A novel design of LNG containment system is set to make its operational debut, with the imminent handover in China of the 45,000m3-capacity Saga Dawn, writes David Tinsley.

As the culmination of nearly 10 years’ research and development, the LNT A-BOX concept is initially focused on the small to mid-size LNG carrier segment. The rationale has been to devise a comparatively simple, cost-effective system that would enable more shipyards to build LNG vessels at competitive prices.

Following construction at the Haimen yard of China Merchants Industry Holdings in eastern Jiangsu province, Saga Dawn recently completed gas trials under the auspices of Singapore-based LNT Marine, an affiliate of owning group Landmark Capital. She will be deployed by Landmark subsidiary Saga LNG Shipping.

The LNT A-BOX solution was devised by LNT in cooperation with Swedish ship designer FKAB. It is founded on proven technologies, adopted in an innovative, patent-protected configuration, and employing IMO type A independent, prismatic tanks. Conventional cargo tank support arrangements and classical ship structural principles apply.

The cargo tanks form the primary barrier and liquid-tight, thermal insulation attached to the inner hull surface acts a full secondary barrier. As the insulation is not exposed to any static or dynamic loads from the cargo, the insulation material is optimised for thermal performance. Boil-off rate is given as being approximately 0.15% per day. The void space between the tank and insulation facilitates visual inspection of both tank and insulation surfaces.

The prismatic tank design allows flexibility in shape and geometry, offering optimum volume utilisation of the hull envelope and ensuring a virtually flat deck area. The internal structure of the design mitigates sloshing and obviates restrictions on partial loading, a vitally important factor for the planned operating profile of the ship and its intended primary role in coastal and intra-regional trading.

The ABS-classed Saga Dawn is laid out with three tanks in three separate cargo holds. The combined rating of a total of six Wärtsilä cargo pumps allows for a full-load discharge within 15 hours. The comprehensive power and propulsion packaged supplied by Wärtsilä encompasses a 12-cylinder 50DF-series dual-fuel main engine of 11,700kW output, gearbox and controllable pitch propeller, plus two gensets driven by 20DF-type dual-fuel engines of eight- and six-cylinder formation, respectively.

During normal service, boil-off gas will be used as fuel in the main and auxiliary machinery. A system for forced evaporation is fitted to ensure sufficient fuel gas supply to all consumers at all times.

The driveline features a shaft generator equipped with a power take-in (PTI) capability, energised by the auxiliary gensets, to confer a ‘take-home’ emergency propulsion capability. The ship’s manoeuvring qualities are enhanced by a Wärtsilä tunnel thruster.

Using LNT A-BOX technology, Saga LNG Shipping aims to build, own and operate a series of tailor-made small and mid-sized LNG assets targeted at projects currently in various stages of development, and including bunker barges, floating storage and regasification units and other ‘floaters’, as well as LNG carriers.

An LNGC design of 80,000m3-capacity is in the final stages of preparation. This is distinguished by a 9m fully-laden draught, suited to import traffic into Chinese regional terminals. Approvals in principle (AIPs) have also been obtained for shallow-draught, 28,500m3 ‘Wuhan-max’ and 12,000m3 ‘Yichang-max’ designs conceived to open up trade along the Yangtze River.

PRINCIPAL PARTICULARS - Saga Dawn

Length overall	195.0m
Length bp	184.8m
Breadth, moulded	30.0m
Depth, moulded	20.0m
Draught, scantling	10.3m
Draught, design	9.0m
Deadweight @scantling draught	29,500t
Deadweight @design draught	24,500t
Gross tonnage	c.30,000t
Cargo capacity	45,000m3
Main engine power, MCR	c.11,700kW
Aux gensets, total power	c.2,500kW
Service speed	16.5 knots
Range	c.13,000nm
Class	ABS