actual NDL calculations

[caverdave]

If your ascent is other than a direct ascent to the surface at 60 fpm, the additional time used in the ascent must be added to your bottom time.

It reads as if you may be encouraging 60 fpm or am I reading too much into it and/or your other posts ?


For the sake of the OP- - it may not be possible to use Padi's tables to exactly work out the dive on paper as you wanted. It won't take a large leap in your education though to start comparing the times.


For me that ascent rate has my ears screaming... I would have a hard time believing going that speed was better than taking time (30fpm or slower pending situation). Dives where I come up from 100' or so and spend some nice casual time (20minutes plus) at shallower depths of 30' to then come to 20' to 15 feel ohhh way so much better than a direct shot up. Granted the table won't account for that, but ...

 

[wve]

The question is what to do with any extra time you spend during an ascent that is over and above the time that you should have spent had you ascended at the specified rate. When using the U.S. Navy tables you add any delay in ascent to bottom time and recalculate your status. The PADI tables, regardless of what information the hack writers at PADI HQ decide to put in or to neglect to put in because the adjudge it too complicated for you to understand, Ray Rodgers (the table designer) was quite clear in the many conversations that we had that delayed ascents should be handled exactly the same way as the U.S. Navy Tables.

In my comments I have assumed that anything but a direct ascent changes the profile which requires some kind of adjustment, either adding to the bottom time as you say above, or recalculating the dive as a multilevel dive.

I can see where someone might have thought I was saying ascent time doesn't matter, but that was not what I meant to say.

I was really trying to point out that one should not confuse "dive time" as measured by a computer with "bottom time" as defined by a table. They are not necessarily the same because "dive time" includes the ascent whereas "bottom time" usually does not (deviations from the table's assumptions notwithstanding).

 

[jonathon50]

PADI teaches 18 mtres/60 S.A.F.E. Dive computer may/will advise slower. Personally i always follow my comp ascent rate.

 

[wve]

Wve, you understood my question perfectly. And yes, I did use a comp and tried to retro-fit the dive with the RDP. I'm starting to not like how PADI just gives you a method but there is no reasoning or rather understanding taught to the student. I really want to know the how and why.

So really, my choice seems to only be the erdpml? So if a DIR diver plans a shallow multi-level no deco dive (if memory serves me right, they don't use computers, right?), it would be with an erdpml or similar?

As someone else mentioned, PADI used to have a Wheel that was a modified RDP used to calculate multilevel dives. It was kind of a slide rule-type thing that allowed more bottom time by using 5 ft rounding increments instead of 10, and by allowing you to plan a dive at multiple depths. It was kinda neat, but logistically hard to use.

The Wheel was replaced by the eRDPml (electronic RDP-multilevel). It is easier to use than the Wheel. But you will still find that you can't retro-fit some dives that you make with a computer.

I wouldn't blame it all on PADI. They are responding to the pressures of the industry, namely, trying to make diving simple and fun enough that more people will want to do it, yet trying not to run people off with information overload about concepts that can be difficult to grasp. They take a lot of hits for their approach, some deserved, some not.

 

[Blackwood]

It reads as if you may be encouraging 60 fpm or am I reading too much into it and/or your other posts ?

I read his post as such:

The table assumes you'll be at 1ATM after DepthInFeet/60fpm (minutes). Anything beyond that is bottom time.

So if you are planning an NDL dive to 60ft for 40 minutes, and you intend to ascend at 30fpm, you should plan it as a 41 minute dive.


(note, I generally dive what would likely be considered experimental profiles with very little scientific basis, so take this with a grain of salt), but ... even if he is encouraging 60, do really fault him? Using tools as they are designed seems like a good plan to me. Anything else and you're on your own.

So if a DIR diver plans a shallow multi-level no deco dive (if memory serves me right, they don't use computers, right?), it would be with an erdpml or similar?

No, the true DIR would do an on the fly Ratio Decompression calculation.

Naw, it's just a prescribed ascent of 30fpm to 50% of the bottom level and 10fpm thereon, where the "no deco"ness of the multi-level dive is based on average depth, bottom time, and an N(M)DL table.

Using Ratio Deco would be cumbersome at best (deep setpoint, helium, etc.) for such a dive

 

[scc135]

Heh, and I thought this was gonna be a simple question to answer.... Never thought I'd get 4 pages outa this one.

 

[disbelief]

Heh, and I thought this was gonna be a simple question to answer.... Never thought I'd get 4 pages outa this one.

Decompression theory is not an exact science.

The simple truth is that unless and until you spend some time gaining experience and training beyond introductory level, you'd be well advised to either treat your dives as square profile (or multilevel if you have the tools), or dive well within the limits of your computer according to the manufacturer's instructions.

And if you plan & dive computer then need to fall back to tables, accept the conservativeness your agency will have build in to this process in their training procedures.

Even then, remember it is not an exact science... you have a very strong likelihood of remaining safe, but unearned DCS hits are not unknown. Know the signs and symptoms of DCS and seek immediate attention should you experience them following *any* dive.

 

[Mike Boswell]

Heh, and I thought this was gonna be a simple question to answer.... Never thought I'd get 4 pages outa this one.

Just a friendly bit of advice here: Starting a thread on SB using the word "padi" is likely to get a lot of readers and a lot of posts. Lots of folks here will never forgive PADI.

 

[Peter Guy]

Thal -- a "true DIR" diver (at least one trained by GUE or UTD) would NOT use Ratio Deco for a purely NDL/Recreational dive (i.e., one contemplated by the RDP in its several variations) but, to the contrary, "Minimum Deco." The maximum amount of "bottom time" at "depth" is known and then you do your ascent and stops based on what you have acutally done. A very simple concept with provides a sloped ascent curve and is generally a little longer than an RDP ascent with a 3 minute safety stop.

 

[Thalassamania]

It reads as if you may be encouraging 60 fpm or am I reading too much into it and/or your other posts ?

I am just telling you how the PADI tables were designed to be used. The proper ascent rate is not a mix and match question but rigidly defined by the table's author.

For the sake of the OP- - it may not be possible to use Padi's tables to exactly work out the dive on paper as you wanted. It won't take a large leap in your education though to start comparing the times.


For me that ascent rate has my ears screaming... I would have a hard time believing going that speed was better than taking time (30fpm or slower pending situation). Dives where I come up from 100' or so and spend some nice casual time (20minutes plus) at shallower depths of 30' to then come to 20' to 15 feel ohhh way so much better than a direct shot up. Granted the table won't account for that, but ...

The table won't account for that ... that is the point. In terms of decompression efficiency or how you fell ... those are separate questions. The issue here is how does one properly account for the "delay" during ascent?

PADI teaches 18 mtres/60 S.A.F.E. Dive computer may/will advise slower. Personally i always follow my comp ascent rate.

You're mixing a vegetable with a mineral and expecting to get an animal. It doesn't work that way. Following your computer is fine, but then don't bother looking at a set of tables unless they are based on the same model, and (as far as I know) no computer is based on the PADI model.

I read his post as such:

The table assumes you'll be at 1ATM after DepthInFeet/60fpm (minutes). Anything beyond that is bottom time.

So if you are planning an NDL dive to 60ft for 40 minutes, and you intend to ascend at 30fpm, you should plan it as a 41 minute dive.

Yes!

(note, I generally dive what would likely be considered experimental profiles with very little scientific basis, so take this with a grain of salt), but ... even if he is encouraging 60, do really fault him? Using tools as they are designed seems like a good plan to me. Anything else and you're on your own.

All I'm trying to do is to explain to people that simply slowing your ascent rate is only half of what you must do to keep from breaking the model, you must also add the delay time to your bottom time. I'm not encouraging anyone to do anything but use the model as it was designed.

Naw, it's just a prescribed ascent of 30fpm to 50% of the bottom level and 10fpm thereon, where the "no deco"ness of the multi-level dive is based on average depth, bottom time, and an N(M)DL table.

Using Ratio Deco would be cumbersome at best (deep setpoint, helium, etc.) for such a dive

Sorry, you're right, I just could not remember the term for that and misspoke.

It reads as if you may be encouraging 60 fpm or am I reading too much into it and/or your other posts ?


For the sake of the OP- - it may not be possible to use Padi's tables to exactly work out the dive on paper as you wanted. It won't take a large leap in your education though to start comparing the times.


For me that ascent rate has my ears screaming... I would have a hard time believing going that speed was better than taking time (30fpm or slower pending situation). Dives where I come up from 100' or so and spend some nice casual time (20minutes plus) at shallower depths of 30' to then come to 20' to 15 feel ohhh way so much better than a direct shot up. Granted the table won't account for that, but ...

PADI teaches 18 mtres/60 S.A.F.E. Dive computer may/will advise slower. Personally i always follow my comp ascent rate.

I read his post as such:

The table assumes you'll be at 1ATM after DepthInFeet/60fpm (minutes). Anything beyond that is bottom time.

So if you are planning an NDL dive to 60ft for 40 minutes, and you intend to ascend at 30fpm, you should plan it as a 41 minute dive.


(note, I generally dive what would likely be considered experimental profiles with very little scientific basis, so take this with a grain of salt), but ... even if he is encouraging 60, do really fault him? Using tools as they are designed seems like a good plan to me. Anything else and you're on your own.



Naw, it's just a prescribed ascent of 30fpm to 50% of the bottom level and 10fpm thereon, where the "no deco"ness of the multi-level dive is based on average depth, bottom time, and an N(M)DL table.

Using Ratio Deco would be cumbersome at best (deep setpoint, helium, etc.) for such a dive

Thal -- a "true DIR" diver (at least one trained by GUE or UTD) would NOT use Ratio Deco for a purely NDL/Recreational dive (i.e., one contemplated by the RDP in its several variations) but, to the contrary, "Minimum Deco." The maximum amount of "bottom time" at "depth" is known and then you do your ascent and stops based on what you have acutally done. A very simple concept with provides a sloped ascent curve and is generally a little longer than an RDP ascent with a 3 minute safety stop.

I stand corrected.