Feature 1 | TANKER TECHNOLOGY Innovation fills the Doughnut Tanker


Designers of the Cubic Doughnut Tank System say the innovative design will be cheaper than existing tankers to build and will be comparable with the membrane tankers as far as space utilisation is concerned


T


he Cubic Doughnut Tank System (CDTS) was originally developed in 1973 and a patent was awarded


in 1976. The main design principle behind the initial design concept was the construction of a near prismatic shape using 12 substantially identical cylinders that were interconnected to each other so that it would have the structural efficiency of a spherical tank and the volumetric efficiency of a membrane tank. Unfortunately, this was the time when


the US broke off diplomatic relations with Algeria cancelling all contracts to import LNG. Six new LNG Carriers were immediately laid up and interest in LNG containment technology in the USA waned until recently. In 2005, Altair Engineering, Inc. was


providing advanced structural engineering analysis tools to the University of Michigan and applied it to the CDTS as a case study. Tis in turn developed into an interest to develop this Type ‘B’ tank concept further resulting in the awarding of multiple improvement patents to Altair’s Product Design team in 2013, 2014 & 2015, and Approval-in-Principle (AIP) by ABS in March 2015. Since 2005, the development has been continuous, as shown in Figure 1, with the design efforts focused on the use of CDTS for both the marine transport (LNG Carriers) and Floating LNG Processing and Storage Platforms (FLNG). Alcoa joined this effort in 2012 providing


• Te average LNG ship size has increased, increasing the need for sloshing mitigation


material recommendations as well as manufacturability assessments, and Dongsung Finetec in 2014, providing insulation solutions. Te details of the CDTS have been presented at the Offshore Technology Conference in 2009 and 2010 as well as LNG Conferences in London in 2009 and ICCAS 2009. Since the original concept was patented:


• Altair has identified and solved functional and structural problems with the original


concept and patented the improved design • Te economics of transport costs have 22


Figure 1: The different stages of development for the CDTS


made efficiency an even more significant economic opportunity


Te marine transport of LNG is a mature


technology that is almost 50 years old. In the early years of LNG Carrier designs, a number of containment systems were developed and the most successful were the Moss Rosenberg Spherical Tank and the Gas Transport Membrane Lining System. Te CDTS has much better volumetric


efficiency (0.85) than the Spherical Tank (0.52) and is close to the membrane system (0.88). This high hold space volumetric efficiency coupled with the CDTS being of an independent tank construction and self-standing allows for higher utilisation of available space above and below the main deck resulting in a significantly smaller ship length for the same cargo capacity. Recent development of the extended Spherical Tanks has improved the Volumetric Efficiency to 0.56. Te major benefit of the CDTS is that


for the same LBP it offers 35% more capacity than Spherical and 24% more than a Membrane and IHI SPB ship, or a reduction in ship or platform length for equivalent Cargo Capacity; 12%


• Significant reduction in Gross Tonnage


• Eliminates the restriction on partial filling of tanks for sloshing, allowing


membrane tank system


• Reduced estimated cost of LNG carrier by 10% compared to Spherical


multiple discharge locations


• Provides ease of construction and ease of installation in the ship


and 5% Membrane • Offers superior structural efficiency • Utilises a simple support system


• Less installed power and thus fuel savings in service


• Better protection from side collision damage – 4m versus 2.5m for


• Better protection from bottom damage – 4m versus 2.75m for Membrane Ships


• Excellent Boil off Gas performance


Membrane Ships and 3.25m for Spherical Tank Ships


• Internal Connectivity provides Natural Conductive Cool-Down Pathways – low


The Naval Architect March 2016


compared to Spherical and 6% compared to Membrane ships. The use of the CDTS results in the following additional advantages:


• Significant reduction in the overall construction schedule compared to the


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