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

[Celt]

Aren't all NDL tables like this? Not just navy?

My US navy tables includes deco giving a repetitive group up to and including 40 minutes at 190 feet. I've no knowledge of other tables.

 

[Akimbo]

My US navy tables includes deco giving a repetitive group up to and including 40 minutes at 190 feet. I've no knowledge of other tables.

Do you know what tables the Royal Navy uses? I think they had their own tables well into the 1970s.

 

[Celt]

Do you know what tables the Royal Navy uses? I think they had their own tables well into the 1970s.

The manuals were loose leafed with BR numbered. I think my brother has an early copy I'll check it out.

 

[boulderjohn]

Repetitive diving was not common in the early days. Here is a warning printed on the PADI tables, starting nearly 40 years ago:

Note: Since little is known about the physiological effects of multiple dives over multiple days, divers are wise to make fewer dives and limit their exposure toward the end of a multiday dive series.​

 

[Eric Sedletzky]

Repetitive diving was not common in the early days. Here is a warning printed on the PADI tables, starting nearly 40 years ago:

Note: Since little is known about the physiological effects of multiple dives over multiple days, divers are wise to make fewer dives and limit their exposure toward the end of a multiday dive series.​

Once when I was down diving off the Peace Dive Boat out of Ventura, we were on a two day liveaboard. I belonged to a club out of Socal that chartered the boat and they were all seasoned veteran divers. The charter master set up 6 dives on the first day and 4 dives the second day (which was typical) so 10 dives in two days in cold California water! Pretty aggressive.
Anyway, I was using computer but just for fun I kept a running table log of the dives we were doing. I was diving 32%
A majority of the sites were fairly square profile dives. They were putting us on a lot of flat areas with some low lying shelf rock and such looking for lobsters.
Amazingly, all the dives pretty much lined right up with the PADI 32 tables I was using. The depths progressively got shallower as we moved on through the day, and surface intervals were spaced just about right. The last and 6th dive if the day was when we were anchored up in a cove and it bottomed out at about 35-40 feet for the night dive.
Either the captain lucked out or was just really good at his job because gas supply-time and depth all lined up just about exactly right to the tables. I just kept a running total following the pressure groups and it worked fine.

 

[boulderjohn]

Amazingly, all the dives pretty much lined right up with the PADI 32 tables I was using. The depths progressively got shallower as we moved on through the day, and surface intervals were spaced just about right.

More than 10 years ago, a debate in one (actually more than one) thread centered upon the concept of the reverse profile--in repetitive dives, doing later dives deeper than earlier dives. A conference about 20 years ago tried to determine where this rule came from. The earliest known reference was to a 1972 PADI OW manual, and doing the deepest dive first was a suggestion without an explanation. As time went on, that suggestion turned into a hard and fast rule, again, without explanation. Representatives of PADI at the conference had no explanation. They did not know who had made the original suggestion, and they did not know the reason for it.

In the thread, one ScubaBoard member (knotical) suggested the reason, and I am sure he hit it on the nose. Using tables for dive planning, if you do the shallower dive first, you end up with much longer required surface intervals than if you did the same dives with the deeper dive first. The schedule you describe would not have been possible if the dives were not done progressively shallower, especially in 1972, when the US Navy tables with their long surface intervals were the norm.

I am sure that over the years, the captain learned exactly how to run the dives so that everyone got in the dives they wanted to do. That's why the captains get the big bucks.

 

[Eric Sedletzky]

More than 10 years ago, a debate in one (actually more than one) thread centered upon the concept of the reverse profile--in repetitive dives, doing later dives deeper than earlier dives. A conference about 20 years ago tried to determine where this rule came from. The earliest known reference was to a 1972 PADI OW manual, and doing the deepest dive first was a suggestion without an explanation. As time went on, that suggestion turned into a hard and fast rule, again, without explanation. Representatives of PADI at the conference had no explanation. They did not know who had made the original suggestion, and they did not know the reason for it.

In the thread, one ScubaBoard member (knotical) suggested the reason, and I am sure he hit it on the nose. Using tables for dive planning, if you do the shallower dive first, you end up with much longer required surface intervals than if you did the same dives with the deeper dive first. The schedule you describe would not have been possible if the dives were not done progressively shallower, especially in 1972, when the US Navy tables with their long surface intervals were the norm.

I am sure that over the years, the captain learned exactly how to run the dives so that everyone got in the dives they wanted to do. That's why the captains get the big bucks.

I remember the debate.
The eventual outcome was something to the effect of ‘it really doesn’t matter as long as you obey the NDL’s’. About that time computers were making their way into the mainstream so maybe that had something to do with it? A lot easier to track nitrogen loading and way more accurate. Computers changed diving quite a bit, let’s not forget.

 

[boulderjohn]

I remember the debate.
The eventual outcome was something to the effect of ‘it really doesn’t matter as long as you obey the NDL’s’. About that time computers were making their way into the mainstream so maybe that had something to do with it? A lot easier to track nitrogen loading and way more accurate. Computers changed diving quite a bit, let’s not forget.

Yep. Even if you are only using tables, you can do the deeper dive after first--you just have to follow the table limits, and if you do the shallower dive first and don't have a long surface interval, that second, deeper dive will be more limited than you might like.

The problem is that people somehow got the idea that there was some kind of safety effect involved. In fact, at the aforementioned conference, Bruce Wienke argued that was the case, and because of Wienke's insistence, the conference ended up keeping the deeper dive first recommendation for tech dives. I am sure you will still find instructors insisting that there is a serious safety problem with reverse profiles, although they will not be able to tell you what it is.

 

[Eric Sedletzky]

Yep. Even if you are only using tables, you can do the deeper dive after first--you just have to follow the table limits, and if you do the shallower dive first and don't have a long surface interval, that second, deeper dive will be more limited than you might like.

The problem is that people somehow got the idea that there was some kind of safety effect involved. In fact, at the aforementioned conference, Bruce Wienke argued that was the case, and because of Wienke's insistence, the conference ended up keeping the deeper dive first recommendation for tech dives. I am sure you will still find instructors insisting that there is a serious safety problem with reverse profiles, although they will not be able to tell you what it is.

Nitrogen uptake is nitrogen uptake, it doesn’t matter the order.
However, if you do your shallow dive first wouldn’t that mean that your fast tissues would be loading more than slow tissues?
Then doing the deeper dive second meaning your dive would be shorter, wouldn’t that mean less time saturating the slow tissues as opposed to doing the deep dive first to full NDL.
So in other words by doing the same amount of NDL only in reverse, would that mean that there would be less slow tissue uptake overall, or would it be the same?

 

[boulderjohn]

Nitrogen uptake is nitrogen uptake, it doesn’t matter the order.
However, if you do your shallow dive first wouldn’t that mean that your fast tissues would be loading way more than slow tissues. Doing the deeper dive second and your dive would be shorter, wouldn’t that mean less time saturating the slow tissues as opposed to doing it the first dive to full NDL.
So in other words by doing the same amount of NDL only in reverse, would that mean that there would be less slow tissue uptake overall, or would it be the same?

I'm sorry, but I do not feel confident enough in this question to offer an opinion.