Final answer:
The Portuguese under Prince Henry the Navigator changed navigation methods through advancements in instruments like the compass and astrolabe, as well as the introduction of the caravel ship. These changes allowed them to explore Africa and establish a powerful sea empire.
Step-by-step explanation:
The Portuguese under Prince Henry the Navigator changed navigation methods through several advancements.
Firstly, they developed new instruments such as the compass and the astrolabe, which allowed them to successfully navigate the open sea above and below the equator. These inventions, originally from China and Arabia, greatly improved their navigation accuracy.
Secondly, the Portuguese introduced a new type of ship called the caravel. The caravel was a light and agile ship with triangular sails and a square rig, enabling it to carry a large cargo with a small crew.
These changes in navigation methods allowed the Portuguese to explore the coast of Africa and establish trading posts, marking the beginning of Portugal's powerful sea empire.