The authors present the design of the shipping simulation SEL and its integration in the MSP Challenge Simulation Platform. This platform is designed to give policymakers and planners insight into the complexity of Maritime Spatial Planning (MSP) and can be used for interactive planning support. It uses advanced game technology to link real geo- and marine data with simulations for ecology, energy and shipping. The shipping sector is an important economic sector with influential stakeholders. SEL calculates the (future) impact of MSP decisions on shipping routes. This is dynamically shown in key performance indicators (e.g. route efficiencies) and visualised in heat maps of ship traffic. SEL uses a heuristic-based graph-searching algorithm to find paths from one port to another during each simulated month. The performance of SEL was tested for three sea basins: the firth of Clyde, Scotland (smallest), North Sea (with limited data) and Baltic Sea regions (largest, with most complete data). The behaviour of the model is stable and valid. SEL takes between 4 and 17 seconds to generate the desired monthly output. Experiences in 20 sessions with 302 planners, stakeholders and students indicate that SEL is a valuable addition to MSP Challenge, and thereby to MSP.