The Pequod meets nine ships at sea, in encounters Ishmael calls “gams.” In whaling vocabulary, a gam is a social meeting between whale-ships, traditionally involving visits between their captains and chief mates.
The encounters punctuate the Pequod's voyage and give Ahab opportunities to ask other sailors whether they have seen Moby Dick. The first is with the Goney, also called the Albatross; later ships include the Town-Ho, Jeroboam, Jungfrau, Bouton de Rose, Samuel Enderby, Bachelor, and Rachel. These meetings vary greatly in length and importance.
A subtle point is that Ahab does not always observe the normal social custom. His obsession with finding Moby Dick makes him impatient, so some encounters are shortened or fail to become full, friendly gams. The Rachel is especially important because its captain asks Ahab to help search for a missing boat. After the Pequod sinks, the Rachel returns and rescues Ishmael. The number nine refers to the novel's total sea encounters, not nine ships involved in the final chase.