Reconsidering an Innovative Integrated Tug-Barge Concept
During the 1970’s, the engineering department of Marine Industries Ltd of Canada developed an innovative coupling concept for an integrated tug-barge capable of sailing through heavy seas. By late 1982, engineers had built a wooden scale model of the integrated tug-barge that had been shown to Departments of Transport in both the U.S. and Canada, also to Lloyd’s. Due to lack of available funding during a period of high interest rates and an economic downturn, the concept faded into history.
During the early years of tug-barge transportation, tugs occasionally towed barges offshore along the ocean coast. However, most tug-barge transportation occurred on the calm waters of inland waterways. Following the era of paddle wheel river boats, American barge operators learned to lash barges together both sideways and lengthwise to carry mainly bulk cargo along the Mississippi, Ohio and other inland waterways, with tugs simultaneously pulling by cable at the assembly bow and pushing and navigating at the assembly stern. The 1,200-feet of length and 110-feet of width of navigation locks determined American inland waterway transportation.
A tug of 100 feet length could push and navigate an assembly or 15 barges of 200 feet length and 35 feet beam tied three widthwise and five lengthwise through the navigation locks. Ocean sailing provide greater water depth and the economics of tug-barge operation led to the development of ocean tug-barges, with the ocean barge built to the beam and perhaps 60 percent the length of a 15-unit river barge assembly. Oceanic sailing involved wave conditions not encountered along inland waterways and required extensive modifications to the tug-barge coupling, with V-notch and U-shaped indentations built into ocean barge stern areas.
Ocean Tug Barge
While ocean barges sail well in calm seas, severe wave conditions as occurred several years ago on the Bay of Bengal revealed some disadvantages to ocean barge transportation. The severe pitching motions of the tug in severe ocean conditions made sailing across the Bay of Bengal problematic to the point where conventional ships replaced the ocean tug barges.
The Crowley Marine tug barge is designed to sail in waves of 20 feet (6.1 meters) that occur offshore along the American East Coast. However, North Atlantic wind storms can produce wave heights of 40 to 45 feet.
Marine Industries Ltd developed a very deep stern indentation that resembled a short navigation lock extending rearward from the stern. A tug could snugly fit into the equivalent of the navigation and lock itself to the barge using clamps built into the tug bow area as well as on both sides. The Marine Industries integrated tug barge (MITB) coupling eliminated tug pitching motions while its physical strength allowed the tug to exert maximum sideways force for rapid steering input. It was intended to match ship capability while sailing in rough seas that typically occurred off Canada’s East Coast.
Catamaran Tug Barge
A competing design involves a catamaran barge with extended hulls at the stern, providing the equivalent of a short navigation lock into which to partially enclose the tug. Its advantages become evident when carrying lighter weight of bulk cargo and include reduced roll and reduced pitching when sailing directly into waves up to a certain height. Waves that exceed that height can submerge the barge unless an upper level had been built to compensate for severe wave heights. By comparison, the bow of a mono-hull barge would rise upward when sailing directly into a severe wave.
While the catamaran hull integrated tug-barge could carry containers, a single hull design of equivalent length, beam and sailing draft would provide additional space to carry more containers. Likewise, a single hull design would carry greater bulk tonnage than the catamaran design that could operate as a passenger ferry or passenger cruise vessel in several locations internationally. However, the single hull MITB may be the optimal design of tug-barge capable of sailing through the severe wave conditions that occur on the Bay of Bengal and Atlantic Ocean off Eastern Canada.
A barge-to-tug coupling design that reduces or eliminates tug pitching motions relative to the barge offers the potential to increase sailing speed. The catamaran design would have an advantage due to reduced hydraulic cross sectional area at the bow. An electrically powered paddle wheel installed between the two hulls at the catamaran bow could reduce the bow wave by increasing rearward water flow rate between the hulls. The tug would provide the electric power and the tug-barge could offer higher sailing speed with smaller bow wave along inland waterways where vessel bow waves have eroded river banks.
Reduced relative tug pitching on mono-hull integrated tug barges would allow for increased engine power and higher sailing speed on the open. The combined market application would involve the mono-hull barge functioning as both a transportation technology as well as a storage terminal while moored at port. It would offer greater interior storage volume and greater tonnage capacity than a catamaran barge that would serve very different markets that involve less tonnage such as passenger ferry or Ro-Ro vessel along an inland waterway. The mono-hull integrated tug barge would also find application on North America’s Great Lakes.
Shipowners have traditionally sought ways by which to increase earnings by increasing vessel payload capacity. During the early 20th century, one operator on the North American Great Lakes converted a steam-powered ship to sail power, increasing payload capacity by removing boilers, piston engines and coal bunker. At a later time, vessel owners removed diesel engines and fuel tanks to increase payload capacity and converting the former powered ship to a tug-barge after modifying the stern with a U-shaped indentation to match the bow curvature of a tug, a possible precedent for future conversions.
A future ship-to-barge conversion could involve the layout developed by Marine Industries Ltd involving the combination of the U-shaped stern indentation and a pair of short catamaran hulls extending rearward from the stern and built into the main vessel mono-hull. The conversion could involve a redundant Seaway max size of ship where the elimination of relative pitching of the tug could allow for great increased tug engine power, allowing it to propel a much heavier barge at greater speed than present ocean-going tug-barge designs that involve relative tug pitching.
Cruise ships occasionally lose engine power while at sea. A pair of catamaran hulls and U-shaped indentation designed into the stern of the vessel could serve a combined purpose. When the ship of perhaps 650 feet length moors offshore, the stern hulls could serve as a dock for small vessels that shuttle between the ship and a nearby port. A mesh structure could be lowered between the stern hulls and function as an ocean swimming pool. A high-powered rescue tug could easily be coupled to the vessel stern to provide propulsion, the absence of tug pitching allowing for increase sailing speed.
An integrated tug-barge design such as the MITB concept could be applied to the cruise ship industry, with vessel navigation and the tug being remotely controlled from the ship’s bridge. Removing main engines from the ship interior provides additional space for passenger accommodation and related passenger services. Tug propulsion allows for easy exchange of ship propulsion during layovers at main cruise terminals, reducing the risk of power loss while at sea courtesy of specialized engine maintenance at a repair/maintenance facility especially built for such a purpose.
An integrated design of tug-barge that eliminates relative pitching between tug and barge allows for higher engine power in the tug, in turn translating to higher sailing speed on the open ocean as well as easier sailing through severe ocean waves. The concept is applicable to both mono-hull barge designs that include a short twin hull rear catamaran section as well as a full-length twin-hull catamaran barge design built with an extended stern section that includes a curved cross member that matches the bow profile of a tug. There may be present day application for the design concept.
The patent of the MITB may have already expired, leaving the design as an open source concept. The concept may be applicable to short ships (up to 650 feet length) sailing in severe wave conditions or large vessels sailing through calm water.
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.