Speaking of long tanks.....through the years, I have tried many different tanks....for pure "invisibility" ( you don't feel the tank--it is like it is not there), the old steel 72's were the best..though this could have some fond thinking in it from old memories
As to larger tanks, while I used to like the lp120's because they could be cave filled ( jacked/overfilled) to become approx the same size as double 80's....but, As Bob Sherwood demonstrated to me, the have so much more diameter with high mass, that they actually try to roll your body to the left or right, if you come to a stop and try to hover, and even if you are just swimming slow without constantly correcting for the roll with fin actions....
Lately I have been diving on Splashdown Divers alot off Boynton Beach Fl, and have done alot of diving with the long hp120's they have....These are narrow like an 80, and if tanks follow the same physics that boat hulls do, there should be much less drag in swimming them through the water, with their much lower cross section.....and this is what it feels like. These narrow tanks allow me to do big kicks and very long glides, much more like the old steel 72's....and I do not feel any of the rocking forces that the big diameter lp 120's cause. As to the argument that doubles are even more stable, that may well be due to the catamaran effect of the wings and center of gravity, but the functional need for more stability than is possible with the long hp120 would not exist in 99% of the diving population ---I see this as only slightly relevant to the very tiny population of exploration grade divers involved in highly technical tight penetrations in high danger environments, where a great deal of hovering may need to last for long periods of time---this essentially irrelevant to most diving. And of course, the huge DISADVANTAGE of doubles is that they are huge drag ( makes the diver work much harder to go at a given pace) and the likelihood of a diver injuring themself goes up dramatically with doubles, by virtue of there being something of a critical mass to how much weight a diver can safely move around without hurting their back.... Plenty of single tank choices will below this critical mass weight....and most doubles will be dangerous for the "back health" of the "average scuba diver".
In any event, I really like the long HP 120's, and find them the most desirable tank for me to use for almost any kind of dive I enjoy doing. They won't be useful for 300 foot deep stuff, but that's not really relevant to 99% of the world's divers
