Which term describes the act of theft committed by a vessel's crew?

The term that best describes the act of theft committed by a vessel's crew is barratry. Barratry refers specifically to wrongful acts done by a ship's crew or master that harm the ship's owners, which includes theft of the vessel's property or cargo. This can be seen as a breach of the trust that the owners place in the crew, making it a serious offense within maritime law.

In contrast, piracy denotes armed robbery at sea and typically involves acts committed by individuals or groups against ships for personal gain but does not specifically refer to acts carried out by a vessel's own crew. Sabotage refers to deliberate destruction or damage to a vessel, often to impede its operation, while smuggling refers to the illegal transportation of goods or people, which does not inherently involve theft by the crew but rather a violation of customs laws. Therefore, barratry is the most appropriate term in this context.