as well as the effects of being in cold water, the second third should be planned for the return including his stop or stops. If he were my student planning this first deep dive on his own I'd want to see him at the surface with 1300-1500. As he gains experience he can see if cutting it a bit closer is ok. He should also have a couple of contingency profiles including an emergency deco schedule should he run over. The 8-10 minute stop instead of three or even a 15 minute one is a bs method if he does not have the gas to do it.
Personally my feeling is if he does not know his SAC he should not be planning a 100 ft dive. That should have been covered in class and then determined on at least one of his dives. I like to do it on the uw nav dive. Rule of thirds and be back with 500 psi is fine for 60 ft reef dives. Woefully inadequate for deep diving, especially in challenging conditions.
Sent from my DROID X2 using Tapat

Noted . I know /how/ to determine my SAC and RMV, but I haven't actually done it -- and we didn't do it in class. I think I'll work on building up more comfort around that first under more familiar conditions and shallower depths.

 

[Bubbletrubble]

However, a point of advice? What's the best way to collect meaningful consumption rates, if I am diving rather multilevel? Should I just be scribbling down depths and time and psi on my slate as I go? Is there a better way? My computer isn't air integrated (which I am sure would make all this calculation much easier).

Your computer doesn't need to be air-integrated in order for you to track gas consumption rates. An average RMV can be calculated from the following variables: start psi, end psi, tank service pressure, tank capacity at service pressure, average depth, and total run time.

You don't need to do anything special. Just calculate the average RMV per dive, record it in your divelog, and note conditions which may have affected your gas consumption on that specific dive (current, activity level, fear/apprehension, feeling excessively tired/cold, problems with ear clearing, gear issues, helping out your buddy, etc.).

By doing this, you'll get a better handle on your gas consumption rates under various dive conditions...and this will help you pad your gas supplies appropriately while dive planning.

 

[xdjio]

Awesome! Well, I have all that data in my computer and logs at home, now i just need to put the two together and start getting some numbers. I'll be making this a part of all new dives too so soon I should start getting a sense of RMV and SAC under various conditions.

Thank you very much everyone - I'm looking forward to working towards a more intuitive feel for gas planning once I have plenty of real practical data logged.

I'm also glad I listened to myself - and to you guys! - about doubting my plan for a deep dive. Based on what I've learned and my own doubts, it obviously doesn't make sense to do it until my buddies and I have gradually worked up to it for a while yet.

 

[xdjio]

Hey guys: I just calculated a recent dive that I did (from memory of my logs):

(3000 psi in - 500 psi out) / 27 minutes = 92.59 psi per minute
15.7 m / 10 + 1 = 2.57 ATA
92.59 / 2.57 = 36 psi per minute


the RMV that we could use for this (a 100 ft3 tank): baseline 95 cuft / 3000 working psi (leave a 500psi buffer) = 0.031 cuft per psi


36 * 0.031 = 1.116 RMV


that's 1.116 cubic feet per minute.

That seems high! So lets say I wanted to use this to plan a future dive, similar circumstances, same equipment. And to make it easy, same depth. ie. let's say I am going to do the identical dive again.

Now I know that I breathe about 1.116 cubic feet per minute. I'm going to dive a 100 cubic foot tank (so call it 95 feet). I know that my SAC is going to be around 36 psi/min at the depth I plan to visit, so should I just say 95 cubic feet / 1.116 cubic feet per minute and solve for minutes? Because that says I have 85 minutes of air!

Perhaps I am missing something here.

 

[rhwestfall]

that is your surface rate...
@ 33' its now doubled
@66' its tripled
@99' its quadrupled

Boyle, Henry, Dalton? Any of those ring a bell?