BC Ferries has now published the full 2018 schedule for ferries between Departure Bay and Horseshoe Bay.

From January 2, departure times change at both ends of the route, with the spring schedule running through to May 16. From May 17 there are further changes in service lasting through to October 8, after which the spring schedule returns. As before, there are extra sailings in peak summer (June 23 to September 3) and at busy weekends throughout the season. Full details can be found at www.bcferries.com. 

This summary of the revised schedule can be downloaded here.