Norfolk Line, P&O Irish Sea and Stena Line operate crossings to Northern Ireland from England, Scotland and the Isle of Man with a crossing times just under 8 hours. 

Norfolk Line is Liverpool Birkenhead to Belfast with 13 sailings a week. Stena Line is Fleetwood to Larne with 3 daily sailing.

From Scotland with P&O Irish Sea is Troon to Larne 13 sailings a week and crossing time is approx 2 hours. Cairnryan to Larne is only 1 hour sailing time with 8 daily sailings and Stanraer to Belfast with Stena Line 6 daily sailings with 2 hours in crossing time.

Douglas to Belfast is the Isle of Man route and this operate 2 sailings a week with Isle of Man Steam Packet Ferries.