In a narrow channel, which vessel must keep to the starboard side?

Answer: B — The vessel with a draft that secures a safe navigational route

In a narrow channel, the vessel that must keep to the starboard side is the one with a draft that secures a safe navigational route. This is because vessels are required to navigate in a way that minimizes the risk of collision while ensuring safe passage, particularly in constricted waters where navigation can be more complex. Keeping to the starboard side of a channel allows for safer passage as it follows the customary navigational practices, ensuring that two vessels can pass each other safely. When vessels maintain this practice, they conform to the Rule 9 of the COLREGs, which addresses the conduct of vessels in narrow channels and traffic separation schemes. It emphasizes the importance of keeping to the starboard side for vessels navigating in these situations, regardless of their size or power. This principle ensures that there is consistent navigation behavior among vessels, thereby enhancing safety and predictability on the water. The other answer choices do not stand under the regulations since they focus on characteristics like draft size, power, or sail status instead of the navigational rule concerning safe passage in narrow channels.