Average depth calculation

[wedivebc]

Hi Dave,

Just as Karen said there are many people, myself included,who use depth averaging for multi-level dives. We find it works great if executed properly, but is not something someone should just jump in and do without training. There are many reef structures that we like to explore that are in the 200'+ range. However, the only way to dive them is with either a boat, or on scooters. Since we use scooters it takes us about 25-30 minutes (sometimes more) just to get where we're going. Then there's the time spent exploring, the trip back and the deco that must be completed. 5thd-x put a PDF out that gives a little bit of info on it, if you haven't downloaded it yet you may want to look into it.

Link doesn't seem to work.

 

[JeffG]

Link doesn't seem to work.

http://www.5thd-x.com/xducation/pdf/ratiodeco.pdf

 

[CIBDiving]

The Link into 5thdxdoesn'talways work either It took a lot of tries to get that pdf.
It's about as clear as MUD as far as a real explaination also.
drop me a PM with an email address and I'll send it to you, if you wish.

 

[JeffG]

It's about as clear as MUD as far as a real explaination also.

Yep...Its not an easy read. LOL

 

[Diver0001]

I know you do a lot of deco diving and use these programs.

I mean run various multi-level profiles compared with an "averaged" profile for a limited depth range and see what you come up with.

Checking every five minutes you could theoretically be way off.

For example. You could register

5min - 100ft
10 - 60ft
15 - 65
20 - 40

average depth looks like about 65ft

When you really dove

8min - 100ft
2min ascent to 60
descend to 85 for 3 min
return to 60 and register time at 65
remain at 60 for another 3 min and ascend to 40

which probably puts your average depth at about 80ft

There are other examples too. Lamont has a really good one but I don't remember it off the top of my head.

You'll probably say -- "but good DIR divers have the discipline to not dive like that". I'm sure that's true but if you have the discipline then it's just as easy -- and in my mind gives you a lot more freedom and peace of mind -- to work with tables.

Working with tables is really incredibly easy. You only have to remember a couple of numbers: turn time, turn pressure, maximum depth and the time at which you need to start your ascent. If you stay within these parameters, your dive is on track and you *know* it's on track; there is no need to keep checking details.

Moreover I personally think that if you're going to work with depth averaging you're much better off to use a computer, which samples depth every 2 seconds or so. Modern computers are perfectly adequate (if used intelligently) unless you're making extremely deep dives, (over the 200-250 metre range) at which point, divers are getting all kinds of physiological problems regardless of which model they use.

My conclusion would be that I don't see any value in using depth averaging. In my mind it only creates (a) a complication by making you perform unnecessary tasks (namely, one extra task every 5 min) and (b) an additional problem in the possibility of human error or inaccuracy and (c) doesn't solve any problems as compared to other perfectly adequate techniques (tables or computers). Given the choices I'd go with tables every time.

R..

 

[*Floater*]

Checking every five minutes you could theoretically be way off.

For example. You could register

5min - 100ft
10 - 60ft
15 - 65
20 - 40

average depth looks like about 65ft

When you really dove

8min - 100ft
2min ascent to 60
descend to 85 for 3 min
return to 60 and register time at 65
remain at 60 for another 3 min and ascend to 40

which probably puts your average depth at about 80ft

In that case I would have just marked 100ft on for the 10th minute sample. The point being that you can use your head too when executing this procedure, rather than doing it robotically, and during the tenth min you can still remember where you were 2 min ago.

There are other examples too. Lamont has a really good one but I don't remember it off the top of my head.

You'll probably say -- "but good DIR divers have the discipline to not dive like that". I'm sure that's true but if you have the discipline then it's just as easy -- and in my mind gives you a lot more freedom and peace of mind -- to work with tables.

Working with tables is really incredibly easy. You only have to remember a couple of numbers: turn time, turn pressure, maximum depth and the time at which you need to start your ascent. If you stay within these parameters, your dive is on track and you *know* it's on track; there is no need to keep checking details.

Moreover I personally think that if you're going to work with depth averaging you're much better off to use a computer, which samples depth every 2 seconds or so. Modern computers are perfectly adequate (if used intelligently) unless you're making extremely deep dives, (over the 200-250 metre range) at which point, divers are getting all kinds of physiological problems regardless of which model they use.

My conclusion would be that I don't see any value in using depth averaging. In my mind it only creates (a) a complication by making you perform unnecessary tasks (namely, one extra task every 5 min) and (b) an additional problem in the possibility of human error or inaccuracy and (c) doesn't solve any problems as compared to other perfectly adequate techniques (tables or computers). Given the choices I'd go with tables every time.

R..

Have you tried it? Sure it adds task loading, but it's not a big deal once you get used to it - besides, I hold off on it if I'm doing something else at the time, and just make a mental note of the depth for later use/recording. Keeping track of average depth also made me think more about my dives more in a nice way and made me more aware of my profiles.

As for the table thing you talked about I'm not sure what it is. I wasn't taught how to use tables for multilivel dives except with depth averaging so I can't comment on that. For all I know your method may be better.

 

[wedivebc]

As for the table thing you talked about I'm not sure what it is. I wasn't taught how to use tables for multilivel dives except with depth averaging so I can't comment on that. For all I know your method may be better.

When you talk about depth averaging and tables you are not talking about ratio deco are you?
I must be really thick because I am not getting it. I read 5th-d write-up on ratio deco and it does not use tables that I can see.
So for the love of god will someone please tell me how to average your depth and how it relates to tables?

 

[Diver0001]

....snip.... I hold off on it if I'm doing something else at the time, and just make a mental note of the depth for later use/recording.

With all due respect, that sounds like a good way to turn an already marginal technique into a gut feeling..... not for me.

Keeping track of average depth also made me think more about my dives more in a nice way and made me more aware of my profiles.

Well, there's nothing wrong with that I guess.

As for the table thing you talked about I'm not sure what it is. I wasn't taught how to use tables for multilivel dives except with depth averaging so I can't comment on that. For all I know your method may be better.

Well, I use what I feel right with. So do you.

R..

 

[*Floater*]

When you talk about depth averaging and tables you are not talking about ratio deco are you?
I must be really thick because I am not getting it. I read 5th-d write-up on ratio deco and it does not use tables that I can see.
So for the love of god will someone please tell me how to average your depth and how it relates to tables?

I have some tables for recreational diving, for example the EAN32 table I use is this:

depth time
60 90
70 60
80 45
90 35
100 30
110 25

Then I just keep track of my average depth and use it with this table. So if I spend 25 min at 100 and 25 min at 60, then that would give 50 min at 80 ft, which is 5 min over the limit, so I might add a 5 min to my safety stops for example. However, some others use 50min for the 80ft limit so it doesn't really matter. I also ascend at 10ft/min starting from 80% of ATA; 30 sec ascent, 30 sec pause per 10 ft, and extend the pauses to 1 min stops at 30/20/10 ft, or might do 2 min stops in this particular example as I stayed 5 min over the limit. It's not an exact science, and this is just what I do. I don't know what others do, nor do I recommend anyone else use this, and I may change how I do this in future anyway.

 

[wedivebc]

I have some tables for recreational diving, for example the EAN32 table I use is this:

depth time
60 90
70 60
80 45
90 35
100 30
110 25

Then I just keep track of my average depth and use it with this table. So if I spend 25 min at 100 and 25 min at 60, then that would give 50 min at 80 ft, which is 5 min over the limit, so I might add a 5 min to my safety stops for example. However, some others use 50min for the 80ft limit so it doesn't really matter. I also ascend at 10ft/min starting from 80% of ATA; 30 sec ascent, 30 sec pause per 10 ft, and extend the pauses to 1 min stops at 30/20/10 ft, or might do 2 min stops in this particular example as I stayed 5 min over the limit. It's not an exact science, and this is just what I do. I don't know what others do, nor do I recommend anyone else use this, and I may change how I do this in future anyway.

The problem is that technique is OK for a nice easy dive like you described but if you apply depth averaging to something more agressive see what happens:
here is a dive with 2 level components using v-planner

Dec to 200ft (4) Trimix 15/55 50ft/min descent.
Dec to 250ft (4) Trimix 15/55 60ft/min descent.
Level 250ft 5:10 (10) Trimix 15/55 1.28 ppO2, 74ft ead, 94ft end
Asc to 200ft (11) Trimix 15/55 -30ft/min ascent.
Level 200ft 10:00 (21) Trimix 15/55 1.06 ppO2, 55ft ead, 72ft end
Asc to 130ft (24) Trimix 15/55 -30ft/min ascent.
Stop at 130ft 1:00 (25) Trimix 15/55 0.74 ppO2, 29ft ead, 40ft end
Stop at 120ft 1:00 (26) Trimix 15/55 0.69 ppO2, 25ft ead, 36ft end
Stop at 110ft 1:00 (27) Trimix 15/55 0.65 ppO2, 21ft ead, 31ft end
Stop at 100ft 1:00 (28) Trimix 15/55 0.60 ppO2, 17ft ead, 27ft end
Stop at 90ft 2:00 (30) Trimix 15/55 0.56 ppO2, 14ft ead, 22ft end
Stop at 80ft 2:00 (32) Trimix 15/55 0.51 ppO2, 10ft ead, 18ft end
Stop at 70ft 2:00 (34) Nitrox 50 1.56 ppO2, 32ft ead
Stop at 60ft 2:00 (36) Nitrox 50 1.41 ppO2, 26ft ead
Stop at 50ft 3:00 (39) Nitrox 50 1.26 ppO2, 20ft ead
Stop at 40ft 3:00 (42) Nitrox 50 1.10 ppO2, 13ft ead
Stop at 30ft 5:00 (47) Nitrox 50 0.95 ppO2, 7ft ead
Stop at 20ft 7:00 (54) Oxygen 1.60 ppO2, 0ft ead
Stop at 10ft 10:00 (64) Oxygen 1.30 ppO2, 0ft ead
Surface (64) Oxygen -30ft/min ascent.

And here we have the dive usiing the average of the 2 depths

Dec to 200ft (4) Trimix 15/55 50ft/min descent.
Dec to 225ft (4) Trimix 15/55 60ft/min descent.
Level 225ft 15:35 (20) Trimix 15/55 1.17 ppO2, 65ft ead, 83ft end
Asc to 150ft (22) Trimix 15/55 -30ft/min ascent.
Stop at 150ft 0:30 (23) Trimix 15/55 0.83 ppO2, 36ft ead, 49ft end
Stop at 140ft 1:00 (24) Trimix 15/55 0.79 ppO2, 33ft ead, 45ft end
Stop at 130ft 1:00 (25) Trimix 15/55 0.74 ppO2, 29ft ead, 40ft end
Stop at 120ft 1:00 (26) Trimix 15/55 0.69 ppO2, 25ft ead, 36ft end
Stop at 110ft 1:00 (27) Trimix 15/55 0.65 ppO2, 21ft ead, 31ft end
Stop at 100ft 2:00 (29) Trimix 15/55 0.60 ppO2, 17ft ead, 27ft end
Stop at 90ft 2:00 (31) Trimix 15/55 0.56 ppO2, 14ft ead, 22ft end
Stop at 80ft 3:00 (34) Trimix 15/55 0.51 ppO2, 10ft ead, 18ft end
Stop at 70ft 2:00 (36) Nitrox 50 1.56 ppO2, 32ft ead
Stop at 60ft 2:00 (38) Nitrox 50 1.41 ppO2, 26ft ead
Stop at 50ft 3:00 (41) Nitrox 50 1.26 ppO2, 20ft ead
Stop at 40ft 4:00 (45) Nitrox 50 1.10 ppO2, 13ft ead
Stop at 30ft 6:00 (51) Nitrox 50 0.95 ppO2, 7ft ead
Stop at 20ft 7:00 (58) Oxygen 1.60 ppO2, 0ft ead
Stop at 10ft 12:00 (70) Oxygen 1.30 ppO2, 0ft ead
Surface (70) Oxygen -30ft/min ascent.

So you see the relationship is not linear. If you add more levels and more time the error can only increase. I am hoping to leann something here so those who reply

If you don't understand it certainly don't use it. Seems to be working well for myself and MANY others for years.

are not contributing anything useful.