Castor and Pollux: Mythical twins with a split personality

No 2 MbH Maart 2014 voor website.jpg 38 1In Greek and Roman mythology, the twin brothers Castor and Pollux were worshipped as the gods who helped shipwrecked sailors and who brought favourable winds to those who made sacrifices to them. Now, they are the namesakes of the latest pair of ships delivered by Shipyard Kooiman.

The ship type of Castor and Pollux is a self-propelled split hopper barge. The vessel does not have its own dredging equipment, but it can be filled by another dredger (or from a shore-based station) and drop its load quickly underwater. Along with Mustang and Duke II, two powerful AHTS tugs from Shipyard Kooiman owned by the same client, the vessels will be used in the oil and gas infrastructure works in waters north of Russia.

Their main tasks will be to dump a protective layer of sand and stones on top of newly laid gas pipelines on the seafloor and for underwater trench backfilling. The ships’ owner is MRTS JSC, one of the largest Russian companies performing turnkey construction of subsea oil and gas pipeline infrastructures.

Three-piece ships

Each of the vessels consists mainly of three pieces: a superstructure and two almost perfectly symmetrical half-hulls. The hulls are joined at main deck level by hinges forward and aft of the hopper. Near the hinge on the main deck, but also in the bottom plating, a male/female tooth connection ensures a strong longitudinal connection between both halves. Located a few metres below either hinge, in a recess outside of the hopper, are the submerged hydraulic rams which give the open/close action to the hull.

The ship’s hull parts are about 15 centimetres apart over the entire length, but a U-shaped rubber tongue-and-groove connection around the hopper ensures that the load stays in the hopper and is not lost while sailing. At the bow,  the starboard hull overlaps the – slightly shorter – portside hull. Besides the esthetical benefit, this feature will also reduce spray on deck in head seas.

hinges

The superstructure is mounted on two conventional hinges on the starboard side, but two hinges with an intermediate shaft on port side. This connection not only allows for the changing distance between port and starboard deck supports when the hopper opens or closes, but also adds some flexibility accounting for the flexing of each hull half when the hopper is filled with a heavy load. It is normal for the hulls to ‘bulge out’ a bit amidships, as there is a lot of transverse pressure of the cargo and the two halves are only held together at the ship’s extremities.

The cabling and piping between the hulls and the superstructure is executed with flexible joints to compensate for the 18-degree variation of angle between hull and superstructure. Freshwater and drainage pipes are well insulated and have electric tracing to prevent freezing in the outside air.

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Ice class

The ships have an ice class notation of 1C, which extends the season for working at high latitudes. They are certified for operation in ice of up to 40 centimetres thick. Visible consequences of the ice class notation are the increased propeller shaft diameters and the size of the gearbox, which should be able to cope with impacts of the propellers with ice. The propellers have a diameter of 1,800 millimetres.

Each hull houses a Mitsubishi main engine of 940 kW at 1,600 rpm and a MAN generator set of 280 kVA. The exhausts pass through a dry damper and go upward through the deck aft of the accommodation, through casings which are fixed to the hulls. These casings are also used for the supply and return air of the engine room ventilation. The electrical installation was done by the in-house electrical contractor in The Kooiman Group: Technisch Bureau Mous. It includes an automation system for unmanned machinery space notation. Each of the hulls has an independent steering gear actuating the rudder with hydraulic cylinders, but the rudders can be electronically coupled as if they were connected with a ram. Castor and Pollux were built under Bureau Veritas class and both sail under the flag of Cyprus.

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Bowthruster

The hydraulic powerpack for the hull-splitting cylinders as well as the electrically driven bowthruster are housed in the portside forepeak, which is a massive space doing little else than providing buoyancy to the vessel. The amount of space is such that it would be possible to retrofit a dredge pump and dredging installation in the starboard forepeak if needed. A rubber ring around the bowthruster tunnel closes the gap between the port and starboard hulls.

Hopper

The 1,500 cubic metre hopper is equipped with a load monitoring system to determine hopper volume and weight. Two fire monitors are positioned on the coamings to clean the hopper of remaining sand. On the port and starboard sides of the hopper are large void spaces. The fuel tanks are located in the engine rooms and forward of the hopper, which gives a means to trim the vessel with fuel. Practically the only non-mirrored item in both of the engine rooms is the fresh water installation. While the portside hull houses the sewage treatment plant for the sanitary discharges, the starboard hull houses the watermaker and water heating equipment. From each of the engine rooms, an emergency escape trunk leads from the lowest level directly to the outside deck.

 

No 2 MbH Maart 2014 voor website.jpg 38 4Accommodation

The accommodation has an office, a captain’s cabin and a chief engineer’s cabin with private bathrooms on the officers deck and three double crew cabins on the main deck. These ships are normally sailed by a crew of eight persons. In addition, there is an extra double cabin on main deck for two guests, such as supervisors of the client. Forward on the main deck are a large store room, a spacious galley and a mess room.

The whole accommodation is provided with airconditioning and mechanical ventilation. The air-conditioning installation is designed to cope with external air temperatures as low as -30 degrees. The wheelhouse on the top deck features electrical floor heating, as do all sanitary spaces, the mess and the galley. A pilot seat is mounted on a sliding track between two consoles, resulting in an unrestricted view through the full-height bridge windows facing forward. The navigation and communication equipment consists of a complete Alphatron package, including Bridge Navigational Watch Alarm System.

 

No 2 MbH Maart 2014 voor website.jpg 38 5Extra work

Castor and Pollux were designed by The Kooiman Group’s own design and engineering office. The four hull halves were built in Turkey, and then towed to Zwijndrecht, where the locally built superstructures were placed on top. The ships are now delivered and will have some extra work on them done before they sail off to the Barents Sea in the spring. One addition includes the fitting of an overflow pipe to each of the hoppers, thus preventing large amounts of water from washing over the deck, and enabling loading spoil with different specific densities.

No 2 MbH Maart 2014 voor website.jpg 38 7Besides a number of refits, the shipyard is also working on the new construction of a multipurpose support vessel, based on the design of the Zwerver 1, delivered in 2007.

Bruno Bouckaert

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