In an unprecedented endeavour, the ship manager Reederei NSB has been widening its Panamax-class container vessels. DNV GL, the class in charge, was on board.
Too young for scrapping, too old to compete: Roughly 500 Panamax-class container ships are less than ten years old, barely half their useful life. But facing overcapacities, low charter rates and fierce competition, the Panamax class is under intense pressure. Compared with state-of-the-art and much more capacious newbuildings, its prospects are dim.
This is mainly due to the way these vessels were designed. To pass the old locks of the Panama Canal, they were built with unusual dimensions – long and thin and with a large amount of ballast water to compensate the poor stability.
“In addition, Panamax ships are equipped with stronger engines that achieve their highest efficiency when operating at higher speeds, rather than slow steaming, which is more common today,” says Marcus Ihms, Ship Type Expert for Container Ships at DNV GL – Maritime.
So shipowners try to make their fleets more competitive by undertaking minor and major ship conversions.
Reederei NSB of Buxtehude, Germany, is causing quite a stir with the idea of widening three of its Panamax container vessels: MSC Geneva went back into service in July 2015 after undergoing the procedure, her sister ship MSC Lausanne was delivered in late October, and MSC Carouge was completed in early 2016. “No one has ever cut a container ship lengthwise from the superstructure to the bow to widen it,” says Tim Ponath, Chief Operative Officer of Reederei NSB. “We are very proud of our team who demonstrated the viability of our concept.”
Innovative and technically sophisticated, this concept was developed jointly by NSB and the Hamburg-based Technolog GmbH. After separating the fore and aft body from the cargo hold in dry dock, the cargo hold is cut in half lengthwise and pulled apart. The new centre sections are inserted and connected to the existing part. “The main idea behind this innovative method is cutting the hull in the least stressed areas and significantly increasing both the container intake and stability by widening it,” says Lutz Müller, Senior Technical Consultant at NSB and one of the key initiators of the project.
Providing guidance
The conversion is carried out by Huarun Dadong Dockyard (HRDD), China. DNV GL, the classification society in charge of the ships, was involved from the early stages. “This is a major conversion project,” emphasizes Ihms. This means that all classification and flag state rules in effect at the time of conversion have to be observed. It is important to discuss with the flag state and the class, what rules must be adhered to under all circumstances, and what parts of the ship can be handled according to existing standards rather than new requirements.
“Our Class Note for Conversion of Ships provides the necessary guidance to owners as well as engineering companies during the design phase,” Ihms points out. For example, in the case of MSC Geneva and her two sister ships, the anchor equipment had to be adapted, as a widened ship is heavier and offers more resistance to wind. “According to our well proven method, additional chain lengths can provide more holding force. Thereby, the retrofit of the entire winch system can be avoided without jeopardizing the anchoring capability,” Ihms reports. From anchor equipment and ship strength and stability through to statutory compliance and cargo lashing, close collaboration between all project stakeholders was crucial for the success of this world premiere.
Added benefits
A conversion adds up to four container rows to the cargo hold, increasing the container capacity by about 30%. In addition, it improves engine efficiency when combined with an optimized propeller, and bolsters stability. “Stability increases exponentially when you widen a ship,” Ihms explains. As an added benefit, the required ballast water per loaded container could be reduced by half. The IMO Energy Efficiency Design Index (EEDI) achieved will equal that of a newbuilding and meet EEDI regulations as per 2025. The life-extending surgery will pay for itself within four years – so in the end it has all been well worth the effort, Ihms assures.
Options for minor and major conversions
A changed economic environment calls for measures to make existing container tonnage originally designed for different operating conditions more competitive. A number of options are available:
Increase the draught
Increasing the draught, and thereby the deadweight, will allow the ship to take on more weight per container. Strength and stability considerations, the resulting visibility line and the location of pilot doors must be accounted for.
Heighten the deckhouse
A taller deckhouse will increase deck container capacity and improve the line of sight at the same deadweight. Appropriate lashing bridges and innovative methods to determine the cargo securing help to fully utilize the benefits.
Upgrade the lashing bridges
Installing lashing bridges or heightening existing ones improves stowage performance. This is often combined with a hatch cover upgrade to enlarge the stack weight. Structural re-approval of the substructure is necessary.
Lengthen the ship
Payload and cargo intake is significantly increased by adding a new midsection. This major conversion changes the ship’s longitudinal strength in particular and requires comprehensive structural verifications.
Widen the ship
This complex conversion means cutting the ship apart lengthwise to add a new centre line section. The cargo capacity and performance is boosted substantially.
Source: DNV GL
