structural:summarization
Shipping

Because Ireland has neither tunnel nor bridge to connect it with Great Britain, the vast majority of heavy goods trade is done by sea. Northern Ireland ports handle 10 million tonnes (9,800,000 long tons; 11,000,000 short tons) of goods trade with the rest of the United Kingdom annually; the ports in the Republic of Ireland handle 7.6 million tonnes (7,500,000 long tons; 8,400,000 short tons), representing 50% and 40% respectively of total trade by weight.

The Port of Liverpool handles 32 million tonnes (31,000,000 long tons; 35,000,000 short tons) of cargo and 734,000 passengers a year. Holyhead port handles most of the passenger traffic from Dublin and Dún Laoghaire ports, as well as 3.3 million tonnes (3,200,000 long tons; 3,600,000 short tons) of freight.

Ports in the Republic handle 3,600,000 travellers crossing the sea each year, amounting to 92% of all Irish Sea travel.

Ferry connections from Wales to Ireland across the Irish Sea include Fishguard Harbour and Pembroke to Rosslare, Holyhead to Dún Laoghaire and Holyhead to Dublin. From Scotland, Cairnryan connects with both Belfast and Larne. There is also a connection between Liverpool and Belfast via the Isle of Man or direct from Birkenhead. The world's largest car ferry, Ulysses, is operated by Irish Ferries on the Dublin Port–Holyhead route; Stena Line also operates between Britain and Ireland.

"Irish Sea" is also the name of one of the BBC 's Shipping Forecast areas defined by the coordinates:

Iarnród Éireann, Irish Ferries, Northern Ireland Railways, ScotRail, Stena Line and Transport for Wales Rail promote SailRail with through rail tickets for the train and the ferry.

The British ship LCT 326 sank in the Irish sea and was discovered in March 2020. In September 2021, the British Navy ship HMS Mercury was discovered; it sank in 1940. The British ship SS Mesaba was sunk by the Imperial German Navy U-118 in 1918 and discovered in 2022. This ship is well known for sailing near the Titanic and for attempting to warn the Titanic about dangerous icebergs.