Skirting the Tables

[artw]

watch it Jim. you may get someone killed with that advice. Don't you know you are supposed to spend hundreds of dollars on a computer and trust your life to it? Sheesh.

 

[JimC]

You need to coke alert this stuff, Art.

You owe Exit Certified a new keyboard.

 

[Sideband]

When I was certified we were told to plan the dive using our intended max depth and to then plan it again using the next greater depth. Is that not taught any more?

A question for those that are saying the drop below 50' can be ignored.
At what point would that dip below planned depth be consequential? 3 feet? 5 feet? What if it was 15 seconds, or for 30 seconds? How much can you violate the tables before you consider it a table violation?

Joe

 

[PerroneFord]

When I was certified we were told to plan the dive using our intended max depth and to then plan it again using the next greater depth. Is that not taught any more?

A question for those that are saying the drop below 50' can be ignored.
At what point would that dip below planned depth be consequential? 3 feet? 5 feet? What if it was 15 seconds, or for 30 seconds? How much can you violate the tables before you consider it a table violation?

Joe

I don't know what is taught anymore. Quite honestly, I don't think it matters what's on the table. What matters is what my body tells me. The common tables were outdated 20 years ago. The world knows this. Why we stick to them is beyond me. I give NAUI a ton of credit for being progressive and revising.

As for how deep and how long you can stay under the planned dive before it's a table violation, that's simple. ZERO. Going below the magic number puts you in conflict immediately. If you're asking how long you can stay or how deep you can go before worrying about DCS issues, then we need more information about the first dive to make an educated decision. It's quite possible he could have stayed 10 minutes at 60 feet and been just fine with the safety stop he did, or even no safety stop. Or maybe that would have put him into mandatory deco for 10 minutes at 15 feet.

 

[in_cavediver]

When I was certified we were told to plan the dive using our intended max depth and to then plan it again using the next greater depth. Is that not taught any more?

A question for those that are saying the drop below 50' can be ignored.
At what point would that dip below planned depth be consequential? 3 feet? 5 feet? What if it was 15 seconds, or for 30 seconds? How much can you violate the tables before you consider it a table violation?

Joe

I'll bite. For me, a short drop below 50' say up to a minute or so no deeper than 52-53 feet, I would ignore if I planned to spend over a third of the dive time above 30 feet. I personally am far more concerned with the shape of my profile than the number on a table. That said, I have training far in excess of the basic OW class. I have spent numerous hours playing with deco software and I have sat down and derived and calculated basic dive tables (straight Buehlmann algorithm).

That said, I would NEVER recommend doing it to someone. Divers should know and understand the tools they use and use them correctly.

 

[JustinW]

Hi,

remember that the tables were made using people in relative good shape. I think that when planning, it is better to keep a security margin between the limits and the actual dive... just in case something happens and force you to stay a bit longer. Your dive was probably safe if you calculate it as a multi-level dive... but you did not.

If you feel confident in the water now and have taken a bit of experience, i strongly suggest taking an advanced cours with multi-level specialty. but even then, you could be tempted to bend the rules and this time, your security margin is reduced. So the first thing to learn for you is to respect the rules and the tables you are qualified
to use.

I always prefer to plan my dives with a security margin, this way, after the dive i have fun and remember the good dive instead of being nervous and extra attentive to DCS symptoms.

dive safely

Well stated.

 

[markfm]

"What matters is what my body tells me."
THAT is spooky. I know you didn't intend it, but it sounds like an "I know better, to heck with what is taught" mentality which is kind of frightening. Back in the old days, when men were men and divers got bent, that's the best folks could do, see what didn't kill them or their friends. The research which went into developing the tables, and computer algorithms, was done just to get rid of that "wing it" approach.

As an admittedly pretty new diver, what I was taught is that we aren't supposed to go to the table NDLs, at least that is what is in the PADI course, stressed multiple ways, that it's just not smart to push the limits. Maybe NAUI is different, that they say it's no problem, go right to the edge on the tables.

Any answer other than "you're probably fine, but it's not a swift move, take more classes, get a wheel and/or buy a computer if you want to extend the envelope" seems inappropriate.

 

[PerroneFord]

Mark, you'll note that the vast majority of divers here gave the response that you indicated was appropriate, and only railed against the more hardline stances.

As to me, I was PADI trained. Don't be frightened by my response. You probably read it a LOT differently than I intended. The idea of being conservative sits well with me. I'm not 20 years old anymore. However, the idea of doing something because this plastic card says it's safe does NOT sit well with me. I listened in HORROR a couple of weeks ago as a PADI AOW diver in our club meeting casually described his diving *6* times one day while on a liveaboard. To me, that's asking for trouble. So take my comments to mean this:

I will dive to what *I* think is safe. My dives will often be off the NDL tables, but will follow conservative calculations for that type of diving. That often gives profiles that look FAR safer than what is printed on the NDL tables for most agencies. Have you ever wondered about the NDL tables that let you go to 130ft, then ZIP up to 15 feet for your safety stop? That is outside the parameters of what I consider safe diving. And the SI for some of topside waits is incredible.. in some cases giving over 3 hours of leeway. So I listen to my body. If my SI is supposed to be 45 minutes, and at that 45 minute mark I am still tired, I am NOT getting back in the water, I don't care what the plastic card or the electronic gizmo says.

"What matters is what my body tells me."
THAT is spooky. I know you didn't intend it, but it sounds like an "I know better, to heck with what is taught" mentality which is kind of frightening. Back in the old days, when men were men and divers got bent, that's the best folks could do, see what didn't kill them or their friends. The research which went into developing the tables, and computer algorithms, was done just to get rid of that "wing it" approach.

As an admittedly pretty new diver, what I was taught is that we aren't supposed to go to the table NDLs, at least that is what is in the PADI course, stressed multiple ways, that it's just not smart to push the limits. Maybe NAUI is different, that they say it's no problem, go right to the edge on the tables.

Any answer other than "you're probably fine, but it's not a swift move, take more classes, get a wheel and/or buy a computer if you want to extend the envelope" seems inappropriate.

 

[Diver0001]

I should have calculated this as a 60 foot dive and come up 15 minutes earlier.

It sounds like you already know the answer to your own question. It was a 60ft dive. Safety first.

R..

 

[Diver0001]

What matters is what my body tells me.

What if your body is telling you that you're horribly bent? It won't tell you that until it's too late. It sounds like you're just waiting for the pain and concluding after the fact that you're not bent. Unless you meant something else by this I'm going to get all worried about you.

The common tables were outdated 20 years ago. The world knows this. Why we stick to them is beyond me.

20 years ago almost nobody was diving with computers and the ones that were available got neat little nick-names like "bend-o-matic". Tables worked 20 years ago and they still work. Computers make them less relevant for puddlestomping than they used to be but that's about it.

It's quite possible he could have stayed 10 minutes at 60 feet and been just fine with the safety stop he did, or even no safety stop. Or maybe that would have put him into mandatory deco for 10 minutes at 15 feet.

"quite possible" .... "maybe" .... it's the very fact that he's guessing that has people concerned. Guessing isn't the way to plan dives. There are better ways to extend your exposure safely. Don't you think?

R..