I think the best known ferry here to run across the Irish sea from Dublin would have been the Mail Boat. Ran from Dún Laoghaire to Hollyhead, where the train to Euston station, London waited to meet it.. or more accurately to meet the most important cargo i.e. the mail.
As far as I know it was was run by a subsidiary of British Rail ?
I'm sure there were ferries to Liverpool also, but any of them would have been near to a railway to allow travel on to Morecambe.
Shane