Ship-Trap island is presented in three ways. First, it is mysterious. Not only does the text say that it is rather mysterious, but everything about it is mysterious. No one really knows what is there. According to Whitney, the sailors hold onto legends about the island. Moreover, it is implied that this island is only marked on old charts.
Second, the island gives off the feeling of danger. The name of the island suggests this, as does the the fear of the sailors, who know the seas very well. The text makes this point clear.
`This place has an evil name among seafaring men, sir.' Then he said to me, very gravely, `Don't you feel anything?'--as if the air about us was actually poisonous.
Third, the place elicits curiosity. Whitney, Rainsford's friend, speaks of sailor's "curious dread" of the place. In addition, we see that Rainsford is curious as well. He is so curious that he peers into the island from the ship. When he thinks he hears shots, he looks even more intently and falls off the ship.