Elements from our Navy’s Littoral Warfare Support Group were flown to Tonga in an RNZAF Hercules on 7 August, to assist in the search for the sunken ferry Princess Ashika. The inter-island ferry is believed to have been carrying 129 people when it sank late on Wednesday night, 4 August.
Fifty-four people were rescued, two bodies were recovered, but 73 passengers and crew were unaccounted for, believed drowned. The Princess Ashika was sailing from Nuku'alofa to Ha'afeva, in the Nomuka Islands group, when it sank, after issuing a Mayday call, about 50nm northeast of the capital. An RNZAF Orion took part in the initial searches for survivors, along with local vessels. Despite the intensive aerial and surface search there was no further sign of survivors from the ferry.
The short notice deployment of personnel to Tonga, from the Navy’s Operational Diving and Mine Countermeasures Teams, was announced by the Prime Minister, John Key, on Friday 6 August. He said assistance was being sent after consultation with the Tongan government. The RNZN team, and a Royal Australian Navy diving team, both arrived in Tonga aboard Air Force flights during the night of 7-8 August. Their rapid deployment demonstrated that both countries were ready to assist in the face of such a tragedy, with all the professionalism and preparedness of their respective naval and Air Force capabilities.
During the first day in Tonga, the teams deployed to the search area onboard the Tongan Defence Services Vessel Voea Pangai to commence searching for the Princess Ashika.
After two days of unsuccessful searches using divers and the Remote Environmental and Underwater System (REMUS) the teams returned to Nuku’alofa for a further 2 days until the weather abated.
A subsequent search on 12 August, using the REMUS vehicle under the control of the RNZN Mine Counter Measures Team, identified an object on the sea floor that resembled the missing ferry.
The sunken vessel was located 11nm south southwest of Nomuka in the Ha’apai Group of islands; it appeared to be intact, in an upright position, but at a depth of 110 meters. The position identified by the REMUS system coincided with the positions given by both the Emergency Position Indicating Radio Beacon (EPIRB) and by the Master in his final radio call. The position was also corroborated by the presence of an oil slick, some debris and a mooring line.
Discovery of the object in such deep water came with a degree of disappointment to both the RAN and RNZN Diving teams who do not have the capability to conduct recovery operations beyond 50 metres depth. LTCDR Andrew McMillan, commanding the RNZN Operational Diving Team, said “The RNZN Diving and Underwater Search Teams were pleased to have been able to find the location of what appears to be the Princess Ashika; however we are sad that due to the depth of the vessel this will not lead to closure for the Tongan people. Our hearts and sincere condolences go the families of the victims of this tragedy.”
Manawanui's Role
While the diving and REMUS search operations were underway, our Diving Support ship MANAWANUI made steady progress toward Tonga against challenging weather conditions.
Prime Minister Key had announced that the Manawanui had sailed from the Devonport naval base as a contingency measure to support the search efforts and she was due to arrive in Tonga on Saturday 15 August.
The voyage north was rough, with the ship battling 40-50 knot winds and five metre waves; many of the 18 personnel on board were confined to their bunk when off watch. LTCDR Phil Rowe said it was the worst conditions he had seen. "For the past seven days we have been praying on getting here safely."
Manawanui arrived in Tonga on Saturday 15 August to embark the ROV (which had been deployed to Tonga by the RNZAF with the ODT). Onboard, they took a brief respite and re-roled to support the underwater search operations.
After her arrival in Nuku’alofa, the Manawanui proceeded to the site of the sinking to undertake further reconnaissance operations on the Princess Ashika using the remotely operated vehicle (ROV). The Sea Eye Falcon ROV is a tethered, manoeuvrable mini-submersible vehicle fitted with both photographic and sonar capability.
Manawanui anchored in a depth of 110m above the sunken ferry to provide a stable platform for the ROV operation. Following several days of challenging weather, the arrival of Manawanui also brought an improvement in the weather allowing the ROV task to proceed.
"It was extremely frustrating for us," the search commander LTCDR Andrew McMillan said after having to sit out the rough weather. He explained the sailors would use the ROV to confirm the sonar target was the ferry, by searching for the ship’s nameplate. He commented that the sonar images showed that the sunken ship was surrounded by debris and at that stage he could not guarantee to send the ROV actually into the ferry.
The ROV dives were successful and by 18 August the Team confirmed the sunken vessel was in fact the Princess Ashika. In fact it proved possible for the ROV to enter the cargo hold and its images have provided information to the investigators. Further ROV searches were undertaken to assist in the transport accident investigation to establish the cause for the sinking. An Australian accident investigator was embarked in Manawanui to help with the underwater photographic survey of the wreck.
REMUS Underwater Robot
REMUS is the acronym for Remote Environmental Monitoring Units. The RNZN acquired the REMUS in 2007. It is a robotic ‘torpedo’ that navigates without a human crew onboard and without cables connecting it to a mother ship. They are designed by Ocean Systems Laboratory and Woodshole Oceanographic Institution and built by Hydroid Inc, in Massachusetts, USA. REMUS vehicles can dive to 100 metres deep and are capable of conducting an 80 km survey at a speed of 3 knots. The REMUS is about 160cm long, 19cm diameter and weighs 37kg and has a speed of 3-5 knots (battery powered); can run for 80km (about 10 hours)and uses a high frequency side scan sonar and also measures water conductivity, temperature and depth.
It is controlled with a lap top computer and pre-programmed before its dive. It navigates with acoustic transponders that are located by GPS. The REMUS is the lead weapon for mine countermeasures for the RNZN.
The Sea Eye Falcon Remote Operated Vehicle
The RNZN currently utilises the Sea Eye Falcon Remote Operated Vehicle (ROV) which is a tethered manoeuvrable mini-submersible. Being remotely operated, it is attached by an umbilical cord through which the pilot sends control orders via joystick to the various propeller thrusters that allow it to hover, turn, descend and rise under power.
The RNZN ROV has a small sonar in the nose and the pilot with his control box can look at echo returns on his screen. The Sea Eye Falcon also has a video camera in the nose for visually identifying a target. The Falcon is very portable and uses single phase 100-270 V electricity.
This ROV has a 300m depth rating with a 16 kg payload, a high-resolution colour camera on a 180º tilt platform, variable intensity 150 watt lighting and a portable surface control system with video overlay and daylight readable display.