To get to Roonagh Quay from Westport, take the Louisburgh Road (R335) 21km (13 miles) to Louisburgh. Continue straight through the town and over the bridge. About 0.4 km (1/4 mile) after the town, turn right at the signpost for Roonagh pier and the ferries, about 6.5km (4 miles) down this road.
The last road is narrow so leave yourself plenty of time to catch the ferry!
See below for more info on Ferry Timetables: