Skirting the Tables

[NSDiver]

This might not apply to everyone, since I'm sure a lot of you use computers instead of strictly adhering to tables, but here goes. For some background, I was certified a few weeks ago and was on dive 10 today in Haymarket, VA. I use an OMS bottom timer and NAUI air tables for NDLs.

It was my second dive of the day, I started in group E. Planned depth was 50 feet, which would give an AMDT of 42 minutes. For 60 feet, AMDT would be 25 minutes (not including any safety stop).

For most of the dive, our depth was in the 40-45 foot range. However, at one point I dropped to 52 feet for a few seconds (literally). Towards the end of the dive, having already seen what we wanted to see, we spent several minutes watching some OW students at a 30' platform. At 40 minutes we were at 15 feet doing a safety stop, and surfaced 43 minutes after submerging.

Strictly adhering to practices taught by (I think) all the agencies, I should have calculated this as a 60 foot dive and come up 15 minutes earlier. However, I rationalized that the stay at 52 feet was brief enough (and most of the dive shallow enough) that the dive could be calculated as a 50 foot dive.

Though I'm safe (not bent) - was this bad practice? Perhaps I should have stayed at safety stop depth for a couple more minutes (the schedule on the NAUI tables calls for a 7 minute stop)? Thoughts/experiences if you have any...

 

[Jeff Toorish]

So, on your tenth dive you are trying to get around the tables...is that what you are asking?

Jeff

 

[Uncle Pug]

Well, if you know what you are doing you can multilevel dives and use the shallow portion to decompress from the deep portion and come out cleaner (free of inert gas) than if you followed either a table or a computer.

If you don't know what you are doing you could bend yourself.

Best bet for you as a new diver is to plan a dive using tables and then stick with the plan. It would also be a good time to start researching decompression theory.

 

[NSDiver]

So, on your tenth dive you are trying to get around the tables...is that what you are asking?

Jeff

No - I just rounded down instead of up because I viewed my 52 foot depth stay as insignificant. Doing the dive, I understood that I would be fine because it was literally less than five seconds - but I think it's probably bad practice because one could start to rationalize even more (i.e. 'only five minutes past my planned depth is fine' - when it's not).

 

[Uncle Pug]

The difference between 50' and 52' is smaller than the margin of error on your depth gauge. A little common sense goes a long way.

If your head happens to spend most of the time at 50' and your feet are at 52' will you get a toe bend?

 

[Don Burke]

Though I'm safe (not bent) - was this bad practice? Perhaps I should have stayed at safety stop depth for a couple more minutes (the schedule on the NAUI tables calls for a 7 minute stop)? Thoughts/experiences if you have any...

By any measure, this is an abuse of the algorithm.

You had 42 minutes of bottom time to play with, used up 40 of it with a dive with a deeper excursion, and then bailed yourself out with a 3 minute safety stop, which may have actually been a required decompression stop if the true profile was considered.

With the uncertainty of the tables, trying this again could result in Type I DCS.

In fact, you may have taken a hit but are in denial about it.

This is the worst idea I have heard in a while.

 

[PerroneFord]

Exactly Pug. People bounce more than 2 feet on deco... I don't see it as a big deal either. VPlanner didn't even indicate a safety stop with a 45 minute SI.

However, it would be good if you learned some deco theory as UP indicated so you have a better understanding of what you CAN do safely.

 

[redacted]

There are a number of saftey margins built into tables and most computers. 2 ft and 1 minute is PROBABLY OK. And maybe 4 ft and 2 minutes will work next time - maybe not. But if there is no compelling reason to do it, why temp fate. There is seldon a good reason to push the edge, especially with a limited gas supply that restricts your compensating options.

 

[dmmike]

IMHO, they make tabels for a reason, and they have rules for special conditions for a reason. If you are not going to follow the rules you have to accept what happens. I know you said it was only 2 more feet for a couple of seconds, but now is the time to create good safe habits and to include for such a error during your dive plan. With only 10 dives you should be diving well within the limits.

 

[Tigern]

to echo everyone else..stick with what you were taught. If you don't practice what you were taught and keep rationalizing then one day you are going to rationalize yourself to death. Either learn how to plan multi-level dives or buy a computer. But remember that most computers will still allow you to dive in a way that is not safe. ALWAYS back up any calculations your computer does for you with a table.
And of course listen to the tried and true advice of "PLAN your dive, DIVE your plan."