Place of dive tables in modern diving (Split from the basic thread)

[boulderjohn]

That a small group of people think it's a "rule" or a "good idea" for "some divers only" to follow doesn't make it a rule that people know, care about, or follow. I've certainly not followed it (having never heard of it until today)

I never heard of it until this thread as well.

 

[lowviz]

I took the OW course twice, more than a decade apart. In neither case did any "80" rule come up at all. That a small group of people think it's a "rule" or a "good idea" for "some divers only" to follow doesn't make it a rule that people know, care about, or follow. ...//...

Nobody cares if you follow it or not. I most certainly don't, I've evolved into a solo diver who doesn't want to see anybody U/W. (OK, there are a couple of exceptions.)

But if you choose to follow 'rock bottom' thinking as a solid dive buddy then you realize that there is a certain amount of gas in your tank that isn't yours. It is your buddy's gas and you better come back with it. As you and your buddy progress, you learn how to spend that gas on ascent without violating rock bottom 'rules'. All of a sudden, the 'don't overdive your tank' starts to make sense.

'Rules' are called rules because you either choose to adopt them without modification or you choose to ignore them. Your choice...

 

[The Chairman]

But if you choose to follow 'rock bottom' thinking as a solid dive buddy then you realize that there is a certain amount of gas in your tank that isn't yours. It is your buddy's gas and you better come back with it.

This isn't bad. Even better is to know your buddy's air supply even as you know your own. There's a few strategies to do this without consuming your attention the entire dive. IOW, my buddy running out of gas is just as unacceptable as me running out of gas.

 

[AfterDark]

This is a really dangerous myth, especially in the Basic Scuba section. Anybody except an air hog can easily stay too long at (say) 100 ft, then can easily come up too quickly. Work it out: 100 ft is 4 ATM, so a SAC of 0.7 cuft/min (not a great SAC, by the way) means 2.8 cu ft/min at 100 ft. So NDL is 20 mins on Navy tables, 12-16 on other tables, PDCs give 9-16 depending on brand and setting. But 2.8 goes into 77 (not 80) 27.5 times, so even if you spend a couple of minutes getting down, and don't even go too fast on the ascent, you can STILL have more gas than NDL. By a lot, depending on what table/computer you are using.

I think what you describe is one of the reasons SS are done these days.

 

[AfterDark]

Oops, yes, I grabbed the 110ft numbers. Tables may be perfect, but their operators are not.

measure twice cut once.

 

[BRT]

I think what you describe is one of the reasons SS are done these days.

If they start up at 500 lb it shortens that time up

 

[lowviz]

@BRT Serious, sarcastic, or sardonic?

Your post may confuse the newbie lurkers on this Basic thread.

 

[BRT]

@BRT Serious, sarcastic, or sardonic?

Your post may confuse the newbie lurkers on this Basic thread.

Very serious. I don't use a lot of air and am happy to be at 110' plus with an AL80 but I'd rather not be at 100' below 700 lb or so. Leaving 100' before you reach 500 lb takes 1/6 of those 77cf out of the equation for the amount of time an AL80 lasts at 100'. Makes it so a lot less people can exceed NDL's at 100' on a first dive with an AL80.

 

[lowviz]

Ah. I totally get that as a solo diver. Self-centric view of diving and surviving.

But this is in Basics and one is expected to support the need to be there for one's buddy. As in Scorscse's 'After Hours', different rules apply.

 

[BRT]

Ah. I totally get that as a solo diver. Self-centric view of diving and surviving.

But this is in Basics and one is expected to support the need to be there for one's buddy. As in Scorscse's 'After Hours', different rules apply.

Are you replying to me??