Port and starboard vessel's starboard side by green and its port side by red. Aircraft are lit in the same way. Port and starboard Port and starboard are nautical and aeronautical terms of orientation that deal unambiguously with the structure of vessels and aircraft. Their structures are largely bilaterally symmetrical, meaning they have mirror-image left and right halves if divided long-ways down the middle. One asymmetric feature is that on aircraft and ships where access is at the side, this access is usually only provided on the port side. To understand which is which, when a person is facing the bow on a
Ship motions or "roll axis", is an imaginary line running horizontally through the length of the ship, through its centre of gravity, and parallel to the "waterline". A roll motion is a side-to-side or port-starboard tilting motion of the superstructure around this axis. There are three special axes in any ship, called vertical, transverse and longitudinal axes. The movements around them are known as roll, pitch and yaw. There are methods for both passive and active motion stabilization used in some designs. They include static hull features such as skegs and bilge keels, or active mechanical devices like counterweights, antiroll tanks and