Final answer:
When entering a US harbor from the sea, red marks with even numbers should be left on the starboard side (right side) of the boat to stay in the channel.
Step-by-step explanation:
When entering a US harbor from the sea, you should leave red marks with even numbers on the right side (starboard) of your boat to stay in the channel.
This is based on the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) system, which is used in the United States. Under this system, entering a harbor, red marks are placed on the right side of the channel, and even numbers are used to mark them.
For example, a buoy or marker with a red light and an even number like 2, 4, 6, etc., would be placed on the starboard side of the channel to guide boats into the harbor.
When entering a US harbor from the sea, the red marks with even numbers should be left on the right side of your boat to stay in the channel. This aligns with the 'red right returning' rule, which is an easy way to remember that the red buoys should be kept on the starboard (right) side when returning from the sea or heading upstream. It is a navigational practice used to guide boats safely through channels and avoid hazards when entering a harbor.