Friday, April 30, 2021

KRI Nanggala 402 Submarine - The first submarine tragedy in Southeast Asia

On 25 April (Sunday), photos taken from the Deep Search and Rescue Six (DSAR6) submersible vessel reveal that KRI Nanggala 402 submarine is broken into at least 3 pieces lying on the 850m seabed. The DSAR6 is carried onboard MV Swift Rescue, a submarine rescue vessel deployed by the Republic of Singapore Navy.

Military personnel are trained for warfare. They may loss their lives when defending the sovereignty of a nation in time of war or conflict. Such tragic incident during peacetime is an occupation hazard which submariners are subjected to as a team.  

My heart goes along with the families of our Indonesia neighbour.

KRI Nanggala 402 submarine during exercise in 1992. Photo: Wikipedia


Sequence of events

Sub miss: On 21 April (Wednesday) the KRI Nanggala 402 submarine asked for permission to dive at 3am Indonesia time. At 4.30am the submarine went missing with 53 people on board when taking part in a torpedo drill in north Bali waters. Those people include 49 crew members, one ship commander and three weapon specialists.

Sub sank: On 24 April (Saturday) the Indonesia military chief Hadi Tjahjanto was speaking at a press conference, saying that the navy had found oil spill and recovered debris and items which are evidence that the KRI Nanggala had sunk. These items would not have come outside the submarine if there was no external pressure or without damage to its torpedo launcher. Those objects include part of a torpedo, part of a praying mat, grease and a submarine part that was manufactured in South Korea.  The KRI Nanggala 402 was retrofitted in South Korea in 2012.

No miracle: On 25 April (Sunday), closed range photos shot by DSAR6 confirmed the mishap.

The submarine is a German Type 209 variant, built to withstand up to 500m depth. The pressure hull will collapse beyond 500m. The way a pressure vessel collapse is usually crushed like an empty Coca Cola can, torn apart and may break into several pieces. Indeed, the disintegrated hull sections and fittings of KRI Nanggala 402 were captured by underwater cameras. 

An image from the camera of the MV Swift Rescue vessel, captured at a depth of 838m, showing hull parts from the sunken submarine. Photo: The Indonesian Navy

The recent submarine incidents

The speculation for KRI Nanggala 402 submarine tragedy is probably due to power failure. Torpedo explosion has been ruled out because in the event of such detonation, the hull would be fragmented into many smaller pieces. 

While the oxygen tanks may enable the crew to survive up to Saturday, such collapse implies that the crew may have lost their lives at the instance when the submarine dove beyond its depth limit. It is within seconds.

On 27 April (Tuesday), Two Indonesia senior naval officers suggested that another possible cause is strong underwater wave forcing the submarine to descend at an uncontrollable manner. At the spot where the submarine was missing, the movement of a strong internal wave is captured by the satellite image report of Japanese weather satellite Himawari 8 as well as European one. Such underwater wave was created due to seawater density difference between the Lombok Strait and the much deeper waters north of Bali where the KRI Nanggala 402 was.   

Such tragedy reminded me several other submarine incidents happened during my former career.

In August 2000, Russian Oscar II class submarine (the world's largest cruise-missile submarine), Kursk sank in the Barents Sea. A leak of hydrogen peroxide in the forward torpedo room led to the detonation of a torpedo warhead which in turn triggered the explosion of around half a dozen other warheads about two minutes later. Investigation revealed that 118 sailors died on the spot. 23 survived from initial explosion and subsequently perished from cold and Carbon Dioxide build up in another watertight compartment.

On 8 Jan 2005, the Los Angeles class submarine, USS San Francisco collided head-on with an undersea mountain 350 miles south of Guam. The submarine experienced a rapid deceleration from about 35 knots to 0 in 4 seconds. One sailor died and around 60 sailors injured in the accident. The submarine sustained severe damages and had been decommissioned.

Source: John D. Shaw presented to the 24th International System Safety Conference 3 August 2006


Loads on a submarine pressure hull

During my postgraduate study and subsequent exposure, I learned about design of submarine and the BS5500 pressure vessel code in greater depth. BS5500 is now PD 5500 “Specification for unfired, fusion welded pressure vessels”.

Comparing surface ship with submarine, surface ship operates in a 2D environment i.e. on sea surface. Submarine operates in a 3D environment with an additional dimension of depth when submerging underwater.

Modern submarine has a pressure hull joined with a dome and a cylindrical body to withstand water pressure (hydrostatic pressure). Structurally, round form has the best all rounded strength to withstand various stresses with the least materials. 

The plate thickness of a pressure hull would range from about 18mm for a WW2 German’s U-boat to 76mm for a nuclear submarine. For comparison, the weight of the 59m KRI Nanggala 402 is about 1400 ton. A surface warship of similar length but armed with many more warfare equipment and machinery would be around 500+ ton. It shows how massive a submarine pressure hull contribute to the overall weight.

KRI Nanggala 402 specifications. Source: BBC

Submarine also has an external light hull (casing). The casing is a non-watertight hull which provides hydrodynamically efficient shape. It allows for free flooding in order to achieve pressure equilibrium.

During operations, the loads acted on a submarine’s pressure hull can be classified as follows:

1.  Loading due to external underwater pressure

Based on physics, every 10m underwater is equivalent to an additional load of about 1 atmospheric pressure (1 bar). 1 atmospheric pressure is the air pressure we live on land. Hence, at 10m depth, we are subjected to double the normal air pressure.

For the case of KRI Nanggala 402, it means the structural integrity will be completely lost when subjected to 50 times atmospheric pressure (50 bar) at 500m depth.

Indeed, depth is one of the most important and deciding structural design criteria. The pressure hull must be able to withstand such high differential pressure while maintaining normal air pressure within those internal watertight spaces.

There are maximum operating depth (service depth), emergency depth (dive deeper than the service depth under emergency conditions such as escape from enemy) and collapse depth (crush depth). Collapse depth is what KRI Nanggala 402 had encountered.

2. Shock Loads

Submarine is designed for war to withstand loads generated by underwater mine explosion. Such explosion would generate large underwater gas bubbles. When such bubbles burst, they release huge energy (shock load) which may cause severe structural damages. The common engineering term for this is called “shock factor”.

Apart from direct shock load, each shock wave (travel at about 1500 m/s, 5 times the speed of sound in air) from a single underwater explosion generates a wave of vibration propagate along the submarine hull. Vibratory loads reduce fatigue life and can cause resonance resulting in major structural failure.

Navy ship subjected to an underwater shock test. Photo source: Wikipedia. By Camera Operator: PH1 Toon, USN - ID:DN-SC-87-05360 / Service Depicted: Navy, Public Domain

3. Other dynamic loads

A submarine, when surfaced, is just like any other surface ships, subjected to longitudinal bending, transverse shear and torsional stresses due to wave action. Other localised loads come from heavy machinery such as generator engines, and weapons such as torpedoes and missiles, among others.


Quality control

The pressure hull is generally constructed using thick high-strength alloyed steel with complex stiffening reinforcement. The pressure hull is usually separated with watertight bulkheads into several compartments to enhance survivability.

Quality control during construction and maintenance for submarine has to be very stringent and require high degree of discipline and precision. Not many shipyards in the world are able to undertake such skillful tasks.

For example, any small notch on the pressure hull is equivalent to a stress riser that weakens the load bearing capacity, hence out of roundness standard is a vital component in the pressure vessel code. Welding of thick materials tend to create hazardous heat affected zone (HAZ) which reduces material strength. Hull penetration for piping and electrical cables would compromise watertight integrity. These are just part of the many work control processes for those who worked on submarine safety program.

For many, these tight measures are implemented to save assets. To me, these measures are to save lives.

Friday, April 23, 2021

你打针了吗? ---- 冠状病毒疫苗接种


2021年331日和421日,相隔21天,我共打了两剂辉瑞(Pfizer-BioNTech COVID-19)疫苗,这是美国制药公司辉瑞(Pfizer)和德国医药公司BioNTech联合研制成的产品。由于有效期估计为9个月(厂家的看法)至18个月(新加坡的看法),因此可能在疫情未完全控制下来的期间,必须打第三针。

我选择设在Tampines Hub旁临时搭建的疫苗接种中心,由Fullerton Health Group负责。现场有许多年轻人,使用华语和英语跟到场打针的人士沟通。这些年轻人可能是毕业后找不到正职,刚好有份临时差事可做。







两针辉瑞疫苗的技术原理是这样的:通过信使核糖核酸疫苗(mRNA)来指导细胞产生S抗原蛋白(SARS-CoV-2特有的一种刺突蛋白),使身体产生免疫反应,并将该信息保留在记忆中。临床试验的有效率为95%mRNA m就是messenger,信使了。


辉瑞疫苗必须稀释,稀释后的单剂量为0.3 毫升(ml),稀释剂 0.9%氯化钠注射液(0.9% Sodium Chloride),也就是每公升水溶液含9克氯化钠。氯化钠就是俗称的生理盐水或打点滴


Modena的技术原理相似,不过单剂量为0.5 毫升,不需要稀释。临床试验的有效率为94%。疫苗储存温度为-25-15°C。第一剂被抽出后,药瓶的储存温度为+2+25°C,必须在6小时内使用。






202012月辉瑞和莫德纳分别将疫苗的相关临床数据刊登在每周出版,权威性的《新英格兰医学期刊》(The New England Journal of Medicine),中国大力推销的科兴疫苗则没有这么做。





Friday, April 16, 2021

将东陵福的旧时光化为永恒 Tanglin Halt


踏出以蓝为主色的联邦地铁站,步行约5分钟便可抵达位于联邦通道第46-3座的 我爱女皇镇展览馆。那是民间组织我的社区My Community)向建屋局租用的店面,将一楼用作《光影·女皇镇》展览用途,展览内容每几个月更新。




印象中的东陵福是火柴盒组屋区。约半个世纪前,中三中四每个星期都有一天来到这里的东林工艺中学上工艺课。日后在杜佛路新加坡工院上课那三年,这里是必经之路。 十层楼的外表千篇一律,就像整齐排列的火柴盒,不过日久生辉,展现出岁月的芳华。











Friday, April 09, 2021

风行一时的“十二支” (Chap ji kee)








(此人下注的是老厂,也就是大坡大同。开的是八--六,四对字中了两对:其中一对是直落$1.20,赔$120;另一对是排排坐$0.70, 赔$35。总奖金$155。)















[1] Stella Danker, “The town’s biggest cheap thrill is all but buried”, The Straits Times 27 July 1986.

[2] Jose Raymond, “Cops cripple chap-ji-kee syndicate”, Today 3 Sep 2004.


Friday, April 02, 2021

长堤的邻居 ——支那河溯源





(拆除前的甘榜罗弄花蒂玛,背景为马西岭的点式组屋。From Yeo Hong Eng collection, photographer unknown.)


位于长堤西面,称为甘榜罗弄花蒂玛(Lorong Fatimah)的水乡,消失的年份并不久远。上世纪80年代末拆除时,傍海而居的村民搬迁到附近的组屋。有些老人家对生活一辈子的地方依依不舍,当局特别通融三个月,让他们沉淀心情。日后新的关卡大厦坐落在甘榜原址上。






一、1828年第二任驻扎官哥罗福发表的Franklin and Jackson图:这是英国人制作的第一幅新加坡地图,标志着岛上的主要河流,不过图上没有支那河。

二、1850年代新加坡地图(Map of the Island of Singapore and Its Dependencies):这幅地图出现支那河(S China)、陈厝港、刘厝港、巫许港和烂土港等字眼。




五、1924年测量图(Federated Malay States Surveys Number 7):陈厝港原址出现汉口(Han Kow Estate)和晋江(Chin Klang Estate)两个新地名。


七、1969年新加坡街道图:第115图显示支那河上游有个甘榜双溪支那Kg Sungei China)。根据老街坊反馈,甘榜的居民主要是华人和少数马来人。新加坡独立前,他们甚至每天早晨骑着脚踏车到新山买菜,顺便吃早餐。

八、2020年公园局地图:公园局在兀兰滨海公园设置的地图,将这条小河命名为Sungei Cine。以Cine取代China,因为支那这个中性词,在二战之后被普遍认为是日本军国主义者侮辱华人的词汇。






顺道一提,支那河畔陈厝港的港主是陈开顺19世纪中叶,天猛公伊布拉欣借鉴本地的甘蜜与胡椒经济效益,在柔佛推行港主制度。陈开顺获得地不老河(Sungai Teberau)的港契,率领潮州弟兄渡海开辟另一个陈厝港。他们一行人接着将新山打造成行政区,恭请天猛公迁都,从此奠定义兴公司在柔佛的至尊地位。目前友诺士一带的普照禅寺所保管的70多座反清义士神主牌,候明义士陈开顺(号贞国)乃其中之一,因此不排除他为了避难才逃到南洋的。