Hi Niel
Outside of main season, the ferry schedule is adapted to fulfill the needs of the people living on the island, which means that the catamaran ferry leaves island early in the morning and return in the afternoon so that the people from the islands can get to work, that is reason why you can not find ferries which fits your needs.
You don?t need to bring car to Vis, there is bus from Vis city to Komiza which leaves in front of ferry terminal, after the ferry has arrived.
In Vis harbour there is also plenty of places where you can rent scooter and bikes to cross the island.