Tables question (PADI tables) could apply to all i guess

[Charlie99]

I don't make "direct ascents" anymore. Sunday, I did a wreck the Sea Tiger (127) and I took a long time to ascend since I am throwing in a couple deep stops. Should I be cognizant of something more?

Only that slow ascents are good, but at some point a super super slow ascent becomes a multilevel dive.

The wording on most tables is that bottom time stops when you start your "direct ascent" to the surface or safety stop depths. So what does "direct ascent" mean?

ascending too slowly (long-table divers please read)
is a rather lengthy, convoluted thread which discusses this.

 

[JustinW]

Yep, it doesn't include ascent time, but I believe it does include descent time.

 

[Henryville]

I am an instructor for both PADI and NAUI. The rules are different for the tables produced by each agency, which adds to confusion. For the PADI tables, actual bottom time is calculated to the beginning of the ascent. For the NAUI tables, it is calculated to the point at which you reach the surface, less the safety stop.

 

[Cacia]

I always counted my "direct ascent" from the veritical part of the profile which was after the safety stop. I was OW NAUI so maybe that explains why I did it this way.

 

[GDI]

The tables assume a square profile so the ascent would be from the maximum depth directly to your safety stop, of course using a nice slow controlled ascent. This ascent and your safety stop do not count toward your bottom time.

Mark Vlahos

The definition for BT has been altered since dive computers have come onto the scene so this is really not a bad question. Some tables work differently to others so it is best just as you should with computers to have the dive team work using the more conservative limits

As Mark stated the tables work on a model of a relatively square profile. They (some) are based on the portion of the dive which has the greatest gas uploading, the accumulation of time for the descent and the time of exposure at depth. The moment that you begin your descent to depth this gas upload begins and thus your BT clock starts. At the moment that you begin to ascend (with the intent of not dropping back down - think average depth here) then you have reduced pressure on your body starting the off gasing process of your dive (there is a time lag here). From a table perspective this is the point at which your BT ends and your ascent time starts. Computers offer the ability to credit for this off gasing. However they are still in many cases based on the same algorithms as tables for the on-gasing portion.

If you think about it a computer and a table will have the same time restraints on a diver descending to 60 ft/20 m. Once the diver reaches that depth both the table and the computer will read and agree on the total NDL remaining (within a minute or two based on computer vs table conservatism). the computer of course has the luxury of providing real time dive information feed back, tha table is static.

Some tables will only permit your total dive time to be that of the limit based on the depth you went to. Example a 100 ft dive with a NDL of 20 minutes. The entire length of dive cannot exceed 20 minutes from surface to surface

Many divers will say they have just completed a dive and have a BT of say 60 minutes. The truth is more likely they have a total dive time of 60 minutes surface to surface as counted from a computer. Their BT may in fact be only 40-50 minutes and then they had taken 10-20 minutes for the ascent - computer timed.

With this in mind many OW classes should be teaching that the diver needs to watch both their table and computer limits working hand in hand with each other

So to answer your question

For most conventional tables, If your table limits you to a NDL of 55 minutes @ 60 ft /20 m then you must begin your ascent to the surface/safety stop at 55 minutes or less (preferably less). Violating this limit may, subject to table place you into a deco obligation and for some contingencies that you may not be prepared for.

 

[dbg40]

From the time you get into the water, you are loading gas, this counts as your total bottom time which ends when you begin your "direct ascent". Which is a straight ascent to the surface with only your safety stops included. If you stop to hang out any longer than a safety stop would take, it turns into a multi level dive.

 

[dbg40]

Many divers will say they have just completed a dive and have a BT of say 60 minutes. The truth is more likely they have a total dive time of 60 minutes surface to surface as counted from a computer. Their BT may in fact be only 40-50 minutes and then they had taken 10-20 minutes for the ascent - computer timed.

With this in mind many OW classes should be teaching that the diver needs to watch both their table and computer limits working hand in hand with each other

So to answer your question

For most tables, If your table limits you to a NDL of 55 minutes @ 60 ft /20 m then you must begin your ascent to the surface/safety stop at 55 minutes or less (preferably less). Violating this limit may, subject to table place you into a deco obligation and for some contingencies that you may not be prepared for.

This is where computers confuse the issue, it's nice to plan the dive and enter it into the conputer. Then you can follow the profile you set by the tables.

 

[Cacia]

Uncle Pug posted the old 120 rule awhile back, which I had never heard but find very useful, since I am not someone who carries tables and only does recreational depths, although on the deep side since most all our sites are 100+. It has some limitations on the far extremes but works well for me diving with a conservative computer (Sunnto).
Especially when I get task loaded with a camera and alter my profile. My profiles are often not pre-planned because I am going to decide what I want to shoot when I get down there. if I decide to go to the deepest point and shoot the wreck looking up at it, and I stay to my limit, I need to check my profile mentally against my computer.
Sunday, I did have a little issue because the numbers were not making sense...I think I was narc'ed to be honest. I am still trying to figure it out. This is one reason i was asking about DIR photographers, because you would need a mind like a steel trap to run tables, and shoot manual, and be a good buddy, at technical depths. I know that some people can probably do it but I know it is beyond my capacity at depth, beyond 100 ft.

yes, I got into deco on my deep stop, and was too foggy to realize what had happened. poor form.

 

[O2BBubbleFree]

...as stated above.

YMCA added an 'additional safety margin' by changing their definition of bottom time to be from start of descent to start of safety stop (used to be start of ascent).

So I guess when you plan your dive you must calculate when to leave the bottom so that you reach your safety stop by the NDL time. In other words, beginning of ascent must be no later than NDL minus the time it takes you to get from the bottom to the safety stop.

A pain, if you ask me.

 

[Vayu]

You should not be pushing your tables to the no-deco limit anyway. These are not magical numbers that create a border where on one side you are bent and on the other you are perfectly healthy. They are, at best, advice based on algorithms that have been derived from studies on goats and navy divers. Since most people on this board are not either I would advise starting your ascent a few notches before you reach the tables NDL, then make it a slow ascent and extended stop anyway. Every dive is a decompression dive... don't let the square profiles fool you into doing away with conservative diving.

-V