What is the primary purpose of a nun buoy in navigation?

The primary purpose of a nun buoy in navigation is to designate the port side of a channel. Nun buoys are typically cylindrical and colored red, and they serve to help mariners identify the correct channel to follow when navigating through waterways. The system of marking channels with buoys is part of the lateral system of aids to navigation, which ensures that boats and ships can safely navigate by adhering to specific side markings.

In this context, a nun buoy specifically indicates that the left side of the channel is situated on the port side when entering from the open sea or from upstream. This helps maintain proper navigation and safety by ensuring that vessels stay within the marked channel and avoid hazards. The distinctive colors and shapes of buoys provide quick and easy recognition, allowing mariners to make informed decisions while navigating through potentially challenging waters.