The Isle of Man Steam Packet Company's crossing to Larne is moved from Wednesday to Tuesday.
The discovery was made when officers searched a lorry travelling from Scotland to Larne Harbour on Monday.
The Manxman resumes sailings between the Isle of Man and Heysham after weekend cancellations.
The investigation by the Health and Safety Executive for Northern Ireland (HSENI) commenced following the death William Houston.
Luke Littler became world champion in 2025, which inspired a whole new generation to take their first steps up to the oche.
Emergency services responded to reports of a man overboard from a ferry travelling between Scotland and NI.
Lyons was investigated over a Facebook post after immigrant families were forced to flee their homes during racially-motivated riots.
Gordon Lyons was investigated over a Facebook post published during racist violence last summer.
The ferry operator will run sailings to the port each week as well as increasing Dublin connections.
