The correct answer is C) a line diagram of the vessel's transfer piping. The transfer procedures for tankships are required to contain a line diagram of the vessel's transfer piping. This is because the line diagram provides a visual representation of the piping system used for cargo transfer operations, which is crucial for ensuring the safe and proper handling of hazardous materials. The line diagram helps personnel identify the various components of the transfer system, their locations, and the flow of cargo during the transfer process. The other options are incorrect because they do not align with the specific requirement for a line diagram of the transfer piping. Option A) is incorrect as it refers to the duties of personnel, which is a separate requirement. Option B) is incorrect as it refers to a list of ports, which is not part of the transfer procedure requirements. Option D) is incorrect as it refers to a crew list, which is also not a requirement for the transfer procedures.