Pretty much any tanks **can** be doubled up, and when properly set up can be useful / fun to dive.
OTOH, shorter tanks can make life difficult for the new to doubles diver. Most new doubles dives are heads down. The added weight of the manifold and dual regs high on the body is the usual cause.
Longer tanks help offset this, as does a wing with more lift near the shoulders and less near the waist.
Short tanks also increase the risk of wing damage due to the wing folding back under the lower end of the bottles when donning or doffing. It's better to have tanks that are longer than the wing.
Lastly, don't be seduced by the lighter "dry weight", look at the actual buoyancy numbers. You need enough total ballast, with empty bottles, to offset the buoyancy of your exposure suit = 2-3 lbs. Nothing is gained with "Light" tanks if you need to add lead to reach the necessary total ballast numbers.
Tobin
