Container ships are becoming larger and larger, but also more numerous. As a result, these large ships are pushing their smaller counterparts down the line, until these smaller ships are no longer efficient for trade routes. The focus area of this thesis is on the North Sea and Baltic Sea area, in particular the area between the West coast of Norway to the Russian part of the Gulf of Finland, with most countries in between with feeder activities between them and North European gateway hubs. This area is seeing an increase in port development. As a result, routes that container ships take are being changed. Either larger ships are coming into the region and stopping at more ports, or they are utilised as feeder ships in the region. This thesis aims to investigate the cascading effect of container ships, regarding the choice of feeder ships between German North Sea ports and feeder destinations in Scandinavian countries and countries on the Baltic Sea. To achieve this, an optimisation model is created that calculates differing total costs for container ships with capacities ranging between 200 and 5000 Twenty-foot Equivalent Units (TEU) in the region. This is done by assigning ships to container flows from German North Sea ports to feeder ports in the region, and allowing the model to choose which arcs are used to fulfil the container inflow of the destination ports. To analyse the impact of each ship type regarding the total cost of their routes taken, ship types are tested separately. Experiments have been run for increasing bunker costs based on existing data, for increasing amounts of container inflows, and decreasing the number of ports based on an increase of minimum container inflow.
The results of the experiments varying bunker costs show the total cost to fulfil all container inflows for each feeder ship type is highly dependent on its utilisation of the Kiel Canal. The Kiel Canal restricts the choice of ships with capacities larger than 1250 TEU. The extra time spent for sailing around the Northern tip of Denmark has a negative effect on the largest ships chosen for this thesis. For an increasing bunker cost, a 1500 TEU capacity ship is hindered more negatively than a 5000 TEU ship due to the Kiel Canal. For variations in volume of container flows, the same impact of the Kiel Canal is also seen. However, total costs start to favour the largest ships chosen, with the largest capacity ship (5000 TEU) having the lowest total costs calculated for a 300\% of the original chosen container flows. For decreasing the number of ports from the set based on their container inflow, the largest capacity ships have the lowest total costs from a minimum container inflow of around 400 TEU per week. From this, with current flows and within the near future, it is estimated that the current fleet of around 1000 - 1250 TEU capacity container ships will maintain their position within the North Sea and Baltic Sea region. However, for routes with a substantial container flow volume, larger capacity ships are estimated to be more cost competitive than their smaller counterparts.
This conclusion is based on experiments with only one ship size available for all container flows, with the assumption that all chosen ships are not restricted by berth sizes in ports. Furthermore, all flows originate from German North Sea ports. Recommendations for future research should take all chosen ship types into consideration for arc-flow pairing, and have more origins for container flows. If all ship types are taken into consideration, size restrictions of ports and transshipment between ship types should also be implemented. Origins included should include other major hubs in the region, as well as from outside the region, as an incoming flow. This would allow for an investigation into large container ships sailing between the current chosen origin hub and large ports, and the consequence on the region as a whole.