I have read from several sources that there are major problems with the ferry service right now. There is only one ferry boat servicing both Vieques & Culebra! If you're traveling to Vieques in the next few weeks, you might want to think twice about planning to use the ferry service. Fly!!. If you absolutely need to take the ferry for budget reasons, make sure you get to the terminal as early as possible to secure your ticket.
Maybe other who live on Vieques can add more info to this post.