Read the following excerpt from Prince Henry the Navigator by C. Raymond Beazley. Then answer the question that follows.

The Arab tradition of the Green Sea of Night had too strongly taken hold of Christian thought to be easily shaken off. And it was beyond the Cape which bounded their knowledge that the Saracen geographers had fringed the coast of Africa with sea-monsters and serpent rocks and water unicorns, instead of place names, and had drawn the horrible giant hand of Satan raised above the waves to seize the first of his human prey that would venture into his den. If God made the firm earth, the Devil made the unknown and treacherous ocean—this was the real lesson of most of the medieval maps, and it was this ingrained superstition that Henry found his worst enemy, appearing as it did sometimes even in his most trusted and daring captains.

According to the passage, what were some of the dangers and consequences that Portuguese sailors might have worried about when setting off on a journey along the west coast of Africa in the early 1400s? Write your response in one to three sentences.