US Navy Decompression Table

[Blackwood]

There is no "best" table. Just pick one you are comfortable with and learn it well.

 

[rstofer]

I keep a log book. So the tables will still be important for my next dive if the computer dies on the first dive. I see the point now.

But I am still not sure about no deco limits. Something might go wrong and I would need to do deco stops. I think I must get trained for this, a table will not be enough to decide when to stop, yes?

I have a copy of PADI recreational dive table. For example it is written, the NDL limit for 30 meters is 20 minutes. What I wonder is what if I stay 25 minutes at 30 meters? Will I need to do a deco stop? Could you interpret the table attached (considering this is my first dive ) ? I do not understand at which depths I should stop for how long?

The thing is, for a recreational diver you absolutely NEVER exceed the NDL. Not ever!

You have an awareness of your time under water, you know how deep you are and how deep you have been and you absolutely NEVER exceed the NDL. Just like you don't ever run out of air.

All that said, the 1989 NAUI tables (current, AFAIK) do provide information on safety stops should you overstay the NDL. For example, at 30m
NDL 22 minutes
Overstay to 25 minutes and do a 5 minute stop at 15'. Ascent rate is 30 fpm with this table
Overstay to 40 minutes and do a 15 minute stop at 15'.

NOTE: I do not recommend overstaying an NDL for any reason! Deco diving is for tech divers with specialized training.

That's why I always carried my NAUI tables and a slate where I had written all of my Adjusted NDLs. This all predates computers, of course.

There is no practical way to back up a computer with tables. A computer can handle a multi-level profile and, in general, tables assume a square profile. Unless you kept a log, you wouldn't know how much RNT you might have. Worse, dives you made with a computer will very likely be far outside the table limits simply because of the multi-level nature of the dives versus the square profile assumptions of the tables.

In my view, if your computer breaks, you are done for the day. Or, you have to stay VERY shallow; but that would be guessing. I don't do guessing...

Richard

 

[Thalassamania]

Here are the Navy tables, reformatted in the circular model that NAUI developed and printed by NOAA, the best of all worlds.

http://www.ntis.gov/pdf/noaa-sample-tables.pdf

 

[Cave Diver]

Or, you have to stay VERY shallow; but that would be guessing. I don't do guessing...

Richard

I agree with everything you've said up this point. Every dive is a guess. Some guesses are just better than others.

 

[impulse]

The thing is, for a recreational diver you absolutely NEVER exceed the NDL. Not ever! I know. But what if my buddy suddenly disappears and I need to search for him thus need to exceed the NDL? Or maybe I will be entangled in a fishing net and that's why I am off the NDL. I can never guess what will happen underwater. So that's why I want to learn the rules for decompression. Is there something bad about this?

You have an awareness of your time under water, you know how deep you are and how deep you have been and you absolutely NEVER exceed the NDL. Just like you don't ever run out of air. I know. But as I said, I would want to be in NDL but some incident would force me to exceed NDL. How can I guess what would go wrong underwater? That's what I fear. That would be something that will happen once in a life time. In that time, if I do not know the rules for decompression I would never need to know again. Clear as mud?

All that said, the 1989 NAUI tables (current, AFAIK) do provide information on safety stops should you overstay the NDL. For example, at 30m
NDL 22 minutes
Overstay to 25 minutes and do a 5 minute stop at 15'. Ascent rate is 30 fpm with this table
Overstay to 40 minutes and do a 15 minute stop at 15'.

NOTE: I do not recommend overstaying an NDL for any reason! Deco diving is for tech divers with specialized training.

That's why I always carried my NAUI tables and a slate where I had written all of my Adjusted NDLs. This all predates computers, of course.

There is no practical way to back up a computer with tables. A computer can handle a multi-level profile and, in general, tables assume a square profile. Unless you kept a log, you wouldn't know how much RNT you might have. Worse, dives you made with a computer will very likely be far outside the table limits simply because of the multi-level nature of the dives versus the square profile assumptions of the tables.

In my view, if your computer breaks, you are done for the day. Or, you have to stay VERY shallow; but that would be guessing. I don't do guessing...

Richard

I am at the very extereme end of the scenario but I can never guess all.

 

[fire_diver]

You don't bust NDL to search for a lost buddy, he may be on the surface, he may be dead on the bottom. You don't hurt yourself in the search for another.

You should never be so close to busting NDL that the minute or so to cut away fishing line would cause you to bust NDL. If so, you are pushing the limits WAY to far.

Decompression isn't rocket surgery, but there is a lot more physiology, planning, and understanding that MUST accompany it. Once you have the knowledge, deco is no big deal. Otherwise you should never be going into to deco for any reason. Only a very poorly skilled diver does that sort of thing.

Seriously, you should be concentrating on being a good diver. Focus on being a good dive buddy, on eliminating "danglies", understanding your SAC and propper gas planning and management.

 

[Cave Diver]

I am at the very extereme end of the scenario but I can never guess all.

If your computer fails, you find yourself tangled up in fishing line and your buddy has gone missing it's time to take up golf. Do a slow ascent to 15' then stay there as long as you still have air.

Seriously, I think you're worrying way too much about the wrong thing. Like fire diver stated, there are other skills that you should probably polish first.

 

[rstofer]

There really needs to be a solid wall between recreational diving and technical diving. I'm not much in favor of the idea that there is a gray area. Recreational diving really means there is no 'overhead'; virtual or physical. A physical overhead is something like wreck penetration or cave diving. There is a structure that prevents your direct ascent to the surface. You have to live long enough to get out before you can try to go up.

A virtual overhead is a mandatory deco stop. Again, this overhead prevents your direct ascent to the surface without injury. Recreational diving is based on the idea that, at any time, you can make a direct ascent to the surface without injury.

Then there is everything else: deco diving, cave diving, solo diving, wreck penetration, etc. There are training programs for all of these. TDL, among others, has classes for these types of dives. They are high risk and involve a lot more equipment.

So that's where I put the wall between recreational diving and technical diving. No overhead; physical or virtual.

There should never be a time you lose track of your buddy. After all, you are losing track of YOUR backup. If your buddy is farther away than you can swim with no breath, he's too far away. Not one breath; no breath! After all, you don't know you're out of air until you get NO breath. A situation that should NEVER occur, by the way.

Entanglement for recreational divers is a potential problem more in the discussion than in reality. But it does happen and there was a recent fatality here in Calif where a diver got entangled in kelp near the surface. Odd how the buddy system broke down.

The NAUI and NOAA tables are useful in that they provide a "what if" recovery plan. But I don't think they should be used for deliberately overstaying an NDL. There just really isn't any good reason to ever be in a position where there is a possibility of overstaying an NDL.

But that's the point. Notice how these discussions always start with the NDLs at 30m or more? That's because the NDL is so short that people want to figure out how to stay longer. Or, more likely, recover from a screw-up. Nobody ever asks about overstaying the NDL at 40'. Yet there is more color and more to see at 40' than at 100'. Why is it that everybody wants to dive deep? Been there, done that, have photos. But my favorite dives have been in the 30-60' region.

The mindset for a recreational diver should be: I'm not going to overstay the NDL, I'm not going to run out of air and I'm not going to lose track of my buddy. There are other considerations but these 3 things will go a long way toward living long enough to collect Social Security. It's nice having that check auto-deposited every month!

Richard

 

[HowardE]

Hello,

I want to carry a decompression table while I dive. I heard that the best one is the US Navy Decompression Table. Where can I find one?

Thanks.

So - essentially - you're saying, "I want to dive without a plan, and want to carry a table in case my computer takes a crap?"

The US Navy Tables are by no means "the best" - they are aggressive tables. If you want to be a recreational diver. Use a recreational dive table. PADI, NAUI, SSI, most recreational dive agencies make a conservative dive table, and have it printed on a waterproof card.

Notice how these discussions always start with the NDLs at 30m or more? That's because the NDL is so short that people want to figure out how to stay longer. Or, more likely, recover from a screw-up. Nobody ever asks about overstaying the NDL at 40'.

Obviously. Nobody asks about overstaying the NDL at 40' because it's over 2 hours.

 

[TMHeimer]

I'm not a tech diver but curious. I assume PADI, NAUI, etc. have tables for deco diving, no? Would these tables be more suited to recreational tech. divers than the Navy ones, which may be more suited to whatever Navy divers do? Also, I've read that the Navy tables are used for both deco and non-deco dives, but have less S.I. credit due to the 120 min. compartment being used for all dives (as opposed the the PADI RDP's 60 min. one). Why would a rec. diver consider using the Navy tables at all then?