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Widening of Container Vessels

For over 30 years, the Panmax containership was the backbone of worldwide container sea transport. With maximum capacities of 5,000 TEU and service speeds of up to 25 kn, they were the optimal means of transport at their time for container freight. It was not until the 1990s that they were gradually replaced by the wider Postpanmax ships. To prepare the exisiting Panmax units for the future, REEDEREI NSB offers an innovative widening concept. Three vessels managed by NSB have been widened in 2015 already and are successfully in service. 

For a long time, Panmax ships were considered the standard for capacities up to 5,000 TEU. The rise of fuel prices for HFO from 250 USD/t to over 600 USD/t causes charterers since 2008 to pursue two goals: Firstly, to save fuel by reducing service speeds. Secondly, to improve the economy of scale by enlarging the individual vessel. This development adversely affects classic Panmax ships since they were optimized for higher speeds and are subject to TEU capacity limitations due to their maximum width of 32.2 m – the width of the Panama Canal.

Modifications to hull and ship engineering, however, allow for a reduction of speed and an enlargement of capacity of exisiting Panmax units.

Modifications tailored to the requirements of customers

The lengthening of ships is a tried process and can be taken into consideration if the aim is to improve efficiency of exisiting units. Yet, it is not always the best option: It offers no improvement with regard to the stability ballast water problem. Another factor is that the ship is cut at the place of the largest bending moment and thus highest stress and has to be rewelded. Additionally, in some cases lengthening is possible from an engineering perspective but not from an operational one – some ports in Africa for example can only process vessels up to a certain length.

To cater to the requirements of our customers, we think that the widening of the ship is the best possible option. Ships have already been widened in the past to increase stability. This involved increasing only the displacement and metacentric height as standard for the stability, but not the number of container slots. So despite the fact that this complex modification partly improved efficiency, other opportunities to make vessels attractive to current and potential customers were not taken.

The innovative concept of REEDEREI NSB

We at REEDEREI NSB have developed an entirely different widening concept. The ship will be cut in the hold area at amidships, where the load is low at right angles to the cut and the steel is therefore comparatively thin. The necessary cuts at right angles to the ship are made at the engine room front bulkhead and at the collision bulkhead. Here the bending moments are much lower than at the main frame. The front part of the ship is lengthened by a hold so that the form remains. It is trickier aft. However, we assume that the influence of an ideal form declines with speeds below 20kn. Thus, for a containership of medium size at 18kn the friction resistance is 67%, the wave resistance 9% and the form resistance 24%. The bulbous bow – which has to be replaced by a new one because of the widening anyways – is optimised for reducing the wave resistance with the aid of CFD methods for speeds below 20kn.

Conversion with a welcome side effect

After the separation of the fore and aft ship from the hold in a sufficiently large drydock, the hold is cut lengthways and pulled apart on a heavy load system. Then the resulting empty space is filled up with rectangular sections. This causes a gratifying side effect: a homogeneously loaded, rectangular floating body does not have any smooth water bending moments. This means for the widening that the bending moments of the widened ship do not increase proportionally to the increase in TEU capacity.

A widening of the kind presented is a ‘major conversion’ in terms of ship classification. This means that (if possible) all rules in terms of classification and flag state that are valid at the time of the conversion have to be observed. For this, negotiations with the flag and the class of the ship to be converted are important. It has to be determined which rules must be absolutely complied with and what areas of the ship, if there are new requirements, can remain in the context of safeguarding existing standards.

Three clear advantages of the concept

The concept for the widening of Panmax containerships has three main advantages:

  • Capacity increase
  • Higher stability, i.e. less stability ballast and larger slot capacity at 14t homogenous
  • Lower speed due to large displacement with unchanged engine plant

This results in a much better IMO Energy Efficiency Design Index. Thus, CO2 emissions per tonne mile for the widened ship significantly decline. The result looks even better if the CO2 emissions are related to the pure cargo weight.

With a 4,900 TEU Panmax containership that can be widened from 32.2m to approximately 40.0m, the characteristic dimensions change as follows:

Length p.p.275.0 m283.0 m
Breadth32.2 m39,76 m
Container Capacity4,872 TEU6,296 TEU
14t hom. intake3,109 TEU4,855 TEU
Deadweight (scantl.)63,638 t82,000 t
Speed Design24.0 kn19.0 kn

In this case, a widening by three container rows was selected. It has to be decided in the individual case whether to carry out a widening of two, three or even four rows.


Ship widening initially started as an internal project of REEDEREI NSB to increase the market value of our vessels and to be able to keep them in active duty for a longer period of time. NSB has widened three container vessels in 2015 already: MSC GENEVA, MSC LAUSANNE und MSC CAROUGE.
Of course we also offer widening to external customers. Our services include:

  • Project management
  • Engineering
  • Building supervision during the modification
  • Coordination with and approval by the relevant authorities

This constitutes a complete ship widening package for Panmax containerships. Another possibility for investors would be to buy vessels, have them widened and subsequently managed by REEDEREI NSB.

Older ship units may also be subjected to various retrofitting measures, such as the installation of a new propeller or bulbous bow. These measures will presented in more detail on this website soon.

We are conviced that ship widening is an attractive alternative for investors and charterers: The modified vessels are more energy efficient than present-day Postpanmax vessels of the same size and are priced at a lower charter rate than modern Eco-ships due to their comparatively lower overall costs. Please feel free to contact us to get to know the individual opportunities which our innovative widening concept offers!