The superyacht industry faces an increasing trend of larger dimensions, more open spaces, larger hull openings and more exotic shapes. This puts more effort on the structural design and especially for superyacht longitudinal stiffness is important, since the luxurious interior and delicate systems installed in a superyachts are not allowed to cause creaking noises or be damaged. A method is developed that can provide global and local deformations in operational sea conditions to use for risk assessment and provide guidance on clearances or connections that should be used for interior installment. Wave-induced loads are calculated with a linear response analysis in combination with a regular equivalent design wave. The yacht hull is modelled as a 1D Timoshenko beam including shear deformations and torsion for which good agreement is found with a detailed 3D FE model with shear deformations accounting for 20% to the vertical displacement.