What is the main purpose of Rule 6?

The main purpose of Rule 6, as outlined in the COLREGs, is to ensure that vessels proceed at a safe speed. Safe speed is crucial in allowing a vessel's operator to assess the situation and to take actions to avoid collisions. At all times, vessels must navigate at such a speed that they can take appropriate measures to avoid an accident, keeping in mind factors such as visibility, traffic density, and the maneuverability of the vessel. Operating at a safe speed allows for sufficient stopping distance and the ability to respond effectively to any unexpected situations or hazards.

The other options focus on different aspects of maritime safety and regulation. While ensuring that ships are crewed adequately is important, it falls under different regulations concerning manning and crew qualifications rather than Rule 6 specifically. Regulating cargo transport pertains to stowage and securing regulations that ensure the safety and stability of the vessel but is not part of Rule 6. Defining navigation lights addresses the requirements for vessels to display specific lights while underway at night, which is governed by different rules within the COLREGs. Each of these areas is critical to maritime navigation, but only Rule 6 explicitly emphasizes the importance of maintaining a safe speed to prevent collisions.