Page 10: of Maritime Reporter Magazine (January 1971)

Large Seagoing Unmanned

Barge/Tug Developments

Roger M. Jones and Charles S. Smith*

The never ending search for a better and cheaper way of moving coastwise bulk cargoes in the

United States has brought on some very interesting developments with- in the last decade in the design and operation of large unmanned barges.

For purposes of this report, three generations of tugs/unmanned barges are considered as follows:

First Generation — tug/barges generally over 10,000 dwt. Primari- ly designed for offshore work on a towline but barge may have a stern notch and be designed to have the tug push in calm waters.

Second Generation — similar to the first generation, generally larg- er in barge deadweight and tug horsepower, but designed to permit the tug to stay in the notch in the open sea in light to moderate seas, generally over half the time while offshore.

Third Generation—special pat- ented design. Rigid or semi-rigid connection to permit the tug to stay "in the notch" or pushing con- figuration 100 percent of the time.

As the first generation of barge/ tug combinations increased in size and power it became evident that towing on a hawser in itself pre- sented special problems. The oc- casional breaking of a towline in offshore tows often involved a sub- stantial delay. Changing back and forth from hawser to notch while entering and leaving port also in- troduced a considerable delay fac- tor.

Other than the size and in- creased horsepower involved, the distinctive feature of the second generation was the fact that they were for the most part designed not only with substantial stern notches of improved, more ad- vanced designs but with additional tug/barge strengthening, special chafing gear and better hardware.

As larger barge/tug combina- tions followed, the method of con- necting the tug within the notch also received special attention and today, there are a number of dif- ferent and distinct designs adapted *Mr. Jones, president, Jones, Bardel- meier, Clements & Co., Ltd., Nassau,

Bahamas, and Mr. Smith, technical advisor, Jones, Bardelmeier, Clements & Co., Ltd., Pompano Beach, Flo., presented the paper condensed here before a recent meeting of the South- east Section of The Society of Naval

Architects and Marine Engineers. to push-towing techniques being used or developed in offshore un- manned barge tows.

The emergence of these third generation barge/tug combinations with their rigid or semi-rigid notch connections will provide answers to some of the towing problems.

If favorable experience is obtained with them, a dramatic breakthrough in large unmanned barge/tug tow- ing techniques will have been ac- complished.

Push Towing Connections

The several types of stern-notch push-towing connections used may be categorized into three general groups: non-rigid, semi-rigid and rigid connections.

The non-rigid group includes all conventional designs, involving no patents, in which the connection of the tug within the notch is se- cured by cables or hawsers, allow- ing the tug to move flexibly on its own buoyancy.

The semi-rigid group covers those combinations in which the tug is rigidly connected at some point or points on the barge to pro- vide a hinged effect for controlling some excess tug motions. Such de- signs include the Fletcher Artubar system and the Sealink system.

The rigid group includes the completely connected combinations and here the tug is securely fixed into the barge notch so that the tug stability is wholly dependent upon the barge itself. The Ingram design falls into this category.

Interstate Oil Transportation

Company has a 30,000-dwt barge being built at Bethlehem Steel

Company's Beaumont yard which will go into operation under charter to British Petroleum in the near future. The 520-foot barge will be mated with a 5,740-hp, 135-foot, twin-screw dedicated tug, being built at Main Iron Works. The combined unit is of a conventional design with a deep notch in the barge stern for the tug connection.

The details of this connection have not been made available.

The barge is provided with both fixed and adjustable skegs and is designed with a modified ship's bow. A speed of approximately 12 knots, loaded, in moderate seas is expected while the tug is pushing.

A total crew of 12 has been in- dicated for the tug.

The builder's price for the barge is reported to be $3,700,000 and for the tug $1,350,000.

Ingram Ocean Systems, Inc. has introduced one of the newer con- cepts in offshore towing. The con- cept, which was designed by Breit

Engineering, Inc., consists of a barge unit of normal proportions, having a ship shape bow and deep- ly notched stern into which the tug unit is firmly secured as a rigid connection. The unique feature in this case provides means for slid- ing the tug completely into the stern notch of the barge along guide rails at the upper sides of the two units and then locking it into position by means of hy- draulically operated horns which in effect forces the tug down into the floor of the notch. A hinged locking device on the forward deck of the tug then engages deck bitts on the barge and draws the tug unit securely into its locked posi- tion. A crew of 14 is contemplated for the first unit.

The initial unit is being built as a 532-foot, 33,000-dwt tank barge by Alabama Drydock & Shipbuild- ing Company and Southern Ship- building Corporation is building the 140-foot, 11,250-bhp tug. The reported cost for the combination is $10,000,000. The owners have chartered the unit to a major oil company and have guaranteed a speed of 14 knots, loaded, in seas of up to force 7 weather conditions.

Fletcher "Artubar" System is among the better known semi- rigid, articulated methods of push towing techniques presently under development. This design embodies a barge with normal proportions, a full ship's bow, vertical wing- wall skegs and a deep notch at the stern. The tug is provided with hy- draulically operated steel pins, one each port and starboard, located near the tug's quarter length, for- ward, at a level slightly above the main deck and designed to engage the barge in matching connections at the notch sides.

This system is under considera- tion by several firms. The barge sizes vary from 16,000 dwt to 50,- 000 dwt, and the tug horsepowers vary from 4,200 to 7,000 hp. The cost of a 3,800-hp tug and 14,000- dwt barge unit with the Artubar connection has recently been priced at a U.S. shipyard and is reported by Fletcher Associates to be $2,- 000,000 for the tug and $2,000,000 for the barge. A minimum crew of six men, according to Fletcher, could operate the unit. For tank barge operations, two additional pump men would be needed.

The Sea Link System of push towing has been developed on the

West Coast where it has been ap- plied to smaller barge/tug com- binations. The concept employs the use of a rigid horizontal frame hinged to the stern of the barge at one side and connected through a universal swivel joint to the same side of the tug. A steering strut connects the opposite side of the tug to the barge stern.

Humble Oil & Refining Com- pany is having one of the largest unmanned barge/tug combinations built by Gulfport Shipbuilding

Company. It consists of a 30,000- dwt barge and a 7,000 hp, twin- screw tug. It is designed for push towing approximately 60 percent of the time at a speed of 14 knots in loaded condition. The barge has a deeply notched stern with a fore and aft opening of 55 feet. The notch is contoured to the shape of the tug which is inserted approxi- mately one-third of its length. The tug is secured within the notch by 2-inch wire cables. The reported cost of the barge is $5,940,000 and the tug $3,000,000. A crew of 12 men is planned.

Moran Towing Company has participated in the offshore towing of large unmanned barges since the first generation barge units were introduced in the early 1960s. Late in 1969 the firm took delivery of a 508-foot, 26,000-dwt tank barge, built at Gulfport Shipbuilding

Company, and has been operating it as a push-towing combination with a 5,800-hp dedicated tug. The combination is operated by a crew of nine men. The reported costs for the barge and tug combination was $5,500,000.

Ohio River Company is among the operators who have been very active in the large barge-tug off- shore movement of bulk cargoes.

The company's latest venture into a large unmanned barge/tug move- ment has been the operation of two 26,000-dwt, 472-foot barges using a 5,000-hp tug. A crew of nine men has been used on the tug. The cost of the barges was reported to be $2,700,000 each.

McAllister Brothers Towing

Company is presently operating a 10,000-dwt tank barge with a 1,600- hp tug in the movement of oil from

New York City to Boston and Al- bany. Speeds of 10 knots have been obtained in the ballast con- dition. The tug-barge connection is a conventional one for pushing within the notch with the towing winch located on the barge deck.

A six-man crew operates the tug.

The firm also has extensive ex- perience in push towing through its operations on the Great Lakes and its subsidiary on the West

Coast, Island Tug & Barge Ltd.

This latter firm operates many barges with the 15,000-dwt self- dumping deck log barge Island

Yarder being the most recent addi- tion to the fleet.

Future Trends

Further development and refine- ment of the third-generation barge/ tug designs will depend to a great extent upon the degree of success obtained by those units presently under construction or in the de- sign stage and scheduled for de- livery within the next year or two.

It may take considerably longer to establish the full reliability of rigid and semi-rigid notch connections.

At the present state of the art it does not seem likely that barges in sizes over approximately 30,000 dwt will be built without a semi- rigid or rigid notch connection, and the ability of the tug to stay with- in the notch most, if not all of the towing time, remains a critical test of all the third-generation units. 12 Maritime Reporter/Engineering Hews