The ferry ride between the islands is 92 km and takes about 3 hours.
Two ferry service companies transport passengers (and their vehicles) between the two Islands. The Interislander and Blueridge.
Check out their websites for details and he ferry schedule.
The InterIslander www.greatjourneysofnz.co.nz/interislander
BlueBridge Ferry www.bluebridge.co.nz/
There are night rides with sleep cabins offered, however, we think that the 92 km ride across Cook Strait and into the Marlborough Sounds is so picturesque that we wouldn’t want to miss it. We would recommend a daylight passage.