The US Navy’s DDG-51 Arleigh Burke Class destroyers are the backbone of their present and future fleet. Unfortunately, they have a problem. Two problems, actually.
One problem involves keeping the fleet’s operating costs low, especially fuel use. These ships aren’t as efficient as more modern designs, especially at the low cruising speeds that make up so much of a ship’s operating life. The other problem is that DDG-51 destroyers are having trouble generating enough power, especially if they want to receive new radars like the proposed AMDR. Since this destroyer class includes the majority of American ballistic missile-defense ships, their ability to remain relevant, and to field an upgraded “Flight III” variant, is critical to maintaining US sea power.
A Northrop Grumman team, which includes Curtiss-Wright and L-3, believes that they may have the answer to both problems. Nor are they the only firm looking into this.
Why Get a HED? Problems, and Opportunities
Right now, DDG-51 destroyers are fielded with a ship service electrical system, and an independent main propulsion system of LM2500 gas turbines that are tied to a mechanical drive through the Main Reduction Gear assembly. Each shaft is tied to 2 LM2500 gas turbines (GTMs), which have just 2 speeds: off, and on. Another 3 ship service turbine-generators (GTGs) provide electrical power, with the 3rd designed as a redundant back-up. Using this mechanical arrangement, current DDG-51 Flight IIA ships have a reported total power output of 7.5 MW, and end up using too much effort from their LM2500 gas turbines for propulsion at low speeds.
During underway operations under 15 knots, in low-threat areas, 2 engines are typically on line: a GTM with a trail shaft, and a smaller GTG for basic power to the ship, navigation radars etc. Speed changes up to 15-18 knots are controlled by varying propeller pitch, and are independent of the LM2500 GTM. For more electricity, another GTG generator can be brought online to power the main SPY-1 radar if needed.
At low speeds, Hybrid Electric Drives would allow ships to take the GTM offline, and rely on 1-2 smaller GTGs for both propulsion and power, using less fuel and offering more power flexibility. Ships could also be designed with fixed-pitch propellers, which are quieter than variable-pitch blades.
If a current DDG-51 destroyer or CG-47 cruiser needs to increase speed to 18-24 knots, a 2nd LM2500 GTM is put online. Speeds of 24-28 knots require 3 GTMs online, and are often used by the “plane guard” cruiser or destroyer, on station 3 nautical miles behind the aircraft carrier during launch or recovery. Launches and recoveries require 25 knots of wind over the deck, so calm days are go-fast days. The plane guard refuels every 3 days to maintain 75% fuel, while the rest of the escorting cruisers and destroyers refuel every 7-10 days. The extra fuel burn doesn’t translate into any extra electricity.
Full flank speed above 28 knots will engage all 4 GTMs, but we’ve heard stories of ships that ran at normal speed for 6 hours out of port, then flank speed for 9 hours, and had to refuel.
Contracts are underway to add LM2500 Digital Fuel Control (DFC) kits, replacing the current hydro-mechanical control system and improving performance somewhat. Yet DFCs fall far short of what is achievable with new technologies. During July 31/08 testimony before a House Armed Services Committee panel, Congressional Research Service naval analyst Ron O’Rourke said that adding hybrid electric drive to the DDG-51’s traditional mechanical-drive propulsion could reduce fuel use by about 16%, cutting each ship’s annual steaming cost by abut $2.5 million (at $112.14 per barrel).
That 7.5 MW power output is also a problem. Advanced radars and their cooling systems need a lot of power, especially if they’re slated to perform long-range missile defense roles. That has emerged as a problem in studies to create a more modern DDG-51 Flight III design.
In contrast, the new DDG-1000 Zumwalt Class’ integrated all-electric system can divide up to 78.0 MW of power between propulsion and power to the ship’s electronic systems, offering more efficiency at low speeds, and more power for ship systems at both low and high speeds. Unsurprisingly, all-electric drive systems are a growing trend in military ships. They’re almost the rule in new European warship designs, and can be found in new American designs like the DDG-1000 Zumwalts, LHD 8 Makin Island, the new America Class escort carriers, and T-AKE support ships.
As a bonus, Hybrid Electric Drives (HED) propulsion is less noisy, which is useful when a ship is trying to deal with enemy submarines.
A hybrid-electric drive could theoretically be backfit into existing DDG-51 destroyers, to give them many of the same advantages as counterparts like the DDG-1000s. The catch is that refits dealing with propulsion systems tend to be expensive, because the builder usually has to cut into the hull to move engines around, etc. Still, the class is already going through a major modernization program, and with estimates of a mission-ready, BMD-capable DDG-51 hovering around $2 billion, an HED backfit could still be seen as a bargain. Much depends on how much of a ship’s electrical distribution system, which runs throughout the ship, would need to be replaced.
For new ships, like the notional DDG-51 Flight III, a HED approach could be installed during construction, while requiring much less redesign of the basic ship layout than a full all-electric system. That translates into lower costs, and lower risk.
Contracts & Key Events
May 7/12: GE gets a HED. MarineLog reports that GE has thrown its hat into the ring. GE Marine makes the turbines that power US Navy ships, including the DDG-51s, and has been part of all-electric ships like LHD 8, the USS Makin Island. GE Marine’s GM, Brien Bolsinger, says the firm is now ready to expand its offering to full hybrid-electric solutions, and it doesn’t need any government funding to justify the effort:
“Many shipowners and builders are currently evaluating hybrid electric propulsion designs for existing or new build ships. Thanks to many years in this industry forming key partnerships, GE can now offer more comprehensive hybrid electric propulsion solutions for military and commercial customers.”
GE believes that their dual gas turbine HED configuration requires the fewest ship modifications when applied to a traditional LM2500 CODOG(Combined Gas Or Diesel) vessel, or even a COGAG(Combined Gas and Gas) ship like the DDG-51s. They don’t have an R&D contract like General Atomics or Northrop Grumman, but they have received contracts related to the DDG-51’s propulsion systems before (vid. June 16/09 entry).
If that’s true, it’s about the same cost as a DDG-1000 Zumwalt Class ship, in return for less performance, more vulnerability, and less future upgrade space. AMDR isn’t a final design yet, so it’s still worthwhile to ask what it could cost to give the Flight IIIs’ radar and combat systems ballistic missile defense capabilities – R&D for the function doesn’t go away when it’s rolled into a separate program. Indeed, if the Flight III cost estimate is true, it raises the question of why that would be a worthwhile use of funds, and re-opens the issue of whether continuing DDG-1000 production and upgrades might make more sense. DoD Buzz.
Sept 30/11: R&D NGC. Northrop Grumman Electronic Systems’ Marine Systems Division in Sunnyvale, CA received a $23.1 million cost-plus-fixed-fee contract for research and development associated with their Advanced Hybrid Drive System. Work will be performed in Sunnyvale, CA (38%), Anaheim, CA (33%), Cheswick, PA (28%), and Tallahassee, FL (1%), and is expected to be complete by April 2013. $5.5 million will expire at the end of the current fiscal year, on Sept 30/11. This contract was competitively procured via Broad Agency Announcement, with 7 proposals requested by US Naval Sea Systems Command in Washington DC (N00024-11-C-4224).
Their AHDS adds a Curtiss-Wright EMD electrical machine to the main reduction gear (MRG). It’s the center of the new power system, and can act as a generator, or as a motor. The LM2500 gas turbines are also connected to the electrical machine. Depending on the ship’s internal layout, the turbines can be left in place, or moved back to a position behind the MRG, and alongside the screw’s shaft. An L-3 PPI Bi-Directional Power Converter links the electrical machine to the ship’s generators, and to ship electrical systems. Power can flow in, to drive the screw shaft. It can also flow out, to other parts of the ship.
The linked system operates in 2 modes. The first, Electric Propulsion System (EPS), propels the ship using power from 2 Ship’s Service Gas Turbine Generators, instead of firing up the LM2500s. At higher speeds, the ship operates in Propulsion-Derived Ship’s Service (PDSS) Power Generation mode. In that mode, engineering can shut 1 Ship’s Service Gas Turbine Generator down, while excess power from the LM2500s is directed to combat systems and other ship needs.
Oct 22/10: US NAVSEA issues solicitation #N0002411R4207: “Pre-Solicitation Meeting/Industry Day announcement for the Development and Production of the Arleigh Burke Class Destroyer (DDG 51) HED for Backfit Fuel Savings”. See also Navy e-Commerce Online. Excerpts:
“The large numbers and remaining service life of the DDG 51 Class ships provides one of the best opportunities for long term fuel savings. The HED-EPS shipsets will include the propulsion motors, motor drives and the associated controls, interfaces, and mounting equipment that will be required to install the HED-EPS on DDG 51 Class ships. When installed aboard a ship, the HED-EPS will permit the crew to turn off of one or more propulsion gas turbines and allow more efficient operation of the existing gas turbine generators, which will be generating electric power for the HED-EPS as well as all the existing ship’s electrical loads.”
Aug 13/10: R&D GA. General Atomics in San Diego, CA receives a $6.6 million contract modification to support the development of a proof-of-concept HED system for a full-scale demonstration.
Work will be performed in San Diego, CA (50%), Milwaukee, WI (25%), and Hudson, MA (25%), and is expected to be complete by June 2014. Contract funds will not expire at the end of the current fiscal year. US Naval Sea Systems Command in Washington Navy Yard, DC manages this contract (N00024-09-C-4222).
July 8/09: R&D GA. General Atomics in San Diego, CA wins a $32.7 million not-to-exceed, cost-plus-fixed-fee contract for development of a prototype HED system on DDG-51 Arleigh Burke Class destroyers.
They will perform the work in San Diego, CA (50%); Milwaukee, WI (24%), and Hudson, MA (26%), and expects to complete it by June 2014. This contract was competitively procured under a Broad Agency Announcement, with 23 offers received by the Naval Sea Systems Command at the Washington Navy Yard, DC (N00024-09-C-4222).
June 16/09: GE R&D. The US Office of Naval Research (ONR) awards GE Marine a contract for the DDG 51 Fuel Efficient and Power Dense Demonstrator competition. GE’s program calls for system integration, component and control technology development, and a partial system demonstration.
GE will conduct a laboratory demonstration of the key electrical system features at its Global Research Center in Niskayuna, NY, which is equipped for megawatt-level testing. GE Aviation | Marine Log.
* DID – Adding Arleigh Burkes: H.I.I. is Underway. Explains plans for the class’ future.
* Northrop Grumman – Advanced Hybrid Drive System (AHDS) for Surface Combatants
* IEEE (April 13/11) – Integrated main reduction gears for hybrid drive surface ship applications. “This paper reports on an architecture study completed by Northrop Grumman Electronics Systems – Marine Systems exploring new MRG(Main Reduction Gear) configurations which integrate the hybrid electric machine with the MRG.
* Information Dissemination (July 14/09) – A Good Reason For Flight III Burkes
* US CRS (April 13/09) – Navy DDG-1000 and DDG-51 Destroyer Programs: Background, Oversight Issues, and Options for Congress