Landing a fixed-wing aircraft on a moving aircraft carrier is a risky and inefficient process. Having an accurate prediction of ship deck motion decreases the risk posed to both the pilot and the aircraft and increases the efficiency of landing maneuvers. The present work proposes the use of a sine-summation algorithm to predict future ship motion. The algorithm decomposes recorded ship acceleration data into its characteristic harmonic parameters using a fast Fourier transform. The harmonic parameters are then used in a summation of sine waves to create a fit for the acceleration data, which is projected into future time intervals to predict ship motion. An aircraft carrier can supply the prediction made by the algorithm to an autopilot, which then decides to land or make another attempt. Included in this work is a brief overview of ship motion with six degrees of freedom and a description of the method. The results generated by the algorithm are presented for a specific ship motion dataset to provide a point of comparison between the proposed method and other common methods used. The proposed method appears to be accurate in comparison to similar prediction methods, while reducing the computational cost required to make a prediction.