Info Why are tables not taught in OW classes anymore?

[Chavodel8en]

I've done a lot of tropical dives where you get close to NDL at approx 30m/100', then work your way up to the top of the reefs at around 10m/33' and hang out there for 10-15 minutes before ascending for a safety stop.

That kind of profile is creates less decompression stress on the body than if you had ascended straight to the safety stop from the deepest part of your dive.

Getting off-topic, but this is an interesting discussion, and I may make another thread

Re "riding the NDL". On vacation, I had one shot at diving the Sea Tiger, and I wanted to extend my time on it as much as possible, so I rode the NDL to zero (didnt help that my operator couldnt get me NItrox).

As lowwall mentions, I think alot of us "riding the NDL" aren't trying to brag, we just want to extend our precious vacation dives.

My question, which I will pose on another thread is what folks think about me setting my computer to allow me as much time as possible at depth (Deep 6 Excursion has conservative settings, as well as GF settings). I only do 2 dives per day, and will have at most 4 dives for an entire vacation (my wife doesnt dive).

I feel like since I wont be accumulating over many dives, I have more leeway to "ride the NDL" to the last minute on that one dive I do at depth. Will ask in another thread.

 

[inquis]

So in effect, if one's DC reads 0 bottom time you aren't really quite at 0?

Taking the remaining "NDL" time to 0 means you are AT your intended limit and is absolutely time to ascend. Yes, that is safer than going to 0 with a less conservative setting.

IOW, I've already dialed in the cushion with which I'm comfortable via the conservatism setting. I don't *routinely* need to add even more cushion by always keeping NDL above, say, 5 mins. That said, if I wanted more cushion based on events during the dive, I would ascend "early" rather than increase conservatism & exit "on-time" (at the revised/shorter NDL limit).

 

[boulderjohn]

Correct me if I'm wrong but computers don't use pressure groups (PG). If you want you can reference tables for PG's when filling out your log book during OW dives. Then you will need to understand the use of tables.

Show me how I would reference the tables and put pressure groups in for these two dives I did on June 23. There divers were done using EANx 32. Both were NDL dives--no required decompression.

Dive One
Maximum depth = 126 feet
Total dive time = 83 minutes

Surface Interval = 91 minutes

Dive Two
Maximum DEpth = 88 feet
Total dive time = 92 minutes

 

[Hoyden]

Warm Water Pretty Fish

Might be a pejorative, i now wear it proudly.

In my IDC final, they gave me a Wheel to use that perfectly passed the alignment tests for printing error, but it would not give me an answer to match any of the given choices.

The proctor fiddled with it, chuckled, and said “mark choice C”,

The only question that I missed on my IE was a freaking wheel question like mentioned above and I am still mad about it! In my baby tech classes back in the dark ages, we cut custom tables for every dive. Now I just wear two computers and carry a couple of extras on every trip. Two is one: one is none.

 

[bradlw]

Something I do always wonder about is why the little bit of extra conservatism using tables vs. computers is not mentioned in courses and materials. I'm not talking about square profiles vs. multi-level computer dives or any of that. I mean that when you do a maximum dive of say 90 feet you may be right on the bottom once in a while (oh yeah, never ever touch the bottom....). But most of the time you are at maybe 86-87 feet. Now when you figure 90 feet with tables you aren't really at 90 much at all, even with a very square profile. So, you have a little edge there. With the computer, you get the theoretical "exact" bottom time remaining on the screen. There IS no leeway if you mistakenly let it go down to 0 or close to 0. It is what it is. This is NEVER mentioned.

I think your point might touch on one of the problems I see.

Folks seem to say that tables were defined for military divers that would be doing "square profile" dives.
I say BS to that. Navy divers were very likely often doing stepped depth diving often as well.....maybe not so much when they go down to work on the ship's prop...but for bottom salvage work or whatever I don't recon they were always strict to the absolutely square profile.

I think a HUGE issue if folks no longer have the concept that these are just illustrative models of an estimate. They are only just a ballpark of a concept. Something to set the crude stage of perspective. It's up to the diver to use their brains to interpolate or extrapolate from the available information to adjust the guideline....
add a bit more safety factor here or there...push the time edge a little closer when other variables have already provided some cushion....pull away from the edge when other variables are also closer to the edge.

Every body is different on gassing and off gassing at various rates, subtle ascents and descents during the dive, temperature variables, breathing gas variables, individual health variables, and on an on....
and no matter the algorythm or equations used to calculate those old tables, these are still based on research and ESTIMATES..... probably averages of test data from a few people. ABSOLUTELY NONE of it is related to any live situation going on RIGHT NOW IN YOUR BODY.

our modern computers do the same thing, just using an algorithm....Some are no doubt using newer test data, using larger or smaller data sets, etc.... but they are STILL only just an illustrative model of an estimated physiological profile.... and yeah, it might be refreshed updated and calculated on a much more granular rate....once per second or whatever as opposed to a single max depth step....so they are likely to be able to come closer to some form of reality for the actual dive....but it's still just a ballpark of the concept. A GUIDELINE. Nothing more absolute than that

 

[tursiops]

I think your point might touch on one of the problems I see.

Folks seem to say that tables were defined for military divers that would be doing "square profile" dives.
I say BS to that. Navy divers were very likely often doing stepped depth diving often as well.....maybe not so much when they go down to work on the ship's prop...but for bottom salvage work or whatever I don't recon they were always strict to the absolutely square profile.

I think a HUGE issue if folks no longer have the concept that these are just illustrative models of an estimate. They are only just a ballpark of a concept. Something to set the crude stage of perspective. It's up to the diver to use their brains to interpolate or extrapolate from the available information to adjust the guideline....
add a bit more safety factor here or there...push the time edge a little closer when other variables have already provided some cushion....pull away from the edge when other variables are also closer to the edge.

Every body is different on gassing and off gassing at various rates, subtle ascents and descents during the dive, temperature variables, breathing gas variables, individual health variables, and on an on....
and no matter the algorythm or equations used to calculate those old tables, these are still based on research and ESTIMATES..... probably averages of test data from a few people. ABSOLUTELY NONE of it is related to any live situation going on RIGHT NOW IN YOUR BODY.

our modern computers do the same thing, just using an algorithm....Some are no doubt using newer test data, using larger or smaller data sets, etc.... but they are STILL only just an illustrative model of an estimated physiological profile.... and yeah, it might be refreshed updated and calculated on a much more granular rate....once per second or whatever as opposed to a single max depth step....so they are likely to be able to come closer to some form of reality for the actual dive....but it's still just a ballpark of the concept. A GUIDELINE. Nothing more absolute than that

You might be missing one critical point: the "guideline" is set to try and be on the safe side of the gray area....not right through the middle of it. Your argument is perilously close to, "If we don't know things 100% perfectly then we know nothing." That's just silly.

 

[bradlw]

No, I'm not so sure I agree with that assessment of the point I was trying to make. Well you can call it silly if you want...I mean your statement that we know nothing if we don't know everything.

What I'm trying to get at is knowing as much as reasonably possible about the weeds in the field, but ALSO (or maybe even more importantly) knowing the whole field.

....basically don't get stuck in the weeds, and remember the big picture.​

Doing that helps you to use your brain to try to stay on that safe side of the grey that you write about.....

 

[Seaweed Doc]

Teaching dumbass OOA should also be a far far second to proper gas planning. Teaching "AHHHHHHHHHHHH" from depth because you ran OOA should also be obsolete. It just shouldn't happen... if it did you ****** up a LOT on the way to that point and your instructor failed you miserably or you're in the wrong hobby.


What do I know though... I would probably drown people if I was an instructor. I dive to get away from people!!

Regarding teaching OOA skills: While most (the vast majority?) of OOA situations are the diver's stupidity, occasionally you have the rare equipment failure. I'm thinking back to a guy who died locally (experienced diver, doing a volunteer underwater habitat project) when his first stage blew. Held his breath from 60'.

Having at least a mental checklist for most eventualities is a good thing. You can run down how to handle a situation quickly and easily.

Regarding drowning students: Yeah, I've been tempted with a few.

Edit: The wanting to drown them motivation never occurs underwater. It's always on land. I suspect because underwater they can't open their mouths.

 

[lowwall]

Re "riding the NDL". On vacation, I had one shot at diving the Sea Tiger, and I wanted to extend my time on it as much as possible, so I rode the NDL to zero (didnt help that my operator couldnt get me NItrox).

As lowwall mentions, I think alot of us "riding the NDL" aren't trying to brag, we just want to extend our precious vacation dives.

My question, which I will pose on another thread is what folks think about me setting my computer to allow me as much time as possible at depth (Deep 6 Excursion has conservative settings, as well as GF settings). I only do 2 dives per day, and will have at most 4 dives for an entire vacation (my wife doesnt dive).

I feel like since I wont be accumulating over many dives, I have more leeway to "ride the NDL" to the last minute on that one dive I do at depth. Will ask in another thread.

The whole dive profile matters. Deco diving is a thing after all. Riding the NDL for a couple of minutes isn't necessarily a problem if you have the gas and the plan to hang out (i.e., decompress) somewhere shallower. You can easily end up with lower max tissue loadings than someone who does a basically square profile but leaves several minutes of NDL time. This is where it would be nice to have a SurfGF or tissue graph on your computer.

Yes, if worst comes to worst and you have to skip the shallow part you'll end up with a profile at what your DC considers a limit. But it's still not over the limit. Monitor yourself for incipient DCI symptoms and adjust your SI and next dive appropriately.

 

[rob.mwpropane]

Regarding teaching OOA skills: While most (the vast majority?) of OOA situations are the diver's stupidity, occasionally you have the rare equipment failure. I'm thinking back to a guy who died locally (experienced diver, doing a volunteer underwater habitat project) when his first stage blew. Held his breath from 60'.

Having at least a mental checklist for most eventualities is a good thing. You can run down how to handle a situation quickly and easily.

Regarding drowning students: Yeah, I've been tempted with a few.

So I would think the answer would be to focus heavily on a team diving mentality (for which I am still learning and not great at) or redundant air. The surface still wasn't really the solution. There's too much that can go wrong in that ascent. Panic creeps in, you hold your breath, and things don't turn out good as in your example.

It's like landing a plane where the engine died.. can people do it, sure, but you only get one chance. With diving you can mitigate that need to land right away and take your time to make the appropriate ascent. Heck with the right mentality / training he should have been able to make a complete SS / deco stop and all ended well. The training or his own complacency failed him. The surface is a dangerous option from 60' for most people.

A little OT, but my little bubbles worth