What was the technical principle of sailing against the wind in ancient China?

In ancient sailboats, when sailing against the wind, the angles of the hull and sails were adjusted at the same time, so that the wind against the wind could be decomposed into two forces, one pushing the hull sideways and the other pushing it in the bow direction. The force on the side was offset by the resistance of the hull's draught, and the other pushing the hull forward in the bow direction.

Every once in a while, the crew will change the direction of the hull and sails and let the ship move along a zigzag route. Sailors call this method of sailing "grabbing popular ships".

Extended data:

Until the 1970s, most ships sailed along the coast of China. Sailing boats are not afraid of headwinds, they are afraid of no wind. The headwind is the word for walking, and the headwind becomes a crosswind. The stronger the wind, the better.

There are two sources of power for ancient sailboats, one is wind and the other is manpower. When the wind is downwind or windward, you can sail. If you encounter a headwind, you can lower your sails and find a safe haven to stop.

Human power is used as the driving force to keep sailing when there is no wind. Therefore, under the headwind condition, the sailboat can't move forward, and even the manpower can't be changed. The first sailing against the wind was after the steam engine was applied to sailboats, which is what we call ships.

References:

Baidu encyclopedia-sailing against the wind