When I initially heard about the ferry trip to Zanzibar, I was expecting this to be an old worn-out boat in dire need of repair, slowly shuffling out of the harbor, jam-packed with passengers jostling to find a seat.
Instead, I boarded a brand spanking new boat, after a rather pleasant wait in the ferry terminal in the first-class area. The ferry even has a safety video, plush reclining seats, and a cafe.
There are several "fast ferry" operators offering this service throughout the day, every day. The journey takes about 90 minutes and gives you a fantastic view of Zanzibar and Stone Town harbor, I would definitely recommend first class because your luggage is handled separately and this will avoid you having to join in the absolute mayhem at the baggage carousel.