No, pass does not cover this or other ferry routes.

Both operators do give discounts to passholders, read the benefits page on website https://www.interrail.eu/en/plan-your-trip/pass-benefits or in app under More>Benefits.

These just require you to have a valid pass but not to use a day’s travel or add the journey to the pass.

Ferries can be booked ahead on the operator’s websites but only Stena Line allow discounts to be used directly, for Irish Ferries there is a convoluted procedure of buying full price and e-mailing them details for them to refund the discount.

Both should allow the discount be added if bought from their desks at the ferry terminal.

Stena Line is usually a little cheaper for foot passenger fares.

Be aware that if you are looking to use the Irish Ferries “Dublin Swift” fast ferry, this is very weather dependent and does often get cancelled, it is best to check the operator’s sailing updates pages 1-2 days before and on the day of travel.

The other ships on the route are quite large and rarely fail to run, only extremely bad weather causes delays/cancellations.

A shuttle bus solely for ferryport - city travel is provided meeting all sailings, at last check it is free for Irish Ferries passengers but costs €3 for Stena Line.

I strongly advise against attempting to walk to/from the ferry terminals, they are several Km inside the city’s large industrial port complex, it is not a pleasant walk.

Thank you very much for your time!