Friday ferries to Rakino are at 1000 and 1840 from downtown, pier 3B (please leave plenty of time to unload/find parking, and take into account Fri rush hour traffic!)
For those who need parking in town, a good option is Downtown car park at 31 custom street which is a very reasonable $22 for the weekend, from 1730 Fri until anytime Sun (Not suitable for tall vans/campervan though due to height restrictions!)
Saturday water taxi/shuttles from Waiheke will be at 1230 and 1330, and back at 1830 and 2200. These will depart from Matiatia wharf (where the ferry comes in from downtown). You will find Steve from Auckland Sea Shuttles at the smaller boat pontoons at the end of the wharf road
Sunday return ferry is at 1720 to downtown, pier 3B