Whale Watch Kaikoura is one of the biggest businesses in New Zealand. It is Maori owned and run, and its CEO also chairs Tourism NZ. There are four of these boats, taking 44 people each and going out 3 or 4 times a day. They guarantee up to 80% of your money back if you don't see whales, so they need to be good at finding them.
It isn't cheap (NZ$130 each!) either, but it's also almost unique to have so many large whales come close inshore, and a semi-resident colony of sperm whales. Again, this is due to the Kaikoura canyon which is so close inshore. The nearest point is at Goose Bay (about 50km south of Kaikoura), where the sea depth drops to 800m, less than 800m from the shore.
If you look at a topographical map of the sea bed hereabouts, you see a big ridge which hooks north from Christchurch, and the canyon comes inshore behind this. So not only do you get this very deep water, but also relatively calm seas (emphasising the relatively), as the full frenzy of the Pacific has been broken over that ridge. A storm out there would be an unhappy thing to contemplate.