Which white light is positioned over the fore and aft centerline of a vessel, showing an unbroken light over 225 degrees of the horizon?

The correct answer is a masthead light because it is designed to be mounted on the fore and aft centerline of a vessel and projects an unbroken white light over 225 degrees of the horizon. This configuration allows for visibility of the light from both sides of the vessel as well as from the front, enabling other vessels to determine the orientation and heading of the vessel displaying the light.

A masthead light typically is used on power-driven vessels and is crucial for ensuring compliance with navigational rules, especially during nighttime or in reduced visibility conditions. The light's position and range of visibility are specifically designed to enhance safety at sea by making the vessel easily identifiable to other navigators.

In contrast, a sternlight is positioned at the stern of the vessel and displays a white light with a range of visibility that is limited to 135 degrees to the rear. A towing light, while also white, serves a specific function related to vessels engaged in towing operations and does not provide the same level of visibility as a masthead light. Sidelights, on the other hand, are colored lights that indicate the sides of the vessel and do not fulfill the requirements of a light that covers 225 degrees.