Diving with computer in gauge mode/using bottom timer

[WhiteSands]

Hi,
I've only been briefly introduced to this concept so far. So we have to know how to reconstruct the NDL tables for both air & nitrox to get the NDL times for each depth.

After that what do you do? Do you use max or average depth, or current depth to get the NDL times from the table? Do you write the tables in your wetnotes?

Could someone kindly walk me through a typical rec dive scenario where you may be at different levels and how this works?

Thanks!

 

[PfcAJ]

Tricky question. First things first, deco is not exact science. That said...

I keep tabs on my depth throughout the dive and use the 'average depth' method. NDLs are pretty easy to remember.
(depth)+(no deco limit)=120, or got 32% nitrox (depth)+(no deco limit)=130. That rule gets you pretty close.

For repetitive dives, some folks have came up with little tricks and whatnot, but I just look at the NAUI table, see what my NDLs are for whatever depth I'm planning, and go dive. I also carry a Steinhoff table in my wetnotes (but I rarely look at it).

The 'average depth' method is a bit more aggressive than the 'max depth' square profile method. Imo, with a proper minimum deco style ascent, the average depth method works great and is plenty reasonable for recreational dives up to ~100ft.

 

[decompression]

+1 for min deco.

 

[eelnoraa]

What AJ said for rule of thumb. On top of that, I photocopied a GUE 32% table, laminated and put into my wetnote front cover. GUE table include a residual loading portion for repetitive dives. I use average depth for the table.

 

[TSandM]

I was taught, for repetitive dives, that if the SI is less than an hour, you double the shallow stops (30 feet and up). That's what I do, and so far, it has worked very well.

 

[chrpai]

I've googled the subject of GUE min deco and I've found multiple tables with different NDLs. Is there an official set or are people taught to come up with their own gradient factors and generate their own?

Reference 1:

Minimum deco limits

Reference 2:

http://dir-diver.com/pdf/minimum-deco-tables/english_imperial_A.pdf


My other question would be, in reference 2 all of the NDL's exceed the PADI RDP numbers. It's the next block over that seems to track PADI the most. In reference #1 there's not air depth substitutions as in reference #1.

Reference #1 seems to have 12 hour washout while #2 has 4 hours and PADI has 6 hours.

I'm curious because I'm going on a BlackBeards trip next week where 32% isn't available. I'll have a computer and a bottom timer and I wanted to see if I could plan my dives using min deco instead of PADI RDP and use my computer as a backup.

 

[rivers]

Ratio Deco for Recreational Dives | DIR Theory

 

[WhiteSands]

Firstly thank you everyone for contributing.

Some questions I have. Chrpai posted a GUE table that shows Group letters depending on your SI. Do GUE divers currently still use these letter groupings to determine N2 loading and calculating subsequent NDL?

What I was taught is similar to what TS&M posted. If you do your stops at 1/2 max depth for 1 min and 1 min for every 3m after, SI is fixed at 1 hour. After 1 hr you are considered to have totally off gassed and can consider the next dive as if it were your 1st of the day. If SI less than 1 hour then on the next dive do all stops for 2 mins.

Comments on this welcome.

---------- Post added September 3rd, 2013 at 11:16 PM ----------

I am sorry but I still have no idea how to use the Min deco table for a rec dive.

Min deco table for air as follows:

12m - 170min
15m - 60min
18m - 50min
21m - 35min
24m - 30min
27m - 25min
30m - 20min

E.g. I start the dive at 30m. Following the table I must not stay longer than 20min. If during the dive I ascend to 25m then do I now:

- use my current depth and read off the table? So timer must not exceed 30min?
- use average depth to read off the table?

After my total dive time reaches 30 min i ascend to 18m. So now I can stay down for a total of 50min?

This does not seem right to me because the table assumes I can stay for 50min at 18m if I had spent the entire time at 18m. However I have already spent 20min at 30m and another 10min at 25m. So using average depth seems to make more sense?

 

[rambaldi]

I've googled the subject of GUE min deco and I've found multiple tables with different NDLs. Is there an official set or are people taught to come up with their own gradient factors and generate their own?

Reference 1:

Minimum deco limits

Reference 2:

http://dir-diver.com/pdf/minimum-deco-tables/english_imperial_A.pdf


My other question would be, in reference 2 all of the NDL's exceed the PADI RDP numbers. It's the next block over that seems to track PADI the most. In reference #1 there's not air depth substitutions as in reference #1.

Reference #1 seems to have 12 hour washout while #2 has 4 hours and PADI has 6 hours.

I'm curious because I'm going on a BlackBeards trip next week where 32% isn't available. I'll have a computer and a bottom timer and I wanted to see if I could plan my dives using min deco instead of PADI RDP and use my computer as a backup.

Starting Fundies tonight, when I was going through course materiels Ref#1 was in there and remember it is a 32% table. There are a couple other pages to it though which cover things like basic assumptions (Min Deco ascent etc.) and cover other general rules of thumb to follow for making things simpler. (50% for < 2 hours SI or something like that, when diving 30 at 30).

I am sorry but I still have no idea how to use the Min deco table for a rec dive.

Min deco table for air as follows:

12m - 170min
15m - 60min
18m - 50min
21m - 35min
24m - 30min
27m - 25min
30m - 20min

E.g. I start the dive at 30m. Following the table I must not stay longer than 20min. If during the dive I ascend to 25m then do I now:

- use my current depth and read off the table? So timer must not exceed 30min?
- use average depth to read off the table?

After my total dive time reaches 30 min i ascend to 18m. So now I can stay down for a total of 50min?

This does not seem right to me because the table assumes I can stay for 50min at 18m if I had spent the entire time at 18m. However I have already spent 20min at 30m and another 10min at 25m. So using average depth seems to make more sense?

I haven't gone through the class yet, but the people i have been diving with always use average depth. So say you did 5 minutes at 30 then 5 minutes 24, you would treat it as 10 minutes at 27.

 

[WhiteSands]

Ratio Deco for Recreational Dives | DIR Theory

Hi Rivers thanks for that article. It explains min deco but I think in the examples given it assumes diving at a constant depth, ie 30m or 25m.

I was reading the 2nd last para carefully:

On 32% and using the minimum decompression ascent I have described, you can do 30 minutes at 30 metres. For every 5 metres shallower you are, you can do an extra 15 minutes.

I thought its saying a diver can stay for 30min at 30m and another 15mins at 25m for a total dive time of 30+15=45min but I doubt I read that correctly.

---------- Post added September 21st, 2013 at 01:59 PM ----------

I haven't gone through the class yet, but the people i have been diving with always use average depth. So say you did 5 minutes at 30 then 5 minutes 24, you would treat it as 10 minutes at 27.

Yes I think that makes sense. Thanks.