by boat, any suggestions?
Fran, www.golfoparadiso.it is the ferry system that has the Genoa/Portofino ferry run. It's the Linea Verde (Green) line. Here's a link to some information about the Green line and when it runs.
fran,
Some additional information would be helpful. For example, when is this trip taking place? In some cases, the boats are seasonal or weather-dependent.
The easiest method would be to travel by train from Genova to Santa Margherita Ligure, and then from there to Portofino by the smaller local boat, hiking or Taxi. Use the Trenitalia website to research trains on that route.
It would be easier to offer more specific suggestions if you could clarify your plans.
Cheers!