Depth averaging tables.

[NAM001]

You are right and that makes it hard to work the problem. The problem is the 1 minute and the lack of it on the dive table https://www.google.com/search? If you use the table you can for instance skip the SI process all together and slide up and down the table going from one depth to another. Ie 100 ft for 10 minutes is group d slide up to 60 ft in group d and continue the dive, Its not always precise but workable as long as you are not intending to push the tables to NDL. Also tables do differ between issuer because of different assumptions for three use. Try it on different tables at worse you add one group for each significant depth change.

https://www.google.com/search?q=div..._24oohU_M:&usg=__mHOY2_-8CSdeHBR1DiaIW_AUa8s=

One last comment. the dive the OP posted and the followup activities probably would not even be tried because of computers. if some one was diving tables they woudld probably let a computer diver so the 130 and meed them at 60 ft. No matter what table or method you use ther are varying degrees of errors many when you use one extreem or the other such as 1 minute or 20 minutes when it is a 20 min ndl. My answer was based on If i had to do it and all i had was a table, (computer crash), how would i do it. If anything this thread is getting folks into the tables and making some discoveries and gaining understanding of tables. My self if asked to do a 130 dive to check the anchor for 1 minute and i did not have a computer i would decline and wait for another volunteer to make the trip. If i was 10% into my ndl for 130 and ent to 60 i would do as i explained if i was 80% into ndl i would go to the surface and not push the envelope of combined errors.

It's not a realistic schedule. To get 1 minute at 130 ft, you'd have to descend at slightly greater than 130 fpm, then immediately begin your ascent to the next level. Run times start upon leaving the surface.

Realistically, you'd need a couple minutes to descend and some fraction of a minute to initiate your ascent. Rounding up then, you've incurred 3 minutes of bottom time to apparently just to go to 130' to say you've done it.

A 130' depth for anything up to and including 3 minutes will result in "Group A" on the wheel so it really doesn't matter if you do it any faster than that anyway. 4 minutes will be "Group B" and 5 minutes will be Group C, and anything longer than that goes up about 1 group a minute - just like it does on the PADI RDP.

---------- Post added December 29th, 2015 at 11:29 AM ----------

I have never had a wheel and would like to have one if anyone would like to part with one.

 

[tursiops]

It can be done as a multilevel dive with the RDP, but it's easier with the wheel. I still have a wheel, and I always dive with a computer. However, I do check my si against the wheel regularly, to keep that skill current, and regularly do a multilevel dive profile with the rdp for instructing purposes.

DivemasterDennis

I assume you've seen the PADI instructions for the RDP that it should not be used for multilvel dives?

Are you a DM doing instructing?

 

[EFX]

I'm looking at a jpeg of the PADI RDP tables and I see nothing about multilevel diving. There are special rules for multiple dives. What instructions are you referring to?

 

[tursiops]

I'm looking at a jpeg of the PADI RDP tables and I see nothing about multilevel diving. There are special rules for multiple dives. What instructions are you referring to?

In the Instructor Guide for the Multi-level Diver speciality, it is specifically stated that the RDP table should not be used for ML dives. There is nothing on the table itself that tells you how to use it for ML dives, of course. By the way, the eRDPML CAN be used for ML dives; it is the electronic equivalent to the Wheel.

 

[Basking Ridge Diver]

So for an example, say a diver drops from his boat on the edge of a wall to the floor in 130 feet for less than one minute to check his anchor, but then immediately goes up to 50-60 feet to cruise the rest of the wall.
If the diver followed the tables religiously the dive would have to be figured for the deepest depth regardless, so after 10 minutes max (PADI RDP) the diver would be on their way up.
However, if the diver was able to mimic what a computer does they could figure the 130' in as a penalty on the 55' ft average remaining dive and lets say figure the overall depth average as 70 or 80 feet. In other words, pretty much what a computer does.

I can't seem to let this go - if I use the tables in a multi-level dive - this is what I get. Not sure why you think 10 mins...

Going to 130 for 1 minute (2.2 mins to get down to 130 ft and 1 min at depth - rounded up to 4 mins) and then immediately going up to 50 feet - you can stay at 50 feet for 59 minutes before hitting your NDL.

Can someone with a Wheel validate this?

Thanks.

 

[tursiops]

I can't seem to let this go - if I use the tables in a multi-level dive - this is what I get. Not sure why you think 10 mins...

Going to 130 for 1 minute (2.2 mins to get down to 130 ft and 1 min at depth - rounded up to 4 mins) and then immediately going up to 50 feet - you can stay at 50 feet for 59 minutes before hitting your NDL.

Can someone with a Wheel validate this?

Thanks.

Doing this dive on an eRDPML is the same as the Wheel, except there are fewer errors from the analog nature of the Wheel and its arrows and dials. First dive, air, first level 130 ft for 4 mins gives PG B, second level 50 ft; new ML NDL is 57 minutes. If I try to do the same thing on the RDP, I can't enter 4 mins BT for level 1 because the table jumps from 3 to 5 minutes; however, 5 mins still gives PG B. Going on the table to level 2 of 50 ft, PG B says I have 67 mins NDL......clearly different from 57 minute!

I'm looking at a jpeg of the PADI RDP tables and I see nothing about multilevel diving. There are special rules for multiple dives. What instructions are you referring to?

Multilevel dives is the issue, not multiple dives.

 

[Basking Ridge Diver]

oing this dive on an eRDPML is the same as the Wheel, except there are fewer errors from the analog nature of the Wheel and its arrows and dials. First dive, air, first level 130 ft for 4 mins gives PG B, second level 50 ft; new ML NDL is 57 minutes. If I try to do the same thing on the RDP, I can't enter 4 mins BT for level 1 because the table jumps from 3 to 5 minutes; however, 5 mins still gives PG B. Going on the table to level 2 of 50 ft, PG B says I have 67 mins NDL......clearly different from 57 minute!

First thank you.

The ERDPML seems to be in line with using the Naui tables on multilevel dives.

The Naui and Padi dive tables don't seem to line up directly under your explanation.
I have a question though - when I look at the Padi Table for 130 ft for 5 mins - I agree it looks like PG B - again I am not versed in these tables but they all work on the same principle I think. When I go to PG B to 50 feet I see 13 Residual Nitrogen and drop down to the bottom and I think I see 63 mins at PG T. If I understand the PADI tables you dont go into the darker grey area? (I prefer the NAUI tables because I am familiar with them.)

You don't want to bump up against the NDLs so you back off and to me it looks like backing off from both 57 and the 63 mins approach puts you in the ballpark. Again - all I am doing is showing it can be done with tables - using a conservative approach I think would be wise as well as using a computer to confirm your plan on deeper dives.

That said there is nothing wrong with using this approach to plan a dive to give you your gas and time approach as opposed to a SWAG or no plan at all. YMMV - I use this approach before every dive and I happen to have it all in excel - punch in the depth and time and it does everything for me.

 

[tursiops]

First thank you.

The ERDPML seems to be in line with using the Naui tables on multilevel dives.

This is an accident. The PADI tables and the NAUI tables are based on different assumptions and basic data. The eRDPML is exactly the PADI tables, with the additional capability of 5-ft rather than 10-ft intervals, and doing the necessary adjustments to allow for multi-level dives.

The Naui and Padi dive tables don't seem to line up directly under your explanation.

They won't; they are different, based on different data and different calculations.

I have a question though - when I look at the Padi Table for 130 ft for 5 mins - I agree it looks like PG B - again I am not versed in these tables but they all work on the same principle I think. When I go to PG B to 50 feet I see 13 Residual Nitrogen and drop down to the bottom and I think I see 63 mins at PG T. If I understand the PADI tables you dont go into the darker grey area? (I prefer the NAUI tables because I am familiar with them.)

I do not understand what PG T has to do with this. The Residual Nitrogen for 4 mins at 130 ft is PG B, Yes. If you then apply PG B to a 50 ft dive, that amount of nitrogen expresses itself as 13 minutes of time already used up from the NDL of 80 mins at 50 ft; this leaves 67 mins still available to you at 50 ft before you hit your NDL. All the darker grey means (as it says on the table) is that a safety stop is required if your dive is in that region...anything 100 ft or more, anything within 3 Pressure Groups of the NDL.

You don't want to bump up against the NDLs so you back off and to me it looks like backing off from both 57 and the 63 mins approach puts you in the ballpark. Again - all I am doing is showing it can be done with tables - using a conservative approach I think would be wise as well as using a computer to confirm your plan on deeper dives.

You can also add up all the numbers in a column on the table, and get a really large number. But that has nothing to do with validly using the tables or validly planning a dives. If you are comfortable with "in the ball park," go for it. Personally, I think it is stupid to use the tables for multilevel diving because they are not designed for that (it doesn't matter whether ADI or NAUI) and any errors you make are in a dangerous direction.....the NDLs you get will ALWAYS be larger than those that are safe. How much larger (so you can do your guess)? No way to say.

That said there is nothing wrong with using this approach to plan a dive to give you your gas and time approach as opposed to a SWAG or no plan at all. YMMV - I use this approach before every dive and I happen to have it all in excel - punch in the depth and time and it does everything for me.

I submit that what your are doing is indeed a SWAG, and not a good idea. You are using a tool designed for one thing to try and o another, and the errors are dangerous.

There was an instructor a few years ago in a local dive shop that taught multi-level diving using exactly what you are doing. He was fired when the shop owner found out.

 

[Basking Ridge Diver]

I do not understand what PG T has to do with this. The Residual Nitrogen for 4 mins at 130 ft is PG B, Yes. If you then apply PG B to a 50 ft dive, that amount of nitrogen expresses itself as 13 minutes of time already used up from the NDL of 80 mins at 50 ft; this leaves 67 mins still available to you at 50 ft before you hit your NDL. All the darker grey means (as it says on the table) is that a safety stop is required if your dive is in that region...anything 100 ft or more, anything within 3 Pressure Groups of the NDL.

I am using this table
https://www.google.com/search?q=padi+air+table&biw=1600&bih=739&tbm=isch&imgil=XByv9WsA96VuTM%3A%3B9y9hPghhtXgqCM%3Bhttp%253A%252F%252Fwww.scubatoronto.com%252Fhowpadi.asp&source=iu&pf=m&fir=XByv9WsA96VuTM%3A%2C9y9hPghhtXgqCM%2C_&usg=__JJzb2PollxfSRyk11Lus2NeDIpo=&ved=0ahUKEwjuocWUsL7KAhUY9WMKHRHfD7wQyjcIPA&ei=1KCiVu7nGZjqjwORvr_gCw#imgrc=XByv9WsA96VuTM:

From what I see it is 63 mins before you must do a required decompression stop. If you go to 67 mins you are now in the darker grey and no longer in the NDL (not sure why if we are talking NDL's you dont want to go to 67 mins) unless I am completely reading this table wrong...

I am not an instructor - so I can see your point... My point is this gives you a better understanding of what your plan should be and as I said above -

using a conservative approach I think would be wise as well as using a computer to confirm your plan on deeper dives.

I know my dive computer and the tables do not line up - in this case I go with the PDC... Seems like we are at a stalemate.

 

[tursiops]

The safety stop is not a "required decompression" stop.
The NDL at 50 ft is 80 minutes (same as the NAUI tables, by the way).
If you choose to stop at 63 minutes, please note you have already used up 13 minutes because of your residual nitrogen, so you would have to terminate your dive after 63-13=50 minutes at 50 ft.
On your NAUI tables, which do not have the gray areas, your calculation is actually as I gave it originally: 80-13=67. Since the 'correct" answer is 57 minutes, not 67 minutes, use of either the NAUI or the PADI tables for this dive would be dangerous. Sorry, I do not think you get a "better understanding." I think you get an incorrect and dangerous understanding.