...
Marlborough managed tide stations are located at:
Motuara Island (-41.093883°, 174.271459°)
Okukari Bay (-41.201612°, 174.311423°)
Te Weka (-41.249400°, 174.192815°)
AIS Messages
Stations transmit AIS messages 21 and 8 once every six minutes on each channel, offset by three minutes. Message 21 reports the station name and coordinates. Message 8 reports a composite tide height that considers inputs from both pressure and radar sensors.
...