Rule of 120 question

[Diver0001]

RavenC once bubbled...
If you're using the Rule of 120, do you ever use a mathematical equation to compensate for a less than totally square profile?

For example instead of having 40 minutes at an 80ft max depth dive do you compensate for say 1/3 the time at 60 and 3/4 the time at 80 or do you only dive the 120 rule like you would the P tables. Even if you aren't at 80ft the entire time.

Do you lenghten your time by say 10 minutes to compensate for the split difference allowing 50 minutes as long as you aren't at 80 the entire time?

If you're using the 120 rule to calculate your dives on the fly then you'd better stick to square profiles.

There are better ways to plan.

R..

 

[Braunbehrens]

Charlie99 once bubbled...
Maybe that's the reason GUE advocates trimix below 80'.

You're joking, but you've hit on a very important point.

The reason that people who know don't want to give too much away is precisely that. You either do the whole ball of wax, or you don't. Doing it half way and not knowing the whole story is likely to get you hurt.

If you WANT to do the whole ball of wax, take a GUE class.....'cause ya ain't gonna larn it hear.

 

[Big-t-2538]

Walter once bubbled...
"Maybe that's the reason GUE advocates trimix below 80'."

Not a bad idea.

There is more to it than just 120, and trimix....I also know that b/c I know so little about the system, that I need more training in order to dive trimix and more exposure to what it is they do to understand it completely....

Yes, the whole GUE system is a bunch of little pieces put together to create a whole. Any part seperated from the whole can get you hurt if you don't understadn how & why to use it.

The 120 rule is fairly easy, but b/c a lot of people will read anything and say "Well, I read it here...I can dive this way....blah blah blah" is possibly going to get hurt b/c they don't understand why it works, I am not going to discuss what I know more than this. IMHO after my DIR-F class, I came to this conclusion......Tables are fine, if you want to dive a computer, fine, just understand how it works. Lastly, I am going to try to implement the 120 rule in my diving, but I am going to have a computer to back me up, and I am going to have a back-up square profile in my head of max depth and time to back that up.

So is Agnecy "brand X" wrong for teaching their specific method...no, but are there other ways to do things that agency "X" doesn't teach...yes.

 

[Charlie99]

Big-t-2538 once bubbled...
The 120 rule is fairly easy, .......

the "120 rule" isn't even a rule. It's simply a mnenomic to assist in remembering a few NDLs, based on the old Navy table, with a very liberal nostop time of 40 minutes at 80'.

Why not just remember the real numbers off of whatever table you choose.

Here's a system for memorizing the PADI RDP NDLs:

Start with the key NDL of 30 minutes at 80'. Then drop 5 minutes per 10' as you go 90'/25, 100'/20 110'/15(vs. PADI 16), 120'/10 (vs. PADI 13).

Going the other way, just add 10 minutes per 10' for 70'/40, 60'/50 (vs. PADI 55). Then remember 50', 80 minutes. You'll probably be out of gas before hitting NDL for anything shallower.

 

[Big-t-2538]

Yet another method.....

 

[Charlie99]

Big-t-2538 once bubbled...
Yet another method.....

Mnemomic! not a method.


There are lot of rules of thumb out there. One I use, but haven't seen anybody post yet actually matches up well with the sort of multilevel dives I often do.

"If you leave the deepest depth while at 2/3 of NDL and go up 30' or more, then you will have about 1/2 of that shallow NDL left."

In other words, a reasonable multilevel profile is 20 minutes@ 80', then go to 50' and you'll have up to 40 minutes NDL left.

 

[Braunbehrens]

Charlie99 once bubbled...
the "120 rule" isn't even a rule. It's simply a mnenomic to assist in remembering a few NDLs, based on the old Navy table, with a very liberal nostop time of 40 minutes at 80'.

Why not just remember the real numbers off of whatever table you choose.

Here's a system for memorizing the PADI RDP NDLs:

Start with the key NDL of 30 minutes at 80'. Then drop 5 minutes per 10' as you go 90'/25, 100'/20 110'/15(vs. PADI 16), 120'/10 (vs. PADI 13).

Going the other way, just add 10 minutes per 10' for 70'/40, 60'/50 (vs. PADI 55). Then remember 50', 80 minutes. You'll probably be out of gas before hitting NDL for anything shallower.

Charlie, I understand that your point is that around 80 ft with the 120 rule we are coming up against the "limit".

There are a lot of mitigating circumstances, if you dive DIR.

First of all, part of being DIR means being in good physical shape. This will give you an advantage already.

Second, we always do several stops. This allows time to offgas.

Third, DIR = NO AIR. With nitrox or trimix the equation changes in such a way that the single tank rule is much more reliable. In other words, using nitrox 32 you are pretty much guaranteed to run out of gas before ndl.

Yr method is a little too complicared fr me

 

[MikeFerrara]

Braunbehrens once bubbled...



If you WANT to do the whole ball of wax, take a GUE class.....'cause ya ain't gonna larn it hear.

I thought RavenC already do a DIRF?

 

[MikeFerrara]

Big-t-2538 once bubbled...


There is more to it than just 120, and trimix....I also know that b/c I know so little about the system, that I need more training in order to dive trimix and more exposure to what it is they do to understand it completely....

Yes, the whole GUE system is a bunch of little pieces put together to create a whole. Any part seperated from the whole can get you hurt if you don't understadn how & why to use it.

The 120 rule is fairly easy, but b/c a lot of people will read anything and say "Well, I read it here...I can dive this way....blah blah blah" is possibly going to get hurt b/c they don't understand why it works, I am not going to discuss what I know more than this. IMHO after my DIR-F class, I came to this conclusion......Tables are fine, if you want to dive a computer, fine, just understand how it works. Lastly, I am going to try to implement the 120 rule in my diving, but I am going to have a computer to back me up, and I am going to have a back-up square profile in my head of max depth and time to back that up.

So is Agnecy "brand X" wrong for teaching their specific method...no, but are there other ways to do things that agency "X" doesn't teach...yes.

hmmm...lots of little DIR pieces work well by them themselfe...long hose and bucgied backup, back plate, buddy skills, buoyancy control and so on and so on.

The reason nobody gives away the secret of the 120 rule is that there isn't anything to give away. Not much to talk about in fudging average depth, using whatever NDL you like (navy, DSAT, software...) using 32% and making a couple of stops on the way up. If you study the tables and or some output from a decompression software you'll see that the secret isn't in what they do but rather in what they don't do. LOL

 

[Charlie99]

Braunbehrens once bubbled...
Second, we always do several stops. This allows time to offgas.

With EAN32, the 120 rule is reasonably conservative. Add in 8 minutes of stops and you have a large margin

In other words, using nitrox 32 you are pretty much guaranteed to run out of gas before ndl.

To use a term you are undoubtably familiar with: "STROKE ALERT!". 45 minutes at 100' is quite a ways beyond NDL, even with EAN32

Yr method is a little too complicared fr me

Not if you take my DIRF (Diving Is Really Fun) course. Held only in nice spots like Palau. Just $100 + instructor expenses.