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Integrated Tug Barge (ITB) / Tug/Barge Unit (TBU)

Integrated tug/barge units are used widely in the US Gulf and east coast offshore trade. The stern is notched to accept a special tug which can be rigidly connected to the barge, forming a single vessel. The barge is built in the molded form of a normal ships hull. In the most efficient systems, the tug is attached by trunion mountings protruding from the bow into sockets fitted along the inside of the barges recesses. Directional stability and control underway is far superior to that of a towed barge. No particular changes in the size or shape of the tug are required except for a higher pilot house, needed for improved visibility.

The word barge evokes the image of a small, shallow draft unit with very limited carrying capacity that requires extensive shoreside equipment to be unloaded. That image is correct for the inland rivers and they offset the smallish carrying capacity of individual barges by combining 15-20 units into one tow.

However, on the Great Lakes and the US coasts and non-contiguous trades, the word barge has a much different meaning. Here, barges are large units with carrying capacities that rival our largest self-propelled units. The 1,000-foot-long tug/barge PRESQUE ISLE has been serving the Great Lakes iron ore, coal and stone trades since 1973 and routinely carries more than 2.6 million tons of cargo each year. The PRESQUE ISLE was the second thousand foot vessel on the Great Lakes (the Erie-built STEWART CORT which came out in 1972 was the first). The integrated tug/barge PATHFINDER, owned by the Interlake Steamship Company of Cleveland, is longer than all but one of Cleveland's skyscrapers are tall. Interlake invested $23 million in this vessel to meet increased demand for stone and other cargos on the Great Lakes.

Tug Barge Operations

According to MARAD, as of October 1, 1989, the U.S. oceangoing merchant marine fleet consisted of 661 active and inactive vessels. Of these, 383 are active ships; 109 of which participated in the food aid preference trade in cargo preference year 1987-88. The 109 ships consist of 70 liners that carry processed goods; 22 tankers and 16 bulk carriers, both of which carry bulk commodities; and 1 integrated tug/barge. (In addition, 44 oceangoing tug/barges also participated in food aid shipments.)

The sustainment phase of strategic sealift refers to shipping provided by the U.S. Merchant Fleet. That fleet consisted in 2001 of 106 ships: 4 breakbulk ships, 5 bulk carriers, 79 containerships, 4 lighter aboard ships, 4 roll-on/roll-off ships, 9 vehicles carriers and 1 integrated tug barge. The 106 ships, combined, provide an estimated 18.8 million square feet of military useful capacity.

In FY 2000, the Cargo Project Office used six long-term charters to meet unique missions that liner services could not support. These missions included a multi-purpose ship for Diego Garcia support; an ice-strengthened ship for support of the U.S. Air Force at Thule, Greenland, and the National Science Foundation at McMurdo, Antarctica; a combination ship to move ammunition throughout the Pacific; a Jones Act ship to support the Hawaiian Islands and U.S. territories in the Mid-Pacific and a tug/barge and a small supply ship to support DOD missions in the Caribbean.

In FY 2002, four long-term charters met unique missions that liner services could not provide. Break-bulk ships carried supplies and equipment to Diego Garcia; an ice-strengthened ship supported the U.S. Air Force at Thule Air Base, Greenland, and the National Science Foundation at McMurdo Station, Antarctica; a Jones Act ship, required for U.S. port-to-port voyages, supported the Hawaiian Islands and U.S. territories in the Mid-Pacific; and a tug/barge asset supported Navy operations in the Bahamas.

The four lines in the mainland-Puerto Rican trade are Horizon Lines and Sea Star Line, which operate self-propelled container ships, and Crowley Liner Services and Trailer Bridge, which are tug-and-barge operators. Sea Star operates four roll-on, roll-off container ships. In 2005 Crowley, the highest-volume carrier in the trade, chartered a lift-on, lift-off barge from Trailer Bridge to test that method of transporting automobiles from Jacksonville. With its oldest two barges approaching their 40-year projected life by 2010, by 2005 Crowley was already planning its next generation of barges to replace its 10 triple-deck ro-ro barges.

Trailer Bridge's vessels are giant barges, including two 736 foot long, three story vessels that are the largest barges in the world, that are towed with large 8,000 horsepower ocean-going tugs. Trailer Bridge, which has seven ro-ro barges averaging only 8 years old [as of January 2005], operates four tug-and-barge sailings a week out of Jacksonville. Trailer Bridge's Founder, transportation pioneer Malcom McLean, was the inventor of container shipping. The company was the first to use the 53-foot high cube container for Puerto Rico -- giving shippers over 50% more capacity than the standard 40-foot container. In March 2001 Trailer Bridge finalized a long-term agreement with Moran Towing Corporation to exclusively utilize Moran's Heidi class 4,350 horsepower tugs to pull all four of the TBC's deployed by Trailer Bridge. This decision followed the excellent results produced through the Company's use of two Heidi class tugs.

In July 1996 Trailer Bridge took redelivery of the Jax-San Juan Bridge [ex-Resurrection Bay] following insertion of a 250' midbody. This second vessel is now identical to its sister vessel, the San Juan-Jax Bridge [ex-City of Seward], and through lengthening have become the world's largest roll-on/roll-off trailer barges. C.R. Cushing and Co. of New York designed the mid-bodies and Trinity Marine Group of Gulfport Mississippi was contracted to build and insert them. Trinity's Gulf Coast Fabrication, Inc. fabricated the mid-bodies in Pearlington, Mississippi and Trinity's Gulf Repair, Inc. performed the cut and insertion in New Orleans. While construction of the mid-bodies began months ago, actual shipyard time for the vessel cut, midbody insertion and redelivery was less than 60 days. Trailer Bridge maintained weekly service during this time with a replacement vessel.

In July 2001 Trailer Bridge announced that it had finalized a long-term agreement with Crowley Marine Services. Under this agreement, Crowley Marine Services will provide two Invader class 7,200 horsepower tugs to pull Trailer Bridge's Triple Deck Roll On/ Roll Off vessels between Jacksonville and San Juan. The first Invader class tug began service on 20 July 2001 from Jacksonville, towing the SAN JUAN JAX BRIDGE. A week later, the second Invader class tug entered service with the JAX SAN JUAN BRIDGE.

In July 2004 Trailer Bridge, Inc. entered into a definitive agreement to purchase 100% of the stock of Kadampanattu Corp. ("K. Corp.") for $32 million. K. Corp. is wholly owned by the Estate of Malcom P. McLean, Trailer Bridge's founder. K. Corp. owns two 736 ft, triple-deck roll-on, roll-off barges with a capacity equivalent to 405 53-ft trailer units. These vessels, built in 1984 and lengthened in 1996, are towed by very large ocean-going tugs and are believed to be among the largest non-self propelled vessels in the world. The two K. Corp. vessels were chartered to Trailer Bridge for $7.3 million per year until 2010.

The roll-on, roll-off vessels have three decks, each of which is 736' long, and are older than the Triplestack Box Carrier(R) vessels, which are single deck and 400' long. The cost of the 2005 dry-dockings of the roll-on, roll-off vessels were higher than they would have otherwise been had more costly measures been taken during the last dry-docking done five years ago when the Company's liquidity position was severely constrained.

Tug Barge Design

There recently has been an increased interest in the use of tug barge combinations for marine transportation. This interest has prompted the development of a variety of tug barge connection systems incorporating innovative design features. Although the self-propelled vessel is far from obsolete, the trend in the maritime industry, especially in niche or specialized trades, is toward the integrated tug/barge. The class of vessels which has evolved employs a variety of arrangements and designs, some of which simply replace or supplement conventional wire rope arrangements. The safety of these arrangements depends on proper design, fabrication and maintenance; aspects which raise considerations long resolved for the wire rope systems they replace.

The Tug and Barge system offers numerous advantages over self propelled vessels. They require 1/3 less crew and have 1/2 the fuel consumption per mile. Tugs typically have crews of six versus a crew of 23 on the self-propelled vessels. On top of that, tug crew members have a different wage scale relative to crew members on self-propelled vessels. They also feature a lighter environmental footprint, lower construction costs, maintenance & dry docking fees, and are more conducive to moving larger freight. Tug/barges move at nine knots, half the speed of self-propelled vessels, but this slower speed results in much less fuel consumed per mile. In addition, both new construction and maintenance costs on barges are well below similar size self-propelled vessels.

Various systems have been proposed for replacing the traditional towing of barges on a line, which systems fall into the general category of vessels consisting of a tug positioned behind the barge in a pushing mode. These systems fall into two main classes: non-rigid connection systems allowing a certain degree of freedom between the tug and the barge and rigid systems in which all relative motions between the tug and the barge are restrained allowing both to act as a single vessel unit in a seaway.

In the rigid systems, there are also two main classes: integrated constructions where a tug fits snugly into a deep notch in the stern of the barge and an integrated construction where the tug-barge combination consists of incorporating a twin-screw catamaran tug that fits closely over and around the especially contoured barge stern which is tapered and sloped to form a wedge. In the first instance, it has been observed that, although the integrated system is relatively successful, tugs, in some cases, have stability problems when operated independently and, in other cases, are too specialized for normal service. In the second instance, it has been found that the form of the tug hull is quite unsuitable for even occasional independent operation as a tug boat.

The Coast Guard considers an Integrated Tug Barge (ITB) to be any tug barge combination which, through the use of special design features or a specially designed connection system, has increased seakeeping capabilities relative to a tug and barge in the conventional pushing mode. Because of their increased seakeeping capability, speed and cargo capacity and because of their dependence for safe operation on the proper functioning of specially designed features, the Coast Guard considers it necessary to publicize the inspection and certification requirements applicable to ITBs.

Typically, the barge used in such combinations is provided with a slot in the stern portion thereof which receives the bow of the corresponding tugboat. A mechanical connection between the tugboat and the barge has been generally employed to securely and releasably join the two vessels into the composite structure.

The use of conventional bollards in combination with suitable lines and quick release means to connect a tugboat and a barge is known in the art. Such connecting apparatus, however, is fraught with problems which inhibit its usefulness. For example, the tugboat must be properly aligned with a slot prior to entry thereinto. In addition, the requisite lines are susceptible to failure in rough seas, thus creating a potential for disengagement between the two vessels. Further, a connection system employing cables conventionally requires personnel on both vessels cooperating with one another properly to position and tension the cables.

It is also known to employ hydraulically operated members carried by a tugboat to facilitate the connection of the tugboat to a barge. Such hydraulically operated apparatus, however, is typically provided to wedge the tugboat and barge together thereby retaining the two vessels in their composite relationship even in the face of rough seas. Leakage of hydraulic fluid or loss of hydraulic pressure presents a potentially severe problem in that it may allow loss of latching force between the two vessels. Another common problem with hydraulic wedging apparatus resides in the fact that the vessels must be properly aligned before the hydraulically actuated members can be effective to secure and position the two vessels relative to one another. As with the wedging mechanisms, however, the loss of hydraulic pressure, leakage of hydraulic fluid or misalignment of the vessels may present intolerable problems.

It is also known to employ threaded-type connections between two vessels. Such connections, however, are cumbersome, require previous alignment between the two vessels and do not permit the use of rapidly actuated members.

Push tug-barge combinations are generally unable to tolerate high seas. To rectify this problem, various means have been proposed, some of which permit some relative movement between tug and barge. A type of such thrust transmittal means is generally referred to as articulated couplings. All of the designs heretofore known have however included certain inherent shortcomings. Among those designs shown in the above cited prior art patents, several include mechanical coupling retainer means as part of the thrust transmittal system, such that the thrust transmitting members include securing means to prevent coupling disengagement. Such means interfere with the rapid disengagement of the tug and barge, should such disengagement become necessary under emergency conditions. Perhaps for this reason, the Coast Guard has indicated that a tug-barge combination with such coupling means must be considered an integrated unit, with attendant inspection, certification and crew requirements beyond that necessary for tug and barge ordinarily.

Further, a commercially operating push tug-barge arrangement is known in which thrust transmittal is accomplished through members projecting forwardly from the tug and rearwardly from the barge, the mating ends of the projecting members including a cylindric convex surface member at the end of the rearwardly projecting barge piece and a cylindric concave surface at the forward end of the bow piece. This arrangement permits articulation between barge and tug in a vertical plane about the point of engagement of the thrust transmitting device. A notch with rearwardly extending sidewalls on the barge and fenders between the tug and barge prevent relative roll in this system.

An Integrated Tug Barge is any tug barge combination in which a specially designed propulsion unit (tug) is mated to a cargo unit (barge) of a compatible special design or where a propulsion unit (tug) is mated to a cargo unit (barge) with a specially designed connection system such that the combined unit has operating characteristics and seakeeping capabilities which exceed, under all anticipated weather conditions, those of a tug and barge where the tug is secured in the barge notch or on fenders by means such as wire rope, chains, lines or other tackle now commonly used in offshore towing.

This definition applies to vessel construction standards, inspection, certification and manning and may not be applicable with reference. to other regulations and statutes. For example, a tug barge combination will be considered an ITB, when the tug: cannot operate with barges other than those barges specifically designed for joint operation with the tug; or cannot engage in hawser towing (does not meet the towline pull stability criteria or does not have necessary towing equipment installed); or requires significant reinforcement of internal structure to accommodate shelves, wedges or other interlocking mechanisms; or is restrained in the notch of a barge to the extent that the speed and weather operating capabilities of the combined unit approach those of a single vessel.

The Coast Guard recognizes that there are significant differences among the various vessel combinations covered by the ITB definition. For this reason, ITBs are divided into two groups: Pushing Mode ITBs and Dual Mode ITBs.

Pushing Mode ITBs are those ITBs where the tug remains in the combined configuration or has the capability to remain in the combined configuration under the environmental conditions which a ship of comparable size could anticipate on a comparable route. Pushing Mode ITB tugs, in general, are not equipped or capable of separating from the barge and towing on a hawser. Safety regulations and statutory requirements dependent on tonnage measurements are applicable to Pushing Mode ITBs as determined by the aggregate tonnage of the ITB combination.

A Pushing Mode ITB has the characteristics of a ship of comparable size in that it has a similar seakeeping capability and it remains in the pushing mode throughout a voyage under all anticipated weather conditions. A Pushing Mode ITB tug may be -connected to the barge with either a rigid or an articulated connection system. For example, an ITB in which the tug: cannot meet the towline pull stability criteria; or does not have installed or rigged the necessary equipment for towing by hawser; or cannot demonstrate safe separation from the barge under all operating conditions for which the tug and barge are designed to operate as a combined unit; will be considered a Pushing Mode ITB and the tug must be able to remain in the pushing mode under those weather conditions in which a ship of equivalent size could operate.

Dual Mode ITBs are those ITBs where the tug is similar to a conventional tug and is equipped to tow by hawser. The Dual Mode ITB can operate in either the combined configuration or tow on a hawser. The Dual Mode ITB tug can separate safely from the barge and shift to the hawser towing configuration at designated sea states. For inspection purposes, the tug and barge of a Dual Mode ITB will be considered as separate vessels.

A Dual Model ITB is similar to a tug and barge where the tug is secured in the barge notch or on fenders by means such as wire rope, chains, lines or other tackle now commonly used in offshore towing in that it is in all respects equipped to tow by hawser. It does differ, however in that it employs a method of connection which may permit greater speed, improved maneuverability and seakeeping, and which may be easier and safer to operate.

A Dual Mode ITB has all of the following characteristics. The tug has a hull shape which permits safe hawser towing. The tug meets the weather, dynamic and towline pull stability criteria. The tug and barge are equipped and rigged with the necessary gear for hawser towing. This should include a towing engine or bitts, hawser and bridle. The tug has. the capability to separate safely in a timely fashion at a predesignated sea state and shift to towing on the hawser. The capability to disconnect must be demonstrated. The barge is subject to inspection under applicable statutes. If the barge is not subject to inspection, the combined tug and barge will be considered a conventional tug barge combination.

A new style tug and barge combination is called an articulated tug barge unit (ATB). Unlike the older integrated tug/barge style, the ATB has a hinged connection system between the tug and barge. The ATB system "couples" the tug and barge together. The ATB unit's barge has a notch in the stern where its tug bow fits. Pins are located on both sides of the tug's bow that extend out and into the barge locking the vessels together. An ATB tug can be separated from the barge and used alone.

Because a double-hull barge is much larger than a single hull with the same carrying capacity, vessel owners must often invest an additional $9-10 million for a more powerful tugboat to move the larger barge. Retrofitting (adding a double hull to an existing single hull barge) can shorten delivery time by several months, but the cost remains high: some $12-13 million for a 120,000-140,000 barrel barge. The cost of a state-of-the-art articulated tug-barge unit, or ATB, runs $26-27 million.

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Page last modified: 07-07-2011 12:46:56 ZULU