JAKARTA - Indonesian rescuers searching for three missing divers, including a Singaporean, who might have been carried away by undercurrents expanded their search on Thursday (Nov 7) to an area covering 1,400 nautical square miles between Java and Sumatra islands.
The Sunda Strait, the narrow waterway between Java and Sumatra, has strong undercurrents which have swept away divers in the past.
"We have entered the fifth day. We are taking into consideration an exhaustion factor. We are adjusting down the duration, the time (our) divers spend below, and increasing rotations (of divers being deployed)," Mr Muhammad Zaenal Arifin, a senior official at Indonesia's search and rescue operations (Basarnas), told The Straits Times via telephone, describing the search efforts.
"As we search for victims, we must ensure our search personnel remain in good physical shape," he added. The search area was 900 nautical square miles on Wednesday.
Six tourists went out diving on Sunday in two groups, but the missing trio - the Singaporean and two Chinese nationals - did not return to base on Sangiang island in Banten province, near Jakarta.
The two groups of divers started their dive at about 1.30pm local time on Sunday and only one group returned to the surface at about 2.45pm, Basarnas said.
On Thursday, Basarnas deployed 19 search and rescue scuba divers, up from 13 on Wednesday, and is sending more vessels to search the sea surface. Three helicopters were also deployed, from only two previously.
As of noon local time (1pm Singapore time) on Thursday, three sorties of divers had been sent down into the waters. The ideal timing for search operations is between 6am and 8am when sea currents are weakest. After that, the crews must apply extra caution, Mr Zaenal said.
Mr Zaenal, who heads Basarnas' Banten chapter, described what might have happened to the two groups of divers on Sunday.
He said one group went north of Sangiang and the missing Singaporean and two Chinese divers headed towards the south of the island.
The divers in the south might have intercepted strong undercurrents which flow from the sea north of Java and the Strait of Malacca into waters between Sumatra and Java islands.
"Undercurrents there can be unpredictable and change regularly depending on the changing weather. Each island there sees different sea current paths around it," Mr Zaenal explained, referring to islands in the Sunda Strait.
The Sunda Strait has had a number of accidents in the past, including high tides capsizing boats and divers getting carried away by undercurrents, according to Mr Zaenal.
On Sept 8, 2018, Mr James Ade Ignatius Salaka, 32, a North Jakarta resident who did a fun-dive at a depth of between 9m and 12m in waters off Sangiang island was pulled away from his group by an unexpectedly strong undercurrent. He was later found dead.
The waters off Sangiang island are a popular diving spot for foreign and domestic tourists. It takes about an hour by boat to reach the island from the nearest pier on Java island.
"There are a number of islands there, and of course there is Krakatau volcano. It is not recommended to dive there without having a local guide," Mr Zaenal said, adding that local guides are able to suggest the right timings to dive and recommend spots that are safe for diving based on weather conditions.
Basarnas will continue its search operations until Saturday (Nov 9) - the last day of a standard seven-day search period - and will then evaluate whether to continue or end the mission.
"It will depend on whether the chances of finding the missing divers are very slim or even none," Mr Zaenal said.
He added that the victims' families could request operations to go on, but certain conditions apply.