The main rationale of using transshipment hubs is to improve the overall efficiency and geographical coverage of maritime container shipping networks. A transshipment alternative enables linking ports to the global maritime shipping system considering existing ship assets as direct services cannot be established between all ports. The insertion of a transshipment hub within existing networks takes three major forms:
- Hub-and-spoke. The purpose of the transshipment hub is to provide connectivity between short-distance feeder lines (and ports) and long-distance deep-sea lines, linking regional and global shipping networks. It acts as a point of consolidation of regional traffic where the transshipment hub relies on a central location commanding access to a region, such as for the Caribbean (e.g. Kingston) or the Mediterranean (e.g. Gioia Tauro). The ship capacity between the deep sea and feeder services differs significantly since feeder ships tend to be of smaller capacity than those on deep-sea lines.
- Intersection. The transshipment hub acts as a point of interchange between several long-distance shipping routes. Ship capacity between routes is relatively similar but can vary depending on the ranges being serviced. The most suitable locations tend to be bottlenecks, such as Singapore, Algeciras, or Tangier Med.
- Relay. The transshipment hub becomes an interface between shipping routes along the same maritime range but servicing different port calls. Some regional services may call the same port, permitting additional opportunities for relay forms of transshipment. Ship capacity can differ since regional routes can be serviced by smaller ships.
While the hub-and-spoke function accounts for about 85% of all transshipment activities, intersection and relay functions account for about 15%. Transshipment was initially developed to service smaller ports that had poor nautical accessibility (sites unable to accommodate larger containerships) or limited infrastructure, which lead to the setting of hub-and-spoke networks. At a later stage, intersection and relay forms of transshipment were introduced, enabling different connectivity levels within global maritime shipping networks. Intermediate hubs tend to have three dominant locations:
- Funnel. Locations such as strategic passages create a funnel effect for shipping lanes, making them attractive for transshipment because of network convergence.
- Corridor. Important shipping lanes offer the opportunity for a hub having a low deviation to emerge.
- Cluster. Transshipment hubs tend to cluster and compete with each other.