Leonardo da Vinci investigated the double hull as a ship-safety feature that separates a vessel’s outer shell from an inner hull.
A double-hull arrangement creates an additional layer between the sea and the ship’s interior. In principle, damage to the outer hull need not immediately flood the inner spaces. Leonardo’s ship studies show his interest in buoyancy, construction, and ways to make vessels more resilient.
The idea is not the same as a catamaran, which has two separate hulls operating side by side. A double-hull ship has nested layers forming one vessel. Modern tankers and many other ships use double hulls for protection against collision and grounding, although their engineering and regulations are far more developed than Leonardo’s sketches.
Leonardo’s drawing represents an early conceptual investigation, not the modern maritime standard in its complete technical form.