120 Rule

[mikemill]

unless your tables are metric.

<tease>
So you are admitting that the metric system is inferior?
</tease>

 

[Walter]

Hmm -- 60 feet for 60 minutes

Hmm -- Doesn't that exceed the NDL for the RDP?

I think the US Navy is one of the few tables that still has a 60 min NDL for 60 ft.

Others:

DCIEM & Michigan - 50 min
SEI - 51 min
NAUI & PADI - 55 min

The 120 "rule" does work with the RDP at 100 ft.

 

[Blackwood]

Hmm -- Doesn't that exceed the NDL for the RDP?

point being?

 

[Diver0001]

Hmm -- Doesn't that exceed the NDL for the RDP?

It does with the new one. The old one had the same NDL's as the navy table, ie 60/60 and the 120 rule worked to 100ft.

R..

 

[TSandM]

I just want to make the observation that NDLs and ascent strategies are inextricably intertwined. Those of us who are using the memorized 120 table (which is not precisely the rule of 120 at all depths) are ALSO using minimum deco, which means we are executing all dives as decompression dives and doing measured, timed stops for all recreational dives. Going all the way to the 120 rule limits without planning that kind of decompression invalidates the strategy we were taught, and promulgating using those limits WITHOUT discussing the associated deco is not really very fair.

 

[Walter]

point being?

Point being since he teaches a PADI class, teaching to exceed the RDP NDLs would be a standards violation.

It does with the new one. The old one had the same NDL's as the navy table, ie 60/60 and the 120 rule worked to 100ft.

There's a new RDP? Since when? Sorry, but the old RDP did not have the same NDLs as the US Navy tables. One of the reasons PADI stopped using the US Navy tables and started using the RDP was shorter NDLs. That was about 1988 or 89.

Those of us who are using the memorized 120 table (which is not precisely the rule of 120 at all depths) are ALSO using minimum deco, which means we are executing all dives as decompression dives and doing measured, timed stops for all recreational dives.

The 120 "rule" is about staying out of deco. From 60 to 100 feet (every 10 ft) 120 minus the depth equals the NDL. If you are making deco dives, you are not following the 120 "rule."

 

[Reg Braithwaite]

unless your tables are metric.

Try the 30/30/30 rule: Thirty minutes at thirty metres on 30% O₂.

 

[PfcAJ]

The 120 "rule" is about staying out of deco. From 60 to 100 feet (every 10 ft) 120 minus the depth equals the NDL. If you are making deco dives, you are not following the 120 "rule."

"Deco" in some fashion occurs on every dive, to some degree. The RDP, Naui tables, Navy air tables, whatever, are all contingent on following a specific ascent rate. During that time, you're decompressing. Its just smooth instead of defined stops (except for the so called safety stop).

You can follow the 120 rule (or some modified version, such as the 20% depth reduction things for 32% Nitrox) and call your slowed ascent minimum deco. That doesn't make it anything more than a regular "NDL" dive, you're just ascending differently, possibly in a better way.

 

[gcbryan]

Point being since he teaches a PADI class, teaching to exceed the RDP NDLs would be a standards violation.



There's a new RDP? Since when? Sorry, but the old RDP did not have the same NDLs as the US Navy tables. One of the reasons PADI stopped using the US Navy tables and started using the RDP was shorter NDLs. That was about 1988 or 89.



The 120 "rule" is about staying out of deco. From 60 to 100 feet (every 10 ft) 120 minus the depth equals the NDL. If you are making deco dives, you are not following the 120 "rule."

The 120 rule will get you into deco by most tables today. My RDP from 1991 allows 55 minutes at 60 fsw. Combining the 120 rule (modified or not) with something like min deco makes sense (to me).

 

[Peter Guy]

Walter, Walter, Walter. Sigh -- I do believe that even PADI does allow its instructors some freedom to explain to students some practical tools for simple planning. In fact, using the Rule of 120 along with the RDP shows students that the whole notion of a "No Decompression Limit" is something of an arbitrary construct and that one should always plan their dive to be well within that arbitrary construct.

Is the rule of 120 perfect under PADI's RDP/eRDPml? Of course not:

50 feet/ 80 minutes -- 130
55 feet/65 minutes -- 120
60 feet/55 minutes -- 115
65 feet/45 minutes -- 110
70 feet/40 minutes -- 110
75 feet/35 minutes -- 110
80 feet/30 minutes -- 110
85 feet/27 minutes -- 112
90 feet/25 minutes -- 115
95 feet/22 minutes -- 117
100 feet/20 minutes -- 120

Don't you think this is good enough for checking to see if your basic numbers are right? I do.