Swedish owners raise bar in environmental tanker design
Meticulous attention to every aspect of energy demand and usage is reflected in the 1A ice-classed ‘Fure Vinga’. The project lays down a new milestone in product carrier design and construction, writes David Tinsley.
Representing the opening phase in a major investment in environmentally-advanced product tankers by a league of Swedish owners, the 18,200dwt Fure Vinga left her Chinese builder during early April to begin a positioning voyage to Europe. Sailing south towards the Malacca Strait, she took on a cargo at Batam Island off Singapore, with scheduled delivery of the first batch to Castellon in eastern Spain during mid-May, to be followed by final unloading in Rotterdam.
Designed to transport IMO Type 2 and 3 chemicals in addition to oil products, engineered for both IMO Tier III NOx compliance and conformity to sulphur emission control area (SECA) limits, and strengthened to Finnish/Swedish 1A ice class standard, this new generation encapsulates high trading value and asset worth. It achieves a very low EEDI (Energy Efficiency Design Index) measurement, expressing CO2 emissions in relation to transport work.
The design has been developed by FKAB of Uddevalla in conjunction with shipowner Furetank and is claimed to offer a 40% reduction in fuel consumption relative to a vessel of the same size dating from 2006 and operating at 12 knots, as a consequence of comprehensive attention to energy efficiency. When manoeuvring, the savings should be even greater, at about 50%.
Fure Vinga is first-of-class in a series of six booked from the AVIC Dingheng yard in China. Based on the island of Donsoe, off the west coast of Sweden, Furetank ordered three of the newbuilds to its own account, and will manage all six within the commercial framework of the Gothia Tanker Alliance. Furetank’s alliance partners Thun Tankers and Alvtank are the contractual owners for one and two of the other newbuilds, respectively.
In addition to devising the T24C1 vessel concept, FKAB delivered the basic design and detail design to the shipyard through its offices in Uddevalla and Shanghai. MARIN fine-tuned the lines so as to arrive at an optimised, low-drag hull form.
A signature aspect of the technical specification is the nomination of LNG dual-fuel, four-stroke propulsion machinery, complemented by the application of selective catalytic reduction (SCR) technology to the auxiliaries.
Together with a raft of other measures including those relating to electrical power generation, hydrodynamic design, cargo handling and shipboard systems, the design’s environmental footprint will be substantially lessened compared to tankers built only a few years ago. Depending on fuel mode and operational settings, SOx and particulate matter emissions will be virtually eliminated, NOx cut by 80%-plus, and CO2 reduced by half.
Dimensional, design and equipment aspects reflect parameters for trade to north European ports and terminals, including the Eastham Locks on the Manchester Ship Canal, for access to the Stanlow oil refinery, the new lock and enlarged Sodertalje Canal, near Stockholm, due to be ready by early 2020, the Drogden channel through the Oresund between Sweden and Denmark, and draught constraints at various ports. In addition, the design fulfils requirements for operation into the St Lawrence Seaway system.
While 18,200dwt is obtainable at the maximum, summer draught of 9.4m, and 16,300dwt applies at the design draught of 8.85m, the hull envelope affords 13,000dwt at 7.9m draught for working into the Manchester Ship Canal and 12,900dwt on 7.7m marks for navigating the narrow Oresund passage. Furthermore, the Fure Vinga class will be able to offer 10,600dwt at 7.0m draught for shipments into Lake Malaren via the expanded Sodertalje waterway.
The cargo section is divided by transverse bulkheads and a centreline, longitudinal bulkhead to form 12 tanks, one of which is dedicated for slops, giving a total carrying capacity of 20,300m3 and allowing for 12 segregations.
Each tank is fitted with a deepwell cargo pump rated at 300m3 per hour, enabling ship discharge at an outturn of up to 1,800m3/h, and using electric drives in the cause of improved efficiency together with minimised noise pollution in port. The inert gas generator has a dual-fuel capability, allowing operation on LNG for cleaner emissions. Ballasting is accomplished using two 500m3/h pumps.
The scope of the power and propulsion equipment contract award to Wärtsilä underscored both the organisation’s ever-wider portfolio and technical resources and also the increasing value attached by customers to fully integrated ‘packages’. The comprehensive supply deal for each tanker included the medium-speed dual-fuel main engine, controllable pitch propeller and nozzle, shaftline with seals and bearings, shaft generator, auxiliary engines, ProTouch propulsion control system, Energopac rudder, and cargo and ballast pumps.
Manufactured at the Vaasa factory in Finland, the nine-cylinder W34DF main engine has a contracted maximum power output of 4,500kW at 450rpm and turns the nozzled controllable pitch propeller through a reduction gear incorporating power take off/power take in (PTO/PTI) for a shaft generator.
In PTI mode, whereby the 1,800kW/2,250kVA alternator is energised by the ship’s diesel gensets to become an electric motor acting on the shaft, the vessel assumes a take-me-home emergency or auxiliary propulsion capability. The feature is recognised in the BV notation AVM-APS. Rather than being limited to a constant speed, the shaft generator can be used across a wide speed range. The shaft generator and engine can operate on a ‘floating frequency’ between 50Hz and 60Hz.
The two Wärtsilä gensets are nine- and four-cylinder models from the Auxpac range of pre-commissioned, standard aggregates. Based on W20-type engines, the respective sets are rated at 1,600kW/2,000kVA and 685kW/856kVA, and the exhaust streams are treated by an SCR system, so that IMO Tier III compliance can be achieved with the auxiliaries.
One of the most notable features of the design is the adoption of a propeller nozzle, an unusual measure for this type and size of vessel. The high-performance nozzle shroud on the propeller considerably enhances the thrust effect, improving propeller efficiency at the design speed, and allowing for a reduction in the specified power of the main engine in relation to the ice class, resulting in a lower EEDI for the ship. The nozzle is also reported to be effective in attenuating underwater radiated noise.
ENERGY SAVING DEVICES
Fure Vinga incorporates the Energopac system, which integrates rudder and propeller so as to achieve efficiency gains. The rudder comprises a full spade blade and flap section, to enhance manoeuvring performance and reduce drag.
The leading edge is twisted and consequently more aligned with the propeller slipstream, resulting in better water inflow angles and improved cavitation behaviour by the rudder. The fairing cap on the propeller hub and the efficiency bulb fixed to the rudder blade are specially shaped to reduce the separation losses behind the propeller hub increase overall efficiency. The bulb also has the hydrodynamically-advantageous effect of reducing the water velocity through the propeller plane. Close-quarter manoeuvring and berthing is assisted by an 850kW Brunvoll bow thruster.
So as to deliver a functionally integrated system that would achieve optimum propulsion efficiency, Wärtsilä applied its OPTI design methodology to the project. This uses computational fluid dynamics (CFD) analysis to calculate the performance of the propeller, nozzle and rudder, including these components’ interaction with the hull, and ensure efficient matching of the various propulsion elements. The manner of Wärtsilä’s approach underlines the difference between simply providing a wide range of equipment and supply such a package where the individual items are ‘tuned’ to each other and to the ship.
The Swedish tanker provides for a service speed of 13 knots at a laden (design) draught of 8.85m, at 80% maximum continuous output, with a 15% sea margin and with the shaft generator engaged and absorbing 300kW. Anticipated daily fuel consumption in these conditions but excluding the sea margin factor, is 13.7t of marine gas oil (MGO) or 11.3t of LNG plus 0.13t of pilot fuel.
The LNG bunker fuel is carried in two 300m3 tanks positioned forward on the weatherdeck, just abaft the break of the fo’c’sle, while fuel oil is stored in two protectively located underdeck tanks affording a total volume of 540m3.
PRINCIPAL PARTICULARS - Fure Vinga
Cargo capacity @100%
Cargo capacity @98%
Main engine power
1 x 1,600kW; 1 x 685kW
Speed @80% MCR, on design draught
+Hull, +Mach, Oil Tanker, Chemical Tanker, ESP, Dual-fuel (LNG), Unrestricted Navigation, Ice Class 1A, AUT-IMS, SYS-IBS-1, Mon-Shaft, VCS, InWaterSurvey, Clean Ship, EWCT, BWT, AVM-AS, IG (SS)
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