What is the primary function of lateral marks?

The primary function of lateral marks in the IALA Maritime Buoyage System is to show directional navigation within a channel. These marks are designed to guide vessels safely along the intended route by indicating the sides of navigable channels.

In the system, lateral marks are typically used in pairs, with one color indicating the port side and the other indicating the starboard side when approaching from seaward. This helps mariners understand which side to stay close to while navigating through channels and narrow passages. The color and shape of these marks provide crucial information about the channel's orientation, ensuring that vessels do not stray into dangerous waters where hazards may exist.

The other options suggest functions that are not the primary role of lateral marks. They might provide supplementary information, but the main purpose remains focused on channel navigation, making the directional guidance of lateral marks essential for safe and effective passage.