Floating Bulk Transhipment Operation (FBTO), as a link in the whole bulk logistic chain, used to be performed only in well-sheltered water. Current operability assessment of FBTO is mainly based on experience and rules of thumbs, only taking into account environmental conditions such as significant wave height and wind speed. Corresponding to rocketing development of FBTO in more challenging environment, it becomes more and more important to develop a dedicated and reliable methodology which can assess the operability of FBTO properly. Matching the features of FBTO, long duration and multiple operational phases, persistency analysis is introduced in the operability study. However, persistency analysis has still not been thoroughly studied and well-supported by literature. Moreover, among all existing operability techniques, persistency analysis as one of them has its capability and limitation. To be better adapted to FBTO and to further extend the methodology for other offshore operations, it is thus beneficial to decompose the operability assessment procedure and then categorize the available techniques, as well as to understand conditions of each. This thesis report starts with a benchmark study of worldwide FBTO project. Among various FBTO configurations, the most representative scenario is chosen, which consists of 1 capesize vessel, 1 floating crane and1 feeder vessel. Operation procedure and criteria are described based on interviewing different floating bulk transhipment operator companies. After that, this thesis proposes an operability assessment methodology for FBTO and has the versatility in assessing any other offshore operation, if the three components of this methodology, operability assessment table, mechanism and switches, are used properly. The methodology concludes with an operability assessment scheme, in which useful operability study techniques, such as persistency analysis, scatter analysis, frequency-domain analysis etc., are categorized. Then, an in-depth study about persistency analysis is performed. Persistency analysis approaches more reality than scatter analysis because it accounts duration and chronological sequence of the operation, as well as change in weather conditions. Finer persistency data quality and proper selection of sampling interval will both lead to more accurate operability assessment. Last but not least, the case study illustrates how the proposed methodology works. The first case compares persistency analysis to scatter analysis, while the second one studies the influence due to persistency data of different resolution on operability assessment. The last case demonstrates using this methodology to predict expected duration of FBTO including possible suspension.