On a cruise ship, what is the purpose of the boat deck?

The purpose of the boat deck on a cruise ship is primarily to store sufficient lifeboats for all passengers and crew. This area is critical for safety, as it ensures that all lifeboats are readily available and easily accessible in case of an emergency. The boat deck is designed with the necessary equipment to launch these lifeboats quickly and efficiently, which is essential for the protection of everyone onboard.

While the other options describe various activities that might take place on a cruise ship, they do not accurately define the primary role of the boat deck. The areas for entertainment, sunbathing, and navigation crew quarters are typically located elsewhere on the ship and cater to passenger leisure and crew operational needs. Therefore, option C stands out as it directly relates to the safety provisions mandated for all cruise vessels.