Overseas Shipholding Group (OSG) America, a subsidiary of one of the largest tanker companies in the world, has introduced what may be the largest articulated tug-barge unit operating in the world.
|(Brian Henesey photos)|
The 12,100-hp OSG Vision is the first of two similar tugs being constructed by VT Halter Marine of Pascagoula, Mississippi, which is also constructing matching barges for the tugs. With capacity of 342,000 barrels, these barges are also possibly the largest in active service in the U.S. or the world. The cost of each combined ATB unit was originally reported at about $75 million.
First of the series, OSG Vision and her barge, OSG 350, are already at work lightering crude oil tankers on Delaware Bay, having been delivered in early 2010. The first tug/barge combo loaded its first cargo on the Delaware in mid-April. The second is due for delivery later this year. Both of these ATB units are slated for Delaware Bay lightering work.
The specialized tug OSG Vision, is 153 feet in length with a beam of 51 feet and draft of 26 feet. The tug is fitted with one of the largest tug-barge coupler systems made by Intercontinental Engineering of Kansas City, Mo., and her Wärtsilä engines are set up to burn either marine diesel fuel or heavy fuel oil.
The barge OSG 350 is 655 feet in length with beam of 105 feet and a designed capacity of 342,000 barrels. Both of the new barges, with 45,556 dead weight tons capacity, are being completed by VT Halter at their Pascagoula facility. The design of this particular ATB unit has the tug almost completely inserted into the expansive barge notch. Design information about the unit indicates that this feature is necessitated by the need to deploy mooring lines between the outboard quarter of the barge and the ship to be lightered. If the tug, with two massive funnel casings and a deck crane located aft of the elevated tower, were to project out very far from the notch, that would interfere with mooring ability.
The tugs in this series were under contract to be built at Bender Shipbuilding & Repair Co., in Mobile, Ala. After the Bender shipyard filed for bankruptcy last year, however, OSG made the switch to have the tugs completed at the VT Halter yard in Mississippi. Bow sections of the first two barges were built at the Bender yard, but later launched and towed to Tampa.
OSG Vision and her matching barge are part of a series of “Costwise” class design produced by Ocean Tug & Barge Engineering Corp. of Milford, Mass. By their size and power alone, they are among the most spacious and ship-like tugs afloat. Vision, with its medium speed Wärtsilä 9L32 engines, each rated at 6,050 hp at 750 rpm, gets its propulsion power from a pair of Lips controllable pitch (CP) propellers in Kort nozzles with independently steerable triple-shutter rudders.
The tug has a single-chine hull with little or no sheer, minimal fendering and a large elevated pilothouse with 77 feet height of eye. The tug has voluminous interior spaces including expansive crew accommodations, storage and machinery spaces, electrical control room, workshop and repair spaces, engineering offices, a paint locker and even an exercise room. The captain’s suite takes up almost an entire deck in the elevated tower.
Of course any tugboat with capability of burning heavy fuel oil (HFO) needs a lot of extra space. Always an issue with the use of HFO is space for extra tankage required to store and process the fuel. Among the tanks needed for these dual-fuel OSG boats, for instance, are tanks for storing fuel from different sources, day tanks, settling tanks, centrifuge tanks, mixing tanks, and sludge tanks. In addition, all the usual tankage is required to accommodate the storage, processing and burning of regular distillate diesel fuel as well as the heavy fuel.
The fuel management infrastructure is all the more complicated because heavy fuel, from the moment it comes aboard, needs to be kept heated, typically with in-tank coils and plates containing a thermal fluid. In addition, much of the heated storage and processing equipment needs to be separate from the engine room.
One naval architect likened the entire set-up to a small refinery dedicated to the processing and refining of two different fuel sources, one of which has to be constantly heated. In some cases an extra engineer might be needed just to tend to the 24-hour fuel needs of the engine room.
OSG Vision has tankage for 214,000 gallons of HFO, and 60,500 gallons of marine diesel fuel. It is estimated that a 12,100-hp modern ATB such as OSG Vision might consume 35 tons or 12,100 gallons of fuel per day when running at full operation.
Several other types of ATBs have recently been introduced with ability to burn HFO as well as diesel fuel. These include Crowley Maritime’s 9,000-hp ATBs and U.S. Shipping’s 12,000-hp ATBs. All of these have been set up with Wärtsilä HFO-compatible engines with all associated tankage and equipment.
There may be a half dozen U.S. and Canadian ATBs already using heavy fuel, but OSG Vision’s use of controllable pitch propellers is among the first within the ATB fleet. The tug is fitted with a pair of Lips CP propellers, housed within nozzles. Engines have Wärtsilä reduction gears, but no reverse gears because of the presence of CP propellers. Another North American ATB newly outfitted with CP props is the Canadian tug Victorious, recently put into service by McAsphalt Marine Transportation (see story in this issue).
While there are many advantages (and disadvantages) to controllable pitch propellers, the primary benefit for ATB combinations might be the ability to match propeller pitch to the weight of a barge being pushed as it is loaded, empty or in ballast.
“Normally, with a fixed-pitch propeller, we usually size and pitch the wheel for a loaded barge, but with the CP prop you can tune the propeller to match exactly what the barge is requiring at any given time,” said Robert Hill of Ocean Tug & Barge Engineering. The result could be optimum speed and fuel efficiency not only when loaded, but potentially in all modes of operation, he added.
OSG Vision and barge OSG 350 also incorporate the largest ATB coupler system currently installed in a vessel by Intercontinental Engineering. The system employs 64-inch diameter pins, projected out from the sides of the tug and engaged with receptacles on either side of the tug’s notch. Only a half dozen other 64-inch Intercon coupler systems have previously been installed. The coupler system on these tugs includes a provision specifically designed for loading in at-sea conditions as in lightering operations, according to Clare Kuhlman, chief engineer for Intercon. The system, called the Wave Connection system, allows the tug’s crew, at the touch of a button, to quickly withdraw the pins a short amount, allow the tug’s buoyancy to naturally seek a new level for engagement, and then to automatically reengage. The entire realignment process takes just a few seconds, according to Kuhlman.
Despite her impressive size and far-reaching machinery installation, OSG Vision is destined, at least for the immediate future, to spend her days trundling oil from super-sized tankers anchored in Delaware Bay to any of a half-dozen refineries just a few dozen miles up the Delaware River near Philadelphia. The tankers, barges and associated amounts of oil are huge, but the tug’s crews won’t be getting much offshore time, except for the occasional run up to New York or some other East Coast refinery.
More than a million barrels of crude oil are transported up the Delaware each day, most of it by barges like OSG 350. This makes the Philadelphia area the largest center of crude oil importation on the East Coast and among the busiest in the country. OSG, which acquired Maritrans Operating Partners in 2006, is the dominant lightering company on the bay.
OSG has several ATB combinations engaged in Delaware Bay lightering with crude oil being delivered to any of six operating refineries in the region. In addition to its larger size, the new 342,000-barrel barge contains the latest in vapor recovery and vapor balancing technology, while the tug Vision has equipment for new levels of emissions reduction from its machinery.
OSG, which operates a worldwide fleet of more than 100 tankers, also operates more than two dozen U.S.-flag vessels, about half of which are ATBs.