The Eurail Global pass does not give free travel on Eurostar, British trains, or ferries. You do get a discount of some kind on Eurostar and the Holyhead-Dublin ferry, but even so it will be a very long journey.
I would STRONGLY recommend flying even if you have romantic ideas about doing it the "traditional" way. There are no direct flights from Strasbourg to Dublin, but Ryanair fly from Basel to Dublin, and you can get from Strasbourg to Basel by train quite quickly.
Be warned that Ryanair are a budget airline that charges extra for an awful lot of things - read the terms and conditions carefully; you MUST be able to check in online and print out your own boarding pass, or pay a huge penalty charge at the airport; and hand luggage size restrictions are VERY strictly enforced.