Influence of the sea action on the measured vibration levels in the comfort assessment of mega yachts

Understanding the methods to evaluate the comfort on board ships through direct measurements of the vibration levels is crucial for obtaining accurate results, and so a clarifying explanation of the methods required by the ISO 6954:1984 would be useful. The checking is performed using a Maximum Repetitive Value (MRV) that is not clearly defined, nor specified in which circumstances or for which dimension of the ship it should be used or not. Neither has an explanation been given to the use of a conversion factor that inherently represents time dependent vibration phenomena, modulation, which depends on the Sea State. The Crest Factor represents these modulations, and depends on the Sea State and ship dimensions. It is important to understand better the parameters that affect the Crest Factor to evaluate better the comfort on board ships. Some Classification Societies give guidelines on how to use the ISO standard in question, but they do not always cover certain aspects that must be considered. In the paper, suggestions on how to use the standard are given, approaches from Classification Societies are analyzed and a procedure to obtain MRA and the Crest Factor generated. Different influencing factors to the Conversion Factor and the MRA, such as time length and position of the measurement during testing and filter type, have also been analyzed to obtain a more accurate value of the Crest Factor.