120 "Rule" for Repetitive Dives?

[Beth_M]

With much interest, I recently read about the "Rule of 120" to calculate NDL using 32% EANx. Hopefully, without a lot of hullaballoo, somebody can explain how one would apply this for repetitive dives?

Many thanks!

 

[WaterDawg]

Isnt the "120" thing for air? I know that you get 20mins at 100ft and 60 at 60ft.

 

[Diver0001]

With much interest, I recently read about the "Rule of 120" to calculate NDL using 32% EANx. Hopefully, without a lot of hullaballoo, somebody can explain how one would apply this for repetitive dives?

Many thanks!

The "120 rule" (insofar that it can be called a "rule") has outlived it's usefulness and shouldn't be applied in practice, in my opinion. On the old PADI RDP and the navy tables (I think) it used to add up between 60ft and 100ft and made a nice little memory aid, nothing more.

The new PADI tables, however, only add up to 120 at 100ft. The rest of the depths give different (smaller) numbers. If you're planning on using this you'd be best off to add them up to 110 and not 120. At 110 you could put it into practice. At 120 you're pushing it and you'll put yourself over the NDL's listed on the table, which will make you unable to safely calculate repetative dives....

And as far as I know, it only works with air and only the first dive of the day.

R..

 

[lamont]

70 and 80 fsw add up to 110. below that you can take off 5 mins for every 10 fsw. there's some further modifications to give you a little more time deep, but this is close. for EAN32, subtract 20 fsw off your depth (near 100 fsw).

for repetetive diving, imo, do proper stops and deco out a little longer at 10 fsw if you're flying by the seat of your pants... particularly if you're using 21%...

 

[Charlie99]

I always preferred the "440" rule anyway. 440/depth = sqrt(NDL)

Works over a much wider range of depths. Unlike the 120 rule, there is the metric equivalent: 130/depth = sqrt (NDL), or NDL = (130/depth) ^ 2

Also doubles as a narcosis check. If you can calculate it in your head, then it's not likely you're narc'd.

 

[jonnythan]

The 120 rule is kinda useful, but pretty worthless for repetetive diving. Tables and average depth, or software, combined with good planning and execution, are the ticket IMO.

 

[Diver0001]

.....mmmm..... yeah. I don't know how much use rules with a bunch of modifications and exceptions will do you on a real dive. If you're deep enough to wonder about it then you're likely to get all confused and do it wrong anyway.

I just think that good old plan-your-dive-and-dive-your-plan works best. Failing that I would prefer to memorize the NDL's than try to calculate them using some kind of rule that doesn't work anyway and/or simply take a table with me under water.

As a last resort you could also use a computer for puddlestomping. They really do excel at this.

Finally, just the comment that the "average depth" thing has some snakes in the grass too.....

I guess I just really believe that dive planning is something you do before you get in the water.

R..