A large part of impacts that will be generated by a system / product during its life cycle are allocated during the earliest stages of the design process. In this paper we propose to trace the evolution of environmental impacts throughout a complex system design process through an industrial case. We follow the stages of a boat design process for maintenance of offshore wind farms. The different architectures sketched throughout the design process are evaluated in order to measure the impact of design decisions on the environmental performance of the system. The problematic of taking into account environmental constraints upstream of the design process abound methods but they often prove inadequate for complex systems whose subsystems interact in complex ways leading to conflicts in the decision of the right parameters. To meet the stakeholders’ needs, that appear (during the design project) in the iterative design process, the initial design is modified to fit the specifications. This iterative path between designers and users leads to uncertainties over the environmental impact of the system. It is then necessary to use smart design support tools allowing a negotiation in definition phase of system specifications. Thus the preliminary design is modified to incorporate changes and contributions occurred during the negotiation phase functional.