Dives I've done

Dive #1:

Descend directly to 85 feet and swim around the wrecked car for about 5 minutes. Ascended to about 45 feet and spent another 15 minutes between 45 and 35 feet. Max depth 85, dive time 20 minutes.

After a 2 hour surface interval grilling some burgers, we get back in the water. We check our computers and plan to stay above 65 feet. Computers say NDL for that depth is about 30 minutes, so we plan for that. We swim around at 60 feet (max depth 62) for about 10 minutes, get bored, and spend the rest of the time in the more interesting debris around 35 feet. Max depth 62 feet, dive time 35 minutes.

If I went according to the [SSI] tables, this puts me well beyond the NDL on the second dive, this would have been 20 minutes.

Assuming planning the dives with our computers was wrong, what was the right way to do the second (or even the first) dive?

Sounds to me like the dives went along just fine.

If I believe that the computer is hosed before the first dive, then I would just fall back to the tables.

If I believed that the computers barfed after/during the first dive then I would run the tables for the bottom time and depth. The second dive would then be a repetitive dive based on the tables.

If the first dive puts me outside of the tables, then I am done diving for either 12 or 24 hours. I can never remember the actual time, but it is on the SSI table.

If the computer were to barf during the 2nd dive I would just make a normal ascent and repeat the procedure for the computer breaking on the first dive.

That being said, both of your dives sound reasonable for computer dives.

You may want to download the dive profile from the computer and run it through a dive planner and see what it says.

Peter

pdoege once bubbled...
Sounds to me like the dives went along just fine.

If I believe that the computer is hosed before the first dive, then I would just fall back to the tables.

If I believed that the computers barfed after/during the first dive then I would run the tables for the bottom time and depth. The second dive would then be a repetitive dive based on the tables.

If the first dive puts me outside of the tables, then I am done diving for either 12 or 24 hours. I can never remember the actual time, but it is on the SSI table.

If the computer were to barf during the 2nd dive I would just make a normal ascent and repeat the procedure for the computer breaking on the first dive.

That being said, both of your dives sound reasonable for computer dives.

You may want to download the dive profile from the computer and run it through a dive planner and see what it says.

Peter

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The dives went fine, no incidents, and all of our computers more or less agreed on everything.

you are experiencing the benefit of diving with a computer.

From what I can tell with my limited computer use most computer dives will take you off the tables or very close to it if you stay for most of the time that the computer will allow. This is due to the computers ability to calculate the dive every so many seconds or whatever its set to do. With the table you are only working off the max depth for whatever time you logged.

I just ran that profile with my handy PADI tables like it was a multi-level dive, kind of, counting each new level like it was a new dive with 0 SI and this is what I got:

Dive #1:
90' for 5 mins. PG B
0 SI
50' for15 mins. PG H

2 hour SI PG A

Dive#2:
70' for 10 mins. PG E
0 SI
40' for 35 mins. PG O

All within the tables and done rather conservatively, might I add.

Rachel

biscuit7 once bubbled...
I just ran that profile with my handy PADI tables like it was a multi-level dive, kind of, counting each new level like it was a new dive with 0 SI and this is what I got:

Dive #1:
90' for 5 mins. PG B
0 SI
50' for15 mins. PG H

2 hour SI PG A

Dive#2:
70' for 10 mins. PG E
0 SI
40' for 35 mins. PG O

All within the tables and done rather conservatively, might I add.

Rachel

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Running a multi-level dive as two dives with 0 SI? Is that.. right? Seems that since the BT's assume a 30 fpm ascent, it won't be quite accurate. Interesting, though, I'll keep it in mind.

you are experiencing the benefit of diving with a computer.

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That's the point. My question is how would a DIR guy do and plan these dives? Whip out the PADI table and plan for 0 SI?

jonnythan once bubbled...
My question is how would a DIR guy do and plan these dives? Whip out the PADI table and plan for 0 SI?

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The answer frequently posted on Scubaboard is that you should take a DIR-F course and find out how to do it. They say it is simple, but I haven't yet been able to find a coherent description.

As you dive more, you will get a feel for what profiles are acceptable. Alternatively, download a program such as GAP (www.gap-software.com) and play around with different dive profiles. Or download a simulator for your computer and play "what if". Programs, such as GAP, that show calculated loadings of compartments are particularly useful. You might even want to check out the validity of the oft repeated statement that Buhlmann based computers and programs penalize you for deep stops and slow ascents. You will see that while there is some truth to that, deep stops and slow ascents also reduce the loading in the fast tissues, the ones most likely to be involved in type II DCS. In my Oceanic computers, the tissue loading bargraph will frequently go back into the green while I'm doing my deep stops and slow ascent.

The 0 SI calculations using the PADI RDP may not be technically correct since they have an ascent time built into each NDL, but in practice it gives pretty much the same asnwers as GAP, Decoplanner, or Z-Plan. In other words, the PADI RDP is suitable as a sanity check of what your computer is telling you, and suitable for making an approximate multilevel plan.

My attitude towards computers is that they give me both the depth/time info, and also additional information that I can use, and that it would be incredibly stupid for me to turn off the NDL calculations and use it solely as a depth gauge and timer. At the same time, as in the famous Ronald Reagan quote: "Trust, but verify". Another point that seems to be overlooked in the anti-computer discussions is that supposedly you have a buddy --- it is highly unlikely to have two computers simultaneously malfunction (Unless they were both escapees from that lot of 300 that Uwatec put out with bad software).

Charlie99 once bubbled...
The answer frequently posted on Scubaboard is that you should take a DIR-F course and find out how to do it. They say it is simple, but I haven't yet been able to find a coherent description.

As you dive more, you will get a feel for what profiles are acceptable.

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I heat that a lot. However, if you're a rec diver and you listen to the DIR guys, you don't need a computer. If all you have are the tables, how will you ever learn what are good profiles and what are bad profiles?

Thanks for the GAP link.

I would not have thought twice about that series of dives whether I was using a computer or not. Combined they seem conservative to me.

I dive my computer rather than the tables because it is conservative and I'm older than most divers out there (but not old enough!). I commonly do several dives a day to the 80-100 ft range and also reverse profile dives (being a friend of Jon Hardy, now deceased, who helped pioneer them).

The tables would probably never let me do the dives I do, so I value the computer for its ability to integrate real-time data against the algorithms.

Dr. Bill

jonnythan once bubbled...
how will you ever learn what are good profiles and what are bad profiles?

Thanks for the GAP link.

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When you play with GAP, a couple of key variables are the Hi and Lo Gradient Factors (under defaults, then conservatism). Putting the Lo Gradient factor to something like 0.2 will force deep stops. You can adjust the Hi Gradient factor to get the same answers as your particular computer. A 1.0 gives answers close to my Oceanic computer, plugging in 0.85 gives answers that match up pretty closely with bringing the Oceanic TLBG back into the green before ascending. Someone else may have already figured out what matches up with Suunto.

If you put in 0.2/0.85 as gradient factors, plug in a 80' 40 minute dive and click on ascent, the program will calculate a set of deep stops. That general curve is the sort of general curve you should follow on any ascent (in this case 1@40, 1@30, 4@20, 7@10), even if the overall ascent is shorter.

GAP also calculates total gas consumption, using whatever SAC you plug in. This can quickly tell you whether a "what if" profile you entered is one that you might reasonably encounter using whatever tank you use.

Enjoy.

Charlie