Crowley’s ATB Legacy is ready for work
Legacy has left Ancortes to pick up Crowley barge 750-1 before starting work in the Mexican Gulf.
The oversized Articulated Tug & Barge (ATB) tug Legacy has left the yard of its builder, Dakota Creek Industries in Anacortes, Washington USA for Gulfport in Mississippi.
Legacy is the first of a series of three new Crowley 750 Class ATB units. The vessels will operate in the Gulf of Mexico starting later this year. Coupled to purpose built barges the three ATB tugs will provide a combination of a huge carrying capacity, seaworthiness and speed so far unmatched by any other class of ATB.
The three Crowley 750 Class barges are being constructed at the VT Halter shipyard in Pascagoula, Mississippi. Designed to carry 330,000 barrels of refined product, their double skin hull construction complies fully with the Oil Pollution Act of 1990.
Legacy, and sister ships Liberty and Legend still under construction, are the largest ATB tugs ever built and are designed exclusively to operate ‘in the notch’ with its mating barge using the ‘Intercon’ coupling system.
The tugs were designed by Vancouver based naval architects Naviform and meet all of the SOLAS and ABS criteria applicable to an ATB combination of this type. Legacy is 45.11m in length overall, has a beam of 18.29m and a depth of 9.14m.
An interesting and unique feature of the tug’s design is the configuration of the propulsion system and machinery spaces. Two electronically controlled Wartsila 12V32 4SA 320 main engines generate a total of 16,320 bhp to drive a pair of controllable pitch propellers. The engines are capable of running on heavy oil and give the ATB a cruising speed of 15 knots. Each engine is housed within its own engine room with much of the drive line enclosed in a unique pod external to the main hull structure, one on either side. A bulkhead divides the tug’s port and starboard engine rooms, allowing the vessel to continue underway on one engine in the event of a catastrophic incident, such as an engine room fire. The steering system features oversize rudders to achieve the best possible handling characteristics and is also designed to enable a degree of redundancy. This arrangement is believed to be the first its kind to be built to ABS R2 classification, which provides a higher level of redundancy than found on a standard tanker or ATB.
The tug has a deep forecastle designed to match the notch in the stern of the barge and accommodate the port and starboard pins of the ‘Intercon’ connection. The latter are mechanically operated and engage in a vertical rack of teeth located in the notch of the barge. Connection to the barge can be achieved regardless of draft or trim and engagement and disengagement can take place without the crew on deck. Once engaged there is no hull contact between the tug and barge and the tug can pitch independently of the barge but not yaw or roll.
A major concern in the planning and equipping this new series of ATBs has been the reduction of noise onboard the tug and measures have been taken to increase stability and crew comfort. The tugs have a water-foam fire fighting monitor and remote radar gauging in all cargo and ballast tanks aboard the barge.
Although ATBs are few and far between in Europe they are used extensively in and around the USA. Legacy’s sisterships Liberty and Legend and their respective barges 750-2 and 750-3 are due for completion in late 2011 and during 2012 respectively.
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