An Experiment

[Paladin]

Hi, Y'all.

A slightly heated discussion on a couple of other threads got me to thinking. The argument concerned dive computers vs tables. As with anything, there were two sides with one side calling for the abolishment of tables as inferior and the other defending the tables as being more dependable. And, of course, there were the middle-of-the-road guys who use computers with tables for backup.

One of the arguments against using tables was that tables cannot be used for multi-level dive planning.

Back in the '60s and up to the early '70s, the guys I used to dive with (ex-Navy) used the Navy tables for multi-level dives quite frequently. I, personally, have never done it but they showed me how they did it. I hadn't thought about it for a very, very long time and those threads reminded me of it.

As an experiment, I made up a theoretical multi-level dive and worked it up using the PADI RDP. I posted the result on one of the other threads and asked for others to check it out with computers to see how it compared. I got two replies. One claimed his comp called for a 25 minute deco stop while the other said his computer allowed for a 5 minute safety stop and no deco. Not what I could call a definitive result from the experiment.

What I am proposing is that I post another ML dive, using the PADI tables, and have several of you work the dive up on your comps for comparison. The depths I will use will be 100 ft, 70 ft. and 40 ft.

100 ft.........................10 min.
70 ft...........................10 min.
40 ft...........................25 min.
SS..............................05 min.

I am curious to see if their method actually worked or if they just got lucky.

 

[Teamcasa]

Most computers track an actual dive so testing your multi-level dive is tough. Although you could use dive planing software to get the numbers but even then, they would differ from your actual computer.

 

[Doc]

Back in the '60s and up to the early '70s, the guys I used to dive with (ex-Navy) used the Navy tables for multi-level dives quite frequently.

They would have looked at it as a 100' dive for 45 minutes. I don't recall any no-deco multi-level dive tables. Their period Navy tables (square profile) would not have been happy.

The "wheel" is, in and of itself, a "table', and yes- you can use it to plan multi-level dives.

One that never made it:

The new and the old:

 

[Paladin]

The procedure they used was this:

!0 minutes at 100' puts you in group E. Count the next level as a repetitive dive with no SI. 10 minutes at 70' then puts you in group L. Then 25 minutes at 40', finishing with a 5 minute safety stop (they didn't use safety stops. I added this). Their method was to treat each new level as a repetitive dive with no surface interval. I've never tried it, but they claimed it worked for them.

Except for my mentor, Harold, these guys were working divers. They did underwater construction, demolition, salvage, etc.

 

[Bubbletrubble]

The procedure they used was this:

!0 minutes at 100' puts you in group E. Count the next level as a repetitive dive with no SI. 10 minutes at 70' then puts you in group L. Then 25 minutes at 40', finishing with a 5 minute safety stop (they didn't use safety stops. I added this). Their method was to treat each new level as a repetitive dive with no surface interval. I've never tried it, but they claimed it worked for them.

Isn't this exactly what PADI's RDP Wheel does? I don't own one, so I can't verify this. Anyone know?

 

[Paladin]

I don't have the wheel, either. All I have are the Navy and PADI tables. I used the Navy tables until recently but the PADI tables are more conservative so a bit safer.

 

[Blackwood]

100 ft.........................10 min.
70 ft...........................10 min.
40 ft...........................25 min.
SS..............................05 min.

I have a hard time believing that a properly functioning computer would call for a 25 minute stop on that profile.

It's like 90 for 20 followed by a bunch of deco.

 

[NvScubaSteve]

The eRDP ml comes up with this which is similar to the results of Paladin954

100 feet for 10 min = pressure group E (20min NDL at this depth)
70 feet for 10 min = pressure group L (20 min NDL at this depth)
40 feet for 25 min = pressure group R (76 min NDL at this depth)

The eRDP ml calls for a required 3 min safety stop at 15 feet (rule 2).

I dont have my dive computer with me not that it would help since it does not provide for this type of planning anyway.

(if I screwed anything up on this let me know I am new to the eRDPml)

 

[Paladin]

The 25 minutes at 40' is part of the dive profile, not a required stop.

 

[Paladin]

So, the old guys were right. You can use tables for ML dive planning. I can just imagine them looking down and smiling knowingly.