Text: Marjatta Pietilä
The key drivers in ferry design are efﬁciency improvement, emissions reduction and compliance with future regulations. New regulations set by the International Maritime Organisation (IMO) concern passenger ships constructed on or after 1 July 2010 and must be taken into consideration in the design of ferries that are now on the drafting table. Such regulations are for example the new Safe Return to Port regulations and the Probabilistic Damage Stability regulations.
“New regulations encourage innovative solutions and the building of better ships,” says Oskar Levander, Director R&D, Operational Performance Program within Ship Power Technology.
Improving the overall efﬁciency of a ferry is no simple task. A very signiﬁcant proportion of the energy contained in the fuel is either lost or unused because of heat losses, exhaust losses, and transmission, propulsion and other inefﬁ ciencies. The overall efﬁ ciency of ferries should be improved and the demand for power reduced.
Longer ships, lower resistance
“This can be done by utilizing efﬁciencies of scale, lengthening the waterline, taking advantage of new propulsion concepts, improving methods of heat recovery and taking alternative fuels into use. While similar traditional ferries are usually about 180-210 m long, the Ferry of the Future is designed to have a length of 225 m. The longer the ship, the smaller the resistance. This is because of the low speed/length ratio,” explains Levander.
“Size really does matter. As an example, let’s compare two ferries cruising at a speed of 25 knots. The smaller ferry has a length of 185 m and a breadth of 28 m. The larger one is 225 m long and has a breadth of 31 m. The carrying capacity of the smaller ferry is 2000 lane metres, while the larger offers 2900 lane metres, 45% more than its smaller sister,” Levander says.
“At the same time, the power requirement of the smaller ferry is 31,700 kW while the larger one demands only 30,200 kW, some 5% less. If the demand for power is calculated per lane metre, the difference is even more remarkable: 35% less in the larger ferry. On the basis of this type of investigations we believe that one of the future trends will be a continuing increase in ferry size.”
Conventional shaft lines to history
In the Ferry of the Future, Levander is ready to abandon the conventional double-shaft-line solution and replace it with new propulsion concepts. These include a solution with counter rotating propellers (CRP) or a Wing Thruster which has a shaft line in the middle and two thrusters pulling at the sides. In CRP, the aft propeller recovers some of the rotational energy in the slipstream from the forward propeller. The advantage of Wing Thruster propulsion is that individual propeller loadings are reduced by using three propellers, which improves operating efﬁciency. Having twin steerable thrusters also increases the ferry’s manoeuvrability at slow speeds.
“These new propulsion concepts reduce resistance and result in lower power demands. This leads to lower fuel consumption and reduced emissions, “ says Levander.
Combined CRP and Wing Thruster propulsion with three pulling thrusters and one shaft line.
LNG superior to other fuels
Natural gas has many beneﬁts. It is mainly methane, which contains the highest amount of energy per amount of carbon compared to any other fossil fuel. Its carbon to hydrogen ratio is 1 to 4 and CO₂ emissions are 25% lower than with conventional fuels. Because of the lean burn concept employed in gas engines, NOx emissions are reduced by 85%. Sulphur is removed from the fuel when it is liqueﬁ ed, and particulate emissions resulting from the combustion of natural gas are very low.
“There is no visible smoke and no sludge deposits are formed. Furthermore, liquid natural gas (LNG) is extremely cold, and its low temperature can be utilized for cooling in the ferry’s air-conditioning system,” says Levander.
LNG is already a cost-effective fuel alternative. Even though natural gas is only available in some European ports, the fact that ferries usually operate on regular routes means fuel supplies are easy to organise for many itineraries. As Levander points out, “The LNG supply infrastructure can be built faster than the ferries themselves.”
New bow ramp arrangements could speed up RoRo cargo handling.
Ferry of the Future concepts
Wärtsilä’s Ferry of the Future is available now. The technology and components already exist, the concept simply applies them in a new and innovative way.
All the ‘delicacies’ in the concept are included in the same package. The ferry is powered by combined dual-fuel electric and mechanical machinery using LNG as the primary fuel and marine diesel oil (MDO) as back-up.
“Combining two propulsion concepts – a centre shaft line ﬁ tted with a CRP plus two Wing Thrusters at the sides – offers clear power savings. A diesel-electric power plant provides optimum efﬁciency at low speeds. In addition to propulsion, this power plant handles the electricity demands of the hotel section,“ says Levander.
The Ferry of the Future is large and beneﬁ ts from the resulting economies of scale. It has a large cargo capacity with two extra-wide ten-lane car decks but no lower cargo hold. Loading and unloading is quick because of the new bow-door arrangement and drive-through twin-level link spans.
“Easy manoeuvrability and fast turnaround in port means reduced speeds at sea, which result in lower fuel consumption. The ferry’s overall efﬁ ciency is high and emission rates are low,” says Levander.
Passenger comfort is also high on the agenda. Tax-free shops have disappeared. Reasonably-priced outlets for design products are located on both sides of twin-level indoor shopping streets. News and Internet cafés, ice-cream stands and coffee shops offer refreshments, while small restaurants with an intimate atmosphere serve exotic cuisines. This ferry offers its passengers truly memorable experiences.
“Designing ferry interiors isn’t exactly our ﬁ eld, but to develop our own products and technology we sometimes have to step outside our own segment and visualize the needs of our customers’ customers. Viewing the ship as an operational environment helps us take better account of end-user needs,” says Levander.