Task: Question Answering
Input (English): Passage: In 1823, brash naval officer David Farragut boards the Essex and informs its commander, David Porter, that the Navy is commandeering the ship for a top-secret mission. Although the crew is overdue for shore leave, Porter, a cold, efficient leader, lies to them in order to coerce them to volunteer for the dangerous assignment. Farragut soon reunites with his old shipmate, Chief Petty Officer Link, who tries to convince him that Porter, who years earlier trained Farragut harshly in an attempt to teach him patience and discipline, is not as heartless as he appears. This starts to show itself when Porter later reconciles with Farragut about their past and agree to be civil with one another.
Once the ship is at sea, Porter and Farragut open their orders and are dismayed to discover their mission: to disguise themselves as pirates, with no ties to or protection from the United States, in order to track down pirates raiding the West Indies. One night soon after, Farragut is in charge of the ship when a storm hits. Link becomes trapped beneath a keg of rum from which he has tried to sneak a drink and Farragut is forced to break the ship's rudder to rescue him. Porter discovers the damage, but even when he threatens to court-martial Farragut, the officer refuses to inform on Link.
Within days, the supplies begin to run out, one of the crew contracts scurvy, and Porter steers the rudderless Essex to the West Indies for repairs and supplies. Farragut grows frustrated with the slow drift and, although Porter forbids anyone to enter the shark-infested waters, he tries to repair the rudder himself. When a shark attacks and Farragut's rope catches on a barnacle, he is barely rescued in time, and Porter chastises him again. Six days later, the men finally reach land and Porter orders Farragut and Link to gather supplies. 
Question: What is Porter's ship lacking that causes it to slowly drift?
Output (English): rudder.