Just a bit deeper in Belize...

[ScubaInChicago]

On an AL80 at 100' a good turn pressure where you thumb the dive or go much shallower would be 1500-1600 psi. This takes into account an emergency at max depth and 2 min to sort the problem out. It also takes into account an increased breathing rate of 2 diver sharing air, making their stops, and ascending to the surface. As Ron said above, you should figure out where the numbers are coming from and how to adjust them to better suit you and a teammate.

 

[vladimir]

You guys are tone deaf to sarcasm.

Why not turn it at 2000 psi--just to give yourself another few minutes to sort the problem out? Oh wait, then you can't do the dive, because I promise you the operator who sevices the cruise ship customers doesn't have 100 cf tanks.

I have a surface consumption rate of .50 cubic feet per minute. From 30 meters it will take me 3 minutes to surface at 10 meters per minute. Our average depth will be 15 meters or 2.5 ata, so we'll use 7.5 cubic feet of air to ascend. (3 x 2.5 x 2 x .5)

I know; you'd like me to take a minute to solve the problem at 4 ata, you'd like me to do a three-minute safety stop even though it is optional, and you'd like me to assume that my gas consumption doubles because my neck O-ring just blew at the deepest portion of my dive (what are the odds?). Let's just say that I enjoy living close to the edge and agree that we all have our own risk threshholds.

Even if I triple my reserve to 22.5 cubic feet I still have plenty of gas in my AL80 to do this dive as I described. If I average 25 meters depth during the 27 minute gradual descent to 30 meters, I will expend (3.5 x .5 x 27) 47.25 cubic feet, another (4 x .5 x 3) 6 cubic feet for the 3 minutes at 30 meters, leaving me 24.25 cubic feet for exigencies.

 

[scubadobadoo]

We're going to Fiji in February, and we've already planned on picking up our AOW course and doing the AOW dives while there. Yeah, we could do the dives without AOW, but we'd like to go ahead and get the advanced cert anyway. If we're going to, why not do the dives someplace awesome?

Have you looked into that option for your trip to Belize?

I highly suggest this advice! However, in this case I believe the OP is diving from a cruise ship only once in Belize. He might be able to take an AOW course from the cruise ship but I am not sure I would suggest that. No real way to speak to the instructor and see if they are worth it. I have worked as an actor on cruise ships and spent some time on them. The level of instruction varies greatly.

 

[Scubagolf]

In years past I have done a couple dozen dives with cruise ship excursions. I think you will find that cruise ship excursions dives will generally be in the 60 - 80' range on the first dives if they are offering two tank boat trips which is typical. I would be very surprised to see them deeper than 80'. If you are comfortable in the water I would not hesitate to go that deep. AOW is a good certification to get, at some point, because there are a lot of operators that refuse to take you on deeper dives without it, or maybe if your log book demonstrates deep diving experience.

For additional advice and info on diving off of specific cruise boats, you should go to: Scuba and Snorkeling - Cruise Critic Message Boards

 

[DandyDon]

Ok I over read that it was diving from a cruise, sorry. Probly not much chance in getting Nitrox or 100 cf tanks either one. Since the thread originator has been a member for over 4 years here with only 30 or so dives, he may not want to bother with advanced training - preferring to stick to the occasional vacation dives. I'm not really able to offer good suggestions; sorry for interrupting.

 

[ScubaInChicago]

So you have a .5 SCR rate, you have had the time to figure it out to suit yourself. but assuming the average OOG situation and a SCR of 1 which is not unheard of and is a very good median I'll break down the following; 2 divers diving to 100' (4 ATA) with an AL80 and one goes OOG.

2 divers x 1.0 SCR each x 4 atm x 1 min emergency at 100' = 8cf
2 divers x 1.0 SCR each x 3 atm x 2 min (30' per min)assent time to 50' deep stop = 12cf
2 divers x 1.0 SCR each x 3 atm x 1 min deep stop at 50' =6cf
2 divers x 1.0 SCR each x avg 2 atm x 5 min (30 sec slide and 30 sec stops at 40', 30' 20' 10' then surface)=20 cf
thats 46 cf to deal with an emergency, hit your stops, and surface without the potential of bubble forming and DCS.

77.4 cf in an AL80/3000 psi = 0.025 x 100psi interval marks = 2.5 Tank factor (AKA each 100 psi mark is equal to 2.5 Cubic Feet)

46 cf divided by 2.5 = 18.4 (aka 1840 psi)

Thats the plain and simple math, that takes into account 2 stressed divers from depth safely surfacing. If the S*^@ hits the fan and you had to do a 40' lateral breath hold to get to your buddy do you think .5 SCR is the right number to use???? Will a spare air with 3cf get you back to the surface safely?

Again, use the numbers, if your profile can be multileveled it will allow you to recalculate the number at a shallower depth that you didn't use as an emergency reserve at 4 atm. If you dive with a teammate who will be at your side and know the OOG situation is something you have planned for and can do with a lower SCR, plan for that. Bolt for the surface and we might be reading about you in the passing section or a maybe just a trip to the chamber.

Use what's between your ears for something other then slinging s*&^ at common sense.

 

[vladimir]

So you have a .5 SCR rate, you have had the time to figure it out to suit yourself.

So in addition to doubting my common sense, you doubt my honesty. Nice. It is possible (though it would be pathetic) that I made up a surface consumption rate, but I certainly didn't do it to to suit this discussion--I have reported that rate, or something very close to it, in prior discussions on the Scubaboard. Do a search if you like. Do you find a .50 cu ft per minute SCR implausible for an experienced diver drifting in warm, clear, tropical water?

but assuming the average OOG situation and a SCR of 1 which is not unheard of and is a very good median I'll break down the following; 2 divers diving to 100' (4 ATA) with an AL80 and one goes OOG.

2 divers x 1.0 SCR each x 4 atm x 1 min emergency at 100' = 8cf
2 divers x 1.0 SCR each x 3 atm x 2 min (30' per min)assent time to 50' deep stop = 12cf
2 divers x 1.0 SCR each x 3 atm x 1 min deep stop at 50' =6cf
2 divers x 1.0 SCR each x avg 2 atm x 5 min (30 sec slide and 30 sec stops at 40', 30' 20' 10' then surface)=20 cf
thats 46 cf to deal with an emergency, hit your stops, and surface without the potential of bubble forming and DCS.

77.4 cf in an AL80/3000 psi = 0.025 x 100psi interval marks = 2.5 Tank factor (AKA each 100 psi mark is equal to 2.5 Cubic Feet)

46 cf divided by 2.5 = 18.4 (aka 1840 psi)

Thats the plain and simple math, that takes into account 2 stressed divers from depth safely surfacing. If the S*^@ hits the fan and you had to do a 40' lateral breath hold to get to your buddy do you think .5 SCR is the right number to use????

Thanks for educating me.

Please note that if I use 1 cu feet per minute I still have adequate reserves. Yes, I am willing to skip your deep stop and your safety stop. (By the way, I skip deep stops on every dive. Do you think I should start doing them on the dive that I lose my gas supply?)

I am willing to ascend at 10 meters per minute directly to the surface. The whole trip takes 3 minutes. I realize that is not how you were taught and that is not your practice. Does that make it reckless? I think that there is widespread agreement that that is a reasonably safe, though perhaps not ideal, ascent rate.

I reject your assumption that I have to allow for a minute to initiate an ascent (assent=to agree). Why would I have a 40' lateral swim to get to my buddy? Didn't the guys who taught you rock bottom also teach you buddy skills? But even if I stay for a minute at maximum depth, I still have adequate reserves.

I understand that you like to keep reserves for every possible contingency. I understand that these are strongly held beliefs on your part. I accept that these might be prudent for you and the way you dive. For me, diving in warm tropical water and 80' visibility, in excellent shape and having done CESAs from 60' and 80' in the past, having brought a drowning diver safely to the surface and to shore from depth without panic or undue gas consumption, I am comfortable with a 24.25 cubic foot gas reserve on that dive.

Will a spare air with 3cf get you back to the surface safely?

The Spare Air comment was sarcasm; a joke. If you didn't get it the first time, you should have gotten a hint when I said, "you guys are tone deaf to sarcasm."

Use what's between your ears for something other then slinging s*&^ at common sense.

I guess I'm pretty lucky that the person who has a monopoly on common sense has deigned to bestow some of it on me. Thanks. <more sarcasm>

 

[SwimsLikeRock]

Since the thread originator has been a member for over 4 years here with only 30 or so dives, he may not want to bother with advanced training - preferring to stick to the occasional vacation dives.

Probably true. I typically get to dive about once a year in tropical waters during a family cruise/vacation and once or twice with buddies in the Cape Ann waters of Massachusetts.

While I am interested in furthering my dive education, I'd likely not use my one trip to the Caribbean a year for that purpose and instead do it locally - despite the added complications of the relatively cool water.

Sarcasm not withstanding, I'm learning a lot on this thread. I appreciate all of the input!

 

[vladimir]

Sarcasm not withstanding, I'm learning a lot on this thread. I appreciate all of the input!

I am glad you find some of it useful. What we can all agree on, I think, and the impetus behind my original post, is the need to plan your gas usage. Here is a good explanation of the thought process:

NWGratefulDiver.com

Feel free to adjust assumptions based on your own experience, risk tolerance, and dive conditions.

 

[Hank49]

I am glad you find some of it useful. What we can all agree on, I think, and the impetus behind my original post, is the need to plan your gas usage. Here is a good explanation of the thought process:

NWGratefulDiver.com

Feel free to adjust assumptions based on your own experience, risk tolerance, and dive conditions.

But more importantly, did you see the big a$$ cuberas hanging with the dog snappers at the 3rd buoy from the south at the Elbow. Monsters.
I shot a nice horse eye there a couple weeks ago and had a tax collector in a gray suit with lots of teeth come and grab it right off the spear...taking shooting line and shaft. The Elbow is a "active" spot.