The pontoon is a great miracle in the application of buoyancy in ancient China's history. In the later years, it was developed not only to erect a pontoon on a small river, but also a pontoon on a large river like the Yellow River. It was said that in the early 11th century, near Puzhou. A large pontoon was built on the Yellow River north of Shaoguan. The cable of the pontoon was tied with 8 iron bulls. These iron bulls stood on both banks, each tens of thousands of pounds. Later, due to flooding, the pontoon was washed away. The iron cow also sank into the river. How to salvage the iron cow is difficult under the conditions at that time. The monk is using two large ships filled with mud, sending people to sneak into the water and using iron ropes to iron the cattle. The big ships are tied together, and then the soil in the ship is removed, and the ferry is pulled up by the buoyancy of the big ship.