Fuel saving and low emissions are priorities across the board

All sectors of the maritime market are concentrating on cutting costs and regulatory compliance, and even markets such as naval vessels, largely coming outside MARPOL jurisdiction, are showing a desire to be environmentally responsible.
According to GE Power Conversion – the former Converteam company- the world’s navies are not exempt from operational, financial and environmental imperatives, requiring ships that are operationally dependable, financially efficient and which respect the environment in terms of emissions and fuel economy. In fact, says GE, navies can be even more exposed to the scrutiny of politicians, taxpayers and an environmentally aware public than some of their commercial counterparts.
So how to answer these demands? According to Mark Dannatt, an ex-Royal Navy Captain, now director of naval business at GE Power Conversion: “ I’ve seen the future of naval propulsion, and it’s electrifying.”
Capt Dannatt outlines the latest advances in advanced naval electrical technology from a GE perspective. “Working with the world’s leading navies gives us what may be a unique perspective on the trends that are emerging and a view into the future. Our systems include some of the most advanced and respected solutions in every part of the power generation and drive train from our gas turbines and diesel engines through power distribution systems, variable speed drives, generators and propulsion motors to automation and control systems, which means that we get to see and set trends when they are still in their infancy.”
He believes that we have entered the age of electrically powered and propelled warships and support vessels. “It’s increasingly common for naval ship designers to be directed to give increased weighting to through life costs of naval ships including fuel consumption and routine maintenance costs based on their selected power and propulsion options. These studies often conclude that some form of electrical propulsion is worthy of further investigation based not only on fuel and maintenance costs but also on the consequential impact on improvements in ship availability and extended operational autonomy”.
GE Power Conversion, as part of General Electric, is able to provide complete power and propulsion system packages, including prime movers, power generation, electrical distribution and fixed or variable speed drives, including motors for propulsion, thrusters and other applications – including hybrid propulsion.
The naval market has traditionally been fond of gas turbine prime movers, and these lend themselves equally to an onboard power station concept as to conventional drives. Indeed, CODAG and CODOG (combined diesel and gas turbine and combined diesel or gas turbine) sit happily on specification sheets for naval craft alongside CODLOG (combined diesel electric and gas turbine) installations.
GE Marine’s LM2500 aero-derivative gas turbine, in its various incarnations, is a popular choice. Among current users is the Royal Australian Navy, with two LM2500s and two Caterpillar diesels in each of its three Hobart class air warfare destroyers, being built by ASC in Adelaide. The LM2500s for the third ship have recently been delivered. The AWD design is based on that of the Navantia-built F100 frigate for the Spanish navy, with a similar propulsion system.
The RAN has 16 LM2500 gas turbines in its Adelaide- and ANZAC- class frigates, and will use single LM2500s in a CODLAG configuration to power two Canberra-class LHD ships, currently under construction.
In the US, the Independence class littoral combat ship, a 127m trimaran from Austal USA, is another source of orders for the LM2500. GE Marine has recently delivered a pair for the third in the series, and in total expects to provide 20 LM2500 gas turbines for up to 10 ships over a five-year period. These ships too have a CODAG arrangement.
GE Power Conversion has supplied propulsion systems for various US Navy vessels, including the LHD-8 USS Makin Island which is estimated to have saved over 4million gallons of fuel in its seven-month maiden deployment, representing a cost saving of around $15 million. Its latest contract is with Huntington Ingalls Industries to provide an auxiliary propulsion system (APS) for the future LHA-7 USS Tripoli, a large-deck amphibious assault ship.
GE describes the technology as similar to that of a hybrid vehicle. Two LM2500+ gas turbines provide the main propulsion source and are used when full speed is required. Power Conversion’s APS electrical drive train is connected to the same propeller shafts, to provide a fuel-saving alternative, compared to the gas turbine engines, during low-speed operations when the gas turbines are less fuel efficient.
In Europe too the LM2500 is enjoying naval success. Among the latest applications, in addition to the Spanish F100 mentioned above, is the FREMM frigate, for the Italian and French navies. So far the engines have been supplied for five Italian and seven French vessels, with another five Italian ships and 10 French on order. The Moroccan navy has ordered another ship, and the Greek navy has shown interest in the type.
Each ship has a single LM2500+G4, which is rated 17% higher than the standard LM2500+, in a combined diesel electric or gas turbine (CODLOG) configuration, using electric motors powered by four diesel gensets for low speed and the gas turbine for high speed mechanical drive. The propulsion systems are being packaged by Avio of Italy, and include Avio’s own sophisticated gas turbine control system.
The UK’s Royal Fleet Auxiliary (RFA) new fleet of military afloat reach and sustainability (MARS) tankers is providing a further reference for GE’s electric drive technology. The four, 37,000t MARS tankers are being built at DSME in Korea, and will deliver fuel and fresh water to Royal Navy vessels. They replace the existing obsolescent single-hulled tankers, and the first is scheduled to enter service in 2016.
GE’s drive train will be installed as a key part of the ships’ hybrid propulsion configuration that is designed to be inherently more fuel efficient than conventional propulsion. The system combines electrical and mechanical propulsion technology to turn the ship’s propeller. When operating at moderate and low speeds, the propeller shaft is turned using the electric motor and variable speed drive controller system, and at higher speeds the main diesel engine is connected directly to the propeller through a gearbox.
The company says that the hybrid configuration is versatile and particularly suited to the fluctuating operational scenarios encountered by naval auxiliary vessels. It helps save fuel, reduce emissions and reduce maintenance costs of the main engines, which have to run less frequently.
”Our electrical drive train technology will offer the Royal Fleet Auxiliary’s new fleet of MARS tankers a highly energy efficient, flexible and integrated power and propulsion system available to direct power as needed in support of their crucial military operations around the world,” said Paul English, marine vertical leader for GE’s Power Conversion business.
GE will begin delivering its systems for the first MARS tanker in the fourth quarter of 2014 and is scheduled to finish supplying equipment for the fourth MARS tanker by the second quarter of 2016. The company says that the MARS tanker contract reflects a growing trend among leading navies to use its electric propulsion technology. Other orders include the Royal Navy’s Type 23 frigates, Queen Elizabeth class aircraft carriers and Type 45 destroyers, the US Navy’s Zumwalt destroyers and the French Navy’s Mistral class.
The LM2500 is not, of course, the only popular gas turbine for naval applications. Rolls-Royce has a number of aero-derivative marine units, notably the MT30, which it says is the most powerful marine gas turbine on the market, and the WR21, designed to overcome the gas turbine’s traditional weak spot of low efficiency at partial load.
The MT30 powers the other US Navy LCS design, the Freedom class, the second of which, USS Fort Worth, recently entered service. The Freedom Class is equipped with two Rolls-Royce MT30 gas turbines powering four large waterjets, also made by Rolls-Royce, enabling the vessels to reach speeds in excess of 40 knots.
The MT30 has also been selected for the US Navy’s DDG-1000 Zumwalt destroyer as well as the Royal Navy’s Queen Elizabeth class aircraft carriers and the Republic of Korea Navy’s FFXII frigates.
Another US Naval contract for Rolls-Royce gas turbines is the supply of MT7 engines to power the future fleet of hovercrafts, known as the ship-to-shore connector (SSC), and which will replace the current US Navy LCAC hovercraft fleet. The SSC project is led by Textron Marine & Land Systems, and could extend to 73 craft.
Each SSC will use multiple cutting edge Rolls-Royce MT7 gas turbines, derived from the AE1107 engine, which powers the V-22 Osprey tilt-rotor aircraft. The engines will provide both propulsion and lift, through an interconnected gearbox system, and will offer a power increase of 25% over the previous-generation hovercraft, enabling the SSC to transport 74t of cargo at 35 knots-plus, while burning around 11% less fuel.
Source: Motor Ship