sam1
Contributor
As a person of maturity, when lugging my tanks or, especially, when scrambling over rocks on a shore entry, I often have wished for lighter tanks. This got me thinking about an ideal tank. At first, I thought such an ideal tank would have no weight at all (purely hypothetical, of course). Oh, the joy of diving with such a tank!or so I thought. But then it dawned on me that were such a tank to exist (with conventional size and working pressure) it would be positively buoyant (because, weighing nothing, it would displace a greater weight of water than its own weight). For example, my (steel) HP80s hold 80 cubic feet of gas at a working pressure of 3442 psi, which works out to an internal volume of 0.34 cubic feet (9.7 liters). In water, an empty weightless tank with that capacity would displace 0.34 cubic feet of water and would thus be 21.9 pounds positively buoyant (in salt water). This led me to revise my definition of ideal to be a tank that was neutrally buoyant when empty. Well, my HP80s have an empty weight of 27.7 pounds and are 3 pounds negatively buoyant when empty. Since the negative buoyancy allows me to use three pounds less lead, the effective weight of my tank is 24.7 poundsonly 2.8 pounds more than my so-called ideal tank! All this has led me to be very happy with my HP80s (but somehow I still wish they were lighter!).
(Put another way, "good" tank weight reduces positive buoyancy; "bad" tank weight does not. My HP80s have 24.9 pounds of "good" weight and (only) 2.8 pounds of "bad" weight.)
(Put another way, "good" tank weight reduces positive buoyancy; "bad" tank weight does not. My HP80s have 24.9 pounds of "good" weight and (only) 2.8 pounds of "bad" weight.)