The ports nearest Palau are Olbia and Golfo Aranci; a bit further away are Port Torres and Cagliari. You can also reach Palau travelling from Corsica from the port of Bonifacio to Santa Teresa.
Various maritime companies link these ports daily with Civitavecchia, Genoa, Livorno, Piombino, Barcelona and Marseilles
Ferries to Sardinia:
Grandi Navi Veloci