"Riding your Computer Up" vs. "Lite Deco"

[Basking Ridge Diver]

No, USN tables use bottom time. BSAC '88 uses time until reaching the 6m or the 9m decompression stop, ascent time must be added to the bottom time.

I had to look this up - this is an incorrect statement.

Navy Manual Version 6
"9-3.2 Bottom Time. Bottom time is the total elapsed time from the time the diver leaves the surface to the time he leaves the bottom. Bottom time is measured in minutes and is rounded up to the next whole minute."
Page 9-2.

Bottom time does include the descent time for the Navy Tables.

 

[scubadada]

I had to look this up - this is an incorrect statement.

Navy Manual Version 6
"9-3.2 Bottom Time. Bottom time is the total elapsed time from the time the diver leaves the surface to the time he leaves the bottom. Bottom time is measured in minutes and is rounded up to the next whole minute."
Page 9-2.

Bottom time does include the descent time for the Navy Tables.

What? USN (and all standard) bottom time is descent time and time spent on the bottom. It does not include ascent time. How is my statement incorrect? BSAC is the outlier. We seem to have gotten caught up in a language problem, looks like we meant the same thing. Perhaps it was my intitial misunderstanding of your post.

 

[stuartv]

I had to look this up - this is an incorrect statement.

Navy Manual Version 6
"9-3.2 Bottom Time. Bottom time is the total elapsed time from the time the diver leaves the surface to the time he leaves the bottom. Bottom time is measured in minutes and is rounded up to the next whole minute."
Page 9-2.

Bottom time does include the descent time for the Navy Tables.

Uhh, time from when the diver leaves the surface means it DOES include the descent time. Right?

"Several percent"? Is that true? So you mean more than one out of a hundred typical USN dives is probably going to involve DCS?

Your statement directly implies that all "typical" USN dives are to an exact depth listed in the tables and that the diver stays at that exact depth for the full amount of time specified in the table. I doubt that is the case. I suspect many "typical" USN dives involve depth that is not as deep, but rounded up to the next depth specified in the table. And that the dive doesn't stay at that exact max depth for the entire dive. And that the diver does not actually stay until the NDL timer counts down to exactly 0. And it may even be somewhat normal for the diver to do a longer safety stop than the exact minimum specified. But, I could be totally wrong on all of that.

 

[Basking Ridge Diver]

Uhh, time from when the diver leaves the surface means it DOES include the descent time. Right?

Agreed.

It sounded like Scubadada was disagreeing on a previous post...

 

[Killerflyingbugs]

Uhh, time from when the diver leaves the surface means it DOES include the descent time. Right?



Your statement directly implies that all "typical" USN dives are to an exact depth listed in the tables and that the diver stays at that exact depth for the full amount of time specified in the table. I doubt that is the case. I suspect many "typical" USN dives involve depth that is not as deep, but rounded up to the next depth specified in the table. And that the dive doesn't stay at that exact max depth for the entire dive. And that the diver does not actually stay until the NDL timer counts down to exactly 0. And it may even be somewhat normal for the diver to do a longer safety stop than the exact minimum specified. But, I could be totally wrong on all of that.

A typical deep navy dive is going to be over the NDLs and way into deco, at about a constant depth, they do round to the next table though.

 

[Lorenzoid]

Your statement directly implies that all "typical" USN dives are to an exact depth listed in the tables and that the diver stays at that exact depth for the full amount of time specified in the table. I doubt that is the case. I suspect many "typical" USN dives involve depth that is not as deep, but rounded up to the next depth specified in the table. And that the dive doesn't stay at that exact max depth for the entire dive. And that the diver does not actually stay until the NDL timer counts down to exactly 0. And it may even be somewhat normal for the diver to do a longer safety stop than the exact minimum specified. But, I could be totally wrong on all of that.

My "statement"? I simply asked a question, hoping to obtain clarification of someone else's statement. scubadada's subsequent posts elucidated where the statement came from: a set of test dives. I would expect the test dives were chosen as reasonably representative of what's typical for Navy divers, but I don't know.

 

[stuartv]

My "statement"? I simply asked a question, hoping to obtain clarification of someone else's statement. scubadada's subsequent posts elucidated where the statement came from: a set of test dives. I would expect the test dives were chosen as reasonably representative of what's typical for Navy divers, but I don't know.

Sorry. Your question carried a direct implication.

We were talking about NDLs. Test dives to determine the NDL at various depths with a predetermined target for rate of DCS. No reason at all to think that test dives for that purpose would be representative of any particular kind of dive.

Your question went from an assertion that test dives to a specific depth generated a specific percent incidence of DCS, to a "question" of the correctness of the statement that "typical USN dives" would have one in one hundred results of DCS. Scubadada said apples and you asked about oranges.

Again, my point then and now is that testing to find a specific limit does not at all imply that the tests done are "typical" examples of the intended activity. You might never approach the NDL. Or you might exceed it and go into deco on every dive. Either way, it still makes sense to conduct tests to determine what the NDL is - even those though those tests may be specific dive profiles that you actually never do.

 

[Lorenzoid]

The word "typical" was mine, I admit. I said "typical"--perhaps a poorly chosen word--because I can't imagine why the Navy would test something that is of no practical use to them. If they were testing for limits, then surely the limits have some bearing on the kind of diving they actually do. I would imagine it's not uncommon for them to dive to their limits.

 

[stuartv]

You don't think knowing the NDL is of practical use to the Navy?

 

[scubadada]

Sorry, there is an error in the my table posted in #299 and #300. The USN table NDLs are from 2008. The corrected table is posted below.

The Naval Medical Research Institute pubished reports in 1985 (1% and 5%) and in 1997 (2.3%) on equal risk no decompression limits. I have reproduced some of the results along with USN, DSAT, and Buhlmann ZH-L16C air NDLs: