A person employed on a U.S. or Belgian ship who would otherwise have dual coverage
under the social security taxation and coverage laws of both the United States and
Belgium, will only have coverage under the laws of the country whose flag the ship
flies. If a ship of one country is in the territorial waters or a port of the other
country, this provision will only apply to those workers who are ordinarily employees
on the ship while it is at sea. Others, such as cargo handlers, pilots, maintenance
crews, etc. will be subject to the laws of the country in which they are working unless
they qualify as a detached worker.