Deep Diving - Safe bottom air pressures

[Thalassamania]

Excellent!

[Teamcasa]

Thanks guys for all the informative replies. I consider myself an experienced diver, having logged over 200 dives. However, I have only dived twice to over 40m. and that inadvertently because I drifted down once to 41m. and the other time to 43m. on wall dives.
But these were just bounce dives, I ascended on hearing my dive computer beeping. I am taking the prudent advice of not making the attempt to 60m. until I have more experience with deeper dives. The idea was mooted by a buddy who wanted to explore the bottom of a canyon which was known to be 60m. and he asked me whether I could accompany him. I am glad that I asked ScubaBoard and you guys certainly helped to convince me that it would be a foolhardy attempt.

I think you made a good decision. However, don't give up on the notion of deep diving, just give up doing it without more training and experience. Have fun and dive safe.

[DA Aquamaster]

Several people have alluded to it indirectly, but no one has really come out and said it.

You don't plan your gas on the assumption things will go well on a deep dive, you plan for when things will go wrong.

Anyone can do a bounce dive on a single tank when everything goes perfectly, it is when something happnes that it kills people. If your buddy has a catrastrophic gas loss you need to have enough reserve gas to get both of you to the surface, including the delay while you sort out the problem at the bottom as well as any unintentional or extra deco that accrued due to the delay. And you assume the gas loss will occur at the maximum penetration or just at the point you would have started your ascent.

In the real world, that means doubles, redundant regs and the training to what and how to do what needs done in an emergency.

[peterbj7]

Yesterday I did a wreck dive with a single tank (and 13 cu-ft pony) with about 140 cu-ft in it at 3000 psi. Dropped in swam down to about 140 and then cruised for a few minutes as we drifted toward a wreck. As we got to the wreck, my buddy shot a large fish and drifted off in the 2 kt current.

I saw another fish, grabed onto the wreck at the deck at 160 ft, stalked a fish for maybe a minute, speared it, fought it a little, allowed myself to sink down into the ship to the bottom where I was out of the current (at about 190 ft). I then pulled out my knofe and killed the fish (at that point I remebered I forgot my ascent reel), I then removed fish from the shaft, placed it in my bag, re-loaded the spear, strung the line and loaded one band of gun for sharks. I remember feeling pretty narced and a little out of breath, when wrestling with the fish (I've not been over 140 feet for 8 months probably). I remember breathing faster than I should and could detect a little resistance in the reg, so i must have been sucking pretty hard.

I then ascended at a reasonable pace (my computer had died on the descent), which i did not realize until I was at a depth of about 100 feet. When I first realized the computer was dead, i checked the time and it was 8:25 am.

I hate ascending without a computer (or any depth guage) but I came up following my little bubbles and kinda hurried toward the surface because I wanted to send up a smb, which only had 25 of line on it, so I didn't stop deeper. My watch read 9:36 when I reached 25 feet. I did 12 minutes of hang and hoped that was a reasonable time and ascended.

I still had half my air left (so i used about 70 cu-ft).

I haven't read all this thread, but this post caught my eye. If you had done this in Belize you would have rendered yourself liable to arrest and confiscation of all your gear. Spear fishing on scuba is strongly frowned on.

My gut feeling on the initial question is that this person isn't anywhere near the level of training needed for such a dive. Getting answers in a forum such as this is no substitute for proper training. Gas management is a fundamental part of any "more advanced" training.

[1.3]

I haven't read all this thread, but this post caught my eye. If you had done this in Belize you would have rendered yourself liable to arrest and confiscation of all your gear. Spear fishing on scuba is strongly frowned on.

Very acceptable where I live. Sure beats sunburn and a tank of gas trolling for fish on the surface. Scuba stores sell spear guns and polls.

[Tigerman]

Spearfishing is (imo rightfully so) looked upon in different ways in different places. Also what you can and cant take varies with location.
In Norway its illegal to take lobsters while scubadiving and the penalty can get extreme - as in you risk losig all your gear and any form of transportation used to get there. If I want to take flatfish, crabs, eels or pretty much whatever else I can do so on scuba or freediving, with or without spears/spearguns..