Port is the left side of a boat and starboard is the right side, when you face forward toward the bow. The names belong to the boat, not to you, so they stay the same whichever way you turn, and “port” means the same side to everyone aboard. At night the port side shows a red light and the starboard side a green one.
Bow, Stern, Beam and Other Words for a Boat
| Term | Meaning |
|---|---|
| Bow | The front of the boat, its forward part |
| Stern | The back end of the boat |
| Port | The left side when you face the bow |
| Starboard | The right side when you face the bow |
| Beam | The boat’s maximum width; “on the beam” also means straight out to the side |
| Fore, forward | At or toward the bow |
| Aft | At or toward the stern |
| Amidships | At or near the middle of the boat |
| Abeam | At right angles to the boat’s centerline, off its middle |
| Abaft | Farther aft than something, as in “abaft the beam,” behind the beam |
| Transom | The flat surface across the stern |
The definitions follow the nautical term glossary of the Oregon State Marine Board and the glossary of Bowditch’s American Practical Navigator, which defines port as “the left side of a craft, facing forward” and starboard as the right side.
Directions From a Boat: On the Bow, Abeam, On the Quarter
To point out something on the water, boaters use the boat itself as the reference. Bowditch gives each direction as a relative bearing, measured clockwise from the bow:
| Where it is | Relative bearing |
|---|---|
| Ahead | about 0° |
| On the starboard bow | about 45° |
| Abeam to starboard (on the starboard beam) | about 90° |
| On the starboard quarter | about 135° |
| Astern | about 180° |
| On the port quarter | about 225° |
| Abeam to port (on the port beam) | about 270° |
| On the port bow | about 315° |
So a buoy “on the port bow” is ahead and to your left, and a boat “on the starboard quarter” is behind you on the right. When the bearing is exact, Bowditch uses “broad on the bow” and “broad on the quarter” instead.
Port and Starboard Lights
The Navigation Rules make the colors official. Rule 21 defines sidelights as a green light on the starboard side and a red light on the port side, each showing an unbroken light over an arc of the horizon of 112.5 degrees, from right ahead to 22.5 degrees abaft the beam on its own side. On a vessel less than 20 meters (about 65.6 feet) long, the two may be combined in one lantern on the centerline. The white sternlight shows over 135 degrees astern, 67.5 degrees to each side.
That lets you read another boat at night. A red light means you are looking at its port side, a green light its starboard side, and both together mean it is pointed at you, or nearly so. Recreational boats must show navigation lights between sunset and sunrise and when visibility is restricted, such as in fog or rain, the U.S. Coast Guard’s guide to the federal requirements says.
Port and Starboard in the Rules of the Road
Fixed names for the sides let the Navigation Rules give orders everyone reads the same way:
- Meeting head-on (Rule 14): when two power-driven vessels meet on reciprocal or nearly reciprocal courses, each alters course to starboard so that they pass port side to port side.
- Crossing (Rule 15): when two power-driven vessels cross, the one that has the other on its own starboard side keeps out of the way and, if it can, avoids crossing ahead of it.
Both rules have more detail and exceptions, such as the Inland Rules for a vessel crossing a river on the Great Lakes and Western Rivers, so read the full Navigation Rules before you rely on a summary.
Why Are They Called Port and Starboard?
The words go back to how early boats were steered. Before rudders were mounted on the centerline, boats were steered with a steering oar, and because most sailors were right-handed, the oar went over the right side of the stern. The right side became the steering side, “starboard,” from the Old English stéor (steer) and bord (side of a boat). The left side, which faced the dock, became larboard, the loading side. Larboard was too easily confused with starboard, so it was replaced by port: the side that faced the port, NOAA’s National Ocean Service explains.
How to Remember Port and Starboard
- Count the letters: port and left both have four letters; starboard and right are the longer words.
- Red port wine: “Is there any red port left?” ties together red, port and left, the color and side of the port sidelight.
- Face the bow: the names work when you face forward. Facing aft, port is on your right hand, and it is still port.
Don’t mix these up with “red, right, returning.” That rule is about channel markers, not about your own boat: when returning from seaward, keep the red markers on your right-hand (starboard) side, the U.S. Coast Guard says. The red light on your own boat is on the port side.
Port, Starboard and Beam on Your Boat
- On a boat with a transom, the hull identification number goes on the outside of the transom on the starboard side, within 2 inches of the top of the transom, gunwale or hull-to-deck joint, whichever is lowest (33 CFR 181.29). The Boat HIN Decoder reads it.
- Load the boat evenly fore and aft and from side to side, and keep the load low, the Coast Guard advises. The Boat Weight Calculator adds up what you carry.
- For a boat without a capacity plate, the Coast Guard’s rule of thumb for the number of people is the boat’s length times its width in feet, divided by 15. Never exceed the capacity plate; the Boat Capacity Calculator explains both.
Frequently Asked Questions
Which side is port on a boat?
The left side, when you are aboard and facing forward toward the bow. Starboard is the right side. The sides keep their names whichever way you face.
Is port red or green?
Red. Under Rule 21 of the Navigation Rules, the port sidelight is red and the starboard sidelight is green.
Why is starboard called starboard?
It comes from the Old English words for steer and for the side of a boat. Early boats were steered with an oar over the right side of the stern, so the right side became the steering side, NOAA explains.
What is the beam of a boat?
Its maximum width, across the widest part of the boat. Abeam means at right angles to the centerline, straight out to the side from the middle of the boat.
What are the front and back of a boat called?
The front is the bow and the back is the stern. Toward the bow is forward, toward the stern is aft, and the flat surface across the stern is the transom.
How do you remember port and starboard?
Port and left both have four letters, and the question “Is there any red port left?” links port with left and with the red port light. Starboard is then the right side, with the green light.
Sources
- NOAA National Ocean Service, Why do ships use “port” and “starboard” instead of “left” and “right?” (updated Sep 23, 2026; read Oct 19, 2026): fixed sides, steering oar, larboard.
- U.S. Coast Guard Navigation Center, Navigation Rules (read Oct 19, 2026): Rules 14, 15 and 21.
- U.S. Coast Guard Boating Safety Division, A Boater’s Guide to the Federal Requirements for Recreational Boats (revised Nov 2023): navigation lights, red right returning, loading and the capacity rule of thumb.
- 33 CFR 181.29, hull identification number display (read Oct 19, 2026).
- National Geospatial-Intelligence Agency, The American Practical Navigator (Bowditch), Volume II, glossary: port, starboard, abeam, abaft, aft, amidships, relative bearings.
- Oregon State Marine Board, Nautical Term Glossary (read Oct 19, 2026): bow, stern, beam, fore, aft, amidships, transom.