Tranquillity Island Turtle Sanctuary

We are doing a Royal Caribbean cruise in February. We would like to go to the Turtle sanctuary on Tranquillity Island. As far as I can see, Royal Caribbean does not offer tours that goes there.

Does anyone have any experience of going to the Turtle sanctuary, either on their own or as part of a custom tour with a Vanuatu tour operator?? Not sure what would be the best way of getting to the Turtle sanctuary and whether it's best doing a tour etc.

Any feedback would be greatly appreciated. :)

Thanks! :D

EDIT: It looks like you can do a Coongoola cruise which goes to the turtle sanctuary, but there isn't much information as to how much time you get to spend at the Turtle sanctuary etc. We would like a half day tour if possible.