What's the use of red and green lights on both sides of the ship?

Lights on the left, red, right and green sides are called side lights, and navigation lights should also include front masthead lights and rear masthead lights. It is used to avoid ships. When two ships meet, they usually meet from left to left (that is, the red light). However, if your boat sees the green light, you can't let it go, which is wrong. Within a certain distance, if other ships don't take measures, you will take the initiative to avoid, so as long as the two ships communicate well in advance, they can also meet right to right (that is, the green light).

The current navigation equipment should be said to be very advanced, with VHF (very high frequency telephone) to talk to other ships and shore stations within a certain range; AIS (Automatic Ship Identification System) can display the ship names and other information of nearby ships within a certain range. Radar can scan and display the position of nearby ships, etc. Satellite navigation system can be used for ship positioning and navigation. It is safer to sail on the sea with these ships.