Agilis made the comment, quite some time ago (I copied the post and lost it, and don't want to go back and find it again) that all the issues involved in diving a doubles setup ought to have been covered in OW class. This irked me.
We teach what I consider to be a very good OW class, on the spectrum of what's available. It's not GUE Rec 1, but for a PADI class, it is longer than the normal, and includes quite a bit of extra material that my husband thinks is important. However, whether you like it or not, the standard OW class is designed to teach the vacation diver, who will be renting equipment and following a guide, how to put on and operate his equipment, and how to manage a variety of common failures. The OW class does not include much that is necessary for the person deciding to own his own gear. We talk a little bit about the differences among tanks -- working pressures and volumes -- but not about different buoyancy characteristics, and although I haven't read the new OW manual from cover to cover, I can tell you there are no Knowledge Review, quiz, or exam questions on that topic, so if it is mentioned, it is brief. Lift, as a function of tank selection and exposure protection, is also not discussed. Hose routing is not even mentioned, except to educate the diver to put the regulators on his or her right. Hose length is mentioned in our class, briefly, because we do discuss primary versus secondary donation. We spend time on how to determine proper weighting, but much less on how to adjust static weighting for correct trim, something which can become extremely counterintuitive with doubles, as my experience with my stubborn husband who kept insisting that he needed more weight up high to correct his seahorse posture in his doubles served to illustrate.
There simply is not time in a basic OW class to cover all the information about tanks, weighting, lift, hoses, etcetera, especially since much of that information will be irrelevant to a substantial proportion of the divers we train. Time is spent, instead, on trying to convey critical information, like gas planning, buddy awareness, and good buoyancy and propulsion.
I made the transition to doubles without a class, and I think most people can. BUT -- I had a TON of information available to me to read, and I had a lot of experienced local help. Rjack was generous enough to do my first doubles dive with me, and if I remember right, he was also the person who explained the gas flow through a manifold, something I just hadn't wrapped my head around, despite my reading. I dove my doubles initially as though they were a very large single tank (with more failure points
), with the same intention we generally have with single tanks -- if something went seriously wrong, rather than try to solve it underwater, I would simply end the dive. I taught myself to do valve drills, which was unfortunate, because they would have been easier had I had someone to correct my technique. I have also shut off all my gas on more than one occasion, which I handled okay, but is not something I would say all divers, especially inexperienced ones, would handle with aplomb.
I think Adobo hit the nail on the head a while back. For those of us who have been around a while and done a few things, it's almost impossible to remember what it was like to know very little -- sometimes, not even to know the questions we needed to ask, because we didn't know enough to think of the questions! I remember first learning about gas management, and being stunned. The analysis of wing failure with steel doubles and a thick wetsuit was pretty daunting, too. One of the reasons I often recommend formal instruction is that a class has a curriculum, which ensures that the appropriate material is covered, whereas a mentor may not go over something which has become so much second nature to him that he no longer remembers having learned it.
But yes, you can put on a set of doubles and dive them without any instruction whatsoever. You may be awkward, and you have no business playing with your valves at that point, but if you're conservative, you likely won't kill yourself. The learning curve will be much steeper and shorter if you have some help, and to maximize your knowledge and skill, a mixture of mentoring and formal instruction is probably ideal.
Someone who is asking about how many spgs you need, likely has a lot of knowledge deficits and would benefit from some guidance from someone who knows a bit more than he does. I think that's what Tobin meant at the beginning, and I'm really amazed at how heated (and in places quite impolite) this discussion has gotten. Like everything else in scuba, including doing it in the first place, you can teach yourself, you can learn from peers, or you can take classes. Some routes are riskier, longer, or bumpier than others. When the question someone is asking suggests that the match of their level with their question isn't a good one, I don't think there's anything wrong with answering their question and suggesting they find some help.
