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I think you need both, or shouod have both. Maybe someday down the road you will need tables less, but I think you should have and use both. I bought one on the advice of my instructor because I was doing Nitrox certs, but I still have all the tables from instruction, and I keep them with my dive logs.
 
Well, I have bought a dive computer a SCUBApro Adladin Prime. I had a look at some of the computers at the local dive shops and I liked the features of the Aladin Prime and it didn't have too much I couldn't see myself using. I only have 1 dive on it thus far but it is a little less conservative than the ACUC Tables and that's fine. I'll have to see the difference on a deeper dive. We were only playing at 25 fsw poking around and then doing rescues scenarios.

I knew I had to buy one this month and it'll be a good addition to my gear stockpile. Yes I'll still look at the tables to stay fresh. Don't want my skills to get rusty, especially since now I'm doing more diving with divers trained by different training agencies. Like PADI.

Sue:D
 
There are several arguments for and against but it is my opinion that you should always understand the principles behind the tables and know how to use them but if you dive regularly then they almost become null and void because you begin to understand your personal limits more (tables are only a guide). Also it depends on the sort of diving that you are doing and where you do it because it is misrepresentative as it only produces a square profile. I am also a firm believer that for those part-time divers (those that only dive on their hols) should get a basic computer because to be honest some people will forget 1. how to us it and 2. forget to take it and the computer helps to eleviate any additional stress!!
 
sewcopp:
Guys if you weren't taught to calculate miltilevel dives on a table I'm sorry it is possible and reliable. It's actually not realy any more difficult than calculating repetive dives. Just no SI. It might be something you want to look up for your own personal interest.

Yes computers using the same allgoritms as a table will give you more possible TBT. The tables can do multi-level but only to tens of feet at atleast 20 foot intervals. The table also can only calculate (round) times to the next depth and time interval on the table. Computer are constantly measruing and recording actualities so do not round up and therefore give more time.

Sue

Sue,

Could you explain to those of us who were just taught square profile tables how to calculate a multilevel dive? You've got me curious.

A
 
AaronR103:
Sue,

Could you explain to those of us who were just taught square profile tables how to calculate a multilevel dive? You've got me curious.

A

The simple answer is that you do a bunch of repetitive dives with a surface interval of 0:00.

For example (I have no idea if this dive profile will even work, but it should give you the idea)...

Here is your dive plan: Dive #1 = 80' for 10 mins, SI = 0 min, Dive #2 = 60' for 15 mins, SI = 0 min, Dive #3 = 40' for 20 mins.

1. Find your pressure group (PG) for 80' for 10 mins.
2. With this PG and a surface interval (SI) of 0 mins, find your new PG.
3. Calculate your residual nitrogen time (RNT) from the new PG.
4. Add your RNT to your actaul bottom time (ABT) from dive #2 for your total bottom time (TBT) for dive #2.
5. Using your TBT at 60' for dive #2, calculate your PG.
6. With this PG and SI of 0 mins, find your new PG.
7. Calculate your RNT from the new PG.
8. Add your RNT and ABT for dive #3 to get your TBT.
9. Is your TBT for dive #3 less than the NDL for 40'?

It is possible to calculate a multi-level dive using the tables, but due to rounding and the conservative nature of the table, you are losing tons of bottom time.

Disclaimer: The tables are written with the assumption that you will be making a direct, safe ascent from depth at the end of each dive, so you are off-gassing on the way up. In these examples, you are not actaully ascending all the way and off-gassing. I have not explored the issue of zero SI versus not directly ascending to the surface.
 
ScubaSixString:
So you're in favor of just throwing the tables out?


No, I'm not in favor of throwing them out. I actually enjoyed that part of the PADI Training. I feel knowing your limits before the dive is crucial to safe diving. But I must be honest.... I do tend to rely too much on just the computer. I need to be better about that.
 
AaronR103:
Sue,

Could you explain to those of us who were just taught square profile tables how to calculate a multilevel dive? You've got me curious.

A

I'd love to, but it is not realy the responsible thing to do. It was taught in my advanced course in the deep and wreck diving sections. I am not an instructor and cannot be responsible for how everyone who reads this understands or uses the information.

Dbailey is correct and the not going to the surface and off-gasing enroute is a concern but since, as he stated, the rounding errors in the table's calculations add to the conservativism that should pretty much take care of it. Before you try any of this remember to have a back-up, like a computer, to make sure your calculation were done correctly. The SCUBAboard is not an advaced course and there is no one to check your numbers are correct before you go over the side.

Sue
 
sewcopp:
I'd love to, but it is not realy the responsible thing to do. It was taught in my advanced course in the deep and wreck diving sections. I am not an instructor and cannot be responsible for how everyone who reads this understands or uses the information.

Dbailey is correct and the not going to the surface and off-gasing enroute is a concern but since, as he stated, the rounding errors in the table's calculations add to the conservativism that should pretty much take care of it. Before you try any of this remember to have a back-up, like a computer, to make sure your calculation were done correctly. The SCUBAboard is not an advaced course and there is no one to check your numbers are correct before you go over the side.

Sue

I dive with a computer. I was just curious, as this was not taught during any of my cert courses from OW to DM. The concept seems sound. It seems to me that you ARE outgassing as you ascend from one level to the next, or at least slowing the N uptake as much as you would ascending to the surface at that particular depth. You're not going to outgas on an ascent until you reach a certain pressure anyway. The amount of time you spend ascending in either case is going to be the same, you're just including extra nitrogen-loading at each level at what can essentially be considered extended safety stops, and you're accounting for this added loading with the table calculations.

I'm not going to use the board as a replacement for training, and I'm certainly not going to ditch my computer (God-bless its electronic soul), I just like to have as much of a grounding in the theory as I can. For whatever reason NAUI only taught me square-profile.

A
 
AaronR103:
For whatever reason NAUI only taught me square-profile.
That's because the NAUI table is a slightly modified version of the old Navy table and there hasn't been any multilevel work done with it.

OTOH, PADI/DSAT developed a multilevel dive planning tool called the "Wheel". It has a bunch of extra rules for its use above and beyond the closely related square profile table, the PADI RDP. Of particular importance are the slightly reduced no-deco limits of the wheel, also known as the ML limits.

One can use the PADI RDP as described by a post above, but that method can generate dives that are beyond NDL. The PG (which is based upon 60 minute halftime compartment only) will be correct, but some of the faster compartments may exceed the model limits. In other words, in some instances it can generate decompression dives.

On a practical basis, I just go ahead and use the RDP "zero SI" method to approximately plan multilevel dives, knowing that if I approach the NDLs of the RDP closely, I will in fact be going a short ways into deco.

Luckily, one can essentially "unfold" the PADI Wheel and turn it into a table. One version of that is in my photo gallery with the title "Flat Wheel". A simpler version with just 10' depth increments, plus some gas planning aids is attached as an Excel file. One can also just use the PADI RDP with the following restrictions:

1. 3 multilevel levels maximum.

2. Each new level must be shallower than the next, per these rules ----
.. after 120 or 130' level, the next level must be 80' or shallower.
.. after 100/110' level, next level must be 70' or shallower
.. after 80-90' level, next level must be 60' or shallower
.. after 70', must be 50' or shallower
after 50' or 60' level, next level must be 40' or shallower.

3. Any time between levels gets counted as being at the deeper level.

4. Don't exceed the reduced NDL limits, aka "ML" limits
80' 28 min
70' 35 min
60' 46 min
50' 70 min
40' 128 min
35' 190 minutes.
5. If you get within 3 pressure groups of the ML at any level, then 3 minute safety stop becomes a mandatory decompression stop.

---------------------------------------------------------------
The attached excel file has both an RDP-like / Wheel-like table that is generated using the same deco model upon which the PADI RDP is based. The table entries are +/- 1 minute from the PADI RDP due to differences in how things are rounded up or down.

The SI table is replaced by just one row of numbers, much as on the wheel the SI calculations is just one set of numbers on the back. Take the SI number in your pressure group, add the number of minutes of your upcoming SI to get your "SI from PG Z" and then move to the right as long as your SI from PG Z is greater than the number in SI row. The last PG with SI number lower than your adjusted number is your new PG. (Just like when finding PG from dive depth and time, always round UP on the PG)


------------------------------------------------------------------------
Using those rules and the PADI RDP, one can easily plan the decompression/NDL for a multilevel dive, but that still leaves out one important factor ---- Will you have enough air to do the dive ????


The air consumption table has the ata for each depth, and the ata-minutes or surface equivalent minutes for each depth and for time periods of 10-30 minutes in 5 minute increments. Simply total up the ata-minutes for each level of your multilevel dive to get total ata-minutes for the dive. Then multiply by your SAC to get cubic feet, or even simpler, if you are using an AL80, just use the table that shows you how many ata-minutes you'll get out of an AL80 at various typical SAC rate.

------------------------------------------------

Caveats ---- the attached excel file is not protected, so if you change formulaes or values, you will get garbage. While I believe the table accurately reflects the DSAT model, errors might still be lurking. The intended use of this is for planning a dive that will then be executed using a computer. If you want the real non-computer planning tool, then go buy the PADI Wheel.

Charlie Allen
 
Again the Tables vs. Computer arguments. Both are right, both are wrong. . . The tables or computers are an attempt to use a mathmatical model to predict your health. With either method, there are "undeserved hits". This term is out of favor, but please use this as an easy way to understand a complicated reality. These calculations are trying to find the "truth" for young and old, skinny and fat, relaxed drifting with a current, and fast dive to depth and heavy lifting at depth.

Your instructor sounds like a good one and his answer is right and wrong. I told you this is complicated. When you use the tables the time and depth are calculated in a box. In a real dive you spend more time in between depths that don't "count" in a generous way. Therefore you can't go as deep, or stay as long. The computer is adjusting minute by minute at the depth you are at that moment, so you expect to stay longer.

When choosing the sequence of buying lots of new and expensive gear. Let your husband buy a computer, and you buy gauges. Then for the difference in price, you buy a custom wetsuit while he buys a box suit. You calculate by the tables, and he reads the computers. . . Then choose a safe middle ground in risk of decompression sickness. Also, use the "forum jump" at the bottom of the page and read Dr Deco's teachings on the affect of dehydration, work load, comfort. It's very complicated that's why no one can make it easy. Those people who dive the deepest, dive the longest, are often the most experienced in chamber treatments, $10,000 to $20,000. Don't get scared away, just take it easy until you can learn more.
 

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