5NBQJ departed PH that morning with the original plan to ferry the helicopter to Lagos. 2 crew on board. Once en route crew were asked if they could route via the ERHA to pick up pax and bring them to Lagos. They did, but did not do the proper fuel calculations. 20 mins or so after departing the ERHA with a full load of pax and still far from shore they realized their fuel situation and the fact that they were not going to make it. They decided to "land on water" before the engines would run out of fuel.