Very high car carriers have inherent problems with stability

Sunday, January 25, 2015

Very high car carriers have inherent problems with stability

Maritime trade union and professional organisation Nautilus Int. use the capsized Höegh Osaka to criticize the design of car carriers, which according to them has exceeded all reason. Danish shipbuilder believes that the ships are at the limit of the permitted.

By Martin Bernth January 15, 2015 Ingeniøren

In summer 2006, the car transport MV Cougar Ace lost stability during a change of ballast water in the Pacific Ocean. The ship developed a strong list of 60 degrees to port, and although rescuers succeeded in rescuing all the crew unharmed, the fate was bleak for the more than 4,000 Mazdas on board. They all had to be scrapped when the ship was finally emptied a month later.

On Saturday the 3rd of January this year the captain on board the car carrier MV Höegh Osaka had to act quickly, as his ship also began to list severely to one side shortly after sailing from the southern English port of Southampton. The captain deliberately sailed the ship aground, and since then a demanding salvage effort has been under way to empty the hull of water.

In the wake of the recent incident maritime trade union and professional organisation Nautilus International, representing 21,000 sailors, has aired concerns for the safety of the big and tall ships.

"In fact, these vessels - both freighters of vehicles and live farm animals – are built to the edge of safety due to commercial considerations. Their design has exceeded all reason, and these ships require very careful handling" said the English country manager for Nautilus International Allan Graveson in an interview with the BBC last week.

In 2006, the car carrier Cougar Ace also listed drastically. It took more than a month before the ship was salvaged and a great majority of its 4,812 vehicles on board were later scrapped.

Christian Damsgaard is a Senior Naval Architect at the leading marine engineer & maritime consulting firm Knud E. Hansen A/S: According to him, there may be something in the criticism, but he also stresses that ships are not allowed to go to sea if they are not complying with the regulations of national maritime administrations.

"I would not call them unsafe, but you're out there, where you are on the edge of the existing rules" says Christian Damsgaard and continues:

"As long as you comply with the requirements to operate safely, these ship are not more prone to capsizing than others. It is clear that it is an extreme design, but they fulfill the same stability criteria as all other cargo ships" he said.

The overriding rules regulating maritime safety are called SOLAS (safety of life at sea). This places requirements for, among others, the so-called 'intact stability', which is a measure of the ship's capability to resist heeling and wind moments when it is not actual damaged.

Cars bulkier than they weight

According to Christian Damsgaard, car carriers often have a high profile because the load they carry is relatively light.

"What makes car carriers special is that the load is not very heavy, as cars - so to speak- take up more space than they weigh. In order to transport as many cars as possible it is important to get plenty of deck space on board, and therefore you build as many decks as you possibly can" says Christian Damsgaard.

Limitations of the world's ports and the Panama Canal restricts many car carriers from being wider and longer.

"This is all about loading as many cars as possible so you can keep freight costs per car down. This is why you build upwards and start to have problems with stability" he says and continues:

"When you load the ship upward you also move the center of gravity up. This is not an issue as long as you get some ballast in the bottom. However, in a way, the fact that many of these ships typically require ballast water in all of their loading conditions illustrates that they have a built-in stability problem" says Christian Damsgaard.

Höegh Osaka remains heeled over in the water south of England, where rescue workers are currently trying to empty the ship of water after a leak has caused more than 3,000 tons of water to cascade into the hull.

Read more about stability here

Meget høje biltransportskibe har indbyggede problemer med stabiliteten

Maritimt forbund bruger det kæntrede Höegh Osaka til at kritisere designet af biltransportskibe, som ifølge forbundet har overskredet al fornuft. Dansk skibsbygger mener, at skibene balancer på grænsen til det tilladte. 

Af Martin Bernth 15. jan 2015 Ingeniøren

I sommeren 2006 mistede biltransporten MV Cougar Ace balancen under en udskiftning af ballastvand midt i Stillehavet. Skibet udviklede en kraftig slagside på 60 grader mod bagbord, og selvom redningsfolk havde held med at redde hele besætningen uskadt, var skæbnen anderledes dyster for de flere end 4.000 Mazdaer om bord. De måtte alle skrottes, da skibet endelig blev tømt en måned senere.

Lørdag den 3. januar i år måtte kaptajnen om bord på biltransportskibet MV Höegh Osaka handle hurtigt, da også hans skib begyndte at hælde voldsomt til den ene side kort efter afsejling fra den sydengelske havneby Southampton. Kaptajnene sejlede snarrådigt skibet på grund, og siden har en krævende bjærgningsindsats været i gang for blandt andet at tømme skroget for vand.

Det maritime forbund Nautilus International, der repræsenterer 21.000 søfolk, lufter i kølvandet på den seneste hændelse bekymringer for sikkerheden i de store og høje skibe.

»I virkeligheden er disse fartøjer - både fragtskibe til køretøjer og levende husdyr - bygget til kanten af sikkerhed på grund af kommercielle hensyn. Deres design har overskredet al fornuft, og disse skibe kræver meget omhyggelig håndtering,« sagde den engelske landechef for Nautilus International Allan Graveson i et interview med BBC sidste uge.

I 2006 blev også biltransportskibet Cougar Ace skubbet ud af balance. Det tog mere end en måned før skibet var bjærget og af dets 4.812 køretøjer om bord blev langt de fleste senere skrottet.

Christian Damsgaard er ledende skibsingeniør hos det maritime konsulentfirma Knud E. Hansen A/S. Ifølge ham kan der være noget om kritikken, men han understreger samtidig, at skibe ikke får lov at stå til søs, før de er godkendt af nationale søfartsmyndigheder.

»Jeg vil ikke kalde dem usikre, men man er derude, hvor man er på kanten af de regler, der findes,« siger Christian Damsgaard og fortsætter:

»Så længe man overholder de krav, der er til at sejle sikkert, så skulle sådan et skib ikke være mere tilbøjeligt til at kæntre end andre. Det er klart, at det er et ekstremt design, men de opfylder de samme stabilitetskriterier som alle andre fragtskibe,« siger han.

Det altoverskyggende regelsæt, der regulerer sikkerheden til søs kaldes Solas (safety of life at sea, red.). Det stiller blandt andet krav til den såkaldte ‘intakt stabilitet’, der er et mål for skibets modstandsdygtighed over for krængninger og vindmomenter, når det ikke har en decideret skade.

Biler fylder mere end de vejer

Ifølge Christian Damsgaard får biltransportskibe ofte deres høje profil, fordi den last, de bærer, er forholdsvis let.

»Det, der er specielt ved bilskibe, er, at lasten ikke er særlig tung, da biler så at sige fylder mere, end de vejer. For at få flest mulige biler med, så gælder det om at få masser af dæksareal om bord, og derfor bygger man så mange dæk, man overhovedet kan,« siger Christian Damsgaard.

Begrænsninger ved verdens havne og ved Panama-kanalen gør, at skibene hidtil ikke umiddelbart har kunnet gøres bredere og længere.

»Det gælder jo om at have så mange biler med som muligt, så man kan holde fragtomkostningerne per bil nede. Så er det, at man bliver nødt til at bygge opad, hvor man så til gengæld begynder at få problemer med stabiliteten,« siger han og fortsætter:

»Når du laster skibet opad, flytter du også dit tyngdepunkt højere op. Det er der jo for så vidt ikke noget i vejen for, så længe du får noget ballast i bunden. Det faktum, at mange af disse skibe typisk kræver ballastvand i alle deres lastekonditioner, illustrerer på sin vis, at man har et indbygget stabilitetsproblem,« siger Christian Damsgaard.

Höegh Osaka ligger fortsat og hælder i vandet syd for England, hvor bjærgningsarbejdere i disse dage forsøger at tømme skibet for vand, efter en læk har fået mere end 3.000 tons vand til at fosse ind i skroget.