Computerless Multi-Level dives

[Diver0001]

QKRTHNU once bubbled...

Like I said, I plan on using a computer. I just want to be able to double check it.

This isn't really "exactly what a computer does". Since the computer monitors each compartment separately.

Friend, what do you think the tables do?

The tables and the computer (the Haldanian ones) work the same way. There are some minor differences but the tables are just one implementation that works with square profiles and the computer essentially writes a custom multi-level table based on real-time information for every dive. The technique is essentially the same except your computer recalcuates your dive every 3 seconds or so where as you do it once or twice for a whole dive using the tables. All the computer is really doing is eliminating the rounding error you get with the tables.

The model is the same.....

Has anyone out there compared what the table says NDL is for your true average depth to what a computer gives you for NDL?

Obviously the computer should be more true to actual Nitrogen loading but I'm curious how much of a variance there is.

My computer gives me the same NDL's on square profiles as the PADI RDP. Newer computers have more conservatism built in.

R..

 

[Uncle Pug]

QKRTHNU once bubbled...
Obviously we can't fortell the future

In fact that is what taking control over and responsibility for you dive is all about. I control what my profile will be... I determine by the time I spend at various depths what the graph of my profile will look like in the future when I down load it. Easy as pie.

 

[Freeman]

I made a post earlier in this thread with an example multi level dive and asked if it was possible along with the explanation as to how to figure out using just a PADI RDP table. So far no responses Anyone up for exaplantion on this one? I have already ordered a dive computer but still want to be able to calculate multi-level dives on my own ( plan your dive-dive your plan).

Example dive: 90ft/15min, 60ft/15min, 40 ft/15min, remaining time at 15 ft?

Thanks to those who respond to this

 

[Diver0001]

Uncle Pug once bubbled...

In fact that is what taking control over and responsibility for you dive is all about. I control what my profile will be... I determine by the time I spend at various depths what the graph of my profile will look like in the future when I down load it. Easy as pie.

With all due respect.... The future is never entirely under your control.

I mean, why do you plan for bailout?

Is it because you have 100% control over what your profile will be?

In all conditions?

Every time?

No matter what happens?

Your initial dive planning is an intention, not a destiny. I'd submit that even someone with your advanced level of skill can't be 100% certain at the onset of every dive what the average depth will be at the end it. The suggesting tht this is "Easy as pie" is....uhmmm....how to put this tactfully............"inacurate" to say the least.

R..

 

[Uncle Pug]

Diver0001 once bubbled...
The suggesting tht this is "Easy as pie" is....uhmmm....how to put this tactfully............"inacurate" to say the least.

rot.... you only say that because you've never thought about it.

Actually shaping your dive profile is as easy as pie.

In fact it is so easy... you already do it but without understanding ( and therefore without actively controlling ) what is happening.

Something else:

Stop and think about your rhetorical question:

"why do you plan for bailout?"

and your sarcastic answer:

"Is it because you have 100% control over what your profile will be?"

Bailout (your term) gives you the ability to control what your profile will be when things don't go as planned.

In other words, I carry enough gas to accomodate contingencies and still control my profile and make it what I want it to be.

Don't you? Probably not.

 

[QKRTHNU]

Freeman once bubbled...
Example dive: 90ft/15min, 60ft/15min, 40 ft/15min, remaining time at 15 ft?

Thanks to those who respond to this

Freeman:

If you use the PADI Table and use the No-surface-interval-repeditive-dive-method, this is how it would work:

90ft/15min ---> Group H ---> No surface interval --> Still Group H
(Residual Nitrogen =23, NDL =32) 60ft/15min ---> Group P
(Residual Nitrogen =69, NDL =71) 40ft/15min ---> Group S

Remaining time @ 15ft would be until you run out of gas.


Interesting side note:

It appears "Reading the Table Sideways" on the PADI table gives exactly the same result as using a zero surface interval. Whereas on the Navy based tables it doesn't give the same results.

 

[navy85]

QKRTHNU once bubbled...
If you use the PADI Table and use the No-surface-interval-repeditive-dive-method, this is how it would work:

90ft/15min ---> Group H ---> No surface interval --> Still Group H
(Residual Nitrogen =23, NDL =32) 60ft/15min ---> Group P
(Residual Nitrogen =69, NDL =71) 40ft/15min ---> Group S

Remaining time @ 15ft would be until you run out of gas.

I get the same results with one small technical exception - if you follow the 'rules' for using the RDP table, all dives shallower than 35 feet should calculated as a 35 ft dive. Therefore, the maximum time at 15 ft would be 97 min (which essentially is until your air runs out).

 

[navy85]

QKRTHNU once bubbled...
It appears "Reading the Table Sideways" on the PADI table gives exactly the same result as using a zero surface interval. Whereas on the Navy based tables it doesn't give the same results.

I'm still fuzzy on the difference between the two methods with the PADI table. You stated earlier that you didn't use Table 3 (the back) when "Reading the Table Sideways". Does this mean you add the time at each new depth to the ending pressure group for the previous depth? Is the following how you would step through the earlier example using this method?

90 ft/15 min ==> PG H
60 ft/15 min, add 15 min to time corresponding to PG H @ 60 ft (23 min) = 38 min ==> PG P
40 ft/15 min, 69+15=84 min ==> PG S
15 ft - time at PG S is 108 min and NDL time is 205 (again for depth of 35 ft) ==> you have 97 min remaining.

Gets the same answer as the previous example, so I gues I answered my own question
Looks easier than using an SI of zero since you don't have to use Table 3. But the big question for the deco experts is whether this is a valid approximation. Diver0001 mentioned earlier that with the Wheel you couldn't "just tack any two repetitive depths into a multi-level dive. The depths need to be in a certain range..." This method seems to do just that.

 

[Diver0001]

Uncle Pug once bubbled...

rot.... you only say that because you've never thought about it.

Actually shaping your dive profile is as easy as pie.

In fact it is so easy... you already do it but without understanding ( and therefore without actively controlling ) what is happening.

Something else:

Stop and think about your rhetorical question:

and your sarcastic answer:


Bailout (your term) gives you the ability to control what your profile will be when things don't go as planned.

In other words, I carry enough gas to accomodate contingencies and still control my profile and make it what I want it to be.

Don't you? Probably not.

Let's back up a step. I dno't want to get into a shin-kicking competition with you.

At the point you jumped in the thread I was busy arguing that I didn't think that using " average depth " as a starting point to plan multilevel dives (no computer and no decompression dives, which is where the thread started) wasn't practical for a couple of reasons: (1) because you're never sure what your average depth will be until you're finished. (2) because in normal recreational diving you need to be sure that you don't go over your NDL at any point during the dive. and (3) if your profile deviates from the plan then " recalculating " the dive on the fly isn't feasible for most people. I also said that I don't think you can hang any kind of planning on a method that uses " average depth " as a starting point and I suggested that it quickly reduces down to using a computer and just jumping in and following what it says.

I think you would agree with that. I'm sure we also agree that there are much better ways to plan a dive if you're not going to use a computer.

Using a PC to plan the dive and then " downloading" or transferring to a slate wasn't one of the options that " Q " started with but maybe it should have been mentioned earlier. (Q, if you're still following you can get free PC software to play with at THIS website)

He did, however mention an Uncle Pug method. Equal time over 3ata and under 2ata. I have a couple of questions about that.

- have you verified that this always works? and if so, what did you do to verify it?
- what do you do with the portion of the dive between 2ata and 3ata?

R..

 

[Freeman]

I thank you for the link you provided in your post, its now logged in my Favs list. I notice however that is for mixed gas/nitrox diving. Do you happen to know of any free software like GAP but applicable to just air? Thanks man.

And thanks to "Q" and navy85 for simplifying the whole multi-level dive thing. It seems to make sense.

Are they any no-no's to planning a multi-level-dive using the RDP table? Somone earlier-Pug maybe? mentioned something about 3ata then 2ata or less for 2nd leg of dive...Do you always need to have the 2nd leg of your dive 1ata less than the previous dive depth?

Thanks,