There are good day trips on offer from a number of charter companies based in Tutukaka. There are also two (three?) liveaboard operators as well.
Personally, I think the liveaboard option provides better value (particularly if it's your one and only trip out - plus the chance to do a night dive) but they are harder to organise.
The two main liveaboard operators are Pacific Hideaway (
www.divenz.co.nz) and Oceanblue (
oceanblue.co.nz). Pacific Hideaway is very popular with the local dive shops as the boat sleeps more people (12) and may be booked out for weekends during the summer already! Try contacting Global Dive in Auckland (
www.globaldive.net) who normally book out one or two weekends a month for the whole summer, so that will take a lot of the hassle out of the process. Put in a request for lamb shanks if you go, as Mark the skipper does a killer lamb shank dinner.
Ocean Blue have a smaller boat, and often do 3, 4 & 5 day trips, not just to the Knights but the including other dive sites in the outer Hauraki Gulf and nearby area. Kev and Janine who own OceanBlue will give you a great trip.
On either liveaboard, you could expect do to 7 dives in a weekend.
Charters running day trips include Dive! Tutukaka (
www.diving.co.nz), who are very well set up for visiting divers and run a very slick operation. There are others, but I tend to use D!T the most for day trips, though occasionally I use Yukon Charters (
www.yukon.co.nz) as Noel the skipper also runs a good trip.
Other charters include Adrenalin Charters, Knight Rider, Poor Knights Divers and Bluzone - you'll find the details if you google them. As I don't really use them, I won't give you an opinion on them, others who do use them may be better situated to do that.
We organise fairly regular trips to the Knights, so if you need a hand organising anything then send me a PM. Let me know when you're coming, if it aligns with any of our trips then you can hop on with us - or if it's a free weekend, we'll just arrange a trip anyway!
www.techdivenz.com/calendar.html