jsado
Contributor
How deep are you willing to go on a specific size tank?
For example, on an Al 80 would you dive to 115 ft?
For example, on an Al 80 would you dive to 115 ft?
How deep are you willing to go?
- Thread starter jsado
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
LouieLouie
Contributor
Depends on how long I'm planning to stay down there, what kind of dive it is, and the conditions.
I'm generally reluctant to go deeper than 100 ft without a fully redundant air supply, regardless of tank size. An AL80 should contain sufficient gas for a short and easy dive to 115 ft, though.
I'm generally reluctant to go deeper than 100 ft without a fully redundant air supply, regardless of tank size. An AL80 should contain sufficient gas for a short and easy dive to 115 ft, though.
Well, let's see, assuming:
-Normal SAC of 0.75, stressed SAC of 1.0
-Two minutes to sort out a catastrophic gas failure
-30 second stops every 10 feet starting at 50% max depth, with 30 seconds glide time to the next stop
-30ft/min ascent rate; 60ft/min descent
Gas burned sorting out the problem before starting ascent:
2 min * (1.0 cu. ft. / min) * 4.5 atm = 9 cu. ft.
Gas burned ascending to first stop:
60ft ascent / (30 ft/min) = 2 min
2 min * (1.0 cu. ft. / min) * 3.65atm = 7.3 cu. ft.
Gas burned doing stops at 60,50,40,30,20,10ft:
6 min * (1.0 ct. ft. / min) * 2atm = 12 cu. ft.
-------------------
28 cu. ft. per person * 2 people = 56 cu. ft. gas required
To do such a thing safely (and I agree with the earlier comment about wanting redundancy at that depth), you should turn the dive at 2100psi on an Al80. When was the last time you turned a dive at 2100psi? Seems hardly worth the bother for about 5 minutes of bottom time.
Last edited:
DevonDiver
N/A
I'll calculate my gas requirements. For anything inside an NDL (air), then an 80 is more than sufficient generally. Anything deco, or long duration on nitrox, then I will use twin-80s....more for redundancy than anything else, especially as I will be using the rule of thirds.
smellzlikefish
Contributor
I've hit 151 on an AL80 and I know a guy who went just shy of 400 on an AL80 of air, but this is certainly not recommended. You can go to 218 before you have to start worry about the oxygen partial pressure knocking you out, but because everybody's tolerances differ, some people can go much deeper than recommended. I don't care to push it.
BTW gsk, I turn dives at 2100 a lot, but mostly when diving into current. Rule of thirds?
BTW gsk, I turn dives at 2100 a lot, but mostly when diving into current. Rule of thirds?
rstofer
Contributor
- Messages
- 19,751
- Reaction score
- 18,602
- Location
- Philadelphia and Boynton Beach
- # of dives
- 1000 - 2499
Average dives on the Spiegel Grove and Duane are to a max depths 100-110 feet, average depths of 70-75 feet, and total dive times of 40-45 minutes. I'm quite comfortable doing these dives with an 80 cu ft cylinder
I occasionally dive a bit deeper for short periods on wall dives but the average depths generally end up shallower and the dive times longer. I'm confident and comfortable on these dives also.
Training, experience, planning ability, and conditions will allow each diver to answer this question for themselves. Traveling long distances to dive destinations where 80 cu ft tanks are the norm and lack of one's pony is the usual makes this kind of decision very important.
Good, and safe, diving,
Craig
I occasionally dive a bit deeper for short periods on wall dives but the average depths generally end up shallower and the dive times longer. I'm confident and comfortable on these dives also.
Training, experience, planning ability, and conditions will allow each diver to answer this question for themselves. Traveling long distances to dive destinations where 80 cu ft tanks are the norm and lack of one's pony is the usual makes this kind of decision very important.
Good, and safe, diving,
Craig
Good to hear. I guess if we had workable local diving we might consider diving for 5 minutes of bottom time, but given that we don't and therefore have to travel, we don't plan dives where that's all we're going to get on the bottom. I can also see how it would make sense if you were ascending up a slope and recalculating minimum gas as you went--in that case you would only be at 115 for 5 minutes but you would have plenty of time of actual diving. For many boat dives down an anchor line, that's just not a possibility, though.
Similar threads
