Tuesday, May 25, 2010

New Trends in Marine Propulsion

New trends are emerging in hull and propulsion machinery design, as operators strive for lower fuel bills and a smaller carbon footprint, but the implications may be daunting. At this year’s Connecticut Maritime Association conference, held in March, International Association of Classification Societies chairman Dr Hermann Klein warned that the goal of cutting the shipping industry’s carbon emissions 20 percent by 2020 may require newbuild emissions to be reduced by 80 percent. Klein, who is also a Germanischer Lloyd board member, remarked that “it might sound quite easy to reduce CO2 emissions by 20 percent, but to do this, average emission cuts per vessel would need to be 40 percent given projected industry growth over the next decade.”

Klein noted, “In the shipping industry, average vessel life span is 25 years while the average asset life span in the trucking sector is nine years, thus in 2020 none of today’s trucks will exist. However, because of a vessel’s normal quarter-century life span, over half of ships existing today” will still be in service in 2020. Because of this, “if it is not possible to reduce fuel consumption of existing ships – and fuel consumption is directly related to CO2 emissions – then,” he said, “maybe we have to reduce CO2 emissions of new vessels by 80 percent to achieve the 40 percent reduction implied by the 2020 target date, especially if industry growth is taken into account.”

Slow Steaming
At an earlier conference in London, Klein also warned that “current market conditions and fuel costs” have already brought the optimum speed for container ships down to about 14 knots from nearly 26 knots only five years ago. Although some newbuildings are still being specified with high speeds Klein said he couldn’t understand why. “To justify such speeds,” he remarked, “there would have to be insufficient ships available, low fuel prices and attractive financing,” none of which he saw as likely. “There is no reason to speed up again,” he said. Major shipping companies have already taken note of this, with a rapidly growing number of ships now practicing “slow steaming” to cut fuel costs.

Some carriers, such as Maersk, have adopted “super slow steaming” with speeds dropped to between 12 and 14 knots. Maersk vice president of Fleet Management, Soren Andersen, said the speed reduction has proven to be a great success. “We reduced engine loads from about 40 percent, while slow steaming, to around 10 percent while ships are super-slow steaming,” he said. However, the Maersk executive also cautioned that engine turbochargers need to be “blasted out” regularly to ensure that the machinery can be operated safely and effectively at that range. Because there are also warranty and insurance issues involved in taking main engine speeds down so low, Maersk made a number of tests prior to initiating the procedure. It then took the results to leading engine manufacturers. “The engine manufacturers agreed with us,” said Andersen, “so we talked to the insurers who also said it was OK.”

Turbocharger Kit
Looking at the trend toward slow steaming, Finland’s Wärtsilä has designed a special up-grading kit for turbochargers that allows the practice without potential engine damage. The kit involves fitting shutoff valves in the exhaust duct before the turbocharger turbine, and in the scavenge air duct after the compressor, together with a bypass line to keep the turbocharger rotor spinning at a pre-set constant speed. The valves are remotely controlled and the kit includes fitting a control system to operate the valves. The first of these kits was fitted to the 1,200-TEU container feeder ship Aglaia, owned by Germany’s Koepping Shipping Company, which is powered by a single eight-cylinder Wärtsilä RTA62U engine delivering 15,000 kW at 107 RPM.

In late February, German shipowner Jüngerhans became the latest to opt for the kit, which is being installed on two 1997-built vessels equipped with 7-cylinder Wärtsilä RTA62U main engines. The kits will permit the engines to be run anywhere from 10 percent to 100 percent maximum load without operational restrictions while decreasing the risk of engine fouling and excessive component temperatures. To date, the kits have shown fuel savings of up to 6-10 grams per Kilowatt hour (g/kWh) for 8-cylinder Wärtsilä RTA62U engines and 8-12 g/kWh for the larger 12-cylinder Wärtsilä RT-flex96C engines, which are equipped with three turbochargers.

Lower Output Engines
Maersk, as well as other operators, is also taking a look at engine and propulsion requirements as new ships are once again ordered. A Maersk competitor, China Shipping Container Lines (CSCL), has already scaled down the 20-knot-plus speed originally specified for a set of eight new 4,700-TEU container ships it has ordered to a maximum speed of 18 knots. These ships will now be fitted with lower output 7-cylinder Wärtsilä RT-flex68TD common rail 2-stroke engines instead of higher horsepower engines. “The low fuel consumption across many load parameters was the key technical reason to select the Wärtsilä common rail engine,” said CSCL’s deputy general manager, Li Xueqiang. Wärtsilä, which is already moving much of its production capacity to Asia, recently entered into an agreement with South Korea’s Samsung Heavy Industries to develop a new breed of gas-fueled ships that will be able to meet future environmental regulations. Under the agreement Wärtsilä will provide the propulsion machinery while Samsung will concentrate on ship design and construction. Wärtsilä has already come up with prototype designs for large ferries, ro/ro ships, container vessels and cruise liners that could be propelled by LNG-burning powerplants.

Dual Fuel Engines
Wärtsilä began developing dual-fuel (DF) engines capable of running on LNG more than twenty years ago, using a high-pressure injection principle that allows a wide variety of fuels, such as crude oil, natural gas and heavy fuel oil, to be burned by the same engine. The first lean-burn DF engine, the Wärtsilä 18V32DF, was built in 1996 and used the injection of a very small amount of marine diesel oil (MDO) as a pilot fuel to initiate the combustion of a lean air-gas mixture. By 2003 four small 6L32DF engines were installed in the world’s first gas-driven platform supply vessel, Viking Energy, while in 2004 several larger 6L50DF units were used to propel a series of 75,000 m3 LNG tankers.

Last year, Wärtsilä competitor MAN Diesel built five 8L51/60DF dual-fuel engines with a total output of 40,000 kW for installation in the world’s largest LNG carrier employing electric propulsion, a 174,000 m3 vessel being built by South Korea’s STX Shipbuilding for Spanish owner EN Elcano. This year, Wärtsilä has introduced its 20DF series engines, which can be used in auxiliary applications, such as on-board generating sets or as the prime mover for smaller vessels, such as tugs.

LNG as a Fuel
The move towards LNG as a marine fuel is now becoming more widespread with a number of smaller vessels, such as ferries, already operating on gas. This is because when an engine is being run on LNG its CO2 emissions are reduced by approximately 20 percent, gas having a lower carbon content than liquid fuels. In addition, the lean-burn combustion process employed in the most recent engine designs means that NOx emissions are reduced by approximately 80 percent while SOx emissions are completely eliminated, as natural gas does not contain any sulfur. The production of particulates is also practically non-existent, as natural gas has virtually no residuals. This is seeing new designs drawn up for larger vessels, such as container ships, bulk carriers and tankers, as well as cruise ships and ro/ro ferries, that will operate at least part of the time on LNG, particularly when navigating in coastal waters or within port areas. By employing duel-fuel auxiliaries, such as Wärtsilä’s new 20DF series, these ships will also be able to switch to clean-burning LNG for electrical power while berthed rather than plugging into a shore-based electrical outlet.

Podded Propulsion
Along with refinements to ship engines and the use of LNG as a fuel, shipowners have also been looking at propulsors, hull shapes and other fuel-saving devices. Podded propulsion units first started appearing in the 1990s and were quickly adopted by the cruise industry because of the engine placement flexibility they gave to internal ship design. However, the pods have had their share of mechanical troubles, with lengthy lawsuits initiated against their manufacturers by Carnival Corporation and Royal Caribbean Cruise International. This, plus rather high construction costs, has stalled their adoption by the general cargo sector, despite the fact that they have been shown to reduce fuel consumption by about 10 percent when compared to diesel-electric systems using conventional shafting.

In 2002 podded propulsors using contra-rotating propellers (CRPs) were introduced, a configuration that sees two propellers facing each other but rotating in opposite directions, one propeller able to absorb some energy from the other. This idea has found limited employment to date, largely because of cost, but Japan’s ShinNihonkai ferry company had two sets of ABB-manufactured CRP Azipods installed on two of its newbuildings in 2004. To date it has reported fuel savings of about 20 percent, as well as obtaining 15 percent more cargo capacity, when compared to ships of a similar size using conventional shafted propulsion.

An offshoot of podded propulsion has been the concept of rudder/propeller combinations, such as Wärtsilä’s “Energopac” and Rolls-Royce’s “Promas,” that can achieve a fuel consumption reduction of about 9 percent in optimum conditions. Helsinki-based Finnlines has been one of the first companies to choose this device and is having it installed on six new ro/ros being built in China.

Riding on Air
Another Scandinavian company taking a very active approach to enhancing a ship’s overall efficiency is Sweden’s Stena Bulk, which has begun model testing of its new EMAXair design centered around a 15,000-dwt product tanker being developed for Baltic trading. The main focus of the concept is on dramatically reducing bunker consumption and emissions while incorporating such safety features as double engines, double steering gear and double navigation systems. The “air” part of the EMAXair name comes from the fact that the design will feature a unique hull and bulbous bow shape that will allow the tanker to ride on a cushion of air. The bottom of the hull will have a cavity extended forward with help of the newly developed bulbous bow where air pressure will be maintained by compressors. Since friction between water and air is lower than between water and steel, the vessel’s resistance will be significantly reduced. The new Stena tanker will also make use of duel-fuel engines running on either marine diesel oil (MDO) or LNG to turn large 4.8-meter diameter slow-rotating propellers for an optimal service speed of 13 knots. At this speed the ship will consume about 15 metric tons of LNG per day while producing 35-40 percent less carbon dioxide than an oil-fueled conventional vessel of comparable size, along with 90 percent less nitrogen oxide, no sulfur oxide, and 99 percent fewer particles, all without the use of catalytic converters. When conditions are right the Stena tanker will also make use of a kite sail installed at the bow to reduce fuel consumption even further.

Japan’s ISHIN Ferry
Similar to Stena Bulk’s plan for new energy-efficient tankers is a next-generation ferry drawn up by Japan’s Mitsui O.S.K. Lines. Titled “ISHIN”, which stands for “Innovations in Sustainability backed by Historically proven, INtegrated technologies”, the new ferry, like the tanker, will make use of hull air lubrication technology. The air will be collected and recirculated to save even more energy, and the ship will use an ultra-low friction bottom coating in which micro patterned indentations will form to trap water and help reduce drag. The ISHIN ferry will use LNG as its fuel when under way, and zero-emission operation will be achieved while at berth by the use of shore power and rechargeable lithium ion batteries. These batteries will be partially charged from solar films that will be installed on all cabin windows to reduce light while supplying electricity. The LNG/electric ship will also utilize a contra-rotating propeller system, with the rear propeller absorbing rotation energy from the front, while the propellers will be fitted with MOL-developed Propeller Boss Cap Fins (PBCF) to achieve even more savings.