Why Surface with 500 PSI?

[rsingler]

Thanks for the spreadsheet!

Question on the Ascent Calc#1:
Shouldn't the ascent time depended upon the ascent rate (which may not be a constant of 60 ft/min)?
In other words: =IF(B6>60,(B6-60)/B9,"") instead of =IF(B6>60,(B6-60)/60,"")

I would like to be safer by going at 30 ft/min ascent rate, which would take longer time to ascend and be using more gas, hence, higher rock bottom pressure.

Ah, the Law of Unintended Consequences, lol!
Another SB Buddy made the excellent suggestion to make deep ascent rate user adjustable, because not everyone will be comfortable with a 60fpm ascent from deep to 60'. But I neglected to change the accompanying formula. Thanks for your attention to detail!

To all who have downloaded the spreadsheet:
Please go back to Post #1 and retrieve RockBottomPressure4.xlsx instead.
Thanks for your interest!

 

[Couv]

Excellent! How did I miss this cheat sheet generator?
.
I need to spend more time in the Basic Forum and less time in the DIY section.

 

[rsingler]

...cheat sheet

I am crushed! Here I go, trying to help with all those maths, and I get accused of cheating!
You and I will never see eye to eye, @couv.

 

[johndiver999]

..

Here in the Basic site 60 feet is the max depth anyway so; "Average dive for that 500 rule to work is about 50 feet or less." Works out pretty well.

Yet.. the 500 psi rule is nonsense in my opinion. Divers should be taught how much air to have in the tank when they leave the bottom, not getting on the boat. It is an ass backwards approach to the problem.

The whole premise is a ridiculous over simplification of the issue, but it somehow is simplistic enough to be thought an acceptable compromise by training agencies.

Using a tool like this spreadsheet, should be extremely useful and instructive to a curious and beginner diver.

We can argue about details like ascent rate variability/assumptions, appropriate SAC elevation during an incident and even time on the bottom to "solve issue" before an ascent is initiated, but refining our own personal assumptions is a necessary prerequisite, to being a reasonably competent diver.

A tool like this is VASTLY superior to a "be back on the boat with ..." type of protocol.

The end result of playing with this tool, should be the capability to generate a minimum gas pressure versus depth for each depth and type of tank. The end result is extremely simplistic and way more useful and reasonable than the "500 psi rule".

 

[rsingler]

it is difficult to go through this type of exercise without concluding that a pony bottle makes a whole lot of sense at any considerable depth.

This is the Basic Forum. Please resist the temptation to start the "pony versus doubles tanks" wars. Thank you.

 

[johndiver999]

Sorry that was not my intent. I will remove that comment.

 

[Couv]

I am crushed! Here I go, trying to help with all those maths, and I get accused of cheating!
You and I will never see eye to eye, @couv.

Not a cheat sheet-a cheat sheet generator. I get the information off of your spread sheet and pencil the rock bottom notes onto my slate. Yes, I still use a slate in even though "Everyone Knows Wet Notes are So Much Better."

As far as seeing eye to eye, I believe-with a bit of help, you'll learn.

 

[rsingler]

Sorry that was not my intent. I will remove that comment.

Oh, no! Your comment was spot on!
It's those "other guys" (doubles POV warriors) out there that I'm worried about. Please put it back!

 

[BoltSnap]

Yet.. the 500 psi rule is nonsense in my opinion. Divers should be taught how much air to have in the tank when they leave the bottom, not getting on the boat. It is an ass backwards approach to the problem.

The "500PSI" rule is a rule by divemaster/boat captains for what you need to have on the surface when you end your dive. It isn't their job or responsibility to figure out a dive plan for you or what your tank pressure should be when you have to start your ascent from the dive to end up with 500PSI at the surface. They tell you what the "end result" must be and it is your responsibility to figure out how to meet the requirement. You don't expect the divemaster or boat captain to sit with every single passenger on their boat and bring out the calculator to work the math for the "end dive" pressure, do you? It is no more so than it is their responsibility to sit with each passenger to work out the dive tables for them or go over their computer.

 

[rsingler]

I get the information off of your spread sheet and pencil the rock bottom notes onto my slate. Yes, I still use a slate in even though "Everyone Knows Wet Notes are So Much Better."

A slate. Unbelievable. Archaic.
You probably dive those old chrome 109 thingies too, don't you?