## 1 Introduction
The pathway to estimate ship stability using vulnerability criteria and simplified operational measures is addressed in [1,4] and [3], respectively. Similar to the three independent pathways of assessment, any combination of simplified operational measures outlined below could be used independently for assessing the ship's stability for each failure mode. For a ship to have unrestricted operation, the ship must pass the threshold criteria laid out in the SGISC without operational measures. The ship which fails to meet the threshold criteria with the standard WST can use a modified WST, limiting the operation to the modified WST's location, route, or season. Further, the operational limitations could be defined at a specific significant wave height for the standard WST or modified WST based on a given SGISC assessment. This process limits the operation of the ship to a defined significant wave height across the globe if assessed against the standard WST or restricted to the modified WST's region, route, or season. However, in the case of failure to achieve a successful combination with operational limitations, the ship can operate with the operational guidance based on the modified or the standard WST if the design assessment is accepted. This allows the ship to operate with the operational parameters advised. The above combination of operational limitation and operational guidance is only accepted if the ship's total operation failure time to the total ship operation time estimated based on the standard or modified WST is less than 0.2 for the considered operation limitation and operation guidance [1,3]. Figure 2: Sea area nomenclature with hindcast significant wave height snapshot. Therefore, the operational time for a ship considering an individual wave is important in estimating acceptance criteria and is defined by the magnitude of the probability of occurrence of the wave in the WST. The total operational time is the summation of individual operating time in encountering each wave case with non-zero probability in the WST. The change in the WST will result in a change in the probability distribution of wave occurrence and hence the operating time. Thus, the individual operating time of the ship in encountering each wave varies with different WSTs. On the other hand, changing the WST according to region, season and route gives a more accurate reading of wave probability with respect to time and location [4; 9]. By doing so, the OM will be defined based on the actual operating condition, i.e., the region and seasonal circumstance; thus, using the modified WST improves the accuracy of weather data and furthers the accuracy of design assessment. Therefore, it is vital to verify the representation of the wave and its probability of occurrence in the WST used for the SGISC assessment. This paper investigates the existing standard WST representation of the wave profile when compared to individual sea areas. The investigation compares the quality and representativeness of waves in the recommended standard WST with the hindcast data WST and compares OM outcomes for both region and season. The novelty of this paper appears in investigating the need for regional and seasonal WST over the standard WST. The use of real-time weather data is a different approach compared to intact stability regulations given in the 2008 IS Code [10]. It allows for achieving real-time operational stability using SGISC. Two factors are considered important to achieve the required assessment: real-time weather data and ship operation status. The forecasted WST can be used for the ship operation guidance if data are available for number of days. Therefore, real-time ship stability analysis during operation will emerge as a systematic, regulated and recognised approach [11]. A review of the SGISC specifically on OMs and subsidiary topics can be found in [PERSON] et al. [12], and there is an increasing number of publications on OMs [13; 14].