Developments in ice navigation, winterisation and tanker and LNG ship technology are paving the way towards the Arctic LNG carrier. The interest in Arctic LNG transport arises from the expansive, as yet largely untapped gas fields in the Western Arctic regions of Russia. LNG ship technology is already beginning to encompass the possibility of future ice navigation, with the first orders for first-year ice-class LNG vessels for Russian service having been placed in yards in Korea and Japan in 2005, mainly to Lloyd’s Register class and for service to the gas export terminal at Prigorodnoye on Sakhalin Island.
The first-year ice-class LNG ships currently being built are based on existing designs with slight modifications. It is expected, requirements for Arctic LNG carriers for operation in multi-year ice, will demand a fresh design approach. The recent developments in large LNG carrier design and propulsion, coupled with the introduction of large ice-class double-acting tankers, point towards the future direction in terms of design and operational requirements. A number of additional factors will have to be considered, including:
- ice interaction scenarios
- ice class selection
- impact of hull-ice interaction on cargo containment system integrity
Ice-class Rules define a minimum standard of safe design for hull structural strength based on theoretical derivations, as well as in-service experience. Where limited Rule-based knowledge or service experience exists, the adoption of a ‘direct design’ approach for the hull and propulsion system using realistic ice interaction and operating scenarios can be used to aid ship design. This approach may be advisable for Arctic LNG carriers where:
- more severe loads are anticipated than those derived from existing Rules, e.g. ice interaction scenarios on azipod structures in astern mode for double-acting propulsion
- ice interaction occurs which is not envisaged by the Rules, e.g. hull bottom areas where ice entrapment could occur in shallow water shelf areas
- specific safety-critical elements are not explicitly addressed by the Rules, e.g. the possibility of hull structure deformation and the maintenance of LNG cargo containment system integrity.
The adoption of ship-design and trade-route-specific technical solutions and measures for Arctic operations, often termed ‘winterisation’ measures, will need special attention. Specific items that need to be taken into consideration include:
- steel grades for exposed hull structures to withstand low temperatures
- ice accumulation on deck, stability aspects and de-icing measures
- hull appendages for ice operations, e.g. ice knife, rudder stoppers
- abrasion-resistant and low-friction hull coatings for the immersed areas of the ice belt
- precautions for low-temperature operation of deck machinery and systems
- precautions for low-temperature operation of main machinery and systems such as the design and arrangement of sea chests to prevent ice blockage
- safe working access to working areas on deck and emergency escape routes
- searchlights for ice operation at night, when under escort or when manoeuvring in port.