Another spot on Buckland's Beach where you can launch, a bit more north than the spot that is easier for beginners. Here you're fairly close to the boats, but it's easy to windsurf between them and get into the mouth of the Tamaki river proper. You can launch from everywhere here. And around the corner, to the north, there aren't even any boats.
This is a good spot to launch if you want to windsurf to Browns Island (http://www.doc.govt.nz/Explore/001~Other-Places/002~Auckland/Motukorea-Browns-Island.asp). Or Motukorea in Maori (Motu means island). On a light wind day, just pick the big board, a big sail, some drinks and food and sail away to this secluded island, less than 1 kilometer up north. Cross the big boat lane quickly and sail to Browns Island, leave the windsurf gear on the broad beaches and climb to the summit to have an excellent view of Auckland and its harbour.