To extend and takes Bob's post place words in his mouth and taek it in a direction he never intended, Bob is correct that all of the major innovations were for the most part ctritisized by the old mossbacks in the bunch.
So...just starting this tread suggests potential advancing age and crustiness.
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I have serious reservations about side mount diving off a boat, especially in rough seas.
It's something I'd consider off a six pack a mile or two off Miami Beach where the seas are predictable and the mechanics of both getting in and getting back aboard with not only the primary tanks but also the stage and deco bottles are different than on a larger crew boat or live-aboard. But obviously, I still have a set of doubles, BPO and wing for all the other times when sidemount seems less appealing or less optimum.
However, my house also looks like a dive shop, one that has opened a branch location at Marci's house. Some people have suggestred that it may not be typical for a diver to own vintage double hose, single tank pretty fish diving, doubles diving and sidmount doubles diving rigs. I regard them all as tools that have unique applications, but it's a lot of stuff and over time it represents a large outlay of cash. If I had to limit myself to just one, and only one configuration for the rest of my diving career for use in all diivng environments, a sidemount configuration would be a serious contender as it is very flexible with a broad range of applications - but then again so is a back mounted doubles configuration, the difference is just in where each offers pros and cons in a given environment.
In that regard, a sidemount configuration is, like the .40 S&W, a bit of a compromise in that a sidemount configuration that is useful in large number of environments will not be optimum in any of them. That becomes a major factor to consider, and if "optimum" matters, then you'll find yourself gravitating toward multiple configurations.
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FWIW, Lamar Hire's intention in designing/evolving the Nomad was to create one rig that coudl be used in wide variety of situations from sidemount to back mount doubles to singel tank - but that also by design implies the need to change betwene the three in different situations.