How do the sailors react when they come close to Ship-Trap Island?
The sailors react with superstition and fear as they approach the island.
We are introduced to this gradually; at first we only learn the name of the island, which is foreboding enough on its own. We also learn, through the context of their conversation, that Rainsford and Whitney are not sailors themselves, and are considering the island and the sailor's reactions to it with a mix of curiosity, amusement, and armchair philosophical contemplation.
Whitney then mentions (in a somewhat blatantly expository passage) that the sailors were acting nervous and jumpy that day, including their captain, who was normally an iron-willed leader. The captain mentions the place having an "evil name" among sailors, and Whitney concludes,
...sometimes I think sailors have an extra sense that tells them when they are in danger.