Leeboard. When sailing into the wind, a tacking ship may experience a lot of leeward drift, which forces the ship to go sideways with little progress forward. To correct this problem the Chinese invented the leeboard in the eighth century. This device was first mentioned in Li Chuan's Instruction Manual of the White and Dark Planet (759). The leeboard was a board lowered into the water on the lee side of the ship to apply pressure on the water, stopping drift in that direction and holding the ship erect. Some leeboards would be lowered from a slot in the center of the ship and were therefore called centerboards. The Dutch and Portuguese learned of the leeboard while trading in China, but they did not adopt it until the sixteenth century.

Paddle-Wheel Warship. The paddle-wheel warship arose in the Song age (960-1279). Without rudders...