With the growing offshore wind market comes an increased demand for offshore wind turbine technicians and smaller working vessels needed for maintenance. The hazardous working conditions make technicians’ focus and well-being crucial, with motion sickness presenting a potential obstacle. The Motion Sickness Incidence (MSI) in ISO 2631-1 [1] estimates the percentage of individuals likely to experience emesis after exposure to specific vertical motion. This study investigates the MSIs of a crew transfer vessel over a one-month period and applies spectral eigendecomposition to gain deeper insights into the motion dynamics. Results show low MSI values, with occasional days surpassing thresholds. The study also finds that lateral motion contributes more significantly to vessel dynamics than vertical motion at lower frequencies. The paper highlights both practical and theoretical challenges in applying the MSI in this context and calls for further research, as current metrics may overlook critical factors.