A sailing vessel with her engine on during the day shall display a ____ ____ ____ ______ _____ and at night shall display a masthead light to indicate she is now a _____ ______ ______.

A sailing vessel that has its engine running during the day is required to display certain day shapes to indicate its status to other vessels. In this case, the correct display is a cone with the apex facing down, which signals that the vessel is operating under mechanical power rather than being propelled solely by sail.

At night, the requirement changes; the sailing vessel must show a masthead light, which identifies it as a power-driven vessel. This is crucial for ensuring that other vessels can recognize its status and navigate accordingly, thereby promoting safety on the water. The use of specific day shapes like the cone with the apex down is part of the navigational rules established to prevent collisions and ensure that all mariners are aware of each vessel's mode of operation at a glance.