There are a number of different rules and regulations that must be followed in order to avoid a ship collision. In 1973, the International Maritime Organization (IMO) created specific regulations to prevent such accidents. These regulations state the means that an oceangoing vessel must undertake to avoid a ship collision, such as keeping watch and maintaining reasonable speeds. There are very specific rules regarding which types of ships have the right of way in various situations, and what each vessel should do. Ship pilots can also use extensive local knowledge to further reduce the risks of a ship collision.
In order to prevent a ship collision, vessels are typically required to keep watch during all hours of the day. This means that someone must be physically looking around the ship for any vessels or potential dangers. It also means that someone must listen for other vessels, either for auditory signals or using various radios. As a part of the watch, a ship pilot can use visual references and his knowledge of the local currents and tides to keep the vessel on course.
Ships are also required to carry certain navigation lights to help pilots and crew members carry out watches. Depending on the length of the vessel, the masthead light, sidelights, towing light, and all around lights must be visible from distances of between one and six miles (1.6 to 9.6 kilometers). The masthead light is typically a white light that is centered on the vehicle and shines straight ahead. Sidelights are green on starboard and red on port, and can be used in poor visibility to determine the physical orientation of a vessel to prevent a ship collision.
There are very specific regulations regarding right of way, which typically becomes the responsibility of the pilot in congested waters near a port. When a ship yields right of way, it is said to give-way, while the other vessel is said to stand-on. Powered vessels typically have to give-way to sailing and fishing vessels. Similarly, sailing vessels are usually required to give-way to ships that are engaged in fishing. All vessels are required to give-way to ships that are not under command, which are any vessels that cannot maneuver properly for whatever reason.
Special regulations also exist for certain circumstances. In narrow channels, vessels are required to keep to starboard. Small vessels are also typically forbidden from interfering with the ability of a larger vessel to use a channel when that is the only water deep enough for the larger ship to navigate. In cases where a traffic regulation scheme confines certain vessels to a narrow pathway, other ships that wish to cross that lane must do so at a 90 degree angle if possible. When these and other regulations are followed, a ship collision can often be avoided.