A charter boat reported colliding with an underwater obstacle between Whale Island and Raurimu Island.  The collision damaged the drive leg which resulted in the boat being unable to manoeuvre.  The boat had nine people on board. Assistance was requested and Whakatane Rescue responded with a crew of four. Sea conditions were good with a low NW swell and 10kt westerly breeze. The boat was taken under tow and brought safely back to Whakatane.