Your Gradient Factors?

[jale]

Seems to be 2 thoughts on average depth...
One is on planning your deco as rjack mentioned wrt tables and ratio deco.
And there is using the end of dive (descent, bottom phase and deco) average depth.
Which ever GF I use, I feel best when I exit the water when my total average depth is around 21m.....
If you change your GF, you change the shape of your deco. That can also affect your average depth for the total dive...
Similar in construct to ratio deco, it is a tool one can use to gauge, ‘have I done enough deco?’
_R

Yes exactly.
The first type, has been used within some diving groups. It was quite "popular" in Europe before we got cheap computer. The idea was to chunk the table into small linear bits and to play within a set of limits. Crazy? Maybe but it works for some profiles.
The second type is a way to have GF surface when your computer doesn't have this function. Like Ralph, I got my personal settings.
As said, these are a good ways to gauge if you are happy with your GF choices.

 

[Blackcrusader]

All right, as a recreational diver you drop to 130' for 1 minute at depth, ascend to 60' and stay at 60' for 45 minutes before slowly ascending to a safety stop at 15' for 5 minutes. When you surface will you immediatly die from DCS caused by your 46 minute 130' dive or do you have enough time to stow your gear, eat dinner and have a few beers before you die after having caused an accident while driving drunk?
That's a simple explanation of averaging depth during a dive. Average depths much greater than 60 or 70' end up causing a lot of pain and keep the chamber operators in business.

Michael

Well when I do dive to 40m I do not exceed NDL and will do a slow staying normally around 2 - 4 mins to NDL till around 20m. Then spend some time at 20m then slowly ascend for the rest of the dive. I will often get to 6m for my preset safety stop level and then mostly spend another 10 - 15 minutes plus at 5m dawdling on a reef taking in the view and maybe snapping off a few photos.

 

[tursiops]

All right, as a recreational diver you drop to 130' for 1 minute at depth, ascend to 60' and stay at 60' for 45 minutes before slowly ascending to a safety stop at 15' for 5 minutes. When you surface will you immediatly die from DCS caused by your 46 minute 130' dive or do you have enough time to stow your gear, eat dinner and have a few beers before you die after having caused an accident while driving drunk?
That's a simple explanation of averaging depth during a dive. Average depths much greater than 60 or 70' end up causing a lot of pain and keep the chamber operators in business.

Michael

Now you are just being silly, or obtuse. Your last sentence is certainly true. But the issue is using an average depth with a table. The nitrogen uptake and off-gassing that goes into making a table uses depth.....ambient pressure if you will....not some average depth. But you know that. Don't you?

 

[michael-fisch]

try to explain it to PADI, 30+ years ago they were teaching the RDP (Wheel) which was nothing more than an integration of average depth.

Michael

 

[Blackcrusader]

Now you are just being silly, or obtuse. Your last sentence is certainly true. But the issue is using an average depth with a table. The nitrogen uptake and off-gassing that goes into making a table uses depth.....ambient pressure if you will....not some average depth. But you know that. Don't you?

I do not see why a diver would dive to 130 feet for only one minute as that's not even close to exceeding NDL, then just ascending to 60 feet. I tend to get to around 2 mins to NDL and ride the 2 minute NDL back to around 20m on a slow ascent. No need to rush from 40m to 20m. OK so yes I've been to 2 mins to NDL at 20m after a slow ascent but then if you want a longer dive time just ascend to 15m.

Question, how many recreational divers really change the default GF even in a Perdix or other dive computer? I could ask a lot of OW or AOW or Rescue and even some DM's and they do not understand gradient factors. This year I dove with a DM in Taiwan. She had a Perdix and didn't even know she could change the screen settings or have her Perdix show CLEAR plus added time after the safety stop. She didn't know about GF settings either so was on the most conservative setting which is the default. Yet here she was a PADI DM taking out mainly OW and AOW divers on dives. I helped her setup her Perdix to have things on the screen where she wanted them. Then she asks me what TTS means? I explained time to surface from that point of the dive.

She was a nice lass and really wanted to learn more.

 

[rjack321]

LOL. So we've gone from "widespread use of average depth with tables" to some guys in the Puget sound area, based on Hamilton's tables for trimix, averaging 220 and 240 and getting 230. OK. And Exley averaging depth in caves. OK.

My skepticism remains. In general, tables are NOT designed for use with average depth, and those few who have decided to damn the torpedos and do so anyway are asking for trouble.

Sighs, if you ever actually saw Hamilton's tables you might actually have a clue what (trimix) deco was like 15-25 years ago. Commercial divers had very expensive proprietary tables, the rest winged it and guessed and experimented with how much deco was required based on EAD and various suppositions about helium being worse than air or better than air. Depth averaging was just a different slice of the axe on the guesses

 

[tursiops]

try to explain it to PADI, 30+ years ago they were teaching the RDP (Wheel) which was nothing more than an integration of average depth.

Michael

No, it wasn't. It was based on the same data as the table, but allowing for only partial off-gassing to get up to the next depth level.
http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/4228/DSAT_1994.pdf
https://www.scribd.com/document/267196229/DivePlanner-DSAT-1994

 

[tursiops]

Sighs, if you ever actually saw Hamilton's tables you might actually have a clue what (trimix) deco was like 15-25 years ago. Commercial divers had very expensive proprietary tables, the rest winged it and guessed and experimented with how much deco was required based on EAD and various suppositions about helium being worse than air or better than air. Depth averaging was just a different slice of the axe on the guesses

Nothing wrong with Hamilton's tables, they were impressive.
But they are not the point.
The point is that most of the recreational diving world was NOT doing trimix dives using Hamilton's tables.
Most of diving world (pre-computers) was using tables, like Navy or others that use depth, not average depth.

 

[Ayisha]

I'm sorry, but I am unaware of any widespread use of average depth while using tables. All the tables I am aware of are based on maximum depth. Our "original" tables were from the Navy....no average depth used there...

They might not be widespread, but GUE tables and formulas involve average depth.

 

[tursiops]

They might not be widespread, but GUE tables and formulas involve average depth.

The GUE tables I've seen do not use average depth. Has something changed?