In early August 2009 the Royal New Zealand Navy’s Operational Diving Team and a specialist Remote Search Team were flown to Tonga in an RNZAF Hercules at short notice to assist with the search for the sunken ferry, PRINCESS ASHIKA.
The PRINCESS ASHIKA had been sailing from Nuku’alofa to Ha’afeva in the Nomuka Islands group when it sank on 6 August, after issuing a mayday call, about 60 nautical miles northeast of the Tongan capital. It is believed the ferry was carrying more than 150 people on the evening of 5 August. Fifty-four people were rescued, and two bodies recovered, but more than 90 passengers were unaccounted for, believed drowned.
Following a request for assistance from the Tongan Government, the prompt deployment of Defence Force people from the Navy’s Operational Diving and Mine Counter-measures Teams was announced by Prime Minister John Key on 6 August.
An RNZAF Orion took part in initial searches but despite an intensive aerial and surface search there was no sign of survivors from the ferry.
The Royal New Zealand Navy team and a Royal Australian Navy diving team arrived in Tonga aboard Air Force flights during the night of 7–8 August. The rapid deployment demonstrated that both New Zealand and Australia are able to assist at short notice, with the professionalism and preparedness of their respective naval and air capabilities.
On the first day in Tonga, the teams deployed on board the Tongan Defence Services Vessel Voea Pangai to look for the PRINCESS ASHIKA. After two days of unsuccessful searches using divers and the Remote Environmental and Underwater System (REMUS), they returned to Nuku’alofa for two days until bad weather abated.
A second search began on 12 August, using the REMUS vehicle under the control of the RNZN Mine Counter Measures Team, and identified an object on the sea floor that resembled the missing ferry. The sunken vessel was located 11nm southwest of Nomuka; the ferry appeared to be intact, in an upright position, but at a depth of 110 metres. 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 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 New Zealand and Australian Navy diving teams, neither of which have the capability to conduct recovery operations beyond a depth of 50 metres.
LTCDR Andrew McMillan, commanding the RNZN Operational Diving Team, said “We are pleased to have been able to find the vessel, however very sad to report it is in 110m of water. That means we will not be able to dive on it. This will not lead to closure for the Tongan people. Our hearts and sincere condolences go to the families of the victims of the tragedy.”
Writing to the Hon John Key, the Tongan Prime Minister Hon Feleti Vaka’uta Sevele said he wished to express the “enormous and sincere gratitude of the government and the people of Tonga for the valuable assistance of the P3 Orion … and the courageous and continuing assistance of the New Zealand Navy dive team. The very prompt response was appreciated by all.”
HMNZS MANAWANUI
While the diving and REMUS search operations were underway, the Diving Support ship MANAWANUI sailed from Devonport, Auckland to support search efforts near Tonga. MANAWANUI made steady progress toward Tonga in challenging weather conditions; with the ship battling 40–50 knot winds and five-metre waves. MANAWANUI arrived in Tonga on 15 August to embark the Sea Eye Falcon Remote Operated Vehicle (ROV) (which had already been transported to Tonga by the RNZAF) and support the underwater search operations. The ROV is a tethered, manoeuvrable mini-submersible vehicle fitted with photographic and sonar capability. After her arrival in Nuku’alofa, MANAWANUI proceeded to the site of the sinking to undertake reconnaissance operations on the PRINCESS ASHIKA using the ROV. MANAWANUI anchored in a depth of 110m above the sunken ferry to provide a stable platform for the ROV operation. The ROV dives were successful and by 18 August the team could confirm the sunken vessel was in fact the PRINCESS ASHIKA. The ROV was able to enter the cargo hold and its images provided information to the investigators. Further ROV searches were undertaken to assist in establishing the cause of the sinking. A New Zealand 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. It is a robotic ‘torpedo’ that navigates without a human crew onboard and without cables connecting it to a mother ship. The equipment is built by Hydroid Inc, in Massachusetts, USA. The Royal New Zealand Navy acquired REMUS technology in 2007. REMUS vehicles can dive to 100 metres deep and are capable of conducting an 80km survey at a speed of three knots. The REMUS is 160cm long, 19cm diameter, weighs 37kg and has a speed of 3–5 knots (battery powered); it can run for 80km (about ten hours) and uses a high frequency side scan sonar and also measures water conductivity, temperature and depth. It is controlled via a lap top computer and 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 also uses 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 a 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 16kg 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 a daylight readable display.