Tuesday, May 29, 2012

Propulsion Systems – Looking at the Whole Picture

By Jim Shaw

The traditional view of propulsion, looking at engines, shafting and propellers, is rapidly changing to encompass the entire vessel: anything that can lead to higher efficiency and less pollution. At a meeting of shipping executives in Europe earlier this year Fridtjof Rohde of German classification society Germanischer Lloyd noted that there are many opportunities for finding and exploiting efficiencies to save fuel and money, even in the tight conditions facing the industry today. He added that this can be done while operating a more environmentally friendly ship. The use of new computational techniques, he said, “has opened up the design space for shipping,” both in the development of new designs and in the ability to make improvements during conversions or upgrades to existing tonnage. “Upgrades to propellers, improving the wake field and appendages, and installing new ‘smart’ software systems such as FutureShip’s ECO-Assistant”, he stressed, “could significantly improve” a vessel’s performance. In the newbuilding sector he observed that the use of computational fluid dynamic techniques to optimize the hull form of an existing design, plus selecting the right engine and “smarting up” auxiliary systems, could also result in improved competitiveness and a better bottom line.

EEDI and the Bottom Line
Shipowners in attendance took note of Rohde’s remarks because they have been looking for any ideas that might improve their profit margin, particularly in regards to propulsion efficiency. This is largely because of the dramatic rise in fuel prices that have taken place in just the past few months. During the first quarter of this year oil prices increased by about 14 percent, a jump that saw marine fuel sales in Singapore, one of the world’s largest bunkering centers, fall to a two-year low when bunker-C hit $742.5 per ton. At the same time, new ships have to comply with the International Maritime Organization’s Energy Efficiency Design Index (EEDI), which was agreed upon last July. Under EEDI, shipping costs are expected to be cut by US$5 billion by 2020 through various efficiencies while the amount of carbon dioxide released into the atmosphere is to be reduced by some 20 billion tons.

Matching Engine to Propeller
Nicholas Skiadaresis, Managing Director of ENES Marine Service S.A., pointed out that any means of reducing fuel consumption usually produces other benefits, including reduced CO2 emissions and a better EEDI. Skiadaresis, who has been studying the efficiencies of new Cape-size bulk carrier designs, underlined the fact that propulsion specifying has gone beyond basic machinery to also include such spacial constraints as engine room length, the position of the shafting center line, the base line to propeller tip clearance and aperture clearances, all factors that have to be considered in finding the optimal combination for a particular hull. Although incorporating the required adjustments to a ship’s final design might boost costs the careful matching of engine and propeller, he noted, usually results in fuel savings of some 10- to 11-percent. Skiadaresis also illustrated how the optimal operating point for a vessel could be found by identifying the lowest SFOC (specific fuel oil consumption) at the lowest engine RPM. From this an engine can be identified and matched with a propeller, which could – through studying the required power for specific combinations of propeller diameter and pitch to diameter ratio – produce the most efficient results. Although choosing an engine and matching propeller not specified in a ship’s original base design might raise costs moderately, he observed that due to today’s extremely high fuel prices, these improvements would probably have very short payback periods.

Most Fuel Efficient Design
Tim Blackburn, managing director of the China Navigation Company of Singapore, noted that his firm “specifically focused” on selecting the most fuel efficient Handysize bulk carrier design available when it recently ordered four ships from China’s Chengxi Shipyard. The 39,700-dwt bulkers, priced at about $24 million each, are to be built to the B Delta 37 standard design drawn up by the Finnish naval architect group Deltamarin. According to Deltamarin the newbuildings are expected to deliver the “lowest cost per ton-mile” of any similar sized handy bulk carrier, a projection that has also induced Louis Dreyfus Armateurs and M.T.M. Ship Management Pte/Strategic Shipping to order variations of the design.

The China Navigation ships, which may eventually total ten, will measure 180 meters by 30 meters and have a cargo capacity of 48,500 cubic meters. Deltamarin says that the service speed at design draft will be about 14 knots and that model tests have indicated a daily fuel oil consumption at this draft and speed of about 18 tons, including 15 percent sea margin. Fuel-saving features are to include a modified hull form as well as enhancements to propeller, rudder and main engine.

Super Efficient Supertankers
The move toward highly fuel-efficient ships is also spreading to the largest vessels afloat, the Very Large Crude Carriers (VLCCs), as bunker prices continue to climb while freight rates remain weak. Ship broker EA Gibson predicted in March that the next generation of supertankers will have to be super-efficient and that design speeds may be reduced from the existing standard of around 15 knots to as low as 13 knots. “If newbuilding prices continue to fall and fuel costs continue to rise,” the broker mentioned, “an increase in efficient VLCC orders is likely to prevail, especially as the tanker industry comes under even more environmental pressure.”

John Fredriksen’s Frontline, one of the largest operators of big tankers, has suggested that, at current bunker prices, ships with enhanced engine and hull efficiencies could save close to $10,000 per day. This implies a savings of about 15 tons of fuel per day – but the savings could potentially be even higher. Several highly efficient VLCCs already under construction will be able to super slow-steam, thus dropping bunker consumption to about 30 tons per day less than conventional tonnage of the same size. Based on the assumption of bunker prices remaining relatively high, at around $700 per ton or more, this could translate to savings of about $20,000 per day. At current levels this would make a significant difference to a shipowner’s profitability, especially if bunker prices go beyond $750 per ton which, considering current political problems in the Middle East, they might easily do.

Lower Speeds, Bigger Propellers
One of the first operators to invest in highly efficient VLCCs has been Athens-based ship management company Almi Tankers, which has ordered two of the vessels from South Korea’s Daewoo that will be fitted with the new 7G80ME-C9.2 main engines launched by MAN Diesel & Turbo (MAN) in 2010. These ultra-long stroke power plants, which are being built by Hyundai Heavy Industries under license, are to be test bed run later this year and the twin ships delivered before the end of 2013.

Ole Grøne, senior vice president of Low-Speed Promotion & Sales for MAN, explained that the G series has been specifically designed to turn larger propellers than earlier engines. Traditionally, super long-stroke S-type engines with relatively low engine speeds have been applied as prime movers in tankers. However, Grøne said that following the “efficiency optimization trends in the market,” the possibility of using even larger propellers has been “thoroughly evaluated” with a view to using engines with even lower speeds for propulsion, particularly in VLCCs.

“VLCCs may be compatible with propellers with larger propeller diameters than the current designs and thus higher efficiencies following an adaptation of the aft hull design to accommodate the larger propeller,” he noted. “The new ultra-long stroke G80ME-C9.2 engine type meets this trend in the VLCC market.” MAN has estimated that such new long-stroke engine and large propeller combinations could offer potential fuel-consumption savings of between 4 and 7 percent along with similar reductions in CO2 emissions.

Electronically-Controlled Gas Injection
Japan’s Mitsui O.S.K. Lines (MOL) has also been looking at MAN’s engine research and has decided to temporarily convert a slow speed diesel in one of its newbuildings to an electronically-controlled gas injection (ME-GI) engine for testing purposes. The engine had been designed, manufactured and delivered by Mitsui Engineering & Shipbuilding (MES) with oil injection specifications but will be modified to run on gas or fuel oil at any ratio depending on the relative cost of the two fuels and owner preference.

The ME-GI, which combines gas injection technology and electronic control technology, was first unveiled by MAN at its Diesel Research Center in Copenhagen, Denmark last May. MES, a MAN Diesel & Turbo licensee, adopted the ME-GI as the engine of choice for its newly developed LNG carrier “Double Eco MAX” in July of last year, with the concept vessel expected to achieve a 30 percent reduction in fuel costs and CO2 emissions over currently active LNG tonnage.

MOL, which recently elected to scrap several of its older oil burning VLCCs, despite their double-hull construction (see Pacific Maritime Magazine, Feb. 2012), has been investigating adoption of ME-GI gas injection technology in a number of its future vessels. This research is taking place in parallel with the company’s Sempaku ISHIN project, which has been examining the design and configuration of highly efficient and environmentally friendly ships ranging from car carriers to cruise ferries.

Dual Fuel and Low Speed Gas
The use of gas, or LNG, as a marine fuel is continuing to grow and the largest commercial vessel to use it as fuel to date, other than LNG tankers, is the 25,000-dwt product tanker Bit Viking, completed by China’s Shanghai Edwards shipyard in 2007 and owned by Sweden’s Tarbit Shipping.

The conversion of this vessel to LNG last year saw its original twin 6-cylinder Wärtsilä 46 engines, which ran on heavy fuel oil, converted over to Wärtsilä 50DF dual-fuel engines capable of operating on LNG. At the same time, two 500 cubic meter capacity LNG storage tanks were installed on the ship’s foredeck, along with new piping, valves and safety equipment for bunkering purposes. The converted ship has since been operating along the coast of Norway on behalf of Norwegian oil major Statoil. According to its owners, the conversion has reduced carbon emissions dramatically and has qualified the vessel for lower nitrogen oxide (NOx) emission taxes under the Norwegian government’s NOx fund scheme, a major stimulus for future LNG conversions in that country.

For its part, Wärtsilä has gone on to successfully test its low-speed gas engine technology in trials conducted at the company’s facilities in Trieste, Italy. The tests have demonstrated that the new engine’s performance fully complies with the upcoming IMO Tier III nitrogen oxide limits, thereby setting a new benchmark for low-speed engines running on LNG.

Beyond the Propeller
Looking well beyond the visible horizon Wärtsilä has been investigating new means of propulsion as well as new ship types. One of the most interesting is a large tanker that would transport fresh water while making use of a “Fishtail” propulsion system. The latter would utilize two large horizontal fins that would rotate during each movement to achieve the right angle of attack for incoming water. As the large dimensions of the fins would offer low loadings, and rotational losses would not be present in the vessel’s wake, this system could achieve very high levels of efficiency. However, the vessel’s top speed would be low. The challenge for Wärtsilä engineers is to design a construction that moves the fins in the right way while still offering a high level of reliability.

The power to drive the fins would be generated by engines capable of burning biofuels as well as LNG. In addition, the vessel, which would be similar in size to a conventional double-hull oil tanker with a deadweight of about 150,000 tons, would be equipped with Flettner rotors and a hull air-lubrication system, two developments that have already entered service. Flettner rotors were installed on Enercon’s E-Ship 1, which entered service last year, and NYK-Hinode Line’s twin module carriers Yamato and Yamatai both have air hull lubrication systems installed (see Pacific Maritime Magazine, Sept. 2010).

Biofuels and Algae Harvesters
The expanded use of biofuels for marine propulsion, a development already starting to take place, may generate a use for one of Wärtsilä’s other concept vessels, the “Algae Harvester.” Such a vessel would collect algae from large basins floating in the sea by slowly sailing up and down inside the basin while using hinged booms to direct surface water into the vessel. Once inside, the water would be filtered to separate the algae from the seawater. The algae would then be transferred into two barges stored in recessed openings in the ship’s side, after which they would be collected by a pusher tug and taken to shore for discharge and processing. There would be no full-time crew, as the ship would be operated from a shore-based control station via a satellite link. Most power required would be produced by fuel cells running on biogas stored onboard in liquid form. The cells would supply the base load of electricity during slow-speed harvesting operations but when higher speeds might be needed, such as during repositioning trips, the vessel’s dual-fuel engines would be started. Propulsion would be through a low-loss electric drive system powering two pull-type thrusters. Although still being researched, the creation of biofuel from algae could provide an economically viable, low emission transportation fuel according to ExxonMobil, which has been studying the concept in partnership with Synthetic Genomics since mid-2010.