We went on the Coongoola partly because my 9yo son is mad on turtles and this tour includes a visit to a turtle hatchery. The turtles were interesting (my son enjoyed that bit) but for me the highlight was the snorkelling on the other side of Mosu island - absolutely superb.
Trip started with a bus from Port Vila to the boat, then a short trip across to the tranquility eco resort to see the turtles. From there the boat takes you around to the other sider of the island and a lovely little beach. People can either stay at the beach and relax or snorkel around the coral near the beach, or go out in a dinghy to snorkel on one of the deep water reefs. This was superb with crystal clear water and masses of coral and sealife. The best snorkelling in my stay in Vanuatu. After the initial snorkel, back to the bech for a BBQ lunch and then the option to head out for another deepwater reef to snorkel on. I managed to get my wife and 9yo to come on the second trip and they thought it was fantastic. Then back to Port Vila after an excellent day. Highly recommended.