The Social Security (Ireland) Order (Northern Ireland) 2007

(2) Where a person who is insured under the legislation of one Party and employed either in the territory of that Party or on board any ship or vessel of that Party, is sent by his employer in the territory of that Party to work on board a ship or vessel of the other Party, the legislation of the former Party concerning liability for contributions shall continue to apply to him provided that his employment on board the ship or vessel of the latter Party is not expected to last for a period of more than one year. Where his employment on board the ship or vessel of the latter Party continues after such period of one year, the legislation of the former Party shall continue to apply to him for any further period of not more than one year, provided that the competent authority of the latter Party agrees thereto before the end of the first period of one year.