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A Constraint Programming Approach to Ship Refit Project Scheduling

Authors Raphaël Boudreault , Vanessa Simard , Daniel Lafond , Claude-Guy Quimper

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Author Details

Raphaël Boudreault
  • Thales Digital Solutions, Québec, Canada
Vanessa Simard
  •, Québec, Canada
Daniel Lafond
  • Thales Digital Solutions, Québec, Canada
Claude-Guy Quimper
  • Université Laval, Québec, Canada


Thanks are due to the many members of the Refit Optimizer project team and our collaborators at Dalhousie University, Polytechnique Montréal, Sōdan, Simwell and Genoa Design International. We are very grateful to the many domain experts consulted and to Seaspan Victoria Shipyards for their invaluable feedback.

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Raphaël Boudreault, Vanessa Simard, Daniel Lafond, and Claude-Guy Quimper. A Constraint Programming Approach to Ship Refit Project Scheduling. In 28th International Conference on Principles and Practice of Constraint Programming (CP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 235, pp. 10:1-10:16, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2022)


Ship refit projects require ongoing plan management to adapt to arising work and disruptions. Planners must sequence work activities in the best order possible to complete the project in the shortest time or within a defined period while minimizing overtime costs. Activity scheduling must consider milestones, resource availability constraints, and precedence relations. We propose a constraint programming approach for detailed ship refit planning at two granularity levels, daily and hourly schedule. The problem was modeled using the Cumulative global constraint, and the Solution-Based Phase Saving heuristic was used to speedup the search, thus achieving the industrialization goals. Based on the evaluation of seven realistic instances over three objectives, the heuristic strategy proved to be significantly faster to find better solutions than using a baseline search strategy. The method was integrated into Refit Optimizer, a cloud-based prototype solution that can import projects from Primavera P6 and optimize plans.

Subject Classification

ACM Subject Classification
  • Computing methodologies → Planning and scheduling
  • Theory of computation → Constraint and logic programming
  • Ship refit
  • planning
  • project management
  • constraint programming
  • scheduling
  • optimization
  • resource-constrained project scheduling problem


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