Surfacing at how much air?

[DandyDon]

dallasM5 once bubbled...
My instructor for my course seemed to imply that on most dives, you should start considering working your way to the surface/safety stop when your air gets below 500 psi.

First, welcome to Scuba Diving and to the Board!

Now the others have answered you really well, but I gotta' comment - first, about the quote immidiately above. I don't remember everything my instructor told me, and I think maybe you didn't remember this right - surely! I've been out with many operators, and they all want you back on the boat with at least 500 psi as a safety. In fact places that rent tanks will often charge you for a visual inspection if you don't have 500 psi.

Yes, new divers use air about twice as fast as experienced, generally - with many exceptions. I like to carry my air guage in my left hand and look at it very often. ( Once, I had an assigned buddy to dive on a wreck. We'd been down to 110 feet, and were working back. At 80 feet, I compared guages - I had 1500, butr he had 500. :angry: I was not happy! What if I had needed air? In fact, 4 days later, my regulator failed!! I got him out safely, but nearly freaked. )

I hope you're not going to 80 feet the first trip? I do suggest you book boats with a DM in the water at all times, and if you;re going that deep, hire your own private DM the first time. Worth it, until you get the feel and all.

Keep it fun, but keep it safe... don

 

[Charlie99]

There are several reasons why the ascent psi at Cozumel can be lower than would be wise under other circumstances.

The reef profile on most Cozumel dives lends itself to nice multilevel dives. Good DMs will time the dive so that the group has left the 80'+ depths on the wall and are in the 50' range on top of the reef by the time people are much below 1000psi. So the 700psi is really for ascent from 40' or 50', not 80'.

Another reason that 700psi rock bottom works is that there are generally multiple sources of air in the vicinity ---- and since the viz is so good, buddies going up early are still usually visible to the rest of the group.

The fact that the boat will come to you, rather than you having to swim to the boat also means that a reserve for surface use can be very small.

 

[Walter]

As a new diver, you should start up with a minimum of 1000 PSI. As you gain experience, you might drop that a tad if your air consumption is good. If you get to the surface with less than 500 PSI, you should start up sooner on the next dive.

 

[MechDiver]

jbd once bubbled...
you may have answered your question to MechDiver.

Depending on depth, if you are still at depth and you reach 500 psi or lower before you start your ascent then you may not have enough air to do the safety stop since you are new and likely to go through your air supply quickly.

Thank you.

MD

 

[DeepScuba]

Sorry Charlie, but banking on your buddies air "incase" you run low is not an option you should have on the list.

You know it's there if you need it, I know what you mean, but don't "bank" on it......

Sorry for the pun.

Don't even think about 500 PSI Dallas. Do as these guys say here, be conservative and turn it earlier.

As for what "hand signal the DM wants" (Tim). I sure as hell hope he knows the universal one we're all taught already. Don't change, second guess or modify what you've learned. It starts a bad precidence.

My first Salt dive was Coz, you'll love it for sure, how could you not??

Most Rec divers, IMO aren't even close to conservative enough with a single 80. I put myself FORMERLY in that group, without a doubt. What an idiot, really. It wasn't until I started doing "Tech" stuff, that BONG!! it hit me, I was putting myself in uneccessary risk, and "banking" on the fact that gear today is so good, it would never fail, and my guage would always be accurate to the last PSI.

Listen to an idiot (that's me), don't repeat my sillyness, even though it never hurt me.

Stay disciplined, your routine should be unwavering and automatic. Most of all enjoy, and live to dive another day, as much as it's up to you.

Regards.

And welcome!

 

[Epinephelus]

Sharpen your pencils...
A "new" diver typically (typically - some more, some less, but for the sake of example I choose to use this typical rate) SCR of about .65 CFM, which is about 25psi/min on an aluminum 80.
We want a reserve of 13 CF (500 psi) back on the boat.
From an 80' dive, we need 160 seconds minimum (at 30 fpm) for the ascent at an average depth of 40' (2.2 ATM), which will consume about 4.3 CF.
For a safety stop of 3-5 minutes (we'll figure 5) at 15' (1.45 ATM)we'll use another 4.7 CF, which means we'll need a total of 9 CF for the ascent and safety stop, which means we need to leave the bottom with 22 CF, or about 850 psi in an aluminum 80.
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Now, in Cozumel, most of the DM's have this down to a fine art, and, as has been mentioned, will tailor the dive to make the final ascent from 40-50 feet, beginning at about 700 psi and ending up with 500 on the boat. And while you should closely monitor your own air and make your own decisions, you can also relax and enjoy the ride... these guys have done this before.
E.

 

[SubMariner]

IMHO the easiest way to manage air consumption is The Rule of Thirds:

1/3 out
1/3 back
1/3 in reserve

Don't forget to discuss air mangement with your buddy BEFORE you get in the water! Especially the fact that the dive will be based on whoever reaches the 1/3 first.

DSDO,

 

[MechDiver]

SubMariner once bubbled...
IMHO the easiest way to manage air consumption is The Rule of Thirds:

1/3 out
1/3 back
1/3 in reserve

Don't forget to discuss air mangement with your buddy BEFORE you get in the water! Especially the fact that the dive will be based on whoever reaches the 1/3 first.

DSDO,

Rule of thirds is total overkill for recreational diving, especially bathtub stuff like Coz. Half + 200 maybe.

MD

 

[Epinephelus]

SubMariner once bubbled...
IMHO the easiest way to manage air consumption is The Rule of Thirds

The original question concerned drift dives in Cozumel... there is no "out" or "back" on which to apply the rule....
E.

 

[Charlie99]

DeepScuba once bubbled...
Sorry Charlie, but banking on your buddies air "incase" you run low is not an option you should have on the list.

You know it's there if you need it, I know what you mean, but don't "bank" on it......

Sorry for the pun.

As for what "hand signal the DM wants" (Tim). I sure as hell hope he knows the universal one we're all taught already. Don't change, second guess or modify what you've learned. It starts a bad precidence.

Read the title line of my post "700psi works in Cozumel, but not everywhere". The intent of my post (obviously not made clear enough) is to point out the extenuating circumstances of Coz diving that made going up with this level of air acceptable and reminding people that they won't always have these ideal circumstances elsewhere.

I don't bank on using my buddies air in case I run low. 700psi is plenty of air to ascend. 700psi is plenty of air for 2 calm people to ascend. 700psi is NOT enough air for a highly agitated or panicked diver who just had a major reg malfunction and comes over share air while totally freaked out. That's where using other resources of the team/group/DM come in handy. Different plans for different dives.

--------

As to your advice to Tim that he should use "standard" signals rather than finding out what the DM expects, if you dive various location you'd be amazed at the variety of "standard" signals for air pressure.

For 1000psi I can come up with at least 3 common variants, and there are lots more:

a. 5 fingers on one hand, shown twice (my preferred)

b. 10 fingers displayed at once using both hands

b. 1, 0, 0, 0 shown sequentially, using 2 hands for digit>5. Subvariants of these drop varying numbers of 10's or hundreds.

c. closed fist for 50 bar, followed by 2 fingers for another 20 bar.

d. "cave signals", where 1 to 5 are fingers vertical, 6 to 9 are fingers horizontal.

e. For 1500 psi / half tank / 100 bar --- T signal.

f........ ??? ?????? What's YOUR "universal" standard signal for 1000psi DeepScuba?

As Tim said, "Find out what the DM wants for a signal when you hit 1000".