If it is calm you can drift through them slowly, which is what I often do. Once you know they are terakihi you can then anchor on them. Out along Papamoa in 20-30m of water on the little patches of papa foul you will often see a lot of sign hard on the bottom, if you have a colour sounder and the sign is quite reddish it is usually just little snapper, however if the sign has quite a bit of green in it then there is a good chance they will be terakihi. If you don't have a colour sounder then it is going to be trial and error. If all you are getting is little snapper keep trying different parts of the papa foul until you get onto them or try somewhere else. The numbers of Terakihi off Papamoa is nothing like it was 10 years ago.
Also down off spot R there is quite likely to be terakihi right into 15m of water. To give you an idea of how shallow they can be. at Labour Weekend we were up at Opito Bay and my mate after having a scallop dive finished his tank off on a cray dive in 15m of water right in the bay and said he saw heaps of nice big terakihi and has seen them there a number of times this scallop season, he has never bothered trying to catch them though.