A more thorough explanation:

The home-port doctrine is a rule in maritime law that states that a vessel involved in interstate and foreign commerce is only subject to taxation at its home port, which is usually where the vessel is registered.

For example, if a ship is registered in Miami and travels to New York to conduct business, it will only be taxed in Miami, its home port. This rule helps to prevent double taxation of vessels that operate in multiple ports.

Another example would be a cargo ship that is registered in Japan but travels to the United States to deliver goods. The ship would only be subject to taxation in Japan, its home port.

The home-port doctrine is important for the shipping industry because it provides clarity and consistency in taxation for vessels that operate in multiple ports. It also helps to prevent disputes between different jurisdictions over which port has the right to tax a particular vessel.