Engine technology propels trends in ship design

Advances in propulsion technology continue to be the driving force in new ship designs.

This 807-foot ferry represents a vision of the future developed by Wärtsilä Corp. and Kvaerner Masa-Yards. The 4,200-dwt ro-pax vessel, capable of carrying 2,000 passengers employs dual-fuel diesel technology and would have a service speed of 28 knots.

Wärtsilä Corp., in Helsinki, Finland, has teamed up with the Kvaerner Masa-Yards in Helsinki to propose an 807-foot-long passenger/vehicle ferry designed around the emerging dual-fuel (DF) diesel-engine technology and the latest electric propulsion equipment. The two companies believe ferries operating in environmentally sensitive areas are prime candidates for early adoption of low-emissions DF technology.

The 4,200-dwt ro-pax (roll-on/roll-off passenger) vessel would be 807 feet long, have a beam of 98 feet and be able to carry up to 2,000 passengers.

Four Wärtsilä 12V50DF engines and two 9L32DF engines make up the propulsion package, providing 51.9 MW total installed engine power, giving the vessel an expected service speed of 28 knots.

According to Oskar Levander at Wärtsilä’s Product and Application Development, the two smaller engines are mainly intended for harbor use when the load is low, but they can also be used when maximum propulsion power is needed. During normal operations, the vessel would use natural gas with diesel oil as a pilot fuel, but when necessary, the vessel could operate using only diesel.

“Electric propulsion was selected to get the benefits of constant-speed operation, which is better-suited to gas operation,” Levander explained.

Image Credit: Wartsila

The ferry has one fixed and one podded propeller. They rotate in opposite directions to produce significant gains in efficiency.

One unique propulsion element is the propeller-drive arrangement. A conventional shaft line drives a single fixed propeller. There is also one podded propulsor located directly aft of the fixed propeller. In normal cruising, the pod’s propeller faces forward toward the fixed propeller to achieve the advantages of two contrarotating propellers. “The aft propeller takes advantage of the rotative energy left in the slipstream of the forward propeller as it turns in the opposite direction. This improves the rotative efficiency of the propulsion,” he said.

The podded unit also offers other beneficial characteristics, such as excellent maneuvering and steering capabilities, since the pod can turn 360°. The propulsion configuration allowed Kvaerner Masa to design a single-skeg hull form giving better hull efficiency, especially since rudders, shaft brackets and bossings were not needed, Levander noted.

The Wärtsilä-Kvaerner ferry is designed specifically to use Wärtsilä’s 32DF and 50DF four-stroke working cycle engines. In the liquid-fuel mode, the latest diesel-injection technology is used. In the natural-gas mode, ignition is initiated through the injection of a small quantity of diesel fuel to produce a high-energy ignition source for the main fuel gas charge in the cylinder. The combustion process of gas supply and pilot injection is controlled individually for each cylinder by the engine’s electronic control system. A primary benefit of the DF technology is greatly reduced stack emissions when burning natural gas.

New concepts usually require some tradeoffs, and in the case of marine DF, it is the space required for the LNG tanks and special attention to such factors as constructing the engine-room spaces to reduce the chance of gas pockets forming from any leakage.

Diesel manufacturers are employing the improving intelligent engine technologies for both new engines and in retrofitting existing ones. With traditional mechanical injector systems, engine performance is determined by the timing and injection pressure regulated by the rotation of the camshaft lobes. At any specific engine speed, those values are unchangeable.

Electronic controls offer better adjustment options. Common-rail engine designs replacing conventional camshafts result in better engine performance and improved reliability. Emission-control technologies that introduce water into the combustion chamber are also proving their worth. Wärtsilä offers a system that injects water directly into the cylinders. A competing system from Man B&W, headquartered in Augsburg, Germany, employs fuel-water emulsification to meet high environmental standards.

Caterpillar’s diesel-engine electronic control systems have two options. With the Electronic Unit Injector, fuel-injection pressure is still produced through mechanical links to the camshaft. Fuel-delivery timing and injection duration are precisely controlled through electronic messages sent to the injectors. Fuel settings are continuously adjusted in response to changing conditions.

Caterpillar’s more technically sophisticated control system, known as the Hydraulically Actuated Electronically Controlled Injector Unit, includes fuel-injection pressure as one of the electronically controlled variables. The mechanical link between injector and camshaft is eliminated. A pump and hydraulic-oil manifold system provide the force required to pressurize fuel in the injector. Fuel-injection rates and pressure are adjusted by the electronic control system. High injection pressures are available at slower engine speeds.

In both Caterpillar systems, the electronic engine-control module accepts information from all engine and transmission sensors, and sends out engine control commands at a rate of 20 times per second.

The benefits of state-of-the-art electronic engine controls for reliability, reduced fuel consumption and better emission controls have also become increasingly important for tugboats and workboats. Cummins Marine’s new QSK60 electronically controlled diesel engine with a power range from 1,492 to 1,716 kw “allows for customized calibrations to match the engine to a vessel’s operating environment,” according to Cummins. One of the first U.S. applications of the QSK60 was for a newbuild Harley Marine Services 104-foot z-drive tractor tug.

Man B&W continues to incorporate electronic controls in its large-engine designs to improve performance and environmental compliance. Man B&W’s ME engines combine proven technology with enhanced electronic control to lower fuel and cylinder oil consumption, and to improve emission characteristics, particularly with regard to visible smoke and nitrogen oxides. Their first ME engine, rated at 10.43 MW, is now being built for installation in a newbuild chemical tanker.

Within the industry, upgrading existing diesel propulsion systems involves new components to increase performance and meet upcoming environmental regulations. For example, Fairbanks Morse Engine in Beloit, Wis., is fulfilling a $4.7 million U.S. Coast Guard contract for engine revitalization of the Polar-class icebreakers by installing nine new FM/Alco engine blocks and nine 251 Plus component upgrade kits.

Aeroderivitive gas turbines, such as General Electric Marine LM2500 and LM2500+ engines and Rolls Royce gas turbines, have become the propulsion power of choice for some cruise vessels operating in environmentally sensitive areas, where very low emissions are important, and naval vessels, where gas turbines have the advantage of quick startup to reach fast maneuvering speeds. For some applications, gas turbines, with their low emissions, and diesel engines, with their lower operating costs, make up a hybrid propulsion package providing the best of both technologies to vessel owners.

Marpol’s emission regulations will set limits on sulfur dioxide (SO2), nitrogen oxide (NOx) and CO2 emissions retroactive to January 2000. Various regions are proposing additional limits, such as a European Union proposal to limit sulfur content to 1.5 percent and 0.2 percent in fuels used while in port, or Alaska’s visible-smoke emission criteria. Diesel-engine technology is helping ship operators meet new standards for NOx, CO2 and visible smoke. For example, Wärtsilä’s 9L46D “smokeless” engines are being used on Carnival Spirit.

SO2 can be removed with scrubber equipment built by engine manufacturers, but the U.S. Environmental Protection Agency noted that the majority of particulate matter “comes directly from the high concentration of sulfur in the residual fuel, so the simplest way to reduce those emissions is by removing sulfur from the fuel.”

Navy orders high-temperature superconductor motor

The contract award on March 3 by the U.S. Navy’s Office of Naval Research to a team led by American Superconductor Corp. for a 36.5-MW high-temperature superconductor (HTS) propulsion motor increases the possibility of HTS powering the next generation of Navy destroyers.

“It’s still a test-bed project, but the specifications are for it to be designed and built specifically for the DDX (destroyer) program. It will fit into the DDX, so the Navy will have a direct place to use it if they choose,” said David Paratore, vice president and general manager of ASC.

ASC, based in Westborough, Mass., will be the prime contractor. The team includes Northrop Grumman Marine Systems, Northrop Grumman Ship Systems and Ideal Electric Co. Delivery is set for March 2006.

The value of the contract to ASC will be about $70 million over a period of three years and one month.

An HTS motor can be one-third the size and weight of conventional synchronous electric motors of the same output rating. Superconductivity dramatically increases the efficiency of electric motors by largely eliminating the normal electrical resistance in rotor and stator assemblies. “And because HTS wire can carry significantly larger currents than copper wire, these motor winding coils are capable of generating much more powerful magnetic fields in a given volume of space,” Paratore said.

Superconductivity was discovered in 1911 when experiments proved that when cooled to their critical cryogenic temperatures, certain materials create a path that offers little or no resistance to the flow of electricity. Absolute zero, or 0 Kelvin (K), represents the point at which all molecular motion ceases and metals with the proper interatomic structure offer zero electrical resistance.

Subsequent research has led to the discovery of materials that perform as superconductors up to 127 K. The critical temperatures for HTS are roughly between 30 K and 80 K, while LTS critical temperatures are less than 10 K.

A 5-MW superconductor test propulsion motor rated at 6,500 shaft hp at 230 rpm built by ASC for the Navy is due for delivery July 16. Paratore believes HTS motors for non-military ships could be in service by 2005.

Richard O. Aichele

Under the stern

Propulsion technologies continue to solve many old problems. Lubrication oil leaking from conventional stern tubes and propeller shaft bearings can be eliminated by the installation of Compac water-lubricated shaft bearing systems, according to Thordon Bearings Inc. in Burlington, Ontario. Its design for long wear life is based on a “totally pollution-free propeller shaft bearing system” where seawater replaces stern-tube oil to lubricate and cool the bearings, according to the company.

Waterjets by Hamilton Jet, Rolls-Royce and Twin Disc continue to find new markets in high-speed ferries. Their attributes include excellent maneuverability from the 360° thrusting and their ability to operate in minimal depths because their water intakes are flush with the hull bottom. They can be mounted on transoms and readily installed in existing hull configurations, according to Twin Disc. They are “ready to bolt in with no difficult engine alignment problems,” Hamilton Jet noted.

Four Rolls-Royce 90SII waterjets will give the Alaska Marine Highway System’s 240-foot-long ferries, now being built at Derecktor Shipyards in Bridgeport, Conn., an operating speed of 35 knots.

Electric podded propulsors have steadily proven themselves since the first large ship units were ordered by Carnival Cruise Lines in 1998 to power its 70,367-grt Elation. Pods and the associated electric propulsion equipment have given shipbuilders greater design freedom by eliminating the need for rudders and the long propeller shafting. The result has been the creation of more efficient ship interiors.

Pods provide vastly superior ship-handling capabilities at sea. Example: The 137,300-grt Voyager of the Seas, built by Kvaerner Masa-Yard in Turku, Finland, for Royal Caribbean International, is equipped with three 14-MW ABB Azipods.

The ship’s power plant consists of six Wärtsilä 12V46C diesel engines, each driving an ABB alternator, producing 75,600 kw total power for propulsion and hotel power. Two Detroit diesels provide emergency power.

During sea trials, at full speed the ship had a turning circle of less than two ship lengths, or half the distance of a conventional design. The crash stop distance at the normal service speed of 22 knots was less than 0.5 nm, “and the ship could be kept on course during this maneuver,” according to the shipyard.

Other podded propulsion unit builders include Rolls-Royce/Alstom with the Mermaid system, STN Atlas Marine/John Crane-Lips Dolphin pods, Siemens-Schottel, and Steerprop Ltd. Both Siemens-Schottel and Steerprop have pods with propellers at each end of the unit.

Hannu Jukola, hydrodynamist at Steerprop, explained that the pod geometry, with Steerprop’s dual-ended azimuthing propulsor with contrarotating propellers, “is designed to create a pressure wave in front of it, which acts like an additional wake for the forward propeller. The increase in propeller thrust due to this unique interaction between pod and pulling propeller practically cancels the pod drag.”

Operating efficiency resulting from two contrarotating propellers in line with each other has been known since 1836. Attempts to use the technology have not been successful because of the complexity of running two long conventional concentric propeller shafts turning in opposite directions to power the two independent propellers. The basic pod design with its short shaft lengths and the ease of mounting a propeller at each end promises to simplify the application of the contrarotating propulsion principles. Currently under construction in Japan are two ro-pax ferries that will employ a contrarotating propulsion design similar to the propeller arrangement proposed for the Wärtsilä-Kvaerner DF diesel ro-pax vessel.

Proactive maintenance

The quick adoption of pod propulsion technology produced some difficult learning-curve experiences. Unexpected bearing failures sent several cruise ships into dry docks for repairs, causing cruise cancellations. The Mermaid pods had early problems with wiring connections to the rotors of the electric motors and also several shaft-seal failures that allowed water into the bearings, causing them to fail. The latest incident affected Celebrity Cruises’ Infinity in February. The ABB Azipod units also had early bearing failures due to lubrication problems.

“High-speed, oil-lubricated roller or ball bearings are noted for long life; historically, they are also known to fail with little forewarning,” noted a paper delivered the International Conference on Marine Engineering Systems in May.

With the propulsion pods underwater and out of sight, diagnostic instrumentation can help avoid unexpected equipment failures, said Barry Taylor, a consultant with GasTops Ltd. Electronic diagnostic instrumentation can help protect against similar risks on other propulsion equipment, including diesel engines, gas turbines and electric motors.

MetalScan is a diagnostic monitoring technology developed by GasTops Ltd. in Ottawa, Ontario, to detect metal in bearing lubricants. MetalScan monitors bearings and provides graphical displays if a failure begins to occur. The main display will show the total mass that has been removed from a bearing.

“The (failure) debris comes off the bearing, and the lubricating oil flow carries it toward the filter,” Taylor explained. “Our sensors are positioned just before the filter, so we count the particles before they are removed from the filter. MetalScan will tell you if the debris is ferrous or non-ferrous and how big it is. The software will provide an accumulative total of the mass.”

In one marine application, the system monitored the gradual degradation of a 33-inch bearing that shed 275 milligrams of debris over 10 months, providing the tool to predict a possible total bearing failure.

Another diagnostic monitoring product is stress wave analysis (Swan) developed by SwanTech LLC in Fort Lauderdale, Fla. The Swan technology detects and analyzes sounds as they pass through a machine’s structure at ultrasonic frequencies. The ultrasound, or stress wave, is a result of friction and shock between a machine’s moving parts and is detected by Swan external sensors. The system is designed to detect wear or damage at an early stage, monitor any progression of a defect by the increasing energy content of friction and shock, and use the data to predict when a failure is likely to occur.

Impressive propulsion-related technologies are available to shipbuilders and vessel operators. The skillful use of the technologies will be vital in meeting the maritime industry’s future operating challenges.

Richard O. Aichele (rottoa@inforworks.com) is a free-lance writer based in Saratoga Springs, N.Y.

By Professional Mariner Staff