Why did ocean-going ships need greater freeboard than low-sided galleys?

Ocean-going ships required greater freeboard—the distance between the waterline and the upper deck—primarily to prevent the vessel from being swamped by the sea.12

While low-sided galleys were effective for naval warfare in the relatively calm waters of the Mediterranean, they were highly vulnerable in larger, rougher seas. In these environments, the swell could easily wash over the sides of a low-profile vessel, leading to flooding. By increasing the freeboard, designers ensured that the upper decks remained above water, providing necessary reserve buoyancy and protecting the ship from waves and spray. This structural adaptation was essential for making oceanic navigation more practicable, as it allowed ships to better withstand the dynamic forces and steeper waves encountered in the open ocean compared to the sheltered coastal waters where galleys traditionally operated.234