The SSI tables are the Navy tables.
Rick
Rick
how long can i stay down on dive 3
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I should mention here that if we are to compare the PADI RDP and the Navy tables, we must take into account that the Navy tables define "bottom time" as the time from initiating the descent to the time you begin your direct ascent to the surface, not counting any ascent time or safety stop time. I believe (I don't have the PADI textbooks in front of me, so if I'm wrong one of you PADI folks correct me) that the RDP uses dive time - surface to surface - so an apples-to-apples comparison of the dives we started with would be about a 20 minute bottom time with the Navy tables, and they then allow the dives contemplated, with a 2HR 24MIN minimum surface interval between dive 2 and 3. Even here you'll note that the Navy tables end up being more conservative than the RDP for repetitive dives.
The reasons have to do with the different limiting tissue groups used by the two tables, among other things.. if anybody's really interested in the algorithms I'll be glad to point you to the references.
Rick
The reasons have to do with the different limiting tissue groups used by the two tables, among other things.. if anybody's really interested in the algorithms I'll be glad to point you to the references.
Rick
.........I'll send you a copy of the YMCA tables at cost. That goes for anyone else as well. The Y tables are backed off Navy tables.
It is a very common misconception that the RDP is more conservative than the Navy tables. It is more conservative than the Navy tables for the first dive only. For repetitive dives it is MUCH less conservative. The way the YMCA (and other agencies) have backed off the NDL's the adjusted Navy tables are the more conservative way to go in almost every scenario.
Walter
It is a very common misconception that the RDP is more conservative than the Navy tables. It is more conservative than the Navy tables for the first dive only. For repetitive dives it is MUCH less conservative. The way the YMCA (and other agencies) have backed off the NDL's the adjusted Navy tables are the more conservative way to go in almost every scenario.
Walter
Warhammer
Guest
Rick... PADI also teaches that dive time is from the time you start your descent to the time you begin your ascent and their tables reflect as much.
This is very interesting to me. I went back and checked 15 or so my dives on days that I made repetitive dives and all resulted in the PADI tables being more conservative than the Navy tables. So I guess it just depends on the profile in question. For instance, here's a dive day while in Negril this past Oct:
Dive 1
95' for 20min
Dive 2
50 min surface interval
50' for 34 min
Using the RPD, I was in the O pressure group with no no decompression time left. On the second dive, I was in the S pressure group at the end of the dive with 22 minutes no decompression time to spare.
Using the Navy tables, I was in the F pressure group at the end of the dive with 5 minutes of no decompression time to spare. At the end of the second dive, I was in the J pressure group with 28 minutes of no decompression time to spare.
So in this profile, as all the others I checked in my log book, the RDP was more conservative. I guess I can also assume that an S by PADI's terms isn't the same thing as an S by the Navy's terms?
Alot of my other logged dives are off the PADI chart on the first dive, since I was using a computer, so I can't compare those to the Navy table.
This is very interesting to me. I went back and checked 15 or so my dives on days that I made repetitive dives and all resulted in the PADI tables being more conservative than the Navy tables. So I guess it just depends on the profile in question. For instance, here's a dive day while in Negril this past Oct:
Dive 1
95' for 20min
Dive 2
50 min surface interval
50' for 34 min
Using the RPD, I was in the O pressure group with no no decompression time left. On the second dive, I was in the S pressure group at the end of the dive with 22 minutes no decompression time to spare.
Using the Navy tables, I was in the F pressure group at the end of the dive with 5 minutes of no decompression time to spare. At the end of the second dive, I was in the J pressure group with 28 minutes of no decompression time to spare.
So in this profile, as all the others I checked in my log book, the RDP was more conservative. I guess I can also assume that an S by PADI's terms isn't the same thing as an S by the Navy's terms?
Alot of my other logged dives are off the PADI chart on the first dive, since I was using a computer, so I can't compare those to the Navy table.
.........there are other options available. I agree with your figures with Navy & RDP.
Using RDP - 95' for 20 min results in O. 50 min SIT results in F. F to 50' gives you 24 min RNT added to 34 min ABT is a TBT of 58 min. RDP has an NDL of 80 min at 50' leaving you 22 min available time at that depth.
Using Navy - 95' for 20 min results in F. 50 min SIT results in E. E to 50' gives you 38 min RNT added to 34 min ABT is a TBT of 72 min. Navy has an NDL of 100 min at 50' leaving you 28 min available time at that depth.
Using NAUI - 95' for 20 min results in F. 50 min SIT results in E. E to 50' gives you 38 min RNT added to 34 min ABT is a TBT of 72 min. NAUI has an NDL of 80 min at 50' leaving you 8 min available time at that depth.
Using YMCA - 95' for 20 min exceeds the NDL of 18 min requiring a 3 min deco stop at 10' resulting in I. 50 min SIT results in H. H to 50' gives you 66 min RNT added to 34 min ABT is a TBT of 110 min. YMCA has an NDL of 80 min at 50' leaving you in deco for 10 min on your second dive.
You can not take a letter group from the RDP and move it to any Navy based table, they do not represent the same amount of residual nitrogen. OTOH, you can move them between Navy based tables.
Walter
Using RDP - 95' for 20 min results in O. 50 min SIT results in F. F to 50' gives you 24 min RNT added to 34 min ABT is a TBT of 58 min. RDP has an NDL of 80 min at 50' leaving you 22 min available time at that depth.
Using Navy - 95' for 20 min results in F. 50 min SIT results in E. E to 50' gives you 38 min RNT added to 34 min ABT is a TBT of 72 min. Navy has an NDL of 100 min at 50' leaving you 28 min available time at that depth.
Using NAUI - 95' for 20 min results in F. 50 min SIT results in E. E to 50' gives you 38 min RNT added to 34 min ABT is a TBT of 72 min. NAUI has an NDL of 80 min at 50' leaving you 8 min available time at that depth.
Using YMCA - 95' for 20 min exceeds the NDL of 18 min requiring a 3 min deco stop at 10' resulting in I. 50 min SIT results in H. H to 50' gives you 66 min RNT added to 34 min ABT is a TBT of 110 min. YMCA has an NDL of 80 min at 50' leaving you in deco for 10 min on your second dive.
You can not take a letter group from the RDP and move it to any Navy based table, they do not represent the same amount of residual nitrogen. OTOH, you can move them between Navy based tables.
Walter
Aha!
Y'all are using the old, unmodified Navy tables. After Doppler studies on asymptomatic bubbles, the Navy tables were modified by SSI and others to reflect new limits for recreational (no staged decompression) diving. In the example given above, the doppler NDL for the second dive is 32 minutes, so the 34 minute dive becomes moot, and the Navy table once again becomes more conservative.
Rick
Y'all are using the old, unmodified Navy tables. After Doppler studies on asymptomatic bubbles, the Navy tables were modified by SSI and others to reflect new limits for recreational (no staged decompression) diving. In the example given above, the doppler NDL for the second dive is 32 minutes, so the 34 minute dive becomes moot, and the Navy table once again becomes more conservative.
Rick
Rick,
Navy tables are the unmodified Navy tables. SSI tables are based on the Navy tables, but they are not the Navy tables.
I don't have a copy of the SSI tables, but 32 minutes seems to be an extremely conservative NDL for 50'. Are you sure you are reading it correctly? The most conservative NDL for 50' I see is 75 min on the DCIEM tables. YMCA, NAUI & the RDP all use 80 min while Navy & MDEA use 100 min.
Walter
Navy tables are the unmodified Navy tables. SSI tables are based on the Navy tables, but they are not the Navy tables.
I don't have a copy of the SSI tables, but 32 minutes seems to be an extremely conservative NDL for 50'. Are you sure you are reading it correctly? The most conservative NDL for 50' I see is 75 min on the DCIEM tables. YMCA, NAUI & the RDP all use 80 min while Navy & MDEA use 100 min.
Walter
Warhammer
Guest
I think he is saying that the NDL for my second dive is 32 minutes going by the SSI tables and not referring to the actual NDL of a 50' dive on the SSI tables.
Since we're talking NDLs, tables and all, any of you have any suggestions as to how not to blindly trust a computer? We all know that very few dives are on a square profile, which is what tables were designed for. Computers were designed to take advantage of multi-level diving and that's what most of all our dives are, at least mine are. So how's one to be assured that there hasn't been a malfunction in the software and that he isn't at undue risk?
I guess one could technically use a wheel to do it, but I'd bet most everyone doesn't keep up with a minute by minute profile of a dive, neither do they plan the dive based on a wheel, then dive that plan on a computer. So where's the middle ground here? Or is it basically an all or nothing, no matter if your diving a table, wheel or computer? Some suggest that computer users just use it basically as a depth gauge and actually dive within a table profile. Personally, I fail to see the benefit of having it if you are not using it.
Since we're talking NDLs, tables and all, any of you have any suggestions as to how not to blindly trust a computer? We all know that very few dives are on a square profile, which is what tables were designed for. Computers were designed to take advantage of multi-level diving and that's what most of all our dives are, at least mine are. So how's one to be assured that there hasn't been a malfunction in the software and that he isn't at undue risk?
I guess one could technically use a wheel to do it, but I'd bet most everyone doesn't keep up with a minute by minute profile of a dive, neither do they plan the dive based on a wheel, then dive that plan on a computer. So where's the middle ground here? Or is it basically an all or nothing, no matter if your diving a table, wheel or computer? Some suggest that computer users just use it basically as a depth gauge and actually dive within a table profile. Personally, I fail to see the benefit of having it if you are not using it.
King_Neptune
Founder
Dr Deco,
Im not sure if this falls into your area of research or not but do you have any input as to the different dive tables out there? Such as which are probably the closest to what you find as being the "safe zone"?
=-)
Im not sure if this falls into your area of research or not but do you have any input as to the different dive tables out there? Such as which are probably the closest to what you find as being the "safe zone"?
=-)
There is a good summary in "Deeper into Diving" by John Lippmann - pg 177-391.
And that's a summary. I wouldn't even attempt to encapsulate that in a message - let's just say the derivation and application methods vary, it is very complex, not exact, and a work in progress.
Rick
And that's a summary. I wouldn't even attempt to encapsulate that in a message - let's just say the derivation and application methods vary, it is very complex, not exact, and a work in progress.
Rick
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