Dutch ferry driven by eco-efficiency
A new ‘double-ender’ under construction in northern Spain to serve the Dutch island of Texel will employ several different energy sources, including compressed natural gas (CNG). The vessel reflects the most thorough consideration of intertwined environmental and economic factors, writes David Tinsley.
‘Eco-friendly’ has become an overplayed or exaggerated term, used effusively by many shipowners, operators and builders to describe or highlight their new vessels or designs. Intensified commercial pressures and the proliferation of environmental legislation over recent years have, of course, fuelled accelerated technological progression, raising the ‘eco’ bar across-the-board. But fleet investments have always been underpinned by the normal business goal of increased transport efficiency, which automatically results in lessened environmental impact per unit of payload capacity.
A differentiation as to ’eco’ approach may be made in cases where ensuring the highest practicable environmental standard is ingrained in the corporate culture, or where the specification is tailored to operations in more environmentally sensitive areas, over-and-above the need to satisfy regulatory edicts. In such instances, every aspect of vessel design and engineering is scrutinised at the outset of a newbuild project from an environmental as well as economic perspective. Such a disposition is exemplified by Dutch ferry operator Royal Texels Eigen Stoomboot Onderneming (TESO) in its latest stage of fleet modernisation, entailing a 135m ‘double-ender’ to serve a vital Frisian Islands’ link.
The nascent ferry, to be named Texelstroom, will be powered by a main engine genset installation allowing for primary operation on natural gas, bunkered and carried in compressed natural gas (CNG) form, or alternatively on ultra low-sulphur diesel fuel, with the facility to also draw power from a 1.6MWh battery bank. Reliance on hydrocarbon fuels, especially as regards the hotel load, will be reduced by arrays of solar panels fitted on the uppermost deck, and which will feed into the energy storage system.
Consideration of all elements bearing on fuel consumption has also led to a hydrodynamically-optimised hull form, the adoption of heat recovery methods, and the use of LED-based lighting armatures throughout the vessel.
Texelstroom is under construction in the Bilbao area, at the Sestao yard of LaNaval (Construcciones Navales del Norte), and delivery is anticipated by the end of 2015, with a view to service entry during the spring of 2016. Of entirely symmetrical configuration, the vessel has been arranged to carry up to 1,750 passengers and 350 cars on the 4km route between Den Helder and Texel across the tidal race known as the Marsdiep. The double-ended, drive-through layout will ensure expeditious turnarounds, complementing the 15-minute crossing time.
Texel is the largest and most populated of the Frisian islands in the Wadden Sea, and the westernmost in the archipelago, with a high economic dependence on tourism, and the ferry connection constitutes vital transport infrastructure.
Royal TESO is a community-owned undertaking with a track record in incorporating cutting edge, energy efficient strategies and clean technologies. For example, in 2007, it was the first shipping company worldwide to use GTL (gas-to-liquids) fuel. Realising its latest objectives as expressed in the new ship has been assisted by funding support from the EU’s iTransfer programme. The latter aims to make ferry transport more sustainable and easily accessible, and encourage greater utilisation of the mode, by driving innovation.
An important part of the project was the initiation of a community engagement exercise to elicit ideas regarding ’sustainability’ features, and the subsequent consideration of that feedback. In total, more than 600 suggestions related to the design and operation of the vessel were submitted by crew, operational management, TESO shareholders, service users and other stakeholders, and students. Proposals were assessed and followed up under three categories, namely onboard power consumption savings, reduced power generation emissions, and reduced wastage in other shipboard systems.
Dutch naval architecture consultancy C-Job was appointed to carry out the full conceptual design in cooperation with TESO, while Vripack was subsequently assigned the exterior styling and interior design. Following the Vripack blueprint, the shipbuilder appointed a local Basque company, Oliver Design, to complete the design of the accommodation spaces.
The project team and its contractors were tasked with reducing energy consumption by at least a quarter relative to TESO’s 2005-built Dokter Wagemaker, while also enlarging vehicle capacity by at least 10% within a similar hull envelope governed by the existing berths at each end of the route.
The solution to the requirement to increase the payload within the limits set by the terminals was found by widening the vessel above the level of the mooring arrangements, while maintaining approximately the same waterline width as the earlier vessel. As a result, the Texelstroom’s upper car deck and saloon have been extended laterally, adding two ro-ro lanes. In conjunction with a 5m increase in overall length, this has yielded the requisite additional capacity for cars. The lower vehicle deck on the newbuild is suited to a freight intake corresponding to 34 trucks, plus 52 cars.
The four prime movers, all emanating from the Ghent factory of Anglo Belgian Corporation (ABC), are split between two independent engine rooms, each of which can provide sufficient power to ensure normal service at least up to Beaufort 9 wind force. Two of the ABC engines are of diesel/CNG dual-fuel type, running at a maximum 1,000rpm, and two are 750 rpm diesels, and each has a rated maximum output of just over 2,000kW.
Twin Rolls-Royce azimuthing propellers at each end of the vessel The installation has been rated for an economic speed of 10 knots, and maximum of 15 knots, and the 360 degree-rotatable propulsors afford the essential, high level of manoeuvrability.
The use of LNG was ruled out because of the lack of infrastructure and the higher costs and logistical challenges of direct supply by road tanker or bunker barge. At an evidently cheaper cost per MW of power than either diesel or LNG, CNG was chosen as the fuel form. By coupling to a compressor station ashore near the ferry harbour of Texel, with a connection to the Dutch gas network, CNG will be delivered at night to the banks of CNG cylinders aboard the vessel. The cylinders will be refilled to a pressure of 200bar. It is estimated that one bank of cylinders will suffice for almost a whole day’s operation of the Texelstroom.
Peak shaving through the use of battery power will reduce overall fuel consumption, and is pertinent to the duty cycle of such a ferry, with its large fluctuations in energy requirements in the berthed, berthing, manoeuvring, accelerating and transit phases.
The energy storage system nominated for Texelstroom has been supplied by Corvus Energy, and comprises 252 of the Canadian specialist’s AT6500 48V lithium ion modules. The 1.6MWh battery capacity will be used to increase efficiency and for back-up power. As well as peak shaving, the large battery reserve means that the ferry could be operated on battery power alone in case of emergency. For a very high proportion of the time, it is anticipated that the ship will only need to have one main genset running.
A propulsion calculation matrix was developed by C-Job, and this was used to determine main generator power requirements, combined with battery capacity, during normal sailing.
The energy storage arrangements have enabled the designers to specify smaller main generators, as the batteries can be used to provide short power-up and power-down capabilities. The technology is seen as an effective solution to the hybridisation of commercial CNG-powered vessels, supporting performance by conferring consistent power and reliability.
As an integral part of the advanced energy management system, more than 700m2 of solar panels are fitted on the uppermost deck. Under optimum conditions, the array will deliver 150kWh. While this is less than 10% of the total battery capacity, it is estimated that the photovoltaic panels will cover 40-50% of the hotel load. The electrical requirement at night, when the vessel is in standby mode in the harbour of Texel, can be met from the island’s grid. Some of this electrical power can be stored in the batteries.
Active measures to cut onboard power consumption include the nomination of intelligent sensors for lighting, energy saving lamps, a more efficient ventilation strategy and heat recovery. Using energy from the cooling of the dual-fuel engines, a water tank will be heated to around 85°C. This heated water will ensure overnight heating of the vessel when she is not sailing.
During summer, energy savings will be made by ventilating the lower car deck with natural air flow, by opening the upper part of the doors when under way, obviating the need for forced ventilation. The electric fans will only be switched on when it is necessary for air quality or temperature reasons.
Design adaptation to prevailing lateral wind force on the intended route was determined by naval architecture consultancy Van Oossanen through CFD (computational fluid dynamics) analysis of wind behaviour. This promises a reduction of at least 2% in the drag coefficient. Van Oossanen also employed CFD to analyse hull performance, so as to minimise the underwater hull form resistance.
Relative to her immediate predecessor, Texelstroom features smaller funnel casings and slightly lower wheelhouses, and has no atrium on the upper deck, all of which bear upon wind sensitivity and stability factors.
As well as the innovative power arrangements, the design incorporates features important to ferries operating in the Wadden Sea area of the Frisians. The hull has been strengthened to withstand winter ice, to the requisite ice class. Her Lloyd’s Register notations include Passenger and Crew Accommodation Comfort (PCAC), recognising measures taken to enhance habitability and passenger wellbeing.
Texelstroom will supersede the older of the two current mainstays of the route, the 1990-built Schulpengat. Each year, TESO carries at least 3.5m passengers and about 1.4m cars on the crossing.
Length overall 135.40m
Length, waterline 134.27m
Breadth, maximum 27.90m
Breadth, main deck 22.00m
Depth, to main deck 7.18m
Draught, maximum 4.40m
Draught, design 4.05m
Passenger capacity 1,750
Ro-ro capacity, lower car deck 171 cars or 34 trucks + 52 cars
Ro-ro capacity, upper car deck 209 cars
Main generator engines 2 x 2,081ekW(dual fuel) + 2 x 2,131ekW(diesel)
Total main engine power 8,424ekW
Propulsion thrusters 4 x 1,800kW(2 for’d; 2 aft)
Battery capacity 1.6MWh
Solar power 150kWh
Class Lloyd’s Register
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