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Hey there, welcome to the list! DEEP STOPS The first thing to consider are your diving profiles. Your current profiles are not exposing you to extreme inert gas loads. I don't pretend to speak for Mr. Irvine, but when he says you are treating yourself in the water with EXTENDED shallow stops for deeper stops you should have already made, he probably has especially in mind the profiles that his team dives that require EXTENDED deco. Of course, his logic applies equally to all dives, but it obviously becomes more important the deeper and longer you go. In other words, the more inert gas you take on, the more careful you have to be about exactly how you get rid of it. There is much to read about this, different ways of calculating deep stops (you probably know this already), so learn all you can about it now before you go deeper and it starts getting really important. For now, you can just do what you've been doing without worry. COCHRAN The Cochran does not compute deep stops. Again, don't worry about this for now. If you want, calculate your own and let the computer adjust your shallow stops accordingly (it WILL do this) but then again, it has to keep working throughout your deco in order for you to reap any benefit! I don't care much for these Cochrans for this reason, and because they alarm when you go deco, etc., and I have found them cumbersome to program at sea, and in general more trouble than they are worth. Give me a table anyday. Speaking of tables, make sure you are backing up that thing with a table, computer-generated or otherwise. DECO OXYGEN First of all, oxygen is the ideal deco gas. This is easy to defend with both logic and science. Having said that, let's branch off into the realities of diving in different locations, with different operators and different divers: Regardless of the fact that oxygen is no more dangerous at 20' than 80/20 is at 30', some operators just aren't comfortable with it and no customer is ever going to be able to educate them on this point so that they say, "Oh jeez, what a dunderhead I've been! You're right, let's dump this stuff out and fill it up with O2!" Ain't never gonna happen. If you do go with oxygen, don't use it at just the 10' stop, use it at 20' as well. I can only imagine the looks you would get taking down two deco mixes for the profiles you describe, so you can spend 8 minutes instead of 9 at 15'. Not pretty. So whichever gas you use will often be determined by where you dive and with whom, unless you have an iron will, in which case you will probably just dive less, with fewer people, or quit. Again, with your dive profiles, it just doesn't matter. You're gonna get out of the water in about a quarter of an hour and you're not gonna be bent. Keep it simple. HIGH PRESSURE OXYGEN Well, this pretty much sums up my love of bigger deco bottles, 'cause I don't own a haskel! But again, with the profiles you describe, 30 cu. ft. is plenty. The math to prove this would look something like: (Numbers "approximate") Average depth during deco: 1.5 ata Deco SAC rate: .5 cu. ft./min. Total time on deco: 20 minutes 1.5 x .5 x 20 = 15 cu. ft. There you go, dude. Half of what's in your bottle if it was full. If your bottle is rated at 3000 psi and you only had it pumped to 2000 at your shop, then: 2000/3000 x 30 = 20 cu. ft., which doesn't quite comply with the rule of thirds, but you aren't really going to do a full 20 minutes of deco, so you might be in there, barely. My point is that you wouldn't even have to think about this with a Luxfer 40 (or an 80, talk about not needing a haskel!) under your arm. Ancient Chinese Tech Diver say, "coupla 40's take you long way, glasshoppa..." Finally, I can't resist commenting about your shop's attitude toward high pressure O2. Oxygen is to be respected, not feared (just like the water). Haskels are made to pump O2 so they are not inherently hazardous when pressed into that service... BUT, that is of course if we lived in a perfect world. I'm sure they wouldn't mind filling something they just cleaned to 3000 psi, but they might not want to hook their equipment up to just anything that comes through the door with an O2 service sticker on it. How do they really know what kind of crap has been pumped into that little warhead on the floor? Some shop owners will fill anything with a sticker on it, others will not, and when they limit their fill pressures it's because they're not taking any chances. Hard to blame them, people being what they are. ===== Semper Deep, Ray Nixon towbat@ya*.co* IANTD 46983 __________________________________________________ Do You Yahoo!? Yahoo! Auctions - Buy the things you want at great prices. http://auctions.yahoo.com/ -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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