Lights on a vessel let yourself and other people on the water know how you are approaching each other. This includes the speed, direction, and size of the vessel, helping boaters determine who is to give way when visibility is difficult either because of adverse weather conditions or because it is dark.
There are four types of navigation lights that are most commonly used for vessels in US waters, these are sidelights, all-round white lights, the masthead light, and the sternlight.
These lights are two colored lights that can be seen by anyone approaching head-on or from the side. The green light is on the starboard side and the red light is on the port side of the vessel. These lights are different colors so you can tell which way the vessel is traveling if you are looking at it from the side.
All-Round White Light
This type of light is often used as an anchor light when other lights have been put out, particularly when the sidelights are not on. An all-round white light can be used instead of a masthead light and a sternlight. This setup is most commonly seen on powered vessels that are less than 39.4 feet long.
This type of light is a requirement on all power-driven vessels and must be on when the engine is on. If the light is not on, a vessel is understood to be sailing as sailboats only have sidelights and sternlights.
This mandatory light exists to avoid confusion and help those who are nearby to identify the vessel.
This white light is displayed along the stern, and is only visible from the stern – or rear – of a vessel. This light helps others orientate the vessel to work out which way it is going.
Visible Light Meanings
The best way to understand navigation lights is to visualize their use in practice.
If you can see a single green light, you are traveling towards the starboard side of a vessel. If you are travelling in a narrow channel, be aware that you may have to give way.
If you can see a red and a white light then you are approaching from the port side so the other vessel should give way to you if it is necessary.
If you can see a green and white light, another vessel is approaching from the port side. You need to maintain speed and course as the other vessel has taken early and substantial manoeuvres to keep clear of your vessel.
Any changes at this stage may result in a collision as the other vessel had not anticipated a change of course.
If you can see a single white light then this is probably the sternlight and you are approaching a vessel from behind. If you wish to overtake, you need to make early and substantial steps to ensure that your vessel is well clear and passing at a safe distance.
This includes giving two short horn blasts to inform the vessel that you intend to pass on your starboard side.
Frequently Asked Questions
Which Side Of A Boat Has A Green Light At Night?
A green sidelight is always on the starboard side of a vessel. This is the right side when you look at the vessel from above. Interestingly, red on the port side and green on the starboard is the international norm and even applies to helicopters and other aircraft.
Why Do Boats Have Lights?
Boats are required to have lights for safety purposes as they help orientate and determine the speed and direction of travel when visibility is poor. This helps other vessels take appropriate early action to prevent any incidents on the water.
What Do Starboard And Port Mean?
The left side of a vessel is the port side and will be indicated by a red light. You will also often be able to see a white light from this side as well. The starboard side is the right side of the vessel and is indicated by a green light. The stern is the rear of the vessel.
For clarity, picture a vessel from above on a clock face. The port side is from 8 to 12 and is indicated by a red light. Starboard is 12 to 4 and indicated by green. The stern is 4 to 8 and has a white light.
Why Is Starboard Green?
It is widely accepted that the starboard side of the ship had the ‘steerboard,’ meaning that whoever was operating the vessel could clearly see anyone who was overtaking. This made this side of the ship ‘safe.’
When steering an old ship, the whole port side is a bit of a blind spot and so any ship approaching from this angle will not be seen by the navigator. This is a dangerous way to navigate towards another vessel.
When legislation mandating colored lights on ships was passed, the tradition of ‘safe’ starboard and ‘unsafe’ port side was kept alive – in rudimentary terms, green means go, and red means danger.
When Do Boats Give Way?
If a power-driven vessel meets another power-driven vessel, you must give way on your starboard side. If the vessels meet head-on, both must turn to the starboard side of their vessels.
If a power-driven vessel meets a sailboat, the power-driven vessel must always give way unless the sailboat is overtaking. This, however, is unlikely as sailboats are encouraged to avoid narrow channels where giving way would be necessary.
Even more unlikely would be two sailboats meeting in a narrow channel. Whichever sailboat has the wind to its starboard side has the right of way so the other must give way. If both have wind in the same side then the sailboat that is upwind must give way.
If a vessel fails to give way, the other vessel must take evasive action so should turn starboard. Never turn to the port side as you will most likely place your vessel in the way of the oncoming vessel.
Do I Need A Green Light?
Yes, sidelights are required by law as they help others work out which direction and how your vessel is traveling. This is particularly important if the conditions are not ideal, be it because of the weather or because it is night.
What Lights Do I Need At Night?
At night you are required to have a red and green sidelight – on port and starboard respectively – that are visible for 2 miles (3.2 km) if your vessel is longer than 39.4 feet. If your vessel is less than 39.4 feet these lights only need to be visible for a mile.
You also need to have a sternlight and masthead light if your vessel is over 39.4 feet long, or an all-round white light for shorter vessels.
What does a blue light mean?
A blue light often indicates a law enforcement vessel that is actively engaging in its work. It is similar to a police car having its red and blue lights on with the siren. The light is blue so it does not interfere with the other required navigation lights as this could potentially have an adverse effect on safety.
What does a horn blast from a boat mean?
One long blast: My vessel is underway.
Two short blasts: My vessel will be passing yours on my starboard side.
Three short blasts: My vessel is backing up.
This signal is most commonly heard when reversing in dock waters. Listen out for five short blasts which may mean you are not reversing safely.
Four short blasts: My vessel is getting underway.
Five short rapid blasts: Danger.
This signal can be used if you do not understand another vessel’s intended maneuvers or if you think that the intended maneuver is unsafe.
Seven short blasts: My vessel is changing course to port.
Seven short blasts and one long blast: Emergency.
This is used if there is an emergency on board and will usually be heard alongside alarms, alarm lights, and other indicators.
How can I be safe at night?
Firstly, you need to make sure that you have all legally required lights on and in working order. These are the two colored sidelights, and either an all-round white light or a sternlight and a masthead light if your vessel is long enough.
Other things you can do include wearing a lifejacket or other personal flotation device, and being aware of all of your vessel’s procedures for capsizing, falling overboard, sinking, or running aground.
You need to remain alert at all times when steering a vessel on the water and take all appropriate maneuvers early so that there is no rush or unexpected moves from a vessel. This means that someone who is under the influence of drugs or alcohol should never operate a vessel.