Do the dive tables have a limit on the number of dives per day?

[dmaziuk]

A key goal of the PADI RDP was to cut down the huge surface intervals required by the US Navy tables.

• PADI's research showed that for most dives in the range we now refer to as recreational diving, the 40 minute compartment would work, but they ended up going with the 60 minute compartment. This made the biggest difference, because the navy used the 120 minute compartment.
• They shortened the first dive NDLs, which also allowed for shorter surface intervals. For example, at 100 feet, the Navy NDL was 25 minutes, and on the RDP it was 20.
• Another big impact was in nearly doubling the number of pressure groups. This significantly reduced the rounding errors, which of course were always to the more conservative pressure group.

Workman's (USN) tables didn't have the 60-minute compartment. According to Deco for Divers it was 5, 10, 20, 40, 80, 120, 160, 200, and 240 minutes. DSAT ones are 5, 10, 20, 30, 40, 60, 80, 100, 120, 160, 200, 240, 360, 480. More compartments means smaller "jumps" when leading TC changes which means you can add finer granularity to your pressure groups.

 

[boulderjohn]

Workman's (USN) tables didn't have the 60-minute compartment. According to Deco for Divers it was 5, 10, 20, 40, 80, 120, 160, 200, and 240 minutes. DSAT ones are 5, 10, 20, 30, 40, 60, 80, 100, 120, 160, 200, 240, 360, 480. More compartments means smaller "jumps" when leading TC changes which means you can add finer granularity to your pressure groups.

I am not sure what you are responding to. I did not say that the Navy had a 60 minute compartment. Are you adding another point to mine?

 

[dmaziuk]

I am not sure what you are responding to. I did not say that the Navy had a 60 minute compartment. Are you adding another point to mine?

Yes. Also pointing out that you couldn't just "tune up" Navy tables for recreational diving because their tissue compartments were "too coarse", you really needed to develop a new tissue model.

 

[Akimbo]

Yes. Also pointing out that you couldn't just "tune up" Navy tables for recreational diving because their tissue compartments were "too coarse", you really needed to develop a new tissue model.

That might be a little misleading historically. The US and other navies had identified quite a a large number of tissues that in and out-gassed at different rates by the time Project Genesis began in the late 1950s. The real issue is how many different ranges those tissues were grouped into for the decompression calculations required.

For example, the slowest tissues were not of real concern for the Navy's 190' air tables but were about all that mattered for saturation decompression calculations.

Computing power was relatively cheap and available by the time optimizing tables for recreational diving was seriously considered so 16 and then 32 tissue groups became the practical, first in tables and then as dive computer algorithms.

As I understand it, Dr Bühlmann used less than 16 tissue compartments to calculate Hannes Keller's 1,000' Dive decompression tables in 1960. Computer time and programming was crazy expensive in those days. Doctors Bond, Workman, and Mazzone's tables for the first saturation decompression tables were calculated with slide rules.

 

[Celt]

Seibe, Gorman and Co. had there own tables but were of limited use for scuba as they were designed for use with a chamber, to be of benefit you'd have to get on oxygen at 50 feet.

 

[Bob DBF]

Here is the 1983 version of the PADI tables; I think this was the last before the RDP. No mention of the Navy tables.
View attachment 734695
View attachment 734696

And why would they mention the Navy tables, they were the only tables readily available, and were in the public domain.

 

[EFX]

@boulderjohn
I just ran some PADI RDP tables on a couple dives.
I did a 50’ dive to max NDL of 80 minutes, waited an hour, then went to 110’ for NDL of 3 minutes (the tables wouldn’t let me go deeper) for a total bottom time of 83 minutes.
Did the same depths but did the deep dive first
110’ for 16 minutes max NDL, waited an hour and then did the 50’ dive to max NDL for 61 minutes for a total bottom time if 77 minutes.
So doing the shallow dive first I got more bottom time according to PADI tables.

Your example above highlights the issue with reverse profile dives, that they are inefficient. If you need time (i.e. more NDL) at the deeper depth you need to do the deeper dive first. PADI understood this but as time went on the admonition to avoid reverse profiles became stronger until eventually it became a golden rule. The experts at the conference boulderJohn mentioned realized that almost all recreational divers at some point do reverse profile dives and do them safely. Wienke was the holdout and added constraints to reverse profile diving. He argued that reverse profiles were OK as long as the deeper second dive did not exceed 36 ft (12 m) deeper than the first dive, both dives were within recreational depth limits (130 ft), and they were both NDL dives.