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Why does a loaded ship sink deeper into the water?

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differential manometer, Torricellian barometer, and siphon — fluid mechanics Figure 1: Schematic representations of (A) a differential manometer, (B) a Torricellian barometer, and (C) a siphon.

A loaded ship sinks deeper into the water because of Archimedes’ principle, a fundamental law of fluid mechanics.12

This principle states that a floating object is acted upon by an upward buoyant force equal in magnitude to the weight of the fluid it displaces. For a ship to remain afloat in equilibrium, the total weight of the vessel—including its hull, machinery, and any added cargo—must be exactly balanced by the weight of the water it displaces.134

When cargo is added to a ship, its total weight increases. To maintain equilibrium, the ship must displace an equivalent amount of additional water to generate a stronger buoyant force. Consequently, the ship sinks deeper into the water, increasing its draft until the weight of the newly displaced volume of water matches the increased total weight of the ship and its cargo.14