Why can't I dive twice on the same tank?

[littleleemur]

No, my lungs are intact and quite healthy & the 45-mins is the total dive time (including quick descent and the 3-min safety stop), not 90ft at 45mins. Not sure if my computer will allow 45-min at 90ft.

In a wreck you just chill and do your thing so you don't silt out. So obviously the air consumption will be good. There's also no current inside that wreck. So for 2 penetration dives on that wreck I can get 2 45-min dives off the same tank while surfacing w/ abt 900 or so psi give or take a 100.

When swimming around, esp in current, it's not that good so I don't think I can do 2 dives while still surfacing with over 500psi.

As for the sharing octo part, I have more than enough for my buddy and I to reach the NDL together and surface with 1000psi each. Obviously we don't do the sharing bit while in the wreck (entaglement etc), but it's fine when we're out and going up the line & on the safety stop. We manage our air so that he will have at least 1200psi when exiting the wreck. Then we swim around for a bit to check out the outside of the wreck and head back to the line.