Buoyancy, density, and stability basics

A rubber duck turns basic hydrostatics into a visible demonstration before the discussion returns to ships. The duck's broad, self-righting form shows that maximum buoyancy alone is insufficient: top weight, the height at which a hull rides, and the distribution of submerged volume also govern stability. Displacement depends on average vessel density, so a hull floats by enclosing enough air-filled space to remain less dense than the water it displaces. Seasoned wood, caulking, and later watertight bulkheads are different ways of preserving that buoyant volume. The demonstration also supports the larger point that working technology accumulates layer by layer rather than appearing fully formed.