Wed 28th July 2010, 8:28pm
QUOTE(taiwopanfob @ Tue 27th July 2010, 7:57pm)
Now you want to talk about cults?
When I was taking my advanced scuba course, I walked up to someone fidgeting with some equipment in the back of their car and asked where the course was -- only to realize he wasn't on the course. Instead he was doing something with a fancy rebreather, gear I had never seen up close before. Turned out the guy was an even bigger gearhead than I. He'd found his religion, and it was clear that us lowly bubble-makers are on the one-way road to hell.
True. I'm trying to resist. The new Poseidon/Cis-Lunar Mk VI Discovery thing is one amazing bit of machinery, removing most of the gearhead need. The whole computer, sensor, and battery system is embedded in a piece of plastic that slips in the top-- click. It's totally closed circuit, and handles a simple gas manifold valve between your O2 on one side, and your standard mix diluent (air, nitrox, trimix, whatever) on the other side (which can be used as a bailout bottle or takes a LP line from a separate one if you like). The scrubber cylinder is small enough that it goes in the standard cylinder hole in your old BC, and saved space is because the counterlung bladders are over-the-shoulder on both sides.
Turn the thing on and it goes though dozens and dozens of self-checks. It keeps you at 1.4 atm PO2 at any depth (so long as you're below safety stop depth, obviously-- you're at almost 1 atm PO2 at the surface, breathing nearly pure O2). If anything goes funny, or the system can't figure out something or a sensor goes down-- whatever-- it gives you the big beep to go off the system, and one switch at the mouthpiece puts you on open circuit from your bail bottle and you start blowing bubbles without even changing mouthpieces.
I think it's probably far safer than the old systems, even if it is a sort of "fly-by-wire". The chance of your computer screwing up is now smaller than the chance of your forgetting to turn on your hot mix flow and forgetting to watch your PO2 in the old systems. A famous Nobel-winning nuclear physicist died that way on an old Cis-Lunar, and one of my early dive instructors many years ago using a Drager Dolphin blacked out at 40 feet while teaching students (I wasn't there) and would have died himself had not one of his beginners (on her first dive) been a paramedic who noticed he was just drifting and took him up to the surface.
Of course, you have to weigh the advantages, which are not that great for the type of diving that is my favorite, which is usually coral reefs at 40 to 60 ft in as warm water as I can find. On a standard rental Al-80, if I don't do anything exciting I get about 50 minutes at that depth before I have to head for the safety stop, and if I stay down longer, somebody else has to go up, and the divemaster is not going to wait around more than an hour. People on the boat get restless, there's another dive site often to be set out for, and the rebreather divers, if there are any, don't get much benefit. And quite often 45 minutes at a site is enough for me.
Due to the perversity of the universe, the very places where rebreathers are nice (cold deep water and kelp up here in the north Pacific, long deep wreckdives, etc) are the very places where you're usually wearing a drysuit. In which, when you need to pee after an hour, you can't.
If I buy a Discovery rebreather, it will have to be the combo unit with Depends.