Final answer:
Navigation lights and shapes on vessels may be temporarily lowered for safe passage under bridges, but this should be done cautiously and in communication with maritime authorities, ensuring full compliance with the COLREGs before and after passing the obstruction.
Step-by-step explanation:
According to maritime regulations, navigation lights and shapes, which are used to communicate a vessel's status and activities, are regulated by the International Regulations for Preventing Collisions at Sea (COLREGs). A ship's navigation lights and shapes must be displayed at all times between sunset and sunrise and during periods of restricted visibility, such as fog. However, vessels may temporarily lower these signals if they are impeding the safety of the vessel, such as when passing under a bridge. This action should be done with caution, as it may affect the visibility of the vessel to others. It is essential for the vessel to communicate with local maritime authorities and follow their instructions when altering the display of navigation lights and shapes. Once clear of the bridge, the vessel must return to normal compliance with the COLREGs as soon as safely possible.