According to international rules, what must vessels of all nations obey while at sea?

Vessels of all nations must adhere to international maritime laws while at sea. These laws are established to ensure safe and organized navigation, protection of marine environments, and the rights of all nations regarding the use of the seas. They encompass various conventions and treaties, such as the United Nations Convention on the Law of the Sea (UNCLOS), which sets forth guidelines on territorial waters, shipping rights, and resource management.

International maritime laws provide a framework that applies universally, meaning that regardless of the nation's flag a vessel flies, these laws govern its actions on the high seas. This helps to create a level playing field for all nations and is critical in resolving disputes and issues related to navigation and maritime operations.

Other potential answers, such as local laws or specific country regulations, may apply when in port or navigating within a country's territorial waters but do not have the same global applicability as international maritime laws. Coastal guidelines may pertain to specific environmental protections or navigation protocols within a country's coastal jurisdiction, but again, they vary by country and do not provide the universal standards that international maritime laws do.