The accurate prediction of the added resistance in waves has an important impact on the power correction of the full-scale ship, and it needs to be properly eliminated to accurately evaluate whether the speed at the agreed power meets the requirements. The MEPC 79 meeting held in December 2022 officially recognized the ITTC 2021 version of the “Preparation, Conduct and Analysis of Speed/Power Trials” as a statutory procedure, and the SNNM method for the prediction of the added resistance of ships in waves of arbitrary heading was introduced to fill the gap of current prediction methods. The influences of the period, wave direction, wave spectrum and the shape of RAO curve on the SNNM method have been examined in detail for the power correction in sea trials.