The correct answer is D) Overloading. Overloading a vessel is considered prima facie evidence of unseaworthiness. This means that overloading the vessel is sufficient evidence to establish that the vessel is not in a seaworthy condition, without requiring additional proof. Overloading can compromise the vessel's stability, freeboard, and overall structural integrity, making it unsafe to operate. The other options, such as overstowage, overcarriage, and overbooking, while potentially contributing to unseaworthiness, are not considered prima facie evidence on their own. Overloading, however, is a direct and clear indicator that the vessel is not in a seaworthy condition.