The ATB:A History of the State-of-the-Art

Wednesday, September 11, 2002
(This is Part I of a two-part series on the Articulated Tug Barge from Robert P. Hill. Part II is scheduled to be published in the September 23 edition of MarineNews.) The American coastwise shipping business has grown in a way that differs from many other nations. The high cost of manning and building ships has led over the years to a coastwise transportation network dominated by tugs and barges. But this system of water transport, has been lacking in several respects: • Weather delays caused by the uncertainties of towing of a barge in heavy weather, especially a barge carrying petroleum and chemical products, are a constant problem. Towing a large barge in heavy seas just off the coast is a risky business. The possibility of parted towlines, (not to mention the reality in several hundred cases) and lost, drifting barges, has haunted tug and barge operators - as well as the customers they serve - for years. • Towed barges are extremely slow vessels, and as the cost of a tug/barge has risen, the need to move faster has also risen. • Towed barges are hard to control in congested areas, and often require helper tugs in port. • Towed barges must also often wait for seas to subside before attempting to cross bars at harbor entrances. Once in the harbor, they must switch between towing and pushing gear. This adds delay time and further operational risk. • Changes in petroleum terminal operations which are built around reduced inventories, and "on-time" delivery of replacement product, was in conflict with the towed barge's inherent lack of reliability where scheduling was concerned. The towed barge was influenced negatively by weather, sea conditions, speed variations, and traffic conditions. All of these things conspired to make a towed barge's ETA subject to constant change - sometimes by days.

Towing tugs too, were often smaller vessels, with cramped quarters, and the ride the crew experienced at the end of a towline was anything but comfortable. Yet, even given these various negative factors, the almost universally lower costs associated with barging have generated the business that sustained the industry for well over 100 years. As of the early 1990's, towing technology - which in the 1990's still operated with the same procedures as it did in the1890's, still moved most American coastwise cargoes. But ships in general, were still markedly more expensive to build in the 80's than in previous decades, and the larger crews and pilotage and assist tugs needed for a tanker of any size drove up the cost of operation. Through visionaries like the Hoopers of Interstate Oil Transport, who built the "Ocean" class barges from 90,000 up to 250,000 bbl, and Spentonbush, with the building of the HyGrade 95, barge sizes increased through the 70's and 80's, to where tanker-sized barges were now available. This size increase further eroded the tanker position, and upped the ante to where the small tankers such as the ones Sun built, were just not economical competition to these slow, large and lumbering barges. They were effective competition however, to the smaller towed barges. But over time, as oil companies closed smaller, less efficient terminals, the small capacity of these ships just could not be put to economical use serving larger terminals. Attempts To Make Ships Of Barges The hydrodynamic disadvantages inherent in towing a barge at sea were well known for years. The evolution of the towed barge was stalling, as designers had gotten to the point of wringing every fraction of a knot possible out of existing designs. So over time, attempts were made to improve this situation by pushing the barge instead of pulling it. As early as the 1880's, people were patenting various designs that linked a powered vessel and a non-powered vessel. These were however, largely "rigid" systems, wherein the combined unit looked and behaved, like a ship. This was the genesis of the ITB.

The first practical application of the technology came in the 1950's, when the ITB "CARPORT" was built. This vessel, which essentially was a tug locked onto a stern "ramp" of a notched barge, traded successfully on the New York canal system and the Great Lakes for many years, hauling grain products. However, for various reasons, she was not repeated in quantity. The trade in which she engaged was also populated by conventional tugs working with "notched" barges, and some towed barges. Such units were simpler, less costly to build and more practical. The added speed CARPORT was able to attain was of little advantage in the New York Barge Canal, where locks and narrow channels greatly restricted unit speed. Contemporaries of the "CARPORT" which were operating in the New York Barge Canal were the conventional tugs pushing various barges in a stern notch, linked together by cables. (Actually, "backing wires"). As such they were able to be assigned where needed in a mix and match fashion and the "rigid" ITB tug and barge, found itself facing the same problem it's larger ship cousins faced. A lack of flexibility vs. an independent tug and barge. However, as efficient as the notched barge was for inland operation, the notch was really not developed on canal barges to improve the ability to push offshore. Rather, the notch was a concession to the limited length of the New York Barge Canal locks, and the notch depth was set to allow the tug and barge to fit in the lock together. As economics drove the need for larger capacity barges, the notch gave way to added cargo capacity, and double-locking began to appear in various forms. The barge HyGrade 42 was among the first to eliminate the notch, and it was equipped with a Schottel over-the-bow azimuthing drive. This allowed the barge to be sized to the full dimension of the locks, and the Schottel drive was used to move the barge in and out of locks, while the tug was locked through behind it.

Of course, the elimination of the notch added capacity, but it did nothing for pushing at sea. Even with their relatively deep (for that time) notches, the canal units towed when they got to large lakes, and when they were required to travel coastwise. So, the stage was set for someone to come along and take the large towed barge, and the canal notch - and find a way to make them work at sea. Interstate, with its new large barges, did in fact manage to push cross-Gulf, and to New England from Chester, in the notch in seas up to six ft. using face wires. Moran also did some open water pushing with the large Atlantic Cement barges, Alexandra, Adelaide and Angela. However, the majority of the time was still spent on the hawser dealing with weather delays. The "someone" who was determined to change all that, appeared in the form of two contemporaries - Edwin Fletcher and the Bludworths. The ATB Solution A Florida Naval Architect, named Edwin Fletcher, sowed the first seeds of that solution. His "ARTUBAR" system, conceived in the early 70's, was the first single-degree-of-freedom system to be applied to a large tug and barge. Originally tried with limited success in Japan, the system was eventually applied here in the United States. The road to application in the U.S. was a difficult one. Prevailing U.S. Coast Guard attitudes at the time were a great hindrance. Fletcher's system and its' ship-like seakeeping capability was seen as just that - creating a ship in the USCG's eyes, and unreasonably large crews and regulatory burdens were going to be placed on the design. At the same time, the Bludworth system, with less emphasis on its' seakeeping abilities, was finding at least limited success in evading USCG regulation. However, in 1981, the author, working on an ATB project for Sun Transport, worked with the USCG to help formulate a new policy toward what would become the ATB - an enlightened policy whereby the inherently greater safety of pushing with a mechanical connection - on a true tug and barge - was seen as a positive development. Regulations reverted to the "norm" for a tug and barge built this way, and Artubar was allowed to implemented. While there are not a large number of these designs at work, the units all continue in service, and the principal of the establishment of a transverse pitch-axis through the tug in the barge notch, led to the development of other types of connectors.

Over the years, the pioneering work in the ARTUBAR system and the work of the Bludworth family in developing their flexible push system - and the work of Takeo Yamaguchi of Taisei Engineering, with his "ARTICOUPLE" system, slowly began to cause people to take a second look at mechanically linking a tug and barge. But this time, the idea would be to try and use a real tug and a real barge, as opposed to trying to create a "separable ship". . If the barge hull could be optimized for pushing, and speed increased, and weather delays ended - then maybe the barge could be resurrected in a new form which was at the same time familiar to operators, regulators and shipyards. In his early model testing, Fletcher proved his point well. But the industry was historically a conservative one and acceptance was slow. The connecting draft limitations of Artubar's concept put off oil barge operators, and until the Bludworth System began to be widely applied in the latter half of the 70's, ATB development moved at a slow pace. Companies like Interstate Oil Transport continued to spend money model testing various ideas for an ATB. Their work focused on creating a system capable of connecting at any relative draft of tug and barge.

This changed in 1981, when the USCG created NAVIC 2-81. Under this NVIC tug-barge units were split into two distinct groups; Push-Mode ITB's and Dual mode ITB's. These rules now recognized the unique safety advantages of mechanically connecting a tug and barge at sea, and these improvements were given full recognition and approval. As long as one created a real tug and a real barge, the regulatory and manning standards for an everyday tug and barge, were applied. This is the "Dual-Mode" ITB. (Which we also refer to as the "ATB"). For those units where the tug was in fact in essence a separable engine room, the term "Push-Mode" ITB applied and the regulatory and manning situation followed more along ship lines. Save for occasional updates, this NVIC still stands as official USCG policy. Then in the mid-80's, the author approached the Intercontinental Engineering-Manufacturing Corp. in Kansas City, MO., with an idea for a new connection system, that solved many of the differential loading/draft problems and mechanical problems of the current systems available, From this collaboration the "INTERCON" system was created. Engineers at Intercon, working with the author, along with naval architect Corning Townsend, and the Netherlands Ship Model Basin, developed the all-important mechanical details of the system. Later in the process, the engineering staff of the first customer, Sonat Marine, also contributed to the research effort as their INTERPID/OCEAN 250 combination was to be the first application of the system. The new Intercon device incorporated Articouple's unlimited-draft-connection capability while eliminating the hydraulic ram as a means of extension, replacing it with a mechanical screw drive. Concurrently, the Bludworth and Artubar designs were being improved, and the Articouple system was gaining wide acceptance overseas. Thus, the successes began to outweigh the problems, and more and more operators began to see the ATB as a true transport solution. New connection methodologies have been devised in the person of the JCOMARIN system from Finland, the new improved Articouple designs, and improvements to the Bludworth system. Intercon as well has devised new versions of its' system.

All of these systems provide some sort of hinged connection, which allows the tug to pitch independently of the barge. These systems give the ATB much better sea-keeping ability than the previous ITB systems or conventional towed barge systems. So much so, that, in fact vessels equipped with systems such as Intercon, and Bludworth, have proven to be a very good, safe, less expensive alternative to a ship in many services. The sea-keeping ability of the ATB is so good that many operators say they push virtually all the time. Though ATB tugs are able to tow, few ever do.

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