It turns out blocks are super light for their volume. It makes a certain amount of sense. Blocks allow transfer of fuel, items, oxygen, and power between them, so it stands to reason that most of their internal volume is filled with pipes, ducts, cable runs, etc. But that still leaves the question, just how heavy is a solid block, anyway? First, a few numbers. Liquid water has a density of ~1 ton per cubic meter, and conveniently has a relative density of 1. Our basic large block has a volume of 8 cubic meters. So, 1 large block worth of water is roughly 8 tons. Steel, depending on the alloy, has a relative density around 7.5 - 8. A large solid steel block should weigh somewhere around 60-64 tons. This also explains why our vessels can't really go underwater; even combat steel blocks float.
