Buddy diving on their computer

[fnfalman]

I agree with RSTOFER. Use the dive computer in gauge mode and go super conservative, or get your own dive watch and use the dive table and go super conservative. Calculate your dive per the deepest depth reached. It may limit bottom time but at least you know that you're on the side of caution.

 

[Blackwood]

The problem with guessing whether a few feet matters is that it all depends on the depth. The difference in NDL between 60 and 70 feet is 15 minutes. Somewhere in there, a few feet matter.

10 feet isn't "a few"

Again, this goes back to team skills.

When both divers have a computer, the more conservative computer controls the dive.

In which case two divers are diving one computer.

 

[J.R.]

... I agree with all the "use tables" folk... but would like to suggest that you look at PADI's eRDP or eRDPml (Electronic Repetative Dive Planner... or "multi-level" version) if you have any difficulty with the tables... Either of these devices will give you the same result as the flat tables but make calculations a little faster and "perhaps" reduces the possiblity of error... in any case, whether you have a dive computer or not, I'm a big fan of having a backup system (table or eRDP)... and, of course, extra batteries...

 

[rstofer]

10 feet isn't "a few"

Well, half of 10 feet is a 'few' and somewhere that 15 minutes needs to be divided up. The table just doesn't happen to have 65 feet with the proper intermediate value. To be correct, from a tables point of view, 61 feet must be treated as 70 feet. That's the way the tables are designed and all the round-up is why they work well. And 15 minutes is a lot of time.

In which case two divers are diving one computer.

Not really! Actually, two divers are using two computers and selecting the most conservative result. One diver could have dropped several feet lower or stayed at some depth longer than the other. As a result, that diver's computer will likely determine the end of the dive. But both divers are being properly monitored. Kind of like both divers surfacing when one runs low on air. It's the buddy concept.

The problem with ALL planners is that they can only 'plan' a dive if the profile is known in advance. They can also tell you how fast you need to get to the chamber when used to review a dive.

The proper way to use the tables is to calculate all Adjusted NDLs for the upcoming dive and select the deepest appropriate ANDL as the dive progresses. Write the values on a slate and check your depth gauge and bottom timer.

Or, buy a computer.

As this is the "New Divers and Those Considering Diving" forum, it would be a good idea to keep things conservative.

Richard

 

[rstofer]

... I agree with all the "use tables" folk... but would like to suggest that you look at PADI's eRDP or eRDPml (Electronic Repetative Dive Planner... or "multi-level" version) if you have any difficulty with the tables... Either of these devices will give you the same result as the flat tables but make calculations a little faster and "perhaps" reduces the possiblity of error... in any case, whether you have a dive computer or not, I'm a big fan of having a backup system (table or eRDP)... and, of course, extra batteries...

I have played with the eRDP and I have the eRDP-ML although I have never used it for multi-level calculations.

One thing I miss that the eRDPs don't provide is RNT. I liken the use of eRDPs to GPS. They give you exactly the right answer but they don't provide enough context. What use is the Lat and Lo of a boat unless one knows that there is clear water below. With chart plotters, the situation is far improved but in the early days there were many groundings because the boat's GPS position was never correlated with the chart.

The tables also give a visual reference to the effects of SIT. How the pressure group is changing and the implications on the upcoming dive.

Let's face it! I'm a tables kind of guy stumbling into the computer world. Yes, I like my computer! But I keep the table information in mind.

Richard

 

[Blackwood]

Not really! Actually, two divers are using two computers and selecting the most conservative result.

The sum total of which is: two divers using one computer (to determine when to surface)

 

[Hemlon]

Buy a computer. They are dirt cheap and you will love using it.

 

[Coldwater_Canuck]

Here's a question I have: in addition to the charts why not tell us what the recommended maximum residual nitrogen levels are, how quickly this nitrogen wears off, and a chart of how much residual nitrogen you take on at various depths (or there may even be a simple equation where you plug in the depth)?

This information was obviously used when constructing the tables: so why not just cut out the middle-man and throw that in the OW manual? It would make it much simpler to figure out multi-level dives?

 

[rstofer]

Here's a question I have: in addition to the charts why not tell us what the recommended maximum residual nitrogen levels are, how quickly this nitrogen wears off, and a chart of how much residual nitrogen you take on at various depths (or there may even be a simple equation where you plug in the depth)?

Isn't that exactly what the tables do?

The NDL is exactly the maximum allowed nitrogen exposure for a given depth. The fact that it varies by depth indicates that various tissue types are limiting the dive time.

The SIT portion of the table shows how the nitrogen wears off in terms of pressure groups and the repetitive dive portion shows how much nitrogen you are taking when you plan a subsequent dive to a particular depth.

Everything you asked for, except the equation, is already included in the tables. It is my understanding that PADI created their version of the tables by studying bubble formation with doppler sound measurements.

Now, if you really want to study deco theory, buy the book! "Deco For Divers" by Mark Powell. It has all kinds of numbers and equations. It also cites other documents for further study. There are probably a lot of other books - I just don't have them.

Of course, there is the classic "The New Science Of Skin And Scuba Diving" ($2 at Alibris - try for a 1968 edition) and it has the Navy Air Decompression Tables. These are handy if you want to dive to 300 feet for 50 minutes (figure on 8 hours of deco stops). Interesting stuff! Actually, the book was a training manual for LA County, YMCA, Boy Scouts and NAUI (among a lot of others) in the early years of scuba. You would be amazed at the quality of the program and, perhaps, staggered at how little has changed.

Richard

 

[Peter Guy]

The NDL is exactly the maximum allowed nitrogen exposure for a given depth.

The author of this quote, RSTOFER goes on to give good advice -- if you want to know more about deco, read the books. BUT, "exactly the maximum allowed" -- PLEASE -- there is NO "exactly" in any decompression!

The "mysterious malady" is just that -- mysterious.

Back to the OP -- dive conservatively and have fun.