The original ships were flat-bottomed, because the early ships sailed in rivers or offshore, and flat-bottomed ships were beneficial to sailing in shallow waters. Later, the ship became bigger and bigger and began to sail in the ocean. First, the sea is deep, and sharp-bottomed ships are not afraid of being stranded. Second, the wave breaking ability of a sharp-bottomed boat is stronger than that of a gondola. As for the ability to resist wind and waves, I'm sorry to forget that the wind and waves in the ocean were definitely much bigger than those along the river.