Planet ice and the dual-functional Attenborough

by | 11th January 2017 | News

Home News Planet ice and the dual-functional Attenborough

The Naval Architect: January 2017

Designing Sir David Attenborough posed an unusual challenge, according to Erik Leenders, designer, ship design & systems, Rolls-Royce. Unlike preceding ice-going vessels Rolls-Royce has worked on, it is required to fulfil the duties of a research vessel and a cargo ship, and so demanded a new combination of design features to cater to the contrasting disciplines.

In this sense, continues Leenders, many of the innovations featured on the vessel have been seen elsewhere, but never in the twin skeg, ice class, underwater noise managed combination that Attenborough demonstrates.

A more comprehensive list of its requirements includes the DNV Silent-R notation; minimum bubble sweep down; icebreaking; a shallow draught of 7m; a multi-discipline working deck (cargo/science operations); a large aviation fuel tank capacity (660m3); SPS compliance; and helicopter landing capabilities.

Much of the need for flexibility comes from NERC’s plan to combine the capabilities of its current polar exploration fleet, RSS Ernest Shackleton and RSS James Clark Ross, in a single ship, and Leenders and fellow Rolls-Royce designer Martijn de Jongh stress that flexibility in the vessel’s arrangement was a crucial design node as each scientific cruise the vessel sails on will be different and will require different arrangements of onboard space. 

Leenders explains that the design/logistics puzzle of the vessel was partially solved with adaptable spaces, such as laboratories and hangars that can be rearranged and a helideck that can be re-appropriated for scientific work. But, he continues, it was also by carefully zoning the main deck. This zoning was particularly important (and difficult to achieve) for safely balancing spaces for science operations and the carrying of cargo. Additional gas zones had to be taken into account as Attenborough has the unique charge of transporting aviation fuel to Antarctic bases; a requirement Rolls-Royce has not previously come across in an ice class research vessel.

Other technical specifications include cargo containers to be transported in the hold and on deck (pictured in Figure 1), a skidding system in the hold, scientific containers in the vessel’s scientific hangar and helicopter hangar, as well as the equipment and capability to carry out over side and moonpool operations. These operations were particularly complex to manage as the respective winches for the stern, side a-frames and moonpool needed to be arranged in one room near the stern of the vessel so that their wires could be routed effectively. Leenders and De Jongh say that a close dialogue between the owner and designer was needed to meet the vessel’s winch requirements, which include eight scientific winches, and add that Attenborough is fit to carry out over side and moonpool operations to depths of 9,000m, utilising a moonpool door in the bottom of the ship and a dedicated Conductivity, Temperature and Depth (CTD) handler.

Rolls-Royce’s experience with complex offshore designs and the recent build of Norway’s new polar research vessel, FF Kronprins Haakon, aided in the development of the vessel, but, as mentioned above, new challenges had to be overcome and new trade-offs made to meet NERC’s requirements. “No vessel is the same…there are new requirements and you have to approach them from a new angle,” says De Jongh, adding that “[You can] build upon the challenges before, [but] challenges can be quite different, even conflicting.”

This conflict was felt in the requirement to combine the best characteristics for icebreaking, carrying out research tasks, transporting cargo and seakeeping.

Icebreakers, especially those of a relatively large size like the 128m-long Attenborough, create bubbles that are swept under the hull. These bubbles are usually harmless for such a vessel, but Attenborough’s research function means that they would interfere with research equipment such as sonars and (multi-beam) echo sounders. As a result, the design team spent a great deal of time refining the lines for the bow, compromising on icebreaking lines and bubble streams to achieve the best all-round performance. Testing at the Hamburg Ship Model Basin (HSVA) was consequently extensive to check the correct compromises had been made. It required that normal ship performance tests for an icebreaker, icebreaking tests, as well as normal performance tests for a research vessel and targeted tests to analyse research capabilities were carried out on Attenborough’s design. 

Initial CFD calculations were made to measure hull resistance, before moving on to bubble sweep down/flow behaviour analysis. This simulated the drawing down of air bubbles at the upper water layers and gave Attenborough’s designers an insight into where bubbles would travel. With these results they were able to adjust the vessel’s hull lines and direct bubbles away from Attenborough’s sensor arrays.

The designers worked closely with DNV GL throughout the project in order to fulfil the requirements of the class society’s Silent-R & Silent-S notations. The vessel can consequently travel at a speed of 11knots without creating significant levels of noise and vibration that may be harmful to marine organisms or interfere with the research vessel’s sensor arrays. This allows the vessel to carry out research quietly and at a faster pace than previous research vessels through the use of silent (and more efficient) five-bladed controllable pitch propellers (CPP) and resiliently mounted equipment. Importantly, this ability does not cost Attenborough its icebreaking credentials, as while the propellers’ polar class was downgraded from Polar Class 4 (PC4) in order to reduce noise and vibration through a reduction in their size, the 4.5m diameter CPPs can still handle Polar Class 5 (PC5) level operation – described as “year-round operation in medium first-year ice which may include old ice inclusions” by IACS. 

The design team also had to balance seakeeping qualities with good icebreaking characteristics, as an efficient icebreaking bow is not usually optimal for seakeeping, says Leenders. This challenge extended to meeting the vessel’s dwt requirements and draught restrictions, as the owner additionally stipulated that the vessel would need a 7m draught in order to access a number of shallow harbours. This, considering the size of the icebreaking vessel at 128m in length, is a relatively small draught, and meant that Attenborough could not be of a slender design.

Finally, airflow was also an important consideration. One of the vessel’s research duties will include taking air samples and meteorological measurements, and so necessitates that the air collected is as clean as possible. This has impacted the vessel’s arrangement, with the mast positioned at the bow to take air samples. Similarly, the position of the exhausts had to be considered in relation to air intakes and science measuring points, and helicopter operations also had to be allowed for.

Sir David Attenborough is currently under construction by Cammell Laird, Birkenhead, UK, and is being built according to Lloyd’s Register Class and Maritime Coastguard Agency (MCA) requirements. It is due to be delivered and operational for Arctic and Antarctic duties in 2019.

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