Design and analysis of a multi-trailer system for the Durban container terminal.
Multi-trailer systems (MTS) allow for the transportation of multiple shipping containers in a single movement as opposed to the conventional trailer systems often used within a port terminal environment. The adoption of MTSs creates an opportunity for container terminal operators to reduce the operational costs associated with container movements between the container vessel and stacking areas during the vessel loading and unloading operations while maintaining, and in certain cases improving, the port’s quayside productivity. A reduction in operational costs can potentially result in lower tariffs levied to container vessel operators, improving the competitiveness of a port. While MTSs have been in existence for many years and have been successfully implemented in many international port container terminals, the influence of this type of trailer on the operational costs of the waterside horizontal-transport system and on the quayside productivity within South African ports has not been investigated or demonstrated to date. This study set out to determine the influence which an indigenously designed MTS has on the abovementioned factors at South Africa’s largest container port, the Durban Container Terminal. Discrete event simulations were used to benchmark the current performance of the container movement operations at Pier One of the Durban Container Terminal using the existing tractor-trailer units (TTUs). The performance of the operations was then analysed for the scenario of replacing the TTUs with MTSs that have twice the container carrying capacity. The results showed that nine MTSs can replace the existing fleet of fifteen TTUs without compromising on the quayside performance for the vessel unloading operations, which leads to a 25% reduction in operational costs. A reduction in labour costs accounts for 88% of the saving. Use of MTSs for the vessel loading operations showed minimal benefit and the performance using the existing TTUs for this operation can be considered equivalent. The results imply that an MTS configuration with the ability to uncouple the individual trailers in the set for use as TTUs was required. This lead to the selection of a semi-trailer lead MTS configuration incorporating the use of a converter dolly for the indigenous design conducted here. The indigenous MTS design consisted of two identical semi-trailers connected using a converter dolly, allowing for interchangeability in the MTS set and for use of the semi-trailers as TTUs. The terminal’s existing semi-trailers could have been used with the converter dolly designed in this study for the MTS, however an improved semi-trailer design with regards to mass, cost and manoeuvrability has been provided. The new semi-trailer design was shown to have a 21.4% lower tare mass and a 14.1% lower product manufacturing cost over the existing design. For the MTS configuration, up to an 11.6% improvement in manoeuvrability is expected when using the newly designed semi-trailer.