As well as year-round connections with Lazio's ports, in high summer there are also crossings
that run to and from Naples, operated by the SNAV line - but weekends only!
The Alilauro line's service appears to have ended.
En route the SNAV craft stop in at Ischia (at the port of Casamicciola Terme), from where
Ventotene is then some 50 minutes away before continuing on to Ponza - but do be sure to check
exactly from where, and when, they run BEFORE you set out....