A steel ship stays up not because steel changed, but because the water around it is doing more work than you think. Under every floating hull acts a vertical force described by Archimedes' principle: the water pushes up with a force equal to the weight of the water displaced by the ship's submerged volume. That displaced volume is huge, so the upward force can match the full mass of the vessel even when it is loaded and sitting low in icy seas.
The small bolt loses this contest before it even begins. Its volume is tiny, so the weight of the water it can displace is far less than the weight of the solid steel itself, whose density exceeds that of liquid water. A ship's hull, by contrast, encloses air and spreads the same material into a broad shell, which slashes the vessel's average density when hull and trapped air are considered as one body. If that average density stays below the density of the surrounding water, the buoyant force can balance gravity and the structure floats; if it does not, like the compact bolt, the descent is non‑negotiable.
Even the ice‑cold temperature in polar water only nudges the numbers. Colder water is slightly denser, so the same steel hull can float a bit higher because each cubic unit of water weighs more and thus provides a larger buoyant force. The bolt gains no such advantage; its geometry offers no room to trade solid metal for enclosed air. In the quiet gap between their shapes, not their substance, the fate of ship and bolt separates.
