I think this thread (which has remained delightfully polite) highlights one of the biggest principles in discussing diving, which is that circumstances affect the choices we make in gear and technique.
If I dove solo, spearfishing, or regularly climbed on boats with instabuddies to do deeper dives at resort locations, I'd probably think about a pony bottle, too. Although doubles are my personal solution to redundancy, they aren't very practical for something where you have to move really fast underwater, or for travel. In my shallower dives that I do with a single tank, I rely on my buddy, but that's not an option for a solo diver or, often, for somebody diving alone on charter boats and being paired up with another diver of unknown skill and diligence. And I know what Ron Frank is saying about current -- it takes some serious work to stay within donation's reach of a buddy when current is blowing, and I thought quite a bit about that on some of our deeper Cozumel dives.
What's really great is that we have a novice diver starting this thread who's thinking, and who's recognized that there are "what ifs" in diving that need to be considered, and for which some kind of plan needs to be in place. While I have chosen to solve those problems differently, my solutions may not be ideal for him (although everybody knows the way I dive is the best way, right?
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