ATBs Take Over
Articulated Tug/Barge (ATB) sets now dominate
the coastwise refined products trade and are being designed and built on all four coast lines to handle liquid as well as dry bulk and unitized commodities. Looking back, it's hard to believe that the ATB concept was still under scrutiny just two decades ago when their building costs compared to a conventional tanker were still being questioned as was their ability to safely handle product along the open Pacific coastline.
Historically, the ATB is an offshoot of the earlier ITB, or Integrated Tug/Barge, which has seen limited use in both the chemical and dry bulk trades. Although the idea of mating a tug and barge so that the latter could be pushed rather than pulled was developed as far back as the 1880s the first true ITB seems to have been a little vessel called Carport that first saw light of day in the early 1950s when the vessel was introduced to service on the Great Lakes and along the New York canal system.
Although tugs were pushing barges with notched hulls by this time the introduction of Carport saw the tug locked firmly into the stern of the barge to achieve a faster running speed. The idea worked, with Carport able to move at a faster clip than towed barges on the Lakes, but its speed advantage was lost on the New York canal system and the idea was dropped, although Carport itself survived in other trades for another four decades.
ITB Concept Reborn
As US labor costs in the coastal trades increased during the 1960s, and towed barges continued to suffer substantial delays during heavy weather, particularly in the petroleum sector, the idea of a tug pushing rather than pulling a barge was examined again. Even though very large oil barges of up to 250,000 bbls capacity were being built and put into service, the hydrodynamic disadvantages of towing them was becoming highly evident. This brought a return of the ITB concept where a barge would be pushed rather than pulled to enhance both speed and maneuverability.
Because of the lower manning requirement for a tug, ITB owners could also expect a substantial reduction in operating costs. However, the tug designed to act as the open-ocean pusher looked very little like its kin. Some pushers made use of a catamaran hull, with inner hull contours that accepted a tongue from the barge, while others were monohulls that had indentations on each side to accept forks from the barge. In each case, the idea was to physically lock the two units together securely enough for a safe open-ocean passage.
Most were successful but not all shipowners were willing to gamble on the technology. For one thing, it was often difficult to separate the ITB tug from its barge, such as when drydocking was required, and, once separated, the tug often proved it was not designed to operate independently, at least not on the open ocean.
One of the more prominent losses of an ITB while on open ocean transit was that of Oxy Producer, a catamaran-hulled tug mated to the barge Oxy 4102, both owned by the Occidental Petroleum Corporation. This vessel, one of three similar ITBs owned by Occidental, was being used to move super phosphoric acid from the US to the Soviet Union via the Mediterranean and Black Seas. In September 1981, on its second trans-Atlantic trip, Oxy Producer ran into rough weather off the Azores, which caused substantial movement between itself and the barge. Ultimately, the movement opened up holes in the twin hulls of the tug, which then became disconnected from the barge and sank, fortunately without loss of life.
In a less traumatic case, a similar catamaran-hulled ITB tug could not be delivered to its barge because it rolled and pitched too much, requiring that that barge be brought to it, and the two connected before it could be deemed sufficiently seaworthy enough to set off.
Other ITB tugs experienced difficulty disconnecting from their barges because long-unused and seized connecting devices made separation nearly impossible. For these and other reasons, including the fact that the US Coast Guard began to view the ITB tugs as "separable engine rooms" rather than tugboats, ITB units began to fall out of favor, although they are still being considered for some applications, including Gulf of Mexico oil shuttle work.
Development of ATBs
Steadily taking the place of the unwieldy ITBs have been the ATBs, which were introduced in the 1970s when modern coupling systems were developed to flexibly mate a tug to its barge. One of the first of these systems was ARTUBAR, developed by Florida-based naval architect Edwin Fletcher. ARTUBAR was the first "axial'" connecting system in which the tug rolled and heaved with the barge but pitched independently. It made use of large diameter pins, which were extended hydraulically from the tug's hull into holes located in the notch of the barge. These holes were positioned approximately 7 feet apart vertically, at the loaded and ballast draft lines of the barge.
Although first tried in Japan, where the use of notched barges had gained in popularity on the Inland Sea, the first ARTUBAR system was not successful for several reasons, including the fact that the vessels had to be ballasted properly to get the pins and holes to line up. The system also left a gap between the hull of the tug and the barge notch, which had to be filled with pads to prevent excessive wear and noise. The system, although pointing the way for most other ATB connectors, has not been used on a wide scale.
Coupling System Development
After studying the basic principals of ARTUBAR, a Japanese naval architect, Takeo Yamaguchi of Taisei Engineering, developed a new system called ARTICOUPLE that solved some of the earlier problems of ARTUBAR. Yamaguchi's system used the same hydraulically extended pins as ARTUBAR but at the end of each pin was a helmet with teeth. As the tug and barge connected, these teeth came hard against a vertical row of similar teeth attached to the notched walls of the barge. This arrangement allowed the tug and barge to be connected at virtually any draft and also dampened the side-to-side motion that had been experienced with ARTUBAR.
A major drawback of the original ARTICOUPLE system was that hydraulics were relied on to hold the tug in position in the center of the barge notch. Large side forces out at sea could put a tremendous load on check valves holding the rams out, and failure of a hydraulic hose could lead to an unwanted disconnection.
In addition, the total hydraulic system, including accumulators and hold piping, was complicated and somewhat difficult to maintain. Nevertheless, Taisei Engineering has sold more than 200 ATB coupler units worldwide since first equipping the 4,600-horsepower Japanese tugs Hachiko-maru and No.2 Hachiko-maru with ARTICOUPLE in the 1970s. These tugs were employed to push 8,950-dwt barges fitted with handling gear that carried logs from Siberia to Japan in the summer and from Indonesia and Papua New Guinea to Japan in the winter.
At around the same time as the ARTUBAL and ARTICOUPLE systems were being developed, Richard and Robert Bludworth were developing their Bludworth ATB system. This differed from the other two systems in that it used a clamp or caliper fitted to the stem of the tug, which attached to a vertical bar located at the head of the barge notch. Once gripped to the bar, the caliper became the pitching point for the tug. To take up space between the tug and barge notch two pads were mounted on the tug's hull at about midships position which were moveable. As the tug entered the barge notch the pads were retracted. Once the tug's bow clamp was engaged the pads were extended to fill the notch. This configuration allowed the tug to pitch about the bow clamp while the pads limited roll and sideways movement.
The Bludworth system began to be widely employed in the Gulf of Mexico during the latter half of the 1970s, particularly for the movement of oil barges. However, some operational flexibility is lost with this system because the tug cannot perform ordinary pushing work with the caliper attached to its stem while the bar at the head of the barge notch precludes non-caliper fitted tugs from easily moving it. In addition, the system requires a longer barge notch than the other systems, which adds to barge construction costs and decreases carrying capacity. Nevertheless, the Bludworth design remains among the most-applied ATB systems and is one of the easier coupling systems to retrofit to older equipment.
In the mid-1980's naval architect Robert Hill began working with Intercontinental Engineering-Manufacturing Corporation on yet another ATB coupling system: INTERCON. This system incorporated ARTICOUPLE's unlimited draft connection capability but eliminated the hydraulic ram as a means of extension, replacing it instead with a mechanical screw drive that wouldn't fail in case of a hydraulic hose rupture. The first ATB to use this system was Sonat Marine's tug Intrepid coupled to the barge Ocean 250. Since then many INTERCON devices have been sold while several other coupling systems have been introduced, including Finland's pneumatically actuated JAK pin system. At the same time, the older ARTICOUPLE and Bludworth systems have been modified and improved.
All of these couplers provide some sort of hinged connection which allows the tug to pitch independently of the barge yet are strong enough for open-ocean transit. Other simpler systems have been developed for sheltered water use and most ATB barges can be pushed in calm waters by any tug capable of handling it using stay and backing wires.
ATBs Take Off
The Oil Spill Act of 1990 (OPA 90) that followed the Exxon Valdez incident off Alaska in 1989 opened the door to ATB development as operators were forced to look at new equipment. By this time ATBs had proven themselves on most fronts as being equal to, if not better than, a traditional tanker in both construction cost and manning when overall speed was not a factor.
The North Pacific remained a question mark, but Crowley Maritime was sure the ATB could handle the job and began replacing its older coastal tankers with the tug/barge combinations shortly after the turn of the century and now operates one of the largest ATB fleets in the world. Some of these units feature 16,320-horsepower tugs pushing tank barges capable of carrying up to 330,000 barrels of petroleum, equal to the capacity of a modern coastal tanker.
As an indication of how quickly the ATB progressed in the US flag fleet once OPA 90 was enacted, 56 single-hull tank barges of more than 5,000 gt, with a total capacity of about 0.9 million dwt, were replaced by 106 new double-hull tank barges with a total capacity of about 1.7 million dwt by 2010 with almost all of the barges functioning as part of an ATB unit. At the same time 62 single-hull product tankers with a total capacity of about 2.5 million dwt were replaced by only 17 new double-hull tankers with a total capacity of 0.8 million dwt. Today there are more than 130 tank-type ATBs in service with a combined capacity of more than 15 million barrels and the ATB fleet is continuing to grow.
Newest ATB Construction
The latest additions to the ATB fleet will include a set of two 141-foot by 46-foot push tugs designed by Seattle's Guido Perla & Associates and being built by BAE Systems for SEA-Vista, which is also having a number of traditional product tankers built. The 12,000-horsepower ATB tugs will be the first of their type in North America to incorporate twin independently controlled and operated hydro-dynamic Van der Velden Barke rudders, which can be actuated either independently or synchronized. This is expected to give the two vessels enhanced maneuverability and excellent course keeping stability.
In the Great Lakes, Fincantieri Bay Shipbuilding at Sturgeon Bay, Wisconsin has delivered the 5,300 horsepower tug Barbara Carol Ann Moran and the 468-foot by 78-foot tank barge Louisiana to Moran Towing Corporation for operation along the Atlantic Coast and into the Gulf of Mexico. The delivery follows Bay Shipbuilding's earlier completion of an ATB set consisting of the tug Leigh Ann Moran and tank barge Mississippi for Moran and precedes a recently placed order for a 185,000-barrel capacity ATB barge and 8,000-horsepower tug to be delivered by late 2017, an order that also contains an option for a further ATB unit.
On the Gulf Coast, VT Halter Marine's yard at Pascagoula, Mississippi has delivered the 130-foot by 38-foot ATB tug Frederick E. Bouchard to Bouchard Transportation for operation in the Atlantic coastwise trades. The vessel, equipped with an Intercon coupler system, is powered by two EMD 12-710G7C-T3 engines producing 3,000 hp at 900 rpm each and driving twin screws to give a running speed of 14 knots and a bollard pull of more than 83 tons. Its delivery follows that of sister tug Morton S. Bouchard Jr, which was handed over earlier this year.
On the west coast, Vigor's Seattle yard has delivered the 95-foot by 38-foot, 3,000-horsepower twin-screw tug Dale R Lindsey to Harley Marine Services for operation in Alaska where it has been paired with the 20,000 barrel capacity oil barge Petro Mariner using an Articouple coupler system. Harley has also taken delivery of three 83,000-bbl ATB tank barges from the Vigor yard at Portland, Oregon and has recently ordered two Entech-designed ATB tugs from the Conrad yard at Morgan City, Louisiana, a yard that had earlier completed the ATB tugs Emery Zidell, Jake Shearer, and Barry Silverton to Harley.
The latest tugs from Conrad will be paired with two 82,000-bbl, 430-foot-long oceangoing tank barges to be built by the Gunderson yard at Portland. Gunderson previously delivered two 185,000-barrel capacity ATB barges to Kirby Offshore Marine which have since been paired with the 10,000-horsepower tugs Nancy Peterkin and Tina Pyne, both completed by Nichols Brothers Boat Builders on Whidbey Island.