Optimization of Hull Structures for a 60 meters Mega Yacht

As well known already in earliest phases of a ship project many aspects and choices depend on the structural design which has been defined only at a preliminary level. This trend appears to be similar for merchant ships, passenger ships and motor yachts. Only in the final part of the project some shipyards begin to apply optimization processes, more or less sophisticated, in order to refine the structural design in view of reducing the weight and/or the construction cost. The weight in particular has a very important impact on pleasure vessels, both motor and sailing. Structural modifications suggested by such optimization procedures imply a number of second order changes in related items such as plant, outfitting and others. As a consequence the structural optimization could be particularly useful if it can be applied during the first stages of the project, this way avoiding very expensive time losses and changes caused by any structural modifications.
In this paper the structural optimization of a 60 meters megayacht is presented, performed by LBR-5 code developed by the University of Liege. This code is an optimization tool specifically designed for structures composed by stiffened plates and stiffened cylindrical shells. The optimal solution is reached through an optimization algorithm based on convex linearization and a dual approach.
The LBR-5 software has been successfully utilized to optimize hull structures of a 60 meters megayacht. Differently from large ships, the mega yacht has not a “cylindrical body” in the central part of the hull. So, a new module of the software has been used in order to analyze several sections of the ship and to perform an overall optimization.
For this application the optimization analysis has been carried out by different approaches: assuming the weight as the objective function a gain of about 8% has been achieved, while a least cost optimization allowed a reduction of 15%.