The LASS-C project, "Lightweight construction of a cruise vessel", expanded the concept of making lightweight structures in SOLAS vessels by considering not only superstructures, glass and internal design, but also elements which are part of the hull girder, affecting the ship's global strength. The existing Panamax cruise ship the Norwegian Gem worked as application case in the project where the uppermost five decks were redesigned in lightweight fibre reinforced polymer composite material. Comparing with the previous design, weight savings calculations showed that about 1 200 tons could be saved in load-bearing structures. FEM simulations showed that the weakening of the global strength from using lightweight structures could be compensated by reinforcing the lower decks, still making the residual weight savings economically interesting. Environmental and economic assessments were carried out from a life cycle perspective, proving the lightweight construction has less impact to surroundings and that additional costs would pay back in 2.5 years. The key issue for building ships in plastic composite, namely fire safety, was addressed by performing a risk assessment in line with the method provided for alternative fire safety design and arrangements in SOLAS II-2/17. A preliminary analysis report for the fire safety design was delivered to the Swedish Flag for approval as part of the project.