Germany goes for high-tech emergency towing vessel

Jack Gaston writes: Germany’s present station and patrol area is an increasingly busy location for ships of all kinds using the North Sea shipping routes to the Elbe and Weser, with many vessels carrying potentially hazardous or polluting cargoes. The area is also susceptible to unpredictable and hazardous weather conditions, resulting in a heavy and dangerous swell. In the event of a machinery failure or other serious incident the rapid intervention of a purpose designed ETV could prove vital in preventing major pollution and/or loss of life.

Nordic is owned by the Arbeitsgemeinschaft (ARGE) Kustenschutz consortium and will be operated by Bugsier Reederei und Bergungs of Hamburg for a ten year period, under contract to the German Government in a deal valued at close to €114 million. The contract award followed protracted negotiations covering all aspects of the vessel’s construction and charter. Bugsier also project managed the design and construction of the vessel which bears the insignia of the four participants in the ARGE consortium; Bugsier, Fairplay - Richard Borchard, Unterweser Reederei and Wiking Helikopter.

A decade of careful planning by Bugsier and its partner ARGE went into supporting the German Government’s intention to replace the existing North Sea ETV, Bugsier’s aging deepsea salvage tug Oceanic. The latter carried out the ETV role for about 15 years and the operational experience gained had a profound effect on the design of the new ship.

Nordic was built in the Wolgast shipyard of P+S Werften (formerly Peene-Werft) in Northern Germany. The ship was built using the modular ‘block’ principle, with the hull being constructed in two halves. Each half was fitted out to an advanced stage, with much of the machinery in place, prior to being welded together in dry dock.

The design process, including tank testing, was entrusted to, Skipskonsulent of Bergen, working in close co-operation with technical staff from Bugsier and the ARGE. There were a number of predominant requirements that had to be met to fulfil the role of a future ETV in the eyes of the owners, the operators and the German government. A minimum free running speed of at least 20 knots was specified in order to reach a casualty as soon as possible. The bollard pull of over 200 tonnes was to ensure that the tug can deal with the largest ships likely to frequent German territorial waters. On arrival at a casualty it is also essential for seamen to safely work on deck to make that vital towing connection, regardless of weather conditions. Both the speed and bollard pull had to be achieved from a vessel with a draught not exceeding 6m, a figure determined by the relatively shallow conditions adjacent to the main sea routes into the area. Nordic is also one of the very few ETVs currently in service with the ability to operate in highly volatile or toxic atmospheric conditions, of a kind that might be encountered during an incident with a casualty carrying a chemical, oil, LNG, or other hazardous cargo. The completed vessel meets the requirements of Germanischer Lloyd +100 A5 IW ‘TUG’ +MC AUT ‘suitable for use in hazardous atmosphere’.

Nordic measures 78m length oa, with a moulded breadth of16.4m, a depth (to the main deck) of 8.0m and draught of 6.0m, resulting in a deadweight of 2400 tonnes and gross tonnage measurement of 3,300gt. The 6m draft limitation, a high bollard pull and speed called for a number of compromises to be made with respect to the choice of propellers and nozzles.

The chosen hull form incorporates a prominent bulbous bow, with a considerable flare, and a forecastle two decks high and extending aft to beyond amidships. This, combined with a sheltered after deck with high bulwarks and an enclosed, rounded, stern, enables the vessel to operate at high speeds in rough weather conditions and affords a safer working environment when making a towing connection. Any problems associated with freeing the enclosed working deck aft from excess water is alleviated by incorporating a large transverse channel at the forward end, below deck level and covered by gratings and with freeing ports on either side. Considerable experience with the Oceanic, a true deepsea salvage tug, had a profound influence on the design of the after deck.

The superstructure is over three decks high and has, likewise, been designed to give maximum protection in heavy weather with heavily sloping forward surfaces. A large bridge, with outward sloping windows, is located just forward of amidships and well away from the bow.

Nordic is a twin-screw vessel powered by two MTU 20V8000 M71L GSB diesels, of a new advanced design specially adapted for gas protected operation (GPO). During normal running each main engine generates 8,600kW at 1,050 rpm - its maximum continuous rating - giving the vessel a maximum total of about 23,000 bhp. When operating in a hazardous atmosphere the turbo chargers are shut down and the engines run in a ‘normally aspirated’ mode at a reduced power rating of 4,000kW. Under those conditions the engine exhaust spark arresters are supplemented by a water-cooling system.

The main engines drive Berg Propulsion CP propellers, via Flender reduction gearboxes that also provide a power take-off for the shaft generators. Each propeller rotates within a short, fixed, thrust-augmenting nozzle. Twin high efficiency flap rudders from Becker are normally operated in unison but if required can be controlled independently. Manoeuvrability is enhanced further with the installation of three electrically powered 800kW transverse thrusters, two in the bow and one at the stern.

Electrical power onboard Nordic is supplied by two shaft generators supplied by Leroy Somer, each rated at 2,000 kVA, and two auxiliary generators of 1,350 kVA located in the engine room and powered by MTU 12V 4000 M50A diesels. A 125 kVA emergency generator, powered by an MAN diesel engine, is located in the superstructure on ‘A’ deck. The latter are all capable of gas protected operation and have water-cooled exhausts. The main engines and the two larger auxiliary diesels share comprehensive box cooling systems.

An interesting innovation aboard this new ETV is the small deckhouse located on the towing deck aft, housing an additional auxiliary generator. As part of its normal duties Nordic spends a considerable amount of time at anchor and rarely remains in harbour for more than a few hours. This generator, rated at 350 kVA and powered by an MTU 8V2000 M50 diesel, is enclosed in a SDT sound insulated housing and supplies power when the vessel is at anchor and the main auxiliaries are shut down. This arrangement reduces sound levels throughout the accommodation while at anchor, and the deckhouse also provides an alternative route to and from the towing deck in heavy weather.

The towing gear aboard Nordic is impressive. A hydraulically powered Hatlapa twin-drum ‘waterfall’ style winch is fully protected from the elements in a winch-house, a full two decks in height, located within the superstructure. The winch has a brake holding capacity of 387.5 tonnes (3,800kN) and can accommodate 1,400m of 80mm diameter steel wire towline on each drum. The towlines are deployed via massive fairleads and served by hydraulically powered spooling gear operated by an unusual re-circulating chain cable system.

A hydraulic supply for the deck machinery is provided by an electrically driven power pack located in the engineroom.

When the towlines are deployed, they are high above the deck, making the provision of remotely operated Karm tow pins and a line-handling fork, with a safe working loads of 300 tonnes, essential. Traditional tow beams are placed across the width of the deck to prevent fouling. Two 10 tonne capacity tugger winches working in conjunction with specially designed hinged sheaves also assist in controlling the towlines.

Spare pennants and other towing gear are stored on three powered reels located on the deck above the winch house. Other items of salvage equipment are stowed around the towing deck and a clear space is marked for helicopter winching operations.

A prominent feature on the portside of Nordic is the HMB Lintech Marine crane, designed for offshore use in swells of up to 2m and winds of Beaufort Force 6. The hydraulically operated crane has a maximum reach of 16m and can be used for a wide range of duties including handling boats, skimmers, pollution control equipment and transferring stores. When fully extended the crane has a lifting capacity offshore of 3.6 tonnes and 6.5 tonnes when in harbour. Stowed adjacent to the crane is a 7.20m Hatecke FRB 20-700SUBS fast rescue boat. In suitable conditions the boat can be launched on either side of the ship, using a sophisticated pendulum low handling (PLH) unit attached to the crane jib that also enables the orientation of the boat to be controlled. The boat is powered by a 120kW inboard diesel engine and has a top speed of 30 knots. A smaller, mandatory, man overboard rescue boat is situated on the starboard side and handled by a Global davit.

The fire fighting installation features two Jason monitors, mounted above the wheelhouse on telescopic masts. In the lower position the monitors can each deliver 1,200m³ of water per hour and when fully raised, to 15m above the mounting, 600 m³/h. A self protection water spray system is fitted. The entire installation supplied is by two fire pumps, one coupled to the front end of each main engine via a power-take off and step-up gearbox.

As previously mentioned, the bridge is located almost amidships and is well glazed for good all round vision. The layout is that of a conventional deep-sea tug, with a wide central console forward containing all of the essential propulsion and navigational controls and instrumentation. A smaller console installed facing aft, with seating for two persons and duplicated controls, also incorporates controls for the winch and tow pins etc. A separate chart table, GMDSS radio desk, and a meeting area with a table and seating are provided on the bridge. The outfit of navigational and communications equipment chosen is of a high standard and fully compatible with the duties of a modern ETV.

The superstructure and accommodation aboard Nordic is vast and fulfils a number of functions. In addition to providing comfortable living areas for the crew, space and facilities are available for the care and treatment of large numbers of survivors rescued during an emergency, and the training of apprentices. The vocational training of apprentices in seamanship and marine engineering forms an important subsidiary role while the ETV is on duty at sea. Throughout the vessel equipment has been selected to enable various subjects to be taught, from the very basic to more advanced levels.

Accommodation is provided for a crew of 12 and a ‘boarding’ team of four in 16 single cabins and 12 apprentices in six double berth cabins. The cabins for the Captain and Chief Engineer include a lounge and office and are located along with the other officers’ cabins on ‘C’ deck, just below the bridge. Provision is made for four supernumeraries that may include owner’s representatives, instructors or similar personnel. Separate dayrooms are provided for the officers and crew, and other facilities include mess and dinning areas, a large galley and pantry, a treatment room, hospital, a conference/recreation/classroom, changing rooms and extensive dry and frozen storage arrangements. A dedicated garbage area enables refuse to be stored for disposal ashore.

The configuration of the entire accommodation area is made more complex by the need to operate under ‘closed down’ conditions in hazardous atmospheric conditions. Nordic has two ‘citadel’ areas ‘A’ and ‘B’ which are maintained with an ‘overpressure’ of 4mb and 2mb respectively. Citadel ‘A’ includes the bridge, engine control room, and selected areas on each deck. Citadel ’B’ includes the engineroom, all of ‘B’ deck, the treatment room, hospital, and selected areas elsewhere. Carefully positioned air-locks are provided; some with access to the deck are large enough to accept stretchers, to enable the normal operation of the vessel and for casualties to be brought into the treatment areas. Air-curtain units are installed at the entrances to the air-locks and winch-house to reduce any flow of contaminants into areas beyond them.

Unlike most other vessels equipped to operate under hazardous conditions, pressurisation aboard Nordic is not achieved by using pumped, filtered, air from outside. In this installation a system of stored clean air is used for both pressurisation and to purge the air-locks. Nine modules, each containing a bank of 1,250 litre compressed air bottles, are located in a storage space on the portside of the accommodation. ‘Plug-in’ connections on deck, with adjacent seating, enable deck crew wearing Dräger CPS 7900 chemical protective suits to rest and draw air from the ship’s system. When crew members are required to work on deck they do so in teams of three. Facilities are provided for the care and storage of suits and for decontamination of suits and personnel.

Under ‘closed down’ conditions Nordic can operate for a minimum of 8 hours before having to withdraw to a ‘clean air’ environment to recharge the bottles using onboard compressors. A ‘countdown’ clock is installed on the bridge to account for the time remaining. Much of the system has been installed using equipment and expertise from Dräger Safety, including a network of hazard detecting sensors located in strategic locations around the vessel and pressure monitoring equipment internally.