There is a ferry (90 minutes) from Guadeloupe or Martinique.
Express des Isles. Express des Isles has regularly scheduled interisland jet catamaran ferry service connecting Dominica to Guadeloupe, Martinique, and St. Lucia. The ferry departs from Roseau and travels to Martinique or Guadeloupe on Monday, Wednesday, Friday, Saturday, and Sunday. (Schedules are subject to change.) From Guadeloupe, it continues south to St. Lucia. The Martinique or Guadaloupe round-trip crossing costs €129 and takes approximately 90 minutes. The voyage offers superb views of the other islands. Tickets can be booked through the Whitchurch Travel Agency. H.V. Whitchurch & Co. Ltd., Old Street, Roseau. www.express-des-iles.com/index.cfm?lng=en.