Place of dive tables in modern diving

[tursiops]

But you can cut your dive into segments as long as you can keep track of the loading from the earlier segments.

This is not really true, which is why the tables can't be validly used for multi-level dives, and is why PADI came out with the Wheel, to allow for multi-level dives. The reason for the lack of validity is that the tables assume you are going to the surface at the end of a "segment" and the N2 loading is thereby reduced over what it was at depth, before the ascent. If you try and construct a multi-level dive from the table, you think there is less loading than there actually is. Not safe.

 

[boulderjohn]

Those of you using those basic XXX rules for the Navy Tables and other tables based on them do realize that they are not valid for repetitive dives, right?

Those tables allow longer bottom times than the PADI tables, but they require much longer surface intervals before a repetitive dive. That is, in fact, the primary motivation for the development of the PADI tables--the required surface intervals for the Navy tables were so long that it made 2-tank dives a serious challenge for dive operations. The Navy tables base their surface intervals on the 120 minute compartment. PADI's research showed that for dives within the limits of the table they created, the 60 minute compartment was plenty good enough. That created much, much shorter surface intervals and changed the way 2-tank diving was done.

The surface intervals we are used to using today are consistent with the PADI tables and with most computer programs, but they are IMO more than a tad short if you are using the Navy tables. If you are using US Navy limits for your first dives, you should be using US Navy surface intervals before the second.

 

[lowviz]

This is not really true, which is why the tables can't be validly used for multi-level dives, and is why PADI came out with the Wheel, to allow for multi-level dives. ....

Understood. Which is why I said "as long as you can keep track". And one can't.

I've gone no further than saying that tables are potentially useful as a minimalistic tool to give understanding. Depth, time and nitrogen loading. Add a DC and that is all anyone sees.

BTW, none of us dove tables in class. I did on my own several times, but cut each dive short. -just because...

 

[Diver0001]

Thoughts?

Buy your own computer.

R..

 

[tursiops]

People like simple rules and round numbers. Even when they are wrong.

A 1-h surface interval goes about 63% of the way toward clearing out the longest/slowest PADI compartment, just as a 2-h surface interval would for the longest/slowest (original) Navy compartment. The getting-to-be-common 45-minute SI goes about 53% of the way toward clearing that longest/slowest PADI compartment, but only 31% of the way toward clearing the longest/slowest (original) Navy compartment.

Conclusions?
If you are on tables, it matters which ones.
If you are on a computer, learn to use the PLAN mode, and consider longer SIs.

 

[scubadada]

...So for decades we diligently taught students how to use tables, knowing full well they would then go out and use computers instead, and they would do that with no training on how to use them. Is it any wonder that people who were given no training on computers don't know how to use them?

Do you think the newer, dive computer based classes, teach a sufficient amount for an educated, safe use of a computer?

 

[scubadada]

Interesting point. the whole "Rule of XXX" was based on the sum of depth (in feet) and NDL (in minutes), which turned out to be 120 for the old Navy tables, between 60 and 90 ft. For shallower depths, or deeper depths, the 120 rule was quite conservative...for example it would suggest 10 minutes at 110 ft and zero minutes at 120 ft, whereas the actual table gave 20 and 15 minutes, respectively, at 110 and 120 ft. So, the rule of 120 kept you "safe." On the first dive, only. It was even printed on the watchbands of the day:

This same "Rule of XXX" could be applied to pretty much any dive table or dive computer, for the first dive. Find that depth at which the sum of depth and time is the minimum, and that is your new rule. The PADI RDP gives 110, valid for 70 and feet; at any other depth the Rule of 110 is conservative. For 32% Nitrox, the PADI RDP rule would be 125, 'exact" for depths of 80 and 90 ft, conservative for any other depth.

The newest Navy table, linked above, would have a Rule of 118, "exact" at 70 ft, conservative at any other depth.
DCIEM would have a Rule of 105.
My old DiveRite DUO would have a Rule of 104.
My old DiveRite PLUS would have a Rule of 106.
My old Zeagle N2Ition 3 would have a Rule of 105.
My Oceanic OC1 (DSAT) has a Rule of 110, just like the PADI RDP. Surprise!
My Oceanic OC1 (PZ+) has a Rule of 105.
My Shearwater in Rec Mode with Low Conservatism (GF 45/95),Rule of 105.
My Shearwater in Rec Mode with Med Conservatism (40/85),Rule of 98..
My Shearwater in Rec Mode with High Conservatism (35/75),Rule of 92.
My Shearwater in Tec Mode with GF 30/60, Rule of 81.
My Shearwater in Tec Mode with GF 30/70, Rule of 89.
My Shearwater in Tec Mode with GF 20/80, Rule of 96.
My Shearwater in Tec Mode with GF 49/99, Rule of 109.

An interesting way to look at where a computer lands in the conservative to liberal spectrum for first dive.

 

[boulderjohn]

Do you think the newer, dive computer based classes, teach a sufficient amount for an educated, safe use of a computer?

The computer version of the PADI course teaches the students that generic computers do a bunch of things for you, including diving planning and emergency decompression. They tell you generically how to deal with those things, and they tell you to look for the specific way your computer does it. That enables you to look at the overwhelming computer manual and pick out those key functions. If nothing else, you know that your computer can do those things, and you should be able to look for the details. How many threads have we had on ScubaBoard over the years in which people say things like computers can't plan your next dive, when in fact all of them can do that.

The PADI course includes a link to an online simulator that will take your generic computer through all kinds of situations, showing how the generic computer functions in each. It shows how computers track tissue on-gassing and off-gassing--an instructional feature people who believe it is impossible to teach decompression theory without tables don't seem to know about.

 

[lowviz]

...//... The PADI course includes a link to an online simulator that will take your generic computer through all kinds of situations, showing how the generic computer functions in each. It shows how computers track tissue on-gassing and off-gassing--an instructional feature people who believe it is impossible to teach decompression theory without tables don't seem to know about.

You are an educator.

Is it not best practice to first take the complex and make it overly simple for the sole purpose of not overloading the student to where you just get nodding heads and sideways glances?

One then progresses by adding complexity as it can be handled. Or is it enough to just share that link?

 

[dmaziuk]

People like simple rules and round numbers. Even when they are wrong.

A 1-h surface interval goes about 63% of the way toward clearing out the longest/slowest PADI compartment, just as a 2-h surface interval would for the longest/slowest (original) Navy compartment. The getting-to-be-common 45-minute SI goes about 53% of the way toward clearing that longest/slowest PADI compartment, but only 31% of the way toward clearing the longest/slowest (original) Navy compartment.

My computer's manual says "9-compartment model with half-times from 2.5 to 480 minutes", so I know what its slowest compartment is, but I looked up the manual for the computer in that other thread, and it says (IIRC) "10 tissue compartments". No half-times given.

Show of hands: how many people looked at that page in their computer manuals, and how many of those manuals had the numbers spelled out?