Rock Bottom Spreadsheet

[JasonH20]

So by this table, if I do a dive to 100', I'm heading up at 2000#?

Umm, wow.

In your case Wijbrandus, to ascend from from 100 feet, with a 2 minute deep stop at 50 feet and a 3 minute safety stop at 15 feet, with both you and your buddy sucking like hoovers would require approx 42 CF of air or in other words a bit more that 1/2 of your 80CF tank. 3442*(42/80) = 1800 psi, plus the 200 psi padding gets you to 2000. If you don't want to compute a deep stop and you think you and your buddy can keep your SAC down, change the numbers on the spread sheet and see what you get.

Like mentioned above, the numbers I have plugged in at top are fairly conservative.

I meant to also ask, do these numbers look right to everyone? Also, are there any other variables anyone would like included?

Thanks,
Jason

 

[JeffG]

ok, this has sparked my interest! Now let me see if I have this right. rock bottom is the reserve gas to bring both divers up from max depth?

Yes

Now can you use "some of this gas for your own ascent"?

No...Its not a "Turn Pressure"...its a vol of gas that is removed from the gas planning for a saftey reserve.

(You will notice that it is pretty hard to do agressive deep dives with AL80's under the GUE system)

 

[SuPrBuGmAn]

Nicely done - I printed it out

 

[MikeFerrara]

ok, this has sparked my interest! Now let me see if I have this right. rock bottom is the reserve gas to bring both divers up from max depth? Now can you use "some of this gas for your own ascent"? and what happens if your buddy gets negative and has an "event" after the beginning of the ascent? My guess is that YOU can't go get them. any help?

oh well, can't plan for everything, sure would be nice to have a pony!

Rock bottom as I know it includes gas for...

a minute or so at the bottom sorting out the problem for 2 people at an elevated sac
a 30 fpm ascent and whatever you want as a safety stop.

Most use a rmv of 1 cu ft/min or so for planning.

Since you're sharing air, if your buddy sinks you're going with him so don't let that happen. LOL

 

[MikeFerrara]

I should have added that rack bottom is the gas limit that starts an ascent. If you need to get back to the entry point you need a turn pressure that can do that for you.

If you'd like to get back but it's not really required it could be half of your useable used. If you must get back then it's thirds (after ascent gas is backed out) because now you need has to get 2 people back to the entry point and up in the worst case condition that there is a total gas loss and the max travel point.

 

[JasonH20]

No...Its not a "Turn Pressure"...its a vol of gas that is removed from the gas planning for a saftey reserve.

And just to clarify this changes as your depth changes.

If for example I'm at 100 feet with a HP80 and get to 2000psi I would start heading for shallower water. Lets say when I get to 50 feet I find some interesting stuff to look at and my SPG is now at 1800psi. I'd be OK to stay at 50 feet until I was at approx 1000 psi. I both hope that makes sense and that I'm understanding this correctly!

Thanks,
Jason

 

[novadiver]

Yes


No...Its not a "Turn Pressure"...its a vol of gas that is removed from the gas planning for a saftey reserve.

(You will notice that it is pretty hard to do agressive deep dives with AL80's under the GUE system)

I pay good money for dive boats , I'm not coming back after 10 min of bt on a 100 foot dive. what if you got hosed by a hoover? this is just plain wrong. I'm bringing a pony with the gas to bring up a str@&*, no wonder those 130s are selling like hot cakes. I call em anchors.

 

[jonnythan]

I pay good money for dive boats , I'm not coming back after 10 min of bt on a 100 foot dive. what if you got hosed by a hoover? this is just plain wrong. I'm bringing a pony with the gas to bring up a str@&*, no wonder those 130s are selling like hot cakes. I call em anchors.

You could always just bring small doubles or a single tank that has enough gas to let you safely do the dive you want.

I'd much rather have one 130 that will let me bust any NDL out there than an Al 80 plus a second pony bottle to deal with.

 

[novadiver]

Rock bottom as I know it includes gas for...

a minute or so at the bottom sorting out the problem for 2 people at an elevated sac
a 30 fpm ascent and whatever you want as a safety stop.

Most use a rmv of 1 cu ft/min or so for planning.

Since you're sharing air, if your buddy sinks you're going with him so don't let that happen. LOL

no MF I'm talking about an event that happens after an ascent starts.say your coming up and after your first deep stop, your buddy flakes and does the crash and burn. are you telling me that RESERVE stays in the tank untill your feet dry on the boat?

 

[pipedope]

Rock bottom is part of a system that is rooted in safety and technical diving. It is based on the principle of solving any problem in the water at depth and making a normal controlled ascent.

This builds good habits for such time as you take up things like diving with manditory deco stops and obstructions.

It is a change from the bad old days of sucking a tank until it gets hard to get air and flipping the J-valve and heading up.

Do you need it?
It is your choice but please understand the reason for it before discarding it out of hand.