Results from nonlinear FEM analyses of a plate structure simulating a small piece of a ship hull are presented in this report. The main objective of the work, presented as thesis for the cand. scient. degree (master equivalent), has been to investigate some aspects of the DNV (Det Norske Veritas) provisions for high speed crafts of non isotropic materials. Specifically, focus has been on the deflection and stress limitations given in the DNV rules for structural design of hulls in fibre composite and sandwich construction and on whether these deflection and stress values can be increased beyond those presently given. Towards this end, theories for composite materials, plates, shells and nonlinear analysis were reviewed, and a number of analyses for different materials and boundary conditions were carried out. The analysis results did not allow a general conclusion to be drawn for the problem defined. Therefore, the present design rules can not be revised or simplified based on this report. However, even so, a number of interesting results were found that may provide a good stepping stone for further work. These include nonlinear analysis results documenting the important role of boundary conditions in the problem solution and how small changes in the boundary conditions around the plate make huge difference in displacements. All analyses were carried out with ANSYS.