In focus: HMS Scott, the Royal Navy’s ocean survey vessel

HMS Scott is the Royal Navy’s Ocean Survey vessel. Although the 5th largest ship in the RN fleet, she maintains a relatively low profile, spending long periods at sea on her primary duty, mapping the bottom of the world’s oceans. Here we look at the history, design and role of the ship.

Background

The RN’s Hydrographic Squadron has a long and illustrious heritage that could be traced back to 1681 when the navy was ordered to conduct the first survey of the British coast for King Charles II. British charts of the oceans were a critical enabler in Britain’s domination of the seas in the 18th and 19th Centuries. Today the United Kingdom Hydrographic Office (UKHO) employs around 1,000 people in Taunton and is a world-renowned organisation which generates considerable revenue by the sale of data for commercial use. The needs of the RN are its top priority but the commercial operations of the UKHO turned over around £150M and made a profit of £29M in 2017-18. RN survey vessels, including HMS Scott, supply much of the data although there is now considerable sharing of information between member nations of the International Hydrographic Organization (IHO).

When the US agreed to sell the submarine-based Polaris ballistic missile system to the UK in 1963, the arrangement included bi-lateral sharing of highly accurate bathymetric charts. Maps of the seabed and the thermal layers of the water column are particularly important for the safe navigation and concealment of ballistic missile submarines in the deep ocean. The US Navy had developed the world’s first wide-swath, multibeam bathymetric survey and navigation system which produced charts used by the submarines of both nations. The RN also contributed to the survey work by ordering four Hecla-class combined hydrographic and oceanographic survey vessels, built between 1966-74.

These 2,800-tonne vessels were designed for both deep ocean and coastal surveys and were fitted with air conditioning for hot climates and ice-strengthened. Their diesel-electric propulsion was unusual for the time but gave them a range of 12,000 nautical miles, allowing for long periods at sea. The H-class made use of early side-scan sonars which were towed behind the ship and colloquially referred to as ‘fish’ with data being recorded on reel-reel magnetic tapes. The ships were fitted with modest flight deck and hangar for small Wasp helicopter. When embarked, the aircraft was used to conduct aerial photography, photometric surveys, install tide gauges and move equipment and personnel around.

In the late 1990s, there was a debate over whether the hydrographic survey squadron should be privatised and outsourced to civilian vessels. Their increasingly important part in supporting submarine operations and very much lower manning requirements of the future vessels meant that the RN thankfully retained its hydrographers and ships. It was also decided that the traditional white hulls and buff funnels would be abandoned permanently and all ships would be painted grey to reflect their closer involvement with warfare and integration with the surface flotilla.

In tandem with planning for the Vanguard-class Trident submarines, in 1987 the MoD concluded that it needed the renew and update its ocean-surveying capability. Several options were considered but ultimately the US Navy’s fully integrated Ocean Survey System (OSS) was selected which would be carried by a large purpose-built vessel. HMS Scott was ordered in 1995 from BAeSEMA (a joint venture between British Aerospace and the French Sema Group 1991-98) and the construction was sub-contracted to Appledore Shipbuilders. Although a relatively expensive initial outlay on a high-end solution, the low ‘cost per survey mile’ and quality of data were the prime factors in the decision.

Big ship, small crew

The construction of HMS Scott proceeded smoothly and her hull was floated out of the covered dry dock at Appledore and onto the river Torridge in October 1996. She commissioned in June 1997, just 30 months after she was ordered. She was built to mostly commercial shipbuilding standards and was one of the first ships of the RN to conform to Lloyds ship classification (enhanced in some areas to meet naval requirements). She is a large vessel displacing 13,500 tonnes with a length of 131.1 meters to provide a stable platform for surveying. Her deep draught of 8.3m is due to ballast tanks at the bottom of the ship which hold 8,000 tonnes of water to further improve stability. Water ballast is pumped around 23 inter-connected tanks to control the trim of the ship.

The ship is propelled by two Krupp MaK 9M32 nine-cylinder diesel engines driving a controllable pitch propeller through a single shaft, giving a top speed of 18 knots. A vertically-retracted bow thruster is fitted for slow-speed manoeuvring and to assist with berthing. The ship is intended to operate with unattended machinery spaces and is fitted with remote surveillance and fixed fire fighting equipment.

HMS Scott has an exceptionally small complement which operates a three-watch system. 72 men and women are assigned to the ship’s company, around 42 are on board at any one time while the others are ashore on leave or training. Typically each sailor will spend about 70 days onboard followed by 30 days ashore in a cycle repeating 3 times per year. Onboard systems are low maintenance and a 3-year planned docking cycle was intended to allow the ship to spend an exceptional average for a naval vessel of 300 days at sea each year.

Accommodation is probably the most comfortable of any RN vessel afloat, appropriate for a ship that may spend many weeks in mid-ocean on monotonous survey work. More in line with RFAs or merchant vessels, each sailor is has a single cabin and one bathroom is provided for every two people. Cabins are all in the superstructure and the majority have large windows. The large hull and small crew has resulted in such an excess of space onboard that HMS Scott a large gym area and is even equipped with a squash court.

HMS-Scott-Survey-Equipment-2

The components of the Integrated Ocean Survey System are installed in the mission space on four decks in the centre of the vessel and consists of four sub-systems; navigation, sonar, power and mission control and processing (MCAPS).

MCAP collects, processes and records time-correlated bathymetric, gravity, magnetic and other oceanographic data. Seabed information is displayed in real-time as 3D images monitored by the hydrographers in the mission spaces. The data is further processed and checked before being transferred to the hydrographic office in Taunton.

Out of sight and fitted along the bottom of the hull is the most important equipment carried by HMS Scott, the Sonar Array Sounding System (SASS IV). The SASS low-frequency array is 10 meters long and emits 90 adjoining beams in a 120º fan-shaped acoustic swath pattern transverse to the ship’s track. Their returning echoes are received by a separate large hydrophone containing 144 elements. Digital signal-processing algorithms process the returning signal to develop an across-track profile of the ocean bottom. Thousands of data points are corrected in real-time for sound-velocity variations and for the ship’s roll, pitch, heading, and heave variations between the time of transmission and reception.

An additional narrow-beam sonar uses a 9-degree conical pattern to measure the ocean depth directly beneath the ship. This is used to verify the depth data of the main wide-swath-array sonar and used in waters (less than 50 fathoms) too shallow for the main array.

In order to make accurate depth measurements using sonar, the speed of the sound wave through seawater must be known. Temperature and salinity layers in the waters column affect the density of seawater and the speed that sound travels. Knowledge of this phenomenon is vital in hydrography as well as submarine and anti-submarine operations. HMS Scott takes periodic measurements of the water column by lowering an expendable bathythermograph (XBT) or by towing an aquashuttle oceanographic profiler behind the ships at varying depths

During a run the ship proceeds at around 12kt and surveys the ocean floor at depths between 50 to 2,500 fathoms. At a typical depth of 2,000 fathoms, the sonar scans a swathe of ocean floor about 5.6km wide. Depending on conditions, Scott can map up to 150Km² in an hour. During one 3-month deployment in the North Atlantic Scott surveyed 74,000 Km² area of seabed.

Service history

Despite most of her career spent far out to sea, there have been some notable moments in the career of HMS Scott. Following the Boxing Day tsunami of 2004 which killed around 228,000 people, the ship conducted seabed surveys off the Sumatran coast which revealed huge underwater landslides. The information collected was used by scientists to understand exactly where and why the earthquake had occurred and to inform the placement of sensors to provide warning of future events. Later that year, the ship was chosen as one of the reviewing platforms and hosted the Duke and Duchess of Cornwall and various VIPs during the Trafalgar Fleet Review held in the Solent.

Scott completed a 10-month refit in Portsmouth during 2009 and was then tasked to conduct some of the Antarctic Patrol Vessel duties to replace HMS Endurance (after her catastrophic flood and near loss in 2008). Scott had two spells during the 2009/10 and 2010/11 seasons in the South Atlantic.

In 2013 Babcock was awarded a through-life support (TLS) contract for the ship. Between November 2013 – May 2015 she had her biggest refit at Devonport which included installing a new sewage treatment plant and two new lifeboat davits, as well as a new uninterrupted power supply to the ship’s sonar suite. The propeller and shaft were overhauled and the port main engine crankshaft replaced along with the rudder horn due to cracks in the original casting

Following a serious starboard main engine failure at sea she turned to Devonport in June 2017. For some time her future was in doubt and there were media reports the ship would be scrapped. However, in early 2018 she was prepared to make the 700-mile trip to Babcock’s facility in Rosyth on a single-engine. She was dry-docked and a new 35-tonne replacement engine installed through a hole cut in her hull. The refit period also included a complete overhaul of the sonar array.

On completion of the repairs and work up period, she sailed from Devonport in July 2019 for 10 months in the Atlantic. Further technical issues saw her spend September in dock at Gibraltar. HMS Protector was due to arrive for Antarctica in late 2019 but in October a serious defect was found during planned maintenance in Charleston, USA and she returned to the UK for repair. HMS Scott was again called on as a partial replacement and spent several months in the South Atlantic. During December 2019 she was involved in searching for a Chilean airforce C130 aircraft that went missing. After 95 days continuously at sea, HMS Scott arrived back in Falmouth, just in time for lockdown in March 2020.

Going, going, gone

In Oct 2017 the MoD said that HMS Scott would be decommissioned in 2022 on completion of her intended 25 year-life. With less than two years left, there is no plan to replace her, at least with another naval vessel. Navy Command stated in October 2019 that “Work is underway to understand current and future requirements and how they will be delivered after HMS Scott leaves service”. Scott’s annual running cost is just £4.5M and the profits of the UKHO cover this and the Navy’s other Hydrographic ships. Like several important UK defence assets, there is no funding line for the capital cost of replacement. Either the RN’s deep ocean survey capability will be much reduced, the work contracted to a commercial company or we must rely on data supplied by other nations. The cost of installing a new engine was deemed worthwhile in 2018 to give Scott just 3 more years of service, it is possible she could undergo a life-extension refit but whether it would be worthwhile would depend on the material state of the hull.

During her career, HMS Scott has gathered vast amounts of data and contributed to the scientific understanding of the oceans as well as helped makes charts used by mariners and submariners. To date, mankind in its entirety has mapped less than 10% of 40 million square miles of seafloor. We know more about the topography of other planets in our solar system than we do about the ocean floors. It is worth noting that the Seabed 2030 project has been established, attempting to map the entire seabed by 2030. Commercial sponsorship will fund around 100 survey ships that will circumscribe the globe. The information will be available to everyone (with potential implications for submarine operations). Despite such initiatives, given the UK’s continued commitment to a submarine-based nuclear deterrent, a sovereign surveying capability remains crucial.