I finally get it (or, gauges and why they make sense)

[limeyx]

On our cave trip last November, we did 17 days of diving in a row, and honestly I didn't even give a thought about what kind of surface interval we took.

some of those dives were long (3-4 hour) dives at 20-30 feet
some averaged just 15-20 feet
some were decompression dives (90 mins at 60 or so) (usually with O2 for deco)
some of it was a bunch of bounce dives to do support for deep dive (bouncing down to 100-110 feet on nitrox 3 or 4 times in an hour etc)

No issues whatsoever (including when I flew out the next day)

 

[limeyx]

The rule of thumb seems to be a bit hush-hush. In fact, there's some dispute apparently about 90 vs. 120 minute SIs.

Looks like more time sitting down with tables in my near future ;-)

I cant tell you how to go diving or calculate your profiles/plans

I've never bothered to worry about a 90min SIT, certainly not a 120 min one.
What usually happens here on a boat is by the time you are out of the water and on to the next site, 50-60 mins have gone by, and by the time you get in you are around an hour.

Sometimes we'll do a 4-6 min ascent on recreational dives on #2 and #3 (and always on a tech dive), sometimes not.

I personally haven't found it to make a jot of difference so far.

 

[ScubaFeenD]

Sometimes we'll do a 4-6 min ascent on recreational dives on #2 and #3 (and always on a tech dive), sometimes not.

I personally haven't found it to make a jot of difference so far.

You mean adding the extra time on second an third dives hasn't produced any noticeable difference?

 

[limeyx]

You mean adding the extra time on second an third dives hasn't produced any noticeable difference?

For recreational dives, no. For tech dives, we always do 4-6 mins up from 20 feet.

EDIT: Let me clarify one thing. We also generally (usually due to the nature of the cave) end up with a slow ascent on our cave dives (Mexico) so it's mostly from Open water diving that I dont really notice any difference.

As Laura says, getting 90 mins is not always possible especially on our "standard" dive boats in Los Angeles

 

[lamont]

What would actually be nice would be for someone to write a computer that did straight forwards buhlmann zhl16b (or 8-compartment or 16a or 16c or whatever -- twiddle how you like) and then instead of an NDL countdown or deco time or whatever, just show me the GF% in the leading compartment.

Kind of like CCRs that show you your mV instead of just ppO2... Get at the raw numbers...

 

[kanonfodr]

What would actually be nice would be for someone to write a computer that did straight forwards buhlmann zhl16b (or 8-compartment or 16a or 16c or whatever -- twiddle how you like) and then instead of an NDL countdown or deco time or whatever, just show me the GF% in the leading compartment.

Kind of like CCRs that show you your mV instead of just ppO2... Get at the raw numbers...

I believe you said something about " code not written by lawyers"?? Real-time leading compartment info is way too much knowledge for any tech diver to not abuse.

Peace,
Greg

 

[DiverLaura]

and how many of these methods are from people actually "trained" to do decompression diving? minimum deco doesn't count. last time i checked, fundies isn't a deco class.

you can do a lot of random stuff on no-deco, minimum deco and even easy tech 1 dives situations and get away with it...

So far, I've read about at least four different methods of determining decompression requirements, just in this thread alone.

Is there a single, documented, written-down and verified DIR decompression method, or is it pretty much "roll your own"?

flots

 

[gsk3]

I cant tell you how to go diving or calculate your profiles/plans

I've never bothered to worry about a 90min SIT, certainly not a 120 min one.
What usually happens here on a boat is by the time you are out of the water and on to the next site, 50-60 mins have gone by, and by the time you get in you are around an hour.

Sometimes we'll do a 4-6 min ascent on recreational dives on #2 and #3 (and always on a tech dive), sometimes not.

I personally haven't found it to make a jot of difference so far.

This isn't particularly helpful. I'm glad it hasn't made a jot of difference for you, but decompression algorithms are designed around average* fizzyology, and until I'm absolutely sure I'm one of those folks who is gifted with high bubble tolerance, not bothering about SIT just isn't good advice. If you're doing 50 minute SITs, and "sometimes not" bothering to even a 6-minute ascent (from a 90 foot dive, 1min stops at 50/40/30/20/10 gives you 5 minute ascent...so doubling the stops should be at least 8), then you're diving aggressively relative to the tables. I'm glad it's worked out for you, but it's totally irrelevant for anyone else.

* Well, actually, they're designed around something >90th percentile of physiology.

 

[flots am]

and how many of these methods are from people actually "trained" to do decompression diving?

Beats me. That's why I asked. Everybody here seems to have their own idea about how to do a deco dive and even how to figure out if they're doing one.

And FWIW, yes, I understand about "every dive is a deco dive", however I'm talking about the traditional sense of "if I surface now, will I be bent?"

flots.

 

[limeyx]

This isn't particularly helpful. I'm glad it hasn't made a jot of difference for you, but decompression algorithms are designed around average* fizzyology, and until I'm absolutely sure I'm one of those folks who is gifted with high bubble tolerance, not bothering about SIT just isn't good advice. If you're doing 50 minute SITs, and "sometimes not" bothering to even a 6-minute ascent (from a 90 foot dive, 1min stops at 50/40/30/20/10 gives you 5 minute ascent...so doubling the stops should be at least 8), then you're diving aggressively relative to the tables. I'm glad it's worked out for you, but it's totally irrelevant for anyone else.

* Well, actually, they're designed around something >90th percentile of physiology.

No worries, even if I had tried to give you specific advice (which I didn't), you'd probably be best served by not listening to it.

My only point is don't get too hung up on the specifics "Got to have a 2 min 30 sec stop here, got to have a 93 min SI there" and try to find something you are happy with.

The one thing I have realized more and more is that there isn't too much "hard and fast" and "the tables" are not some iron-cast rules of the road.

Be safe, be prudent and try to evaluate what you find works and what doesn't within the limits of the diving you do.

What I mean by the last one, is "practical" guidelines

- Here, on boats as Laura pointed out in her experience getting a 90 min SI is generally not going to happen, so you can choose to either sit out the second dive, or figure out a decent rule that works for you for smaller SI's
- If you are doing long shallow cave dives, you have a different set of ascent concerns that shorter deeper dives
- If you feel tired, cranky, sleepy or pain after a dive, even "the tables" may not work for you and you might need to adapt them.

As Laura points out, I have no training or standing to teach anyone anything about decompression, I just have some experiences which I think demonstrate that "one rule doesn't and cannot" fit all but some rules probably can work for a lot of people.

Dive however you like.