Navigation rules are a set of rules which apply to people in boats, much like the “rules of the road” apply to car drivers. The goal of navigation rules is to create a standardized system which is used by all navigators, preventing collisions, dangerous situations, and other problems which can arise when people do not follow a standardized set of rules. For example, the “nav rules,” as they are known, describe situations in which boats must yield to each other, and explain which type of craft are expected to yield to others.
There are two sets of navigation rules: inland and international. International navigation rules are standardized all over the world, allowing boats from different countries to follow the same rules when they meet. Inland rules can vary from region to region. Nautical charts typically include a demarcation line which shows when the nav rules transition from inland to international, so that boaters can be aware of changing standards of navigation.
Also called Collision Avoidance Regulations (COLREGS) in some regions of the world, navigation rules essentially dictate a response to every possible situation, including highly unusual situations. When a tanker ship and a sailing boat encounter each other, there's a regulation in the navigation rules which dictates which should occur (the sailing boat must yield). The navigation rules also cover issues like which side of a waterway ships should keep to, depending on whether they are moving inland or out to sea, along with many other topics.
Copies of publications of nav rules are available for free from some boating organizations and government agencies, and they can also be purchased. It is important to periodically purchase or obtain new copies, as the navigation rules are sometimes updated, and sailors want to make sure that they are working with the most recent copy of the regulations. Many sailors keep a copy of the navigation rules in a convenient location on board ship.
Boating safety classes usually brief participants on navigation rules and may test them at the end of the class before offering a certification. People must also demonstrate a knowledge of the rules when they take licensing exams which allow them to operate commercial ships. Failure to comply with the rules can result in citations from law enforcement organizations which cover the water, and it can also expose people to the risk of serious accidents or clog shipping lanes as snarls caused by errant boats are resolved.