I copied this from google ...
Boat to/from Phuket/Krabi There is a direct boat service to/from Phuket/Krabi daily. The boat, leaves Phuket ferry terminal (where the Phi Phi ferries leave) each morning between 08.00 and 08.30 each morning and arrives at Ao Nang Beach (south-west of Krabi Town) about 2 hours later. It returns to Phuket in the afternoon at 15.00 and the service includes a free shuttle service to Phuket Town. Tickets can be bought at the Ao Nang Tourist Centre, telephone 075 637730 or contact Phuket telephone: 076 232040 - 1. The cost is 350 baht one way.