Which of the following ensures that a ship's course won't deviate during a voyage?

The correct response relates to the concept of an implied warranty, specifically regarding seaworthiness in the context of maritime law. An implied warranty is a legal assurance that a vessel is fit for its intended purpose, which includes not only the physical state of the ship but also its capability to maintain a proper course during a voyage. This assurance means that the ship is adequately equipped, maintained, and competent for the specific journey it is undertaking, ensuring that it will not deviate from its intended path due to deficiencies that should have been rectified before departure.

Other options, while relevant to maritime operations, do not directly address the aspect of ensuring a ship's course stability. A salvage award pertains to compensation for saving a ship or its cargo from peril, rather than its course maintenance. A shipping contract outlines the terms of transport but does not inherently guarantee a deviation-free voyage. Port authority approval relates to the compliance of a vessel with local regulations but does not address the ship's navigational integrity. Therefore, the concept of an implied warranty directly supports the idea of maintaining a specific course throughout a voyage.