Why would boats that go out to sea have deep hulls instead of flat bottoms like the river boat?

Boats that go out to sea typically have deep hulls to enhance stability and seaworthiness in rough ocean conditions. A deep hull allows for better handling of waves and reduces the risk of capsizing, as it provides a lower center of gravity. In contrast, flat-bottomed river boats are designed for shallow waters and ease of maneuverability, making them suitable for calm river conditions but less effective in the turbulent ocean. Deep hulls also enable ocean-going vessels to cut through water more efficiently, improving speed and fuel efficiency.