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MOSS improvement to fuel global growth

The Naval Architect: June 2017

The first two vessels in the series, Seri Camellia and Seri Cenderawasih, were delivered by Hyundai Heavy Industries (HHI) on 30 September 2016 and 20 January 2017 respectively. The remaining three will be delivered progressively in 2017 and 2018.

 

Seri Camellia was nominated as one of the top four candidates for the 2017 Nor-Shipping Energy Efficiency Award in recognition of its outstanding design. The vessel was also named as one of the Great Ships of 2016 by MarineLink. The vessels are designed for the export of LNG from the conventional onshore LNG terminal as well as from state-of-the-art Floating LNG (FLNG) vessels.

 

Design process
During the pre-contract stage, numerous ideas and design concepts were tabled due to the Seri C Class’ requirement to load cargo from FLNG offshore. With such high requirements and the need for FLNG operations, many factors were studied, particularly the strength of a cargo tank that can withstand sloshing loads during partial loading at open seas.

 

Membrane and MOSS containment systems, which have a proven track record over many years of operation, have been studied thoroughly in all the relevant technical and commercial aspects. Both systems offer high integrity and unique advantages in the design and day-to-day operations of a vessel, and Hyundai Heavy Industries (HHI), a builder of both Membrane and MOSS systems, was ready to provide either solution upon MISC’s request. In the end, MISC decided to move ahead with MOSS containment systems for the new Seri C Class, complementing its existing Membrane ships to offer greater operational flexibility.

 

The breadth of Seri C Class is sized for the New Panama Canal with the limitation of 49m. The large cargo hold area surrounding the cargo tanks, continuous tank cover and the breadth limitation have resulted in a narrower ship side passage way area compared with conventional MOSS and Membrane LNGC systems. Hence, designers gave significant consideration to the layout and position of deck outfittings such as the cargo manifold, accommodation ladders, mooring, safety equipment, etc.

 

Even with constraints of this kind, the Seri C Class LNGC is still compatible with almost 97 terminals, ensuring the flexibility of trading routes. Moreover, the greater distance between MOSS tank and hull side shell creates a protection barrier to reduce the possibility of tank damage in an event of grounding or collision.

 

In terms of hull strength, the IHS tank applies the concept of structural continuity, enabling the tank cover to be integrated with the primary structure. The overall structural strength of the vessel has consequently been improved while achieving a 3% reduction in steel weight. With the continuous tank cover, the support of the piping and outfitting on the IHS deck have been redesigned with simplified structures compared to conventional MOSS LNGC. Such a design also improves the maintainability of the vessel.

 

For the past decade, research on side-by-side loading has advanced tremendously, making a breakthrough in the understanding of offshore cargo transfers. The important criteria for side-by-side loading with a FLNG includes the multibody dynamic motion and mooring analysis, site specific environmental conditions, wind shielding effect, hydrodynamics interaction, etc.

 

Several novel model tests in side-by-side condition between IHS MOSS LNGC and FLNG have been conducted at the Marine Research Institute Netherlands (MARIN) to analyse the effect of liquid motion during partial loading conditions in a MOSS tank. The detailed berthing simulation performed at the Malaysian Maritime Academy (ALAM) is also crucial to simulate the offshore conditions for navigation and manoeuvring prior to actual side-by-side loading operation.

 

Construction
Synergy between the Project Management Team (PMT) and the builder, HHI has been pivotal to the success of the project so far. HHI, as the world’s largest shipbuilder has revived the production for MOSS cargo tanks after more than 10 years of inactivity.

 

The novel design of the vessel and a short engineering phase (due to a tight delivery timeline) resulted in huge challenges during the engineering and construction stage. The MOSS LNGC build started off with construction of the aluminum cargo tank, and was followed by construction of the hull structure. This was due to the fact that the MOSS tank is independent from the hull structure, and can therefore be fabricated separately and erected onboard when the hull structure is ready. The separate construction of MOSS tanks offers the benefit of making the fabrication process less complicated and improves quality control.

 

Another noticeable advantage of the construction, inspection and repair for MOSS tanks is how their insulation works. Constructed of panels and installed on the outside wall of the cargo tank surface, it is easily accessible via a working platform during installation works.
Another challenge during the construction was the large painting surface that includes the external and internal facades of the IHS tank. Relatively speaking, the painting job is larger than those for the Membrane and conventional MOSS LNGC systems, requiring higher manpower and safety precautions to be taken during construction.

 

Project management
The PMT for the new generation MOSS LNGC was established early on in the conceptual and pre-contractual stage and has seen completion of the project through. Involving the team in the complete project cycle (pre-contract, design review and construction supervision) was advantageous, providing continuity in terms of engineering, project interface, lessons learned and project development.

 

The PMT implemented several initiatives beyond typical shipbuilding practice, namely detailed bulk material testing, joint 3D engineering reviews, and extensive subcontractor/vendor audits. Bulk material tests were carried out on the steel plates, insulation materials, electrical cables and other items that do not undergo specific Factory Acceptance Test (FAT). This was based on previous experiences in which some items with type approval failed or did not meet necessary requirements. The joint 3D engineering review by all parties was essential in the initial development of the new design, pulling optimum human factor engineering, system integration, operability, maintainability and constructability together.

 

The design verification and construction supervision of the vessels were carried out by two Classification Societies (Lloyd’s Register & ABS) for the project with a “Sunshine Clause” that enables open access to comments on the engineering drawings made by Classification Societies.

 

Engineering sustainability
The Seri C Class LNGC has adopted several advanced technologies which include energy efficiency and emissions reduction. The vessels are also installed with the Ozone Ballast Water Treatment System, as well as Selective Catalytic Reduction (SCR) systems in compliance with IMO NOx Emission Tier III requirements. Voluntary adoption of the Eco Notation provides safe working conditions for the ship’s crew and protects the marine environment. No material contains asbestos, Halon, PCB, HCFC, CFC and toxic materials. The usage of Low Friction Anti-Fouling Paint on the vessel also contributes to reduced speed losses during operation. By applying the latest available and proven technology, the Seri C Class LNGC has achieved an attained Energy Efficiency Design Index (EEDI) of about 7 [g-CO2/ton.NM].

 

Seri C Class is designed for sustainability, not only in terms of lifecycle energy efficiency and green technology, but also for prospective LNG shipping requirements. The successful loading of the world’s first FLNG cargo is one of the many capabilities and features of the Seri C Class, but it offers more. The robustness of the MOSS cargo tank can provide a future conversion option, allowing conversion of the vessel to a Floating Storage Regasification Unit (FSRU) without further strengthening of the cargo tank.

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