Shuttle tankers: coping with icing in Arctic waters

Low temperatures, winds, icing, and snow worsen the conditions for carrying out maintenance, causing breakdowns in equipment and machinery, reducing the work performance quality, and increasing the work execution time. Complications can occur while people move around the vessel, increasing the likelihood of injury.

Snow cover and wind impede the operation of the air intakes and vents on ballast tanks and open drainage systems, which leads to additional loads on the equipment, pipelines and cables.

The structure and properties of metal change significantly upon cooling and the exposure time is important, therefore measures to protect and remove ice should not be postponed.

The first attempts to remove pipelines and cables under the casing were made on Arctic tankers in the Samotlor series.

The catwalk on the cargo deck was raised to over 2 m, and closed pipelines and cable routes were installed on both sides of it, while the pipeline routes were insulated with glass wool. These were the first steps taken to prevent ice formation on ship structures and equipment by heating them and providing adequate covering. Later, the solution to these problems brought about fundamental changes in the layout of ship structures. The calculated operating temperature was used as a basis for determining materials for the manufacture of foundations, fasteners, pipelines, coatings, and gaskets.

An electrical heating system was first implemented on the Vasily Dinkov-class tankers (serving the Varandey project) by covering the equipment with heated covers and is still used on many ships today. This system is low maintenance and relatively reliable, provided that self-regulating heating cables are installed properly.

However, this approach has generally failed to pay off. Due to the vessel’s operation under extreme sea conditions and strong winds, the coating fell into a dilapidated state after just one season of operation. Storm surges were devastating to both the protective covers and the equipment underneath.

A ’deck trunk’ closed-heating system was applied on Shturman Albanov-class vessels as part of the Novy Port project. It was fairly simple to stow most of the equipment located on the cargo deck in a room closed off from any outdoor exposure. The main advantage of the closed-heating system is that it helps to protect all the electrical and electronic equipment of the cargo system and facilitates maintenance of the cargo and fire safety systems at low temperatures and in challenging environmental conditions.

The operational experience of the Shturman Albanov vessels showed that maintaining positive temperatures in the trunk had a positive effect on the operation of cargo tank radars, ensured comfortable work when measuring cargo and taking samples, prevented the cargo from freezing and the precipitation of heavy fractions in the cargo lines, and significantly reduced the risk of defrosting trunk systems.

The necessary changes to the design will be taken into account for ships of new generations. According to the Mooring Equipment Guidelines, the distance between the winch drum and the hawse should be at least 19 diameters of the drum width in order not to exceed the deflection angle of 1.5° when laying the mooring line. This requirement is not met due to the fact the winches are on the trunk and the intermediate hawse is installed at the edge of the trunk.

There are other flaws in the system that need to be addressed. These include the need for additional heating of the valves in the inert gas system on the open deck, as the valves freeze due to the condensate inside. Some of the pipes of the atmospheric sampling system are also located on the open deck, which leads to freezing due to the condensate inside and prevents taking measurements. In any closed method, there are still points of contact with the environment, and these represent weak points which require increased attention and a combined approach.

Regulatory documents are revised and changed frequently, but it is normal practice for the design of a ship to be completed and for the ship to begin operating simultaneously with the release of new requirements. In such cases, ship navigators have to make structural changes during periods of scheduled repair. At the same time, this allows crews to take part in the process of adjusting the equipment and gaining experience, as well as influencing the process of developing requirements.

Practical conclusions

Lifting equipment, cranes, and monorail hoists located on the open deck must be of Arctic design with appropriate protection for personnel. Therefore, all cranes on ships operating in the Arctic must be equipped with insulated cabins.

Design solutions for mooring areas should minimise the appearance of snow or icing on easily dumped structures in bulwarks and drainage systems. These areas are susceptible to water splashing and intense icing due to their location at the edge of the end structures of the vessel. Solutions for such structures should minimise icing on the outer surface and ensure their structural reliability.

The company continues to collect data on the reliability and efficiency of the use of such systems on ships to further improve and develop safe conditions and methods for conducting ship operations and reducing environmental impact.

Join us for Shuttle Tanker Technology & Operations Day on 30 March 2021. Register your interest here.