PADI RDP question

[kidspot]

Hey Marek, I'm not sure which of us is wrong, I'm sitting at the LDS and we pulled out a copy of the navy tables (from the table tutor program) But we're still coming up with the same answer - First dive puts you in "F" - 2nd' dive allowed at "F" also - minimum SI listed is 10-41 min... So if we're wrong I really need to know where I miscalculated things - can someone verify?

Here's our work:
1) Table #1 - Dive to 70ft for 30min puts you in pressure group F
2) Table #3 - 50ft colum 56min in "G", 47min in "F", 38min in "E" so I choose group "F" (40min dive rounded up to 47min)
3) Table #2 - Line "F" intersects column "F" at 10-40min point.

Thanks - Tim

 

[hdtran]

Hey Marek, I'm not sure which of us is wrong, I'm sitting at the LDS and we pulled out a copy of the navy tables (from the table tutor program) But we're still coming up with the same answer - First dive puts you in "F" - 2nd' dive allowed at "F" also - minimum SI listed is 10-41 min... So if we're wrong I really need to know where I miscalculated things - can someone verify?

Here's our work:
1) Table #1 - Dive to 70ft for 30min puts you in pressure group F
2) Table #3 - 50ft colum 56min in "G", 47min in "F", 38min in "E" so I choose group "F" (40min dive rounded up to 47min)
3) Table #2 - Line "F" intersects column "F" at 10-40min point.

Thanks - Tim

Let me give it a whack. Using PADI imperial tables, rev 02/03.

First of all, 20 m = 66 ft, for 29 min. Using Table 1, rounding up to 70 ft, looking for 29 min, puts me into Group N.

Next, going to Table 3, in the blue row, 14 m = 46 ft, which rounds up to 50 ft. At 50 ft depth, 39 minutes of bottom time = group M. (The additional residual nitrogen time is 41 minutes.)

Lastly, what surface interval is necessary to get from group N to group M? Going to Table 2, that's 4 to 8 minutes of surface interval.

As a final check, we calculate total bottom time for the second dive. That's 41 + "actual" time. If, in the second dive, you did, in fact, spend 39 minutes, that's a total of 80 minutes "total bottom time." That is exactly the NDL limit for a 50 ft depth, which puts you into group X at the end of the second dive.

From the "special rule," your minimum surface interval after the second dive is 1 hr. Additionally, because you're within the grey zone on the table (or 3 pressure groups of the NDL), a safety stop is mandatory on the second dive.

HTH,

 

[Marek K]

Hey Marek, I'm not sure which of us is wrong, I'm sitting at the LDS and we pulled out a copy of the navy tables (from the table tutor program) But we're still coming up with the same answer - First dive puts you in "F" - 2nd' dive allowed at "F" also - minimum SI listed is 10-41 min... So if we're wrong I really need to know where I miscalculated things - can someone verify?

Yes, it's looking very much as if the U.S. Navy Tables are identical to the old 1980s PADI Dive Tables.

Here's our work:

1) Table #1 - Dive to 70ft for 30min puts you in pressure group F

OK, I'm with you so far... my old PADI tables show the same thing.

2) Table #3 - 50ft colum 56min in "G", 47min in "F", 38min in "E" so I choose group "F" (40min dive rounded up to 47min)

Ah, here's where things aren't right. Looks to me like you're looking at the upper Residual Nitrogen Time (RNT) value (nitrogen time left over from the previous dive), instead of the lower Actual Bottom Time (ABT) value (or more-accurately, adjusted maximum no-decompression bottom times). Your figures are identical to the RNT values off of my old PADI tables.

The way to "reality check" that is that ABT -- the max time you'll actually spend underwater -- should get smaller, the higher a Pressure Group you start out with. The figures you read off are doing the opposite.

So if the second dive is 50' for 40 min (rounded up to 44 min), you'd need to be at least Group G before that dive. Which you already are (since you're actually F).

3) Table #2 - Line "F" intersects column "F" at 10-40min point.

Um, on my old PADI tables, the intersection of F and F on Table 2 is 0:10 to 0:45. But the intersection of G and G is 0:10 to 0:40, which may what you're looking at.

Though, I'll tell you, I'm not at all 100% confident I'm not getting confused.

Moral: We may think we remember how to do our tables, but...

Over to you...

--Marek

 

[jrs_diesel]

Let me give it a whack. Using PADI imperial tables, rev 02/03.

First of all, 20 m = 66 ft, for 29 min. Using Table 1, rounding up to 70 ft, looking for 29 min, puts me into Group N.

Next, going to Table 3, in the blue row, 14 m = 46 ft, which rounds up to 50 ft. At 50 ft depth, 39 minutes of bottom time = group M. (The additional residual nitrogen time is 41 minutes.)

Lastly, what surface interval is necessary to get from group N to group M? Going to Table 2, that's 4 to 8 minutes of surface interval.

As a final check, we calculate total bottom time for the second dive. That's 41 + "actual" time. If, in the second dive, you did, in fact, spend 39 minutes, that's a total of 80 minutes "total bottom time." That is exactly the NDL limit for a 50 ft depth, which puts you into group X at the end of the second dive.

From the "special rule," your minimum surface interval after the second dive is 1 hr. Additionally, because you're within the grey zone on the table (or 3 pressure groups of the NDL), a safety stop is mandatory on the second dive.

HTH,

Thats exactly what I got as well.

 

[Ross567]

OK, Larry, you asked for it - "Larry was dumb enough to offer this software for free as I'm a scubaboard member." Well, a novice to the board, and to SCUBA, but interesting all the different answers that cropped up to what ought to be a simple query - I'd like to use the pctool to use my PADI RDP in confirming dive profiles - can you supply some details please, and then I'll purchase and use the 'unlock code'. I'm based in UK but looking forward to some warmer dives in Med and Red Sea for starters. Ross567

 

[Ross567]

Thanks very much - after all the [wide variety!] of replies, I sat down again with my PADI metric rdp, which gave M and P for the 2 dives, extrapolated out of table 2 to where they meet [0 SI], then worked it back - checks out, tho' virtually max ndl for the depth. Shwos the various dp's aren't more than a guideline tho' and supports my caution - look forward to being in touch again. Ross567

 

[Ross567]

Thanks Marek - lots of replies, gave me confidence and curiosity to look at the PADI metric tables again, found SI 0, but close to NDL - great - talk more later. Ross567

 

[kidspot]

LOL - Thanks for making me look into that Marek - I had 2 instructors working it out with me yesterday at the LDS - we all got it wrong ... I went back and re-learned them (Navy tables are a bit different than the others I had used) You were right - Goes from group F to G - so no SI... Turns out the trouble was that the Navy tables use 4 sections, not 3 - so you have to manually calculate the ABT from the maximum (by subtracting the RNT from the Maximum no Deco times in table 1) ... I was not doing that

Thanks again for keeping me at this till I learned it,

Tim

P.S. I'm spending some extra time in the table tutor program working out problems with different agency tables tonight - Making sure I've got a good understanding of them all...

Yes, it's looking very much as if the U.S. Navy Tables are identical to the old 1980s PADI Dive Tables.

Here's our work:

OK, I'm with you so far... my old PADI tables show the same thing.

Ah, here's where things aren't right. Looks to me like you're looking at the upper Residual Nitrogen Time (RNT) value (nitrogen time left over from the previous dive), instead of the lower Actual Bottom Time (ABT) value (or more-accurately, adjusted maximum no-decompression bottom times). Your figures are identical to the RNT values off of my old PADI tables.

The way to "reality check" that is that ABT -- the max time you'll actually spend underwater -- should get smaller, the higher a Pressure Group you start out with. The figures you read off are doing the opposite.

So if the second dive is 50' for 40 min (rounded up to 44 min), you'd need to be at least Group G before that dive. Which you already are (since you're actually F).


Um, on my old PADI tables, the intersection of F and F on Table 2 is 0:10 to 0:45. But the intersection of G and G is 0:10 to 0:40, which may what you're looking at.

Though, I'll tell you, I'm not at all 100% confident I'm not getting confused.

Moral: We may think we remember how to do our tables, but...

Over to you...

--Marek

 

[Marek K]

Turns out the trouble was that the Navy tables use 4 sections, not 3 - so you have to manually calculate the ABT from the maximum (by subtracting the RNT from the Maximum no Deco times in table 1)

Tim--
I saw late last night (Central European Time) that you'd attached an image of the U.S. Navy tables, but didn't check it out in detail. I hadn't been able to find a copy of the Navy table here anywhere, and was looking forward this morning to comparing it to my old PADI tables.

Unfortunately, in the meantime you edited the Navy tables out of your message!!

I was thinking about this, and was wondering whether the Navy tables maybe only gave RNT... making you calculate ABT by subtracting from TBT. It would make people understand what was going on, but I can't believe they'd require that extra step!

I also can't believe none of the "old timers" here jumped in to clarify that!

No thanks are necessary... this thread was a mini-refresher for me too, and in addition made me realize how different the various agencies' tables are... not to mention what rounding variations between imperial and metric tables can result in (not that much).

Practical problem for us is, my wife, son, and I learned with PADI. The computers we use (one old Sherwood Omega II (Skinny Dipper II clone), and the rest Pelagic "hockey pucks") are close enough to the current PADI tables to allow the two to be used together as reality checks.

But our daughter is now learning with SSI, whose table are much different -- more conservative, looks like. That's going to make it more difficult to plan dives together, and to use the SSI tables with her computer. Unless we migrate her to the PADI tables after she finishes her SSI exam... But I can already tell she's going to want to be a conservative diver...

Meantime, could you please re-post that image of the Navy tables?

--Marek

 

[kidspot]

Hey Marek, Here it is... I assume it's copyright free since it's a public U.S. document...

also I'd encourage you if you have not done so already to pick up a copy of Table Tutor from ScubaToys as it will let you learn tables in both metric and imperial format from: Navy, SSI, PADI, NAUI, as well as nitrox tables and several others...

That's how I learned my tables (including the Navy ones earlier today ) Personally I have found the NAUI table to be the easiest of the major training agencies, but GUE's minimum deco tables are by far the simplest ones - If you ever get the chance to get training in using them jump at the chance (the difficulty is not in the tables, but in the style of diving that allows such a simple table for diving off of)

Aloha, Tim

P.S. I removed it when I realized my mistake - didn't want to lead someone else astray in my calculations...

Tim--
I saw late last night (Central European Time) that you'd attached an image of the U.S. Navy tables, but didn't check it out in detail. I hadn't been able to find a copy of the Navy table here anywhere, and was looking forward this morning to comparing it to my old PADI tables.

Unfortunately, in the meantime you edited the Navy tables out of your message!!

I was thinking about this, and was wondering whether the Navy tables maybe only gave RNT... making you calculate ABT by subtracting from TBT. It would make people understand what was going on, but I can't believe they'd require that extra step!

I also can't believe none of the "old timers" here jumped in to clarify that!

No thanks are necessary... this thread was a mini-refresher for me too, and in addition made me realize how different the various agencies' tables are... not to mention what rounding variations between imperial and metric tables can result in (not that much).

Practical problem for us is, my wife, son, and I learned with PADI. The computers we use (one old Sherwood Omega II (Skinny Dipper II clone), and the rest Pelagic "hockey pucks") are close enough to the current PADI tables to allow the two to be used together as reality checks.

But our daughter is now learning with SSI, whose table are much different -- more conservative, looks like. That's going to make it more difficult to plan dives together, and to use the SSI tables with her computer. Unless we migrate her to the PADI tables after she finishes her SSI exam... But I can already tell she's going to want to be a conservative diver...

Meantime, could you please re-post that image of the Navy tables?

--Marek