JAKARTA, INDONESIA — Indonesia and the world mourned the sinking of Indonesia’s Navy submarine KRI Nanggala-402 in the Bali waters.
Singapore’s MV Swift Rescue had visual contact of the ship—which was split into three parts—at the depth of 838 meters on 25 April.
KRI Nanggala-402 lost contact during a torpedo drill preparation on 21 Apr. Several countries such as Singapore, Malaysia, South Korea, Australia, India, the United States, and Germany joined the search to discover the sunken submarine that carried 53 people onboard.
Indonesia is trying to lift the sunken submarine from the depth of 838 meters at the request of the families of the 53 crew members.
“We are trying to be able to lift the submarine from the depth of 838 meters. The International Submarine Escape and Rescue Liaison Office (ISMERLO) and our partners are offering help,” said Indonesia’s Navy Chief of Staff Admiral Yudo Margono during a press conference on 25 Apr in Bali.
The Navy declared the status of the KRI Nanggala-402 as sunk after numerous parts of pieces of debris belonging to the submarine were found. All the 53 crew members died.
No human error in KRI Nanggala-402 incident, says navy chief of staff
Yudo explained the initial causes of the incident, stressing that there were no human errors and blackouts that made the ship sink.
“We have evaluated from the start … I am sure that the cause of the accident is not a human error, but more due to natural causes,” he said, adding that all diving processes have met the procedure.
Torpedo launching unlikely the cause behind KRI Nanggala-402 sinking, says former U.S. Navy — and other theories on the incident
Regarding speculation on how a torpedo launch could have caused the sinking, former U.S Navy and co-founder of Hawa’ii-based social impact company Mana Pacific, Dan Fugardi claimed that it is unlikely that the torpedo launching was behind the incident, estimating that high pressures of hydraulic systems and ocean water could possibly bring the 40-year old ship underwater.
“I’ve been asked if a torpedo launch could go wrong and water could flood into the boat. I would be willing to say there is almost a 100 per cent chance that would not happen. There are a series of tanks around the torpedo tubes that use hydraulic pressure to move water into and out of the tubes after you put the torpedo in the firing tube,” he told TOC.
Fugardi added that there are two “breach doors” on each side of the torpedo tube with mechanical interlocks or sensor switches on the exterior breach door.
Interior breach doors, on the other hand, are secured with an excessive amount of leverage and are highly unlikely to blow open in a torpedo launch.
“Additionally, a boat could perform an “emergency blow out” by closing the ballast tank vent doors and quickly filling the ballast chambers with air to give the boat instant buoyancy, even if the boat was taking on water,” said Fugardi.
Furthermore, the pressure of hydraulic systems is extremely high and incompressible, he added.
This, coupled with the pressure of the surrounding ocean water, can be stronger than the integrity of the steel, especially in the case of a vessel that is 40 years old, Fugardi explained.
“The brittle fracture fragility point, or point at which the steel becomes weak enough to break, lowers to needing a lot less energy to cause damage as temperature decreases, which obviously happens as the boat dives deeper into the water,” he elaborated.
Another possible cause behind the KRI Nanggala-402 incident, said Fugardi, is an increased “creep rate” that eventually built up to the point of fracture.
The “creep rate”, he explained, is a measure of how additional strain — as a factor of change in applied pressure within a period of time — becomes bigger.
A spike in the creep rate within a shorter time window greatly increases that rate that eventually spikes to the point of fracture, he said.
“Over the long term, the above curve moves to the left as a result of repeated strain cycles … (This means that it) weakens, and the effects of a temperature change become more dramatic (at a) faster (pace),” Fugardi explained. “With enough wear of steel integrity, a vertical curve could reach a catastrophic point rather quickly.”
Additionally, Fugardi theorised that the submarine “could have simply crashed into the ocean floor in a dive”.
“There was at least one time where our crew had a “brace for impact“ alarm go off. We were sitting there with our heart in our throats, saying, “Please, God, let this be a mild precaution.” The ocean depths in the surrounding area got as deep as 1500m,” he recalled.
The KRI Nanggala-402, he noted, had crashed into the floor at 838m — Fugardi is of the opinion that this indicated that “they were attempting to go deeper and miscalculated the topography”.
He questioned investigators’ conclusion on how human error was not involved in the incident.
“Judging by the fact the boat is in three separate pieces, I would imagine this is absolutely a possibility … I’m not sure how they would know that at this point, but if that is true, it’s possible that one of the ballast tank vents did not close. This would let water into the part of the boat that amasses air gain buoyancy and float to the surface,” said Fugardi.
On the process of lifting the submarine off the ocean floor, Fugardi said he could not opine on the matter “more than anyone else could find in a Google search”.
“I do believe it is within range to reach, and a diesel-electric is at least four times lighter than a nuclear sub, so perhaps extracting the three pieces is not going to be extremely challenging,” he said.
KRI Nanggala-402 incident more likely caused by damaged ship converter than age of vessel, says retired Navy Admiral
A retired Navy Admiral, who once headed the KRI Nanggala-402’s engine room, assumed that there was damage in the ship converter, claiming that the age of the submarine had nothing to do with the sinking as the sub had regularly undergone routine maintenance, including a retrofit in South Korea in 2012.
“Based on my analysis, blackouts mean power loss. You cannot move a piece of equipment and the steering wheel while in a diving position. The motor stopped but it was about to go down.
“Maybe, the submarine’s crew may have taken too long to find out the cause of the blackouts because of something. My analysis was there was an error in the converter,” the retired officer stated, as cited in Detik on 23 Apr.
Other experts assumed that the damage in the German-built submarine’s pressure hull—which plays a vital role in protecting the crew members, battery, engine, and regulating air pressure—could be one of the causing factors.
Submarine expert at the Surabaya Institute of Technology, Wisnu Wardhana, said as cited in DW on 22 Apr: “There are boat crew members in a pressure hull, also engines, fuel tanks, and batteries. If the oil spills, my conclusion is that the pressure hull is damaged. The pressure hull has hit the bottom hard so it wrecked. Just imagine, the pressure hull is damaged and the 30-bar water pressure floods the sub.”
Retired U.S. Navy officer Lawrence Brennan elaborated on such a phenomenon, stating that if any of the hulls remained intact, it would establish that the hull had flooded before reaching the depth in which the submarine was crushed.
“If the hull had flooded, water pressure was equalised. Thus, the increase in pressure as the boat descended would not have caused an implosion,” he told TOC in an email interview on 23 Apr.
“This is important if the boat had internal compartmentalisation.”
Prof Brennan, who spent 33 years in the U.S. Navy, added that internal air pressure in a compartment would not be able to control water pressure at such a depth.
“The engine room probably was one separate compartment and most of the crew probably was in a separate forward compartment. The torpedo tubes most likely were in the forward compartment and the after-most compartment if there were three separate compartments. The torpedo tubes were not likely present in the engine compartment,” the New York-based lecturer explained.
More pictures and diagrams are needed to get more details about the submarine’s subdivisions and compartmentalisation, he said.
Prof Brennan further said that the added water, even in a single compartment, “may have been enough to cause the boat to be unable to surface and ultimately descend beneath crush depth before resting on the bottom at 838 meters”.
“If a compartment was not flooded as the boat descended below crush depth, it would have imploded. That would be obvious in the photos.
“On the contrary, if a compartment was open to the sea, and thus fully flooded, that portion would not have imploded since the water pressure was equal on both sides of the hull,” he theorised.
How long will investigations go on?
The investigation will be carried out after the sunken ship is lifted. Yudo said that his side will discuss as it will take a long process to evacuate the ship from the 838-meter depth.
He added that the investigation into the KRI Nanggala-402 incident can also benefit from consultations with experts and prompt interviews of all potential fact witnesses.
Meteorological and oceanographic data also should be collected, preserved, and analysed, he added.
According to Prof Brennan, other factors that should be taken into account during investigation include:
- Unusual underwater phenomena, such as earthquakes, volcanic activities, should be documented and considered as appropriate;
- All electronic and audio data from those ships and aircraft ship to determine all communications and acoustic noises leading to the implosion; and
- The building, rebuilding, operational, maintenance, repair records along with reports of defects.
Prof Brennan predicted that the investigation may take a year, referring to the probe of similar past incidents resulting in total losses of submarines.