DUKE II: KOOIMAN’S LATEST AHTS FEATURES ICE CLASS 1A SUPER FOR ARCTIC OPERATIONS

Impressed by the work of Mustang, one of its subcontractors’ vessels working on a project near Nova Zembla, marine contractor Probus Mare Marine Ltd. decided to acquire the powerful tugboat from its owner Gerrit Bouwman Towing & Shipping. In addition, the company needed a second vessel for its work in assisting a pipelaying pontoon for the oil and gas industry.

At Shipyard Kooiman, the design of Mustang had in the meantime evolved through various builds into a more powerful and larger anchor handling tug supply (AHTS) vessel, with its latest iteration begin the Norne, delivered in 2011. Extremely satisfied with the performance of Mustang, the owners decided to contract the same builder for their new ship, which was to be called Duke II.

1A Super

For Probus Mare, the yard upped the standard set by Norne by giving the vessel an improved ice class rating of 1A Super, according to the Finnish-Swedish ice class ratings. This is the highest ice class rating obtainable for an AHTS, and the last step before entering icebreaker status. It allows the vessel to operate in difficult ice conditions without icebreaker assistance. Although the hull shape and powertrain could remain unchanged from Norne, quite a few modifications were necessary to achieve this high rating.

Handyman

Both Mustang and Duke II are employed in the oil and gas industry, where they work as a versatile support vessel by setting and retrieving anchors, towing pontoons and supplying small quantities of fuel or containers. With her higher ice class rating, it is expected that Duke II can extend the working season into spring and autumn.

The most obvious influence of the ice class rating is seen in the hull structure, where an ice belt above and below the waterline consists of thicker steel plating (up to 18 millimetres in the bow) and added internal framing. The rest of the hull mainly consists of ten millimetres plating. The added weight compared to Norne was relatively small, resulting in Duke II still having the same hull design, albeit with a slightly smaller freeboard.

Ice impact

Another important aspect of the ice class rating is the requirement that the propulsion installation must be able to cope with significant impacts from blocks of ice against any of the propellers. This resulted in increased propeller shaft diameters (from 260 to 335 millimetres) and substantially larger gearboxes, which nearly outsize the main engines. The rudder stocks also have increased diameters and their steering gear is more powerful, allowing for faster manoeuvring. At the trailing edge of each rudder, an ice-knife, consisting of a vertical structure extending below the top of the rudder, prevents blocks of ice from getting stuck between the rudder and the hull when sailing astern.

Holed bilge keels

While Duke II was built under the Cypriot flag and Bureau Veritas class, after her delivery on 29 March 2013, she started the process to be flagged over to the Russian flag and the Russian Register class society. Besides some extra spare parts required to be carried on board, this had no further consequences to the build. The hull design is that of a typical oceangoing tug: a double chined hull with a very shallow aft ship allowing for large slow-turning propellers with good water influx. A notable feature are the bilge keels: instead of closed plates, these consist of an open V-shaped structure with holes on both of the closing plates. The position of the holes is offset, so the water is forced to search a sinuous path through the bilge keel when the vessel is rolling. According to Kooiman’s design engineer, Martien Beeke, this results in more dissipation of energy than forcing the water around the tip of the bilge keel, and thus an increased roll damping.

Duke II has an ice class
rating of 1A Super,
the highest possible
for this type of vessel

Engine room

In the engine room, it is visible that the main engines are spaced quite far apart, which results in excellent manoeuvrability. On the centreline is a 650 kW auxiliary engine driving several hydraulic pumps, among others for the deck crane, the winches and the 440 kW hydraulic bow thruster. An electric motor can also drive the smaller of these pumps, sidestepping the need to turn on the engine for a short hydraulic duty on deck. Electric power is generated by two diesel generators rated at 120 kVA. Normally one is running and the other on standby. An aircooler is installed, enabling operation of one generator in drydock. All engines are from Mitsubishi.

The engine room is protected with a fire extinguishing system with FM200 extinguishing gas, with the bottle stored within the engine room. For noise reduction, each main engine exhaust stack is fitted with both a resonance and an absorption damper, both from Novetec.

Propulsion

The propellers have a diameter of 2.8 metres and rotate in propeller nozzles for additional bollard pull. A rope guide leads from the hull bottom to the tip of the nozzle to prevent ropes from getting stuck between nozzle and hull. The Reintjes gearboxes, with a reduction of 5.5:1, incorporate the thrust bearings and are flexibly coupled to the main engines, allowing the latter to be installed on flexible mounts.

Behind each propeller is a double rudder, creating a steerable jet of water. Each of the rudders has their own double pump set, consisting of both an electric drive and a PTO on the gearbox. With electric pump and PTO combined, a very high steering speed can be obtained: it takes only twelve seconds to rotate the rudder from 58° port to 75° starboard (the other part of the double rudder will then go from 75° port to 58° starboard).

Toolbox

If an AHTS vessel is a ‘man with a van’, the aft deck is without doubt its well-equipped toolbox. Covered in 50 millimetre thick Azobe wood, it features container fittings, a 1,200 millimetre diameter stern roller, and a Heila crane which can lift ten tons just aft of the stern. Hydraulically retractable towing pins keep the towing point centered. The main towing winch contains 1,000 metres of 58 millimetre towing cable and has a towing force of 80 tons, which corresponds with the bollard pull of the vessel. A spare towing cable of 750 metres is stowed on a separate drum. Powerful LED floodlights ensure safe working conditions at night. As on previous Kooiman tugs, all areas subject to cable chafing are executed with liners of stainless steel, which keeps the vessel looking good over a long period of time without excessive maintenance work.

Supplier

For supply of fuel to other ships or pontoons, a reel with fuel hose is located in a locker on the aft deck. Interlocks between the valves on the valve block in the engine room ensure that no more than 200 m3 of fuel can be given off to another vessel, which steers Duke II clear of tanker vessel regulations. Her total fuel capacity is 293 m3 which results in excellent autonomy, enhanced by the watermaker of 5 m3 per day. The fuel transfer pump has a capacity of 60 m3 per hour.

Accommodation

The accommodation is fit for a crew of ten, with an individual cabin with bathroom for the captain and engineer and double cabins with shared facilities for the rest of the crew. The airconditioning and heating system is suitable for worldwide operation, as living conditions inside can be kept acceptable in outside temperatures ranging from -30° to +45° C. The galley and messroom are one large open space. Below the accommodation is a large store room with four full-height freezers, four full-height refrigerators and ample dry storage.

The wheelhouse features both a forward facing navigation desk and a control position facing

Impressed with the build quality and performance
of Mustang, its new owners ordered a second
AHTS from the same builder

the aft deck, with three full-height windows. The mast is hydraulically retractable to ensure easy passage under bridges.

Full-service

For cost efficiency, the hull of Duke II was built in Czech Republic, with outfitting taking place on the covered slipway at Shipyard Kooiman in Zwijndrecht. The yard is currently building two split hopper barges for the same owner. With Duke II, the yard has once again demonstrated its position as a builder of high-quality no-nonsense ships, prepared to go the extra mile to ensure customer satisfaction. Due to the yard’s full-service approach, with almost all aspects of shipbuilding covered in-house, communication lines remain short, which contributes to cost-efficiency, customer satisfaction and reduced construction time.

Bruno Bouckaert