Express Marine goes with ASD drives on new ATB unitJun 7, 2010 12:00 AM
Just a few years ago, Express Marine, a family-owned tug and barge company based in Camden, N.J., took a bold step with introduction of a pair of ASD z-drive tugs for use in pushing and towing barges loaded with coal. This year the same company has introduced the first of a line of z-drive tugs, each with an articulated coupler system for handling similar large coal barges. The company also introduced a new barge to go with the new tug.
|(Brian Gauvin photos)|
|Freedomâs wheelhouse layout, designed around ASD controls, resembles that of a tractor-style ship-assist tug rather than that of a conventional barge handling tug.|
The first ASD/ATB in North America was the tug Dorothy Ann, built in 1999, and still operated by The Interlake Steamship Company. That tug-barge unit, with 7,200 hp, Ulstein z-drives and a Bark River articulating coupler system, was also believed to be the largest ATB in service at that time, although she has been repeatedly eclipsed by larger and more powerful ATB tugs in subsequent years.
|A new 480-foot coal barge, built by Gunderson Marine, has been matched with the new Express tug, Freedom.|
Express tugs Duty, Honor and Freedom are all equipped with azimuthing propulsion gear provided by Steerprop, a private company based in Finland. The Steerprop system includes a portable control station for use at various positions around the pilothouse or even elsewhere.
Freedom, with a deep, full hull and single-chine hull, and with swept up lines leading towards the stern sections, was launched from Patti Shipyard in October 2009. She was delivered about six months later.
The tug was the third and largest built by Patti for Express, the previous tugs being Duty and Honor. Freedom has such deep draft, however, and is so tall with her elevated pilothouse, that she had to be pushed out of Bayou Chico, where the shipyard is located, to a deep-water dock at Pensacola for installation of z-drive units. Because of a low bridge on the way, she had to be ballasted down and then pumped out to clear the bridge and make it clear of shallow water. A local push boat with spuds was employed for moving the big tug so that she could be held in place by spuds when necessary.
For subsequent operations in deep water, those involved with the project already had a fair idea of how the new ATB unit would perform in various conditions of cargo weight and sea state. Extensive model testing was done in large towing tanks at the Institute for Ocean Technology at St. Johns, Newfoundland. Tests included stability studies of how the barge EMI 2400 would behave when being towed instead of being pushed.
The tug by herself turned in top speeds of 14 knots during sea trials and she was measured as producing 85 tons of bollard pull for ABS inspectors. Aside from machinery, a big part of that full hull is devoted to tankage for 112,000 gallons of fuel, according to naval architect Greg Hughes of the Seattle firm Guido Perla & Associates.
“She had to be fairly tall above the waterline to provide pilothouse visibility, and she had to be fairly full below the waterline for tankage and equipment,” said Hughes.
A couple of unique design aspects to the tug, according to Hughes, are the fresh water wash-down system and the extra filtering capability both for engine room air and sea water for cooling.
Because Express Marine tugs are often operating in areas where there is a lot of coal dust in the air, the company has learned to provide extra filtration for air going into the engine room and for air piped directly to the engine turbochargers. There are separate filter banks for both purposes, located in the exhaust funnel casings. Additionally, since the tug will often be operating in shallow rivers or bays with silty bottoms, she has extra filtering capacity built into her sea chest system, with two sea water intakes, one on the bottom and one on the side.
“With two intakes, we get less velocity of water being sucked in, and thus less of a tendency to suck up silt,” said Hughes. There is also a double straining system at each engine, he added. For actual engine cooling, there is a plate heat exchanger system for each engine, plus channel coolers on the outside of the hull and part of the cooling system involves pipes running through the skeg.
Keeping the coal dust off a tug like this could be a deck hand’s nightmare, but Freedom has that problem licked with installation of a 12,000-gallon fresh water wash-down system that covers virtually the entire boat.
While lacking a towing winch on her stern, as is common practice with many dedicated ATB tugs, Freedom does have a substantial capstan on her stern for emergency towing. She also carries a capstan on her bow for assistance making up to a barge or for other general purposes. Both capstans, along with hydraulic power units and controls, were provided by JonRie InterTech, of Manahawkin, N.J. Edit Module