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| A Crowley ATB makes good speed in coastwise waters off the Florida Keys. (Photo: Crowley Marine) |
This company is building so many articulated tug-barges that it is hard to keep track of them all. Somewhere at the headquarters of Crowley Maritime in Jacksonville, Fla., they must have an entire suite of offices dedicated just to construction of this fleet of 17 modern tug-barge combinations, unofficially scheduled to be completely in service over the next five or six years.
When its full fleet of ATBs is complete, Crowley will be operating one of the largest fleets of such vessels in the United States, in good company with East Coast companies Bouchard Transportation, Penn Maritime, OSG (Maritrans) and K-Sea Transportation.
The last three Crowley ATBs to be built in this fleet will likely be the most powerful tugboats operating in the U.S., with heavy-fuel-burning engines producing up to 16,000 horsepower and dedicated barges capable of carrying up to 330,000 barrels of petroleum or chemical products.
So far, as of spring 2008, there are nine of them in service. The first six, all named as part of the Reliance series, were introduced between 2002 and 2006. They are 127 feet in length with 9,280-hp Caterpillar main engines. These tugs are connected to barges through Intercon articulating coupler systems. The first four were 155,000-barrel capacity barges, and the second three were enlarged to handle 185,000 barrels of product, including petroleum and chemicals. In the past year, Crowley has introduced three new ATBs with near-identical barges but with larger and more powerful tugs named Resolve, Integrity and, just coming into service in early summer, Courage. Still to come, going out to 2010, will be the tugs Commitment, then Pride, Achievement, Innovation and Vision. Lastly, with a planned introduction as far out as 2013, will be three more units with 600-foot barges and 148-foot, 16,320-hp tugs.
Of these 17 tugs, the most recent have expanded accommodation and engineering spaces, in part to make room for tankage and equipment related to burning heavy fuel IFO-380 instead of all diesel fuel.
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| Crowley Maritime’s newest ATB tug Resolve plays host to visitors in Charleston, S.C. during christening ceremonies this spring. When its current building program is over, Crowley will be operating as many as 17 ATB units of varying horsepower and cargo capacity. |
These are good-looking little ships with raised forecastle decks, minimal fendering, low exhaust stacks and a single elevated wheelhouse atop two decks of midship house structures. The latest, Resolve, Integrity and Courage, are 135 feet in length with 42-foot beam. Equipped with a 50-inch Intercon pin system, the tugs have clear aft decks, with all that open space interrupted only by a set of H-bits and an adjacent Intercon capstan. Since the tugs are all SOLAS rated, the next deck up features an outboard-powered utility boat with its own launching davit.
In theory, all of Crowley’s ATB tugs and barges will be interchangeable, but as the tugs and barges keep getting larger, each series seems to take on its own class distinctions. Between the first tugs introduced in 2002 and the last (so far) planned for introduction in 2013, their designed lengths have increased from 126 to 148 feet. Similarly, the barges have increased from 490 feet to 600 feet. Beginning with Resolve, all the tugs are set up to burn heavy fuel, a situation that requires extra training for engineers and a second engineer to be listed among the 12-person crew of those particular boats.
The burning of heavy fuel is perhaps the most significant overall engineering change in the evolution of these Crowley ATBs. The use of heavy fuel oil (HFO) itself adds considerable complexity to the design of a tug’s engineering spaces, but the design challenge becomes all the more complex because of the need to burn both HFO and regular marine diesel oil (MDO). Resolve and her sister ships include tankage for 117,000 gallons of heated HFO and 42,000 gallons of MDO, according to the tug’s specifications.
All tugs beginning with Resolve are set up with Wartsila HFO-compatible engines with all the associated tankage and equipment — not to mention that extra engineer required just because of fuel management demand.
“With the price of fuel just going up and up, we came to the conclusion that we had no choice but to switch to the less expensive heavy fuels,” said Ed Schlueter, Crowley vice president of Vessel Management Services. While Crowley has reported that the cost of its newest ATBs is getting close to $100 million for both tug and barge, it is estimated that these construction costs might include several million extra just for design features and equipment related to heavy fuel use.
Heavy fuel is a thick, black liquid that is often referred to as bunker fuel or bunker oil. Its viscosity is such that it becomes thick like tar in cooler temperatures. It smells like tar at any temperature. And, much more than conventional diesel fuel, it makes a heck of a mess if it gets loose.
Before this fuel can be atomized and sprayed into the cylinders of a big diesel engine, it needs to be constantly heated, centrifuged, filtered, segregated and possibly chemically altered with additives. The complications of those processes, plus other related nuances of fuel management, make it impossible for all but the largest of tugboats to make the switch from diesel to HFO.
The good part about HFO is that it can be bought for considerably less than the price of diesel fuel — anywhere from a third to half the price. For a tugboat that might have tankage for up to 150,000 gallons of fuel, that kind of savings can make a huge difference.
Although the four-stroke, medium-speed Wartsila engines in these tugs can burn both diesel fuel and HFO, the two fuels are distinctly different. Diesel fuel, like gasoline, kerosene and No. 2 heating oil, is known as a distillate — a product of distillation in the refining process. Heavy fuel, by contrast, is known as a residual oil — a left-over product after all the more valuable products have been distilled out of the crude oil.
Much of the difficulty in using HFO involves its viscosity. It is notoriously thick — so much so that if it gets below about 86° F (30° C) it simply won’t pour through a funnel. To make this fuel pumpable enough to be moved around the engine room, and fluid enough to flow through a diesel-engine injector, it is normally heated to temperatures of 150° F or higher. Diesel fuel, by contrast, is a lightweight fuel that can be easily pumped around the boat at any temperature, stored almost anywhere, and fed into the engines without complications.
There are different grades of HFO, and even within the same grade, each batch of the fuel is likely to have a different chemical composition, which is one reason why those individual batches must be stored in separate storage tanks.
While large oceangoing ships often get fuel delivered from barges tied up alongside while at anchor, smaller vessels like tugs can also get their HFO from pipelines at the same refineries or oil terminals where they might be loading or discharging product. Crowley’s Resolve and Integrity have been delivering cargoes to chemical plants, however, so most of their refueling has been done with those possibly misnamed bunkering barges. The Commitment will also be involved in the chemical trade, according to Crowley.
A big issue with the use of HFO is the extra tankage required to store and process the fuel. Extra tanks are often needed because the fuel requires separate tanks for storing fuel from different sources: day tanks, settling tanks, sludge tanks and additive tanks. Since, HFO-burning ships and workboats also need to burn diesel fuel in many coastal situations, they also need sufficient tankage for diesel for main engine use and for auxiliary diesel engines on board.
Tanks aboard ATBs used for storing and processing HFO fuel are heated with in-tank coils or plates, all containing a thermal fluid heated either by electricity or by onboard burners.
With all the complications involved with use of heavy fuel, it makes sense that for every dollar saved on the lower price of fuel, a large portion of the savings — perhaps a third or more — is soaked up by construction and operating costs related to use of the same fuel.
Currently three American companies, Crowley, U.S. Shipping and Overseas Shipholding Group (OSG), are building large barge-handling tugs with articulated coupling systems and heavy-fuel engines.
These tugs are all set up to run on both HFO and MDO with different sizes of Wartsila main engines. Other manufacturers of HFO-compatible, medium-speed diesel engines include MAK (Caterpillar) and MAN.
Crowley’s tugs switch over to diesel fuel any time they are approaching port or operating near-coastal, according to company officials.
As Crowley’s new ATB barges have grown larger, they are also becoming faster. While the company’s 650-class barges are designed for loaded running speeds of 13 to 13.5 knots, the next generation of 750-class barges is expected to maintain speeds of 15 knots in reasonable weather conditions.
That next class will measure 600 feet in length with beams of 105 feet and loaded draft of 35 feet, according to Crowley. They will be among the largest ATBs in operation in North America, employing 64-inch diameter connecting pins, the largest ever manufactured by Intercontinental Engineering, of Kansas City, Mo. The 750-class barges will be capable of carrying 330,000 barrels of petroleum cargoes.
