Air management for beginner.

[Blackwood]

I understand your point clearly They should be in shallow water, but I know people, personally, who have been at depths greater than 100 ft on their second or third post OW cert dive and ran out of air because they never gave their SPG a glance after entering the water.

I would much rather have a 500 psi on the boat rule than have such situations occur.

Haha! Certainly. Of course, no rule will help someone who doesn't look at his gauge (aka should not be diving)!

Every five minutes should be taught from day 1, IMO.

 

[daniel f aleman]

There are different calculations that will get you the same answer, meaning there is no one way to caluculate gas management. And, gas management is dive dependent - you may want to use one method for one dive, another for the next dive.

Contact NWGreatfulDiver through a PM, he's an instructor with a developed gas management syllubus for recreational divers.

 

[SparticleBrane]

Personally I feel that rock bottom is great for deeper and ocean diving, but it's a bit conservative for shallow quarry work, which is unfortunately where I spend a good deal of my time.
I have no issues bringing an Al80 down to 700 to 1,000 psi in the local quarry due to my comfort level there.
Depending on what we're doing, we might not go deeper than 30ft, mainly since we don't bring shovels on our dives. Surfacing with 1500psi in my tank from a depth of 30ft in this particular quarry is a bit much, imho. I'd rather get another 20-30 minutes of bottom time working on skills.
If something happened to my buddy at 30ft in this particular quarry, 700psi on an Al80 gives us plenty of time to surface, assuming a nice slow ascent rate and a 1cf/min consumption rate per diver.

This is the only time that I'd be a bit on the liberal side for gas planning.

 

[jbd]

Every five minutes should be taught from day 1, IMO.

It should be, but typically isn't because there is so little time spent on in water training for most people. Typical pool/confined water sessions hop from skill to skill with little if any actual attempts at diving and consequently no looking at a SPG.

 

[PerroneFord]

Sparticle, exactly.

Ginnie Basin is about 14ft deep. Not exactly gonna need to dive thirds there. OG is 45ft, Troy is 70ft but you could swim around the place 3 times with 200psi.

I manage gas a bit differently in those places, but still have enough to get myself and my buddy to the surface. Now when I dropped in on the Oriskany, that was a bit different. You have to plan 120-130ft dives a bit differently.

 

[Blackwood]

Ginnie Basin is about 14ft deep.

Wow. Anything to see there?

 

[H2Andy]

Well, the Ginnie basin is right pretty (for about 10 minutes) and then you can follow the run down to the river, which is nice, and then back again (about a 20 minute dive)

at the Ginnie basin is the entrance to the Ballroom, a nice cave that you can dive with lights at the OW level. it's an interesting dive to say the least.

you can also drop off at Little Devil's, drift down to Devil's Eye and take a look, then drift down to Devil's Ear and take a look (no lights are allowed for non-cavern certified divers), then dive the Santa Fe down to the Ginnie run, and then dive up to the Ginnie basin.

that's a nice dive, lasts about 45 minutes

 

[H2Andy]

Personally I feel that rock bottom is great for deeper and ocean diving, but it's a bit conservative for shallow quarry work, which is unfortunately where I spend a good deal of my time.

just work the rock bottom to your needs; that's the beauty of it

figure out your depth and how long it will take two people at .6 or .8 SAC (or whatever reflects your reality) to spend, say, three minutes fixing the problem and getting set, then come up at 30 fpm, do a three-minute stop, and surface

don't go under 500 psi, as the readings tend to get unreliable under that pressure (in other words, 500 psi is your minimum ever rock bottom, even if you could do it, theoretically, with 300 psi)

 

[spectrum]

I think it's clear that there is no one answer. it is all very dependent on the site, the planned dive, the conditions dujour and to some extent one's risk tolerance or at least tolerance of an inconvenience.

On a local shore dive on a nice day when we know the site well we will turn the dive when the first diver hits 50% of their pressure before they hit the water. Keep in mind that we are in Maine and the water barely is going to be over 60F.

On the first leg of the dive a few hundred PSI will be diminished by chilling. Most divers will begin the dive with a higher consumption rate as they get into sync. On the way out we will meander explore and so forth.

On the return leg the cylinder has been chilled so for the most part what you see on the gauge is yours to use and the diver has settled into their best breathing. On the return leg we avoid significant detours and cover less distance. Using this scheme gets divers back with 500 PSI or greater. Under these conditions the worst that will happen is that we end up with a bit of a surface swim and if everyone follows the plan that does not happen.

Keep in mind that we temper this for conditions, new divers and other factors. These are dives that max out around 40 feet.

Now if it were making a deep dive something like rock bottom would be called for and if it were an overhead situation perhaps the rule of thirds. I say perhaps only because I'm not the one to really speak to overhead environments.

Pete

 

[doghouse]

This is what I have been gleaned from my research, and mind you this is completely based on research and questions I have asked in my training class. I am NOT yet certified (but should be on the 17th). Do your own research and do not consider my information as absolute fact, I may be incorrect on some points! During your check out dives, note the amount of air you use. Use this as a starting point for calculating your SAC rate. Then after every dive do the same calculation until you get a steady rate. Scuba Toys has a great page explaining how to calculate this. (http://www.scubatoys.com/education/sac.asp)

The plan your dive backwards, 1 atm for the air above you plus 1 atm for every 33' fresh water, rounding up if you are close.

1. 15' safety stop to surface @ 30'/min .5 min @ 15' = .5 * 2 atm = 1 min
2. Safety stop 4 min @ 15' = 4 * 2 atm = 8 min
3. Ascent from planned depth @30'/min 2 min @ 60' = 2 * 3 atm = 6 min
4 Descent 60'/min 1 min @ 60' = 1 * 3 atm = 3 min

Using the example on Scuba Toys of 27#/min

You will use 27*18 = 486 psi going up and down.
Now add the 500 for your buddy

So before you get in the water you have used 986 psi.
Now for that 60' dive on a 3000# tank. You are down to 2000 psi.
2000/(27*3) = 24.69 min.

So you can figure on being roughly safe to dive to 60' for about 20 min and have plenty of air to surface and take your safety stop and have enough air for your buddy.

If I have any mistakes here, someone please correct them.