Warship Tehnology: May 2017
As first highlighted in the May 2016 issue of Warship Technology (pp13-16), since their introduction into service the UK Royal Navy’s Type 45 destroyers have experienced ongoing problems with the reliability and resilience of their all-electric power and propulsion system. As reported at the time, the solution to the problems will require a major diesel generator upgrade to the ships to increase electrical generation capacity. More recently, it has been confirmed by the Defence Equipment and Support (DE&S) organisation, part of the UK Ministry of Defence, that the ‘get well’ programme for the Type 45’s propulsion system will be opened up to competition and that the solution will take the form of the replacement of the existing 2MW diesel generators with which the ships are equipped with an additional unit, so that the vessels will have three diesel generators.
Commissioned into service between July 2009 and September 2013, the six Type 45 destroyers are the first front-line warships in the world to introduce an Integrated Electric Propulsion (IEP) system. The decision to adopt IEP – at the heart of which is the Rolls-Royce WR-21 marine gas turbine and its associated recuperation system – was taken in the expectation that it would realise multiple operating benefits including improved fuel efficiency, reduced maintenance and manpower requirements, and lower environmental impact.
Reliability and performance
However, as reported in the May 2016 issue of Warship Technology, early operating experience has revealed a wide range of problems with regard to both reliability and performance. Numerous instances of total electrical failure have occurred during underway operations, and it has become evident that the marine engineering issues affecting the power and propulsion system are deep-seated and systemic in nature.
IEP is fundamentally different from conventional mechanically driven machinery arrangements in that it uses a common set of prime movers to provide power to both propulsion and ship service ‘consumers’. However, while IEP is well proven in the commercial marine sector, it remains novel in a warship application given the requirement for much higher power densities and shock standards compared to existing commercial designs.
Each Type 45 has an IEP system operating through twin shafts, each driven by a 20MW Advanced Induction Motor. Pulse Width Modulated (PWM) converters provide variable frequency power supplies for the two 20MW Advanced Induction Motors directly coupled to the propeller shafts. Unlike all other vessels of this power, these motors are direct fed from the high voltage bus without drive transformers, given increased gravimetric and volumetric density. The drive arrangement of a PWM converter with an Advanced Induction Motor offers the normal benefits of electric propulsion, but additionally brings the shock withstand, low noise and vibration, and fall back/failure modes needed for a full warship.
As currently configured, the electrical power for the propulsion and ships service load is provided by the two 21MW-rated WR-21 gas turbines (each driving a two-pole cylindrical rotor generator at up to 3,600 rpm) and two anchor-load Wärtsilä 12V200 diesel generator sets rated at 2MW each. Two main high voltage switchboards distribute power to consumers, either at 4,160V AC to the VDM25000 propulsion converters, or via transformers at 440V and 115V AC to weapons and ship services.
At the outset, the design intent was that the IEP system would typically run on a single WR-21 gas turbine alternator (GTA) in a single-island mode, with the second GTA brought on line only in ‘high risk’ operating regimes; the two 2MW diesel alternators were to provide power for harbour services and ‘blackout’ recovery, and not foreseen to perform as true backup generators in the event of GTA failure. In actual fact, as reported in the May 2016 issue, current operating practice tends towards one WR-21 and one auxiliary diesel in single-island mode. However, operating experience has revealed significant shortcomings in the IEP system, both with specific equipments and fragility in the overall system architecture. These issues have collectively resulted in numerous ship-wide power outages.
Evidence given at the House of Commons Defence Committee late in 2016 heard that the first problems with the propulsion system became evident soon after its introduction into service and it was noted that, between the launch of the first-of-class (HMS Daring) in February 2006 and the final Type 45 launch (HMS Duncan) in October 2010, approximately 50 design changes were necessary. Despite that remedial work the Type 45s continue to suffer from reliability issues including major power failures. There have been improvements and the current failure rates are now one-third of those experienced in 2010. However, it was noted that there remains a “risk inherent” in using the Type 45.
Peter Roberts, from RUSI, described opting for the innovative IEP approach as “a flawed decision” because he believed that the design did not address either the “high-power densities” or the “differences in load” that the warships required. He contrasted this with the General Electric LM 2500, which he described as “cheaper” and which had a “lower technical risk and more proven background.
By contrast, both of the former First Sea Lords who came before the committee claimed that the benefits of using an innovative engine outweighed the risks. Sir Mark Stanhope, First Sea Lord between 2009 and 2013, described the choice of engine as “a sensible way of improving maintenance requirements, fuel usage and survivability” which, he asserted, had ensured that the UK “remained ahead of the curve in terms of the capability of our future ships.” Admiral Lord West agreed stating that he had “no doubt at all that going for integrated electrical propulsion was the right thing to do.”
It became clear during evidence sessions that the testing programme for the system was inadequate both in terms of facilities and duration. BAE Systems conceded that the test facilities “did not exactly replicate the situations on the ship” and therefore the testing “failed to expose some of the issues that became exposed when the ships entered service.”
Of greater concern was the length of testing. Peter Roberts said that the land-based testing was not funded “to run sufficient hours to understand that there were significant design flaws.” It was also said that testing “was not run sufficiently long enough to demonstrate that the engine was reliable.”
A spokesperson for Rolls-Royce, explained that the WR-21 gas turbine, had undergone over 8,000 hours of testing during the development cycle. However, there was a change in the design (to the recuperator) after about 5,000 hours which resulted in the updated design being subject to only 3,000 hours of testing. The resultant problems experienced by the Type 45s came between 4,000 and 5,000 hours of use. It was conceded that, with hindsight, the amount of testing was insufficient, but it was said that the Ministry of Defence “decreed” that the remaining testing hours would be sufficient “given all the running that had been previously done.”
“It is clear to us that the under-testing of the engine was a key cause of the problems experienced by the Type 45s when they came into service. This is a serious failing of both the Ministry of Defence and of the contractors,” said the committee. “The Ministry of Defence did not explain satisfactorily why there was no adequate clause in the contract with Rolls-Royce specifying responsibility for repairs should the engines develop any further design faults because of the lack of testing time.”
As also highlighted in the May 2016 issue, a second issue with the engine was a loss of reliability when the Type 45s operated in areas with high ambient air and sea temperature. When we questioned on how this came to be, a spokesperson for Rolls-Royce told the committee that the engine “met the specification for the Type 45 class [set by the MoD] and that the system met that specification.”
However, he added: “Are the conditions experienced in the Gulf in line with that specification? No, they are not. The equipment has to operate in far more arduous conditions than were initially required by that specification.”
“Given that the Royal Navy has undertaken significant operations in the Gulf for decades, this appears to be a startling error,” said the committee.
In evidence to the committee, BAE Systems said industry had highlighted to the Ministry of Defence that there would be an upper limit for environmental temperatures and they had sought to produce a design that would have “graceful degradation beyond those temperatures.” In other words, the engine would have the ability to carry on and operate, albeit sub-optimally, which would result in “a bit of drop-off” in terms of top speed.
However, that was not the outcome. It is acknowledged by the Royal Navy that a key failing in the specification was that the WR-21 was unable to operate effectively in hot temperatures and that, instead of a “graceful degradation”, the engines were “degrading catastrophically.”
“It is astonishing that the specification for the Type 45 did not include the requirement for the ships to operate at full capacity – and for sustained periods – in hot regions such as the Gulf,” the committee said. “The UK’s enduring presence in the Gulf should have made it a key requirement for the engines. The fact that it was not was an inexcusable failing and one which must not be repeated in the Type 26 and General Purpose Frigate. Failure to guarantee this would put the personnel and ships of the Royal Navy in danger, with potentially dangerous consequences.”
Turning to the refit plan, the committee noted that in 2014, the Ministry of Defence had established Project Napier to address the continuing problems with the Type 45s. According to the MoD, Project Napier has two strands: an Equipment Improvement Plan (EIP) which will address system reliability to meet the original design intent in the near term; and a Power Improvement Plan (PIP) which will improve system resilience by adding upgraded diesel generators to provide the electrical generation capacity. The PIP should also resolve the problem of the engine “degrading catastrophically” in hot weather conditions.
In a letter to the committee, the Secretary of State said that work on the Equipment Improvement Plan was progressing and that it was already “delivering positive results with increases to availability [of the Type 45] across the Fleet”. Feasibility studies for the Power Improvement Plan had been concluded and the Ministry of Defence was working with four companies to “assess alternative technical options and a variety of delivery models.” That delivery model now seems to be that there should be a competitive tender.
The introduction of additional generators should reduce the reliance on the WR-21, resulting in “greater resilience and greater life out of the WR-21s and a more effective ship.”
When he came before the committee, a spokesperson for DE&S confirmed that Project Napier had now “defined what that modification solution looks like,” and confirmed that implementing the PIP would take around 12 months. However, he explained that this work would be incorporated into the planned maintenance for the ships: “We can do these in parallel with the maintenance periods. While there will be some additional out-of-service time for Type 45, it will not be of the order of 12 months,” he said.
The cost of the Power Improvement Plan will be borne by the Ministry of Defence alone, and not in concert with industry. Defence Procurement Minister Harriett Baldwin MP explained that this was because there were “a set of specifications against which a shipbuilder is liable” but that the Ministry of Defence was liable “if problems arose subsequently.”
“The Type 45 has had a long history of significant engine failures. The Power Improvement Plan is designed to rectify these problems and put an end to the reliability issues which continue to limit the availability and dependability of the Type 45,” the committee concluded.
“The Ministry of Defence has assured us that there are sufficient funds available for the refit programme. However, it has yet to set a start date. In its response, we expect the government to set out, in detail, the costings of this programme and a timeline for the refit across the class of ships. Furthermore, we recommend the ministry to provide us with six-monthly progress reports on the programme.
“In addition, the ministry must provide a detailed explanation of how the funds for the refit were sourced and identified as part of the SDSR process – in particular, whether these funds were a separate addition to the Royal Navy’s equipment budget or were allocated from within it. As part of that explanation, we will require confirmation that no funds were transferred to the Type 45 from funding originally allocated to the Type 26 programme.”