Supporting the Royal Navy at sea – the Tide class tankers
The Royal Fleet Auxiliary is currently taking delivery of four large and well equipped new replenishment tankers. Here we take a detailed look at their construction, design and purpose.
A controversial history
The Military Afloat Reach and Sustainability (MARS) programme was originally begun 2003 and was supposed to produce a family of 12 ships to replace a variety of ageing RFA vessels. By 2007 it was clear that MARS would not be properly funded and it was cancelled in Dec 2008. The Tide class are the result of the MARS project being partially resuscitated to provide replacements for the RFA’s fleet of ageing single hulled-tankers. On 2nd February 2012, it was announced that the MoD had placed a £452M order for four new replenishment tankers to be built by Daewoo Shipbuilding Marine Engineering (DSME) in South Korea.
The decision to build overseas cause an uproar and complaints of “betrayal of British workers”. In fact, most of UK shipyard capacity available at the time was being utilised and even expanded for the construction of the QEC aircraft carriers. No British shipbuilder bid for the contract as they did not need the work and knew they could not match the price of subsidised foreign yards. To muddy the political waters, Italian shipbuilder Fincantieri put in a £625M bid promising to use BAE Systems construct at least one of the ships. The UK government would not stomach the extra £200M and BAES involvement would probably have impacted on the QEC programme. Although the Wave class tankers were delivered with few problems (2003), it should also be remembered that during the preceding Bay class RFA project (2007), British shipbuilders did not cover themselves in glory.
Building the Tide Class tankers in South Korea was the right choice in the circumstances at the time, unfortunately the decision has set an unhelpful precedent.
No brand new RFAs have ever been constructed abroad until now and this should be seen as a one-off. After the success of the QEC project, UK shipbuilders in 2018 are in better shape, very keen to bid for the Fleet Solid Support ships and are likely to be exposed to unfair competition with state-subsidised foreign yards.
The DSME yard at Okpo on Geoje Island constructs large tankers and cargo ships quickly and efficiently using production line methods. The scale of the Tide class ships are modest compared to many of DSME’s other projects and the UK appeared to be getting a bargain. Unfortunately, a downturn in global demand for shipping, (and other issues unrelated to the MARS tanker contract) sent DSME into bankruptcy. The Korean state bank baled them out with $2.6Bn in early 2017. This is not the first government support DSME have received, effectively the South Korean government takes a long-term view and is willing to subside the cost of ships for other nations in order to maintain its manufacturing strength.
In 2012 the Pound was strong against the South Korean Won but Sterling has since weakened considerably. Currency rates and supply problems drove up costs and the final cost of construction was £550M for the four ships. RFA Tidespring was delivered nearly 18 months late after serious issues with electrical design and the discovery that multi-cable transit insulation did not meet new legislative standards. Foreign construction is clearly not the panacea that many believe it to be. Tidespring was finally delivered in April 2017 but the subsequent ships have been delivered promptly; Tiderace (Sep 2017), Tidesurge (Mar 2018), Tideforce (Aug 2018) and are reportedly well constructed.
Despite the hulls being built overseas, a further £150M has been spent with UK companies on design, equipment and fitting out the vessels to naval standards. In January 2015 A&P Falmouth won the £15M contract for the UK Customisation, Capability Assessment Trials and Support (UKCCATS) work to adapt the four ships. This includes dry-docking and some maintenance on each ship after the delivery voyage. About four months of customisation work includes installation of light weapon mounts, ballistic protection, military communications and IT systems. A&P then manage the sea trials and are responsible for supporting the ships in service for the next two years. A&P are hopeful of winning the Future In-Service Support (FISS) ‘cluster’ contract to support the Tide class for at least 5 years beyond the UKCCATS period.
The 39,000-tonne Tide class were designed by BMT Defence Services and are based on their AEGIR concept. This is a family of support ship designs, of which the Norwegian Navy has ordered a 26,000-tonne variant – HNoMS Maud. The Tide class are large and handsome vessels whose primary role is to refuel the aircraft carriers and their supporting warships.
Other than refuelling RN and allied warships at sea, they have a number of secondary roles. As the Wave and Fort class have already demonstrated, these auxiliaries could operate independently on maritime security or humanitarian aid operations. The large flight deck can land a Chinook size helicopter, the ships are fitted with a suite of AGI visual landing aids and a dedicated flying control office (Flyco). The hangar can comfortably house a Merlin and a gantry crane is available, should the helicopter need a rotor head or engine change. There is a magazine and lift for helicopter-launched weapons and a small aviation detachment office and workshop. Plenty of spare accommodation is available for more than 40 RN, military or special forces personnel and there is a small medical complex with a 3-bed hospital ward. Two RN-standard Pacific 24 RIBs are carried in addition to two 130-man Harding LBT emergency lifeboats. They are fitted for but not with 2 x 20mm Phalanx CIWS and 2 x 30mm cannons as well as the usual light machine guns and minigun positions for force protection.
Mobile filling station
17 separate tanks can hold 19,000 tonnes of F76 marine diesel, F44 aviation fuel and a further 1,300 tonnes of fresh water for issue to other vessels. The dual-use fuel tanks can be filled with F76 or F44, depending on the mission. Supporting the carriers, for example, will usually require a larger proportion of F44. Six powerful oil cargo pumps can move fuel between tanks and supply the three RAS(L) rigs. The two rigs on the starboard side of the Tide class are spaced so as to interface with the two port side fuelling points on the QEC carriers and have twin 7” fuel hoses. Using both rigs and 4 hoses, potentially 2,000 tonnes of fuel per hour can be delivered to the carrier. Aircraft carriers have their bridge on the starboard side and their view of the tanker is restricted. For RAS with other warships, the RFA usually acts as the guide and commands the operation but QEC will be guide during RAS. The QEC can take fuel on the starboard side but has only a single fuel reception point and RAS(L) will normally be conducted with the tanker to port.
The single port side rig also has twin hoses but a single hose is sufficient for fuelling most other warships. Apart from other RFAs and the QEC, no RN warships are fitted to receive a twin probe. For merchant ships and vessels not fitted with NATO standard RAS equipment, fuel can be provided using the stern reel fitted below the flight deck for astern replenishment.
The RAS winches and much of the pipework is installed below the upper deck, making maintenance easier. The upper deck has a large clear working area and securing points for 8 TEU shipping containers, 4 of which may be refrigerated, that may hold food or general stores. Two Pellegrini MEP 10-tonne deck cranes are fitted for loading containers and stores. The Tides are also fitted with a movable high point heavy jackstay to allow limited transfer of solid stores or lubrication oil drums. In high sea states or to save time, vertical replenishment (VERTREP) of solid stores by helicopter is an alternative option.
The Tide class are classed as ‘fast tankers’ with a sustained fully-loaded speed of 15kn in sea state 5, but have achieved over 20 knots on trials. Support ships must be able to keep up with the carrier battle group which may have to move quickly at times. RAS and naval operations demand a propulsion system that is efficient across a wide range of speeds. The Tide class employ a flexible CODELOD (Combined Diesel Electric or Diesel) arrangement. A GE motor on each shaft is usually used to propel the ship at low-medium speeds. Two Wärtsilä 2.5MW diesel generators supply the power to the motors and the ship. For higher speeds, there are two 7.2MW Wärtsilä L46F diesel engines which drive the shafts through a reduction gearboxes. A significant innovation is that when propelled by the diesel engine, the motor on the shaft can be switched to become a generator and used to supply the ship’s hotel load. This arrangement is very flexible, eases maintenance and is fuel efficient.
Bow thrusters are installed for manoeuvring in harbour but can also be lowered out of the bottom of the hull and rotated to provide emergency propulsion and steering in the event of failure or damage to the main propellers and rudders.
Considerable design effort was expended on ensuring the Tides would be stable and manoeuvrable when steaming in close company with the much larger QEC. Safe RAS and rapid emergency breakaway manoeuvre can be conducted up to sea state 5. The older Wave class tankers have a simple single shaft arrangement but the Tide class have twin shafts which allow for smaller propellers with lower cavitation and better efficiency. Twin screws and rudders are also safer as they offer greater redundancy should there be a main machinery failure during RAS. The shafts are housed in ‘skegs’ that are hydrodynamically more efficient than conventional bracketed shafts and can deliver up to 3% annual savings in fuel. The unique underwater hull configuration has been a success and the ships handle well at low speeds. During her delivery voyage across the Atlantic, RFA Tidespring also performed well in high sea states, comfortably maintaining 18 knots.
Tidespring was formally dedicated into the RFA in Portsmouth on 27 November 2017. She has successfully conducted sea trails and passed through Flag Officer Sea Training (FOST). The first RN warship to actually receive fuel from Tidespring was HMS Westminster on 11 June 2018 and she has subsequently been actively supporting NATO warships. Thanks to the US Navy’s comprehensive coverage of its operations, it was revealed that Tidespring has been busy in the North Atlantic and Norwegian Sea supporting US Navy 5th Fleet destroyers in 2018. She attempted her first RAS with HMS Queen Elizabeth on 27 February but this was sensibly postponed due to poor weather, the first fuel was finally passed to the carrier on 23 June. The second ship, RFA Tiderace has completed trials and training and has been selected for the prestigious role of supporting HMS Queen Elizabeth on her Westlant 18 deployment to the US. At the time of writing, RFA Tidesurge and Tideforce are both in Falmouth completing their customisation work.
Early signs suggest that these ships will have long and distinguished careers and this procurement project can broadly be considered a success. Although the Naval Service can be very proud of four excellent new vessels, the rest of the RFA is having to pay the price. A lack of manpower and the need to save money has seen the Birkenhead Navy expanding and three RFAs are now laid up without crews on Merseyside. For the first time, both solid stores ships RFA Fort Rosalie and Fort Austin are in long-term lay-up together. RFA Wave Knight is completing maintenance and her future unclear. RFA Wave Ruler is laid up, surrounded by persistent rumours that the arrival of the 4 Tides means one or both of the Wave class may be sold, possibly to Brazil.