The early “notched” barge, then ITB (Integrated Tug/Barge), and now AT/B - all grew out of the demand for low cost, safe, reliable, and more rapid marine transportation. While transportation using the conventional towed barges was less expensive than a ship, they were extremely weather dependent making them unreliable in some conditions and they were also much slower than the ships they often replaced.
Towed petroleum and petrochemical barges have historically suffered horrendously as far as weather-induced delays. In some operations in the Gulf, annualized weather delays for long-term operations of some tug/barge fleets averaged 30% or more. In the Northeast, it ran as high as 40 to 50%, especially in the winter.
The primary reason transportation using conventional, hawser towed tug and barges was less expensive than a ship, was related to things like crew and construction costs (especially in the United States Jones Act Trade). As an example a typical U.S. flag, Jones Act Tanker without a large amount of automation to reduce the overall manning requirements would have a crew of about 19 to 27 people. Whereas a typical U.S. flag, Jones Act conventional tug and barge or for that matter an AT/B with a tank barge, with the same cargo carrying capability can operate with as few as 7 people, but seldom more than 10. The difference in crew cost alone is quite large.
Now the task was to develop a design where you could both reduce the crewing (and costs) and get more speed and reliability, the ultimate goal being something akin to ship-like reliability. The initial attempt to solve this problem was the development of the ITB. When that concept fell on hard times, in both the technical and regulatory environs, the response was the continued development of the AT/B.
In 1980--in his previous position at John W. Gilbert Associates in Boston, OT&BE's principal worked with Taisei Engineering’s ARTICOUPLE System on a project for an AT/B chemical carrier for Sun Transport. Sun wanted a tug/barge unit to operate at a certain speed, in all weather, and was ready to take on the regulatory issues. They selected the ARTICOUPLE design as the connection system to use, and set out to design the vessel.
In order to assure that regulators were comfortable with such a vessel, backed by Sun Transport, he approached the Coast Guard with the goal of having the policy toward mechanically-connected tugs and barges changed. Several meetings and exchanges of correspondence ensued. The argument made, was based on safety and weather reliability, and a provision in return, that the tug would be a TRUE tugboat – not a separable engine room. The tug would be able to operate independently of the barge, in all weather, and would thus be "dual-mode".
As a result of those discussions, and the further input of industry and engineering professionals, U.S. Coast Guard NVIC 2-81 was born. This Coast Guard document, which he had helped to create, declared a new official policy on this matter. As long as a true tug was created, meeting all stability requirements as a towing vessel, the tug would be treated as an independent towing vessel for both regulatory and crewing requirements. This NVIC, was and remains, the single most important and influential event in the continued development and deployment of the AT/B in America.
What the AT/B did, was to solve most of the technical impediments to being ship-competitive, while maintaining the crew and capital cost advantage of the tug and barge. What you have, is weather reliability, in a REAL tug and barge. An AT/B is not a rule beater. So for many types of services, the AT/B shines, as compared to a ship.