A series of sloshing model tests are carried out for an IMO Type B tank of 30K LNG bunkering vessel. Experimental results show that the maximum sloshing impact load occurs at a filling level of 25%H and waves at a 90-degree angle. Lateral sloshing is likely to occur at the bottom of the lowest stringer in filling levels close to the lowest stringer height for this Type B tank. The analysis of hot spot areas in all filling condition indicates that the sloshing impact loads are high in the vicinity of the swash bulkhead and near the filling levels. A more detailed analysis of the experimental results is presented in this paper.
It is confirmed that under a new global cap on sulphur emission set by the International Maritime Organization (IMO), vessels will be required to use fuel oil on board with a sulphur content of less than 0.50% as of January 1st 2020 against the current limitation of 3.50% (Ma, 2012). Since the first use of LNG as a ship fuel in Norway in 2000 (ÆsØ y, 2013), LNG has been increasingly adopted as marine fuel for a variety of vessels, including container ships, cruises, ferries, shuttle tankers, bulk carriers and tugboats. Traditionally, small LNG-fueled ships are fueled by means of truck-to-ship (TTS) transfers.
LNG bunkering vessels have been delivered since 2016 to provide ship-to-ship (STS) bunkering services. Table 1 summarizes the list of LNG bunkering vessels which have been delivered and will be delivered. ENGIE at Belgium took the delivery of the world's first 5,100 cubic meters LNG bunkering vessel (Park, 2018). Shell, a giant energy company, plans to provide LNG bunkering services to large container ships, cruise ships and shuttle tankers using 6,500 cubic meters LNG bunkering vessels. Up until now, all the bunkering vessels are equipped with an IMO independent Type C tank, which has size restriction.
Table 2 indicates the expected capacity and optimal number of LNG bunkering vessels at each port of Busan, Singapore and Rotterdam (Lee, 2017). It shows that a large number of 20,000 cubic meters LNG bunkering vessels would be required. In the case of large container ships, the storage capacity of LNG fuel above 18,000 cubic meters is required for ocean voyage. Recently, membrane type tanks have been applied to large capacity LNG bunkering vessels; however, the risk of sloshing is still high. In this regard, the IMO Type B tanks can be an alternative to overcome the capacity limit of conventional Type C tanks and the risk of sloshing of membrane tanks.