Of the countless vehicles that man uses for the water-borne movement of his goods, the commercial tow-barge is, without a doubt, his most unlovely product. Squat, inelegant, totally lacking the qualities of form and grace that are inherent in most naval construction, the dumpy shape of the tug and her bustle-like barge companion are things of beauty only in the eye of the commercial operator—in whose shrewd view there is, indeed, the undeniable charm of functional efficiency unmatched by any other carrier- form. For their ultimate customers—military and industrial—the enormous value of these ugly ducklings of the transportation world well-merits a better understanding of their design and use.
Coastal and offshore barging operations and construction comprise a major business today and constitute an important factor in our total transportation organization. Recent developments in hull design, construction, tugboat development, and auxiliary equipment are indicative of the widespread use of barge transportation and the realization of its economic and practical potential to U. S. and world trade.
With the increasing interest shown in this field, such as the barge-aboard-ship concept, and the successful completion of the first tows to Vietnam, it is only logical that new ideas and inventions will continue to result in even greater usage of barges in the future.
Let us review the operating abilities, restrictions, and advantages of barge operations with particular emphasis on the West Coast and offshore areas. To do so, we must include an explanation of the propulsion system in use in tugboats along with the various methods of towing barges and their application to the economics of barge transportation.
In the first place, the term “barge” is considered to mean a non-self-propelled cargo-carrying vessel. There are, of course, self- propelled barges. These are, however, extremely limited in number and we shall not consider them. These self-propelled vessels are usually quite small (30'X60'), with the motor mounted on the stern and being of an “inboard-outboard” nature. Study has shown that they are not applicable to coastal and off-shore operations, because of the variance in design, construction-, and power requirements. In order for a self-propelled barge to be fit for oceangoing duty an inordinate expense would be incurred. In fact, it would be more economically feasible to build a conventional cargo ship.
Tugboats are usually grouped into one of three major classifications: (1) Inland tugboats—called “towboats,” (2) Coastal or harbor tugboats, and (3) Oceangoing tugboats.
Towboats are basically of a square design with high “bumpers” or “pushers” located on the bow. (The name towboat is a misnomer as these craft move barges by pushing them rather than towing.) The pilothouse is located extremely far forward, not only for visibility but also for ease in controlling the “tow.” The physical features contrasting most with coastal or oceangoing tugboats are the lack of a raised or “high-pointed” bow and the very shallow draft. The bow is usually no higher than the stern and, in some cases, is even lower.
Coastal Tugboats present a “squatty” appearance with a short, blunt bow, low freeboard (two to three feet amidships) and a rounded stern. They range in length from 45 to 95 feet and from 300 to over 1,500 horsepower. The average coastal tugboat is 65 feet long with a power plant of 800 horsepower. The draft ranges from five to ten feet, which is in keeping with the shallow draft of the smaller barges used within harbors and bays. One of the most interesting facets of many of the small coastal/harbor tugboats is that they do not have a clutch and therefore no neutral gear. Thus, when the main diesel engine is operating, the shaft and, hence, the propeller, are either turning forward or in reverse. Of course movement of the tugboat is barely perceptible at the lowest speeds and in many cases is more than offset by the current.
These harbor tugboats are completely automated and function with a two-man crew when towing barges. This crew is composed of an operator and a deck hand. When docking or undocking a ship, however, two deck hands are required by existing union rules even though there is no more work involved for the deck hand than when towing a barge.
Oceangoing Tugboats range in length from 100 feet to over 250 feet and from 1,500 horsepower to over 9,000 horsepower. The average, however, is 125 feet long and is powered by an engine of from 1,500 to 3,000 horsepower. Draft ranges from ten feet to over 20 feet, with the majority around 16 feet. Speeds range up to 16 knots without a tow. Because of the increase in size, performance required, and duration of cruises, oceangoing tugboats have crews ranging from seven to 15 men depending upon the size of the tugboat and the job to be performed.
The outlook for tugboats seems to be bright. As ships and barges increase in size, so, too, will tugboats. It is also interesting to note that more attention is being given to constructing the tugboat with the characteristics of the barges it will have to tow as the prime consideration. Coastal/harbor tugboats will be restricted in size because of the natural limitations imposed by the harbors and bays. These tugboats, however, will also increase in horsepower and maneuverability.
A universal trend in both towboats and tugboats is toward even more automation. The latest oceangoing tugboats have unattended engine rooms with only a machinery superintendent aboard and with a complete control panel with warning lights located in the pilothouse.
Today’s barges are capable of carrying almost any conceivable cargo, in one configuration or another, the names of which usually indicate the use for which they are intended.
Hopper Barges are the most versatile and next to the least expensive to construct. With minor modifications, they may be adapted to the hauling of practically any kind of packaged cargo. These barges are basically double-skinned, open-top boxes with the inner shells forming a long hopper or cargo hold. The hold is usually free of any obstructions and is ideal for various methods of automated loading and unloading. A recent innovation has been to place hinges in the bottom of these hoppers, allowing them to be used for dumping various wastes at sea.
The Covered Dry Cargo Barge may be either of two different configurations. The more common type, found in ocean/harbor operations, is identical to the hopper barge with the exception that it has a watertight cover on each of the hatches leading to the cargo holds.
The second configuration resembles an enclosed box with a house built upon the deck of the barge. These are often used as floating warehouses where there is a need for temporary storage and where construction of a permanent structure is unwarranted or inadvisable.
The Deck Barge is a simply designed and constructed barge with a box hull that has a heavily plated, well-supported deck. Its primary function is the movement and storage of machinery and construction supplies. Dredging companies use these barges by building cargo boxes upon the deck in which to haul dredged material either to local markets or to sea for disposal. Its major drawback is the high center of gravity created by a high deck load. This results in a loss of stability that may be corrected by increasing the beam of the barge.
One of the more interesting developments using the deck barge principle has been the recent creation of a coastal rail-car barge for operation between Seattle and Anchorage. Known as the Hydro-train barges, they are well regarded for their stability and seaworthiness.
A second interesting development has been the creation of self-loading, self-dumping log barges with capacities ranging upwards of 10,000 tons or two million board feet of lumber. The principle of self-dumping involves the use of self-flooding tanks, located on one side of the barge, to obtain an inclination of almost 40 degrees. At this point the incline exceeds the angle of repose of the load, causing the cargo to dump. Because the bottom of the tipping tank is situated above the light waterline the barge is self-draining and self-righting, thus eliminating the need for a pumping system. Loading is accomplished by means of cranes permanently located on the side of the barge opposite the self-flooding tanks.
Tank Barges are basically one of three types: (1) single-skinned tank barges, (2) double-skinned tank barges, and (3) deck or hopper barges fitted out with independent cylindrical tanks.
Barges having independent cylindrical tanks are used either to transport liquids under pressure or where high pressure is required to discharge the cargo. Two other advantages of this form of tank barge are the ability of the tanks to expand or contract independently of the hull of the barge, and their convertability to conveyors of heated or refrigerated cargoes simply by placing insulation around the cylinders.
A recent example of combining dry cargo and liquid cargo barge concepts is Barge 539 of the Pacific Inland Navigation Company. This barge was designed to handle all of the types of cargo involved in the annual resupply of the Distant Early Warning (DEW) line and other installations in the Alaskan Arctic area. The entire hull below the main deck was used for transporting petroleum products, with the tanks arranged in conventional tanker style with two longitudinal bulkheads. Separate cargo lines were run to each tank to permit the transporting of different cargoes. Located above the main deck is a cargo house 228 feet by 34 feet, with a clear height of 19 feet 6 inches—completely unimpaired by any obstruction. The cargo house was designed to permit the loading of additional cargo on top of it. Three “whirley” cranes along one side of the cargo house permit loading and unloading in remote areas.
The continued emphasis upon greater unitization of loads has had an impact upon the design and operation of barges. A prime example is the container barge John C. Olson, operated by the Oliver J. Olson Company. Placed in operation in 1965, the John C. Olson is designed for unlimited ocean service and is certified by the American Bureau of Shipping for containers, general cargo, and bulk grain. The barge made its maiden run to Hawaii and is still employed on this run.
Various types of other barges are built for specific purposes, such as floating cranes or derricks, refrigerated barges, cattle barges and for almost any conceivable purpose.
Historically, the original barge was nothing more than a rectangular wooden box into which cargo was loaded for transport. It soon became evident that certain modifications had to be made in order to increase the cargo and decrease the resistance offered. This increase in speed, of course, permitted more economical operation.
Various experimentations with length-to- width and length-to-depth ratios were tried, the result being that the American Bureau of Shipping (ABS) had to step in and establish minimum ratios to be observed for safety purposes. All barges constructed in this country today must be certified by the ABS as to the type of permissible service and that the required standards have been met. The existing maximum length-over-depth ratios are: (1) full oceangoing certificate— 14:1, (2) coastwise certificate—16:1, (3) sounds, bays, and limited service certificates—18:1, and (4) recommended standard for river service barges is 20:1. Each barge, however, is considered on its own merits and some recent oceangoing barges have had as high as a 30:1, length-over-depth ratio.
EXAMPLES OF OCEANGOING BARGES BUILT SINCE 1960:*
Name |
LOA |
Beam |
Draft |
DWST |
Cargo |
Region |
Barge 560 |
277’ 6” |
66’ 0” |
14' 8' |
6,800 |
combination |
West Coast |
Adelaide |
420' 0”" |
80’ 0” |
24' 0' |
17,200 |
cement |
East Coast |
Straits Logger |
371' 6” |
76’ 0” |
17' 3' |
10,000 |
logs |
West Coast |
G. W. No. 2 |
263' 0" |
62’ 0” |
13' 0' |
5,000 |
logs |
West Coast |
Umpqua 6 |
260' 0” |
60’ 0” |
10' 10' |
3,600 |
rock |
West Coast |
Valdez |
400' 0” |
76’ 0” |
|
6,460 |
railcars |
Alaska |
Martha B. |
420' 0” |
80’ 0” |
25' 6' |
19,000 |
rock |
Gulf of Mexico |
Caribbean |
475' 0” |
75’ 0” |
23' 5' |
17,900 |
sugar |
East Coast |
Nootka Carrier |
356' 0” |
78’ 0” |
14' 4' |
7,100 |
newsprint |
West Coast |
John C. Olson |
305' 0” |
70’ 0” |
|
|
(337 containers, 36,000 bbl. |
Hawaii— |
|
|
|
|
|
liquid, dry cargo) |
West Coast |
*Marine Engineering Log, August 1966.
With maximum dimensions established, various progressive experiments with shaped hulls have established that the towing resistance may be substantially reduced with but a minor loss in the cargo carrying capacity.
For the designer, the major consideration, regardless of the type operation envisioned, is to ensure that the surface of the barge first meeting the surface of the water is at an angle. This simply means the headlog must be sufficiently high to clear the bow wave at the designated smooth-water operation of the type of service contemplated for the barge. This consideration is established by conducting model-basin studies.
Once the required height of the headlog is determined, it then becomes necessary to determine the rake slope and the rake radius. Rake radius refers to the radius which is tangent to both the rake slope and the bottom of the barge. The longer slope used on the harbor/river barge is permissible because of the smoother water surface encountered. Various encounters with rough waters have shown the long rake slope pounds very badly. This results in serious structural damage and imposes lower speeds. The shorter rake slope of coastal and oceangoing barges minimizes pounding and, in addition, results in stiffening of the unsupported areas of the rake slope between frames. This short rake slope increases the resistance offered to the water when being towed. This increase, however, in towing resistance is offset by drawing in the deck line and increasing the bilge knuckle radius.
Experimentation with a standard pointed ship bow has shown it to have a very high tendency to yaw at the end of a towline, and also a high tendency to “dig in” when attacking a wave. This greatly increases its resistance to yaw correction. The addition of large skegs increased the resistance noticeably without a corresponding decrease in the amount of yaw.
In some barges, both the bow and the stern are almost identical in design. As might be expected, these barges are almost always used for short hauls which entail frequent loading and unloading with very short turn-around time. When towing a barge of this nature, however, there is an appreciable increase in resistance. For long hauls a deck transom aft, with an increased stern rake radius and flatter rake angle offers an appreciable reduction in resistance.
It has been found that resistance is slightly lowered by increasing the bilge radius. However, this decrease in resistance is more than offset by: (1) the loss of cargo space— most noted in dry cargo barges, (2) the increased cost in construction, and (3) the tendency for the barge to slide sideways when being towed in a light condition. Most of the barges that are under construction today have small radius bilges.
One of the major problems encountered in the design of barges is the tendency to yaw while under tow. Research with actual barges and model-basin studies have established that: (1) the higher ratios of length to beam, and lower ratios of length over draft increases the tendency to yaw, (2) blunt sterns may offer sufficient resistance to reduce, and in some cases eliminate, the tendency to yaw, (3) a barge constructed with a low resistance stern and anti-yaw skegs will enjoy a lower total resistance, and (4) low resistance barges more readily accept yaw correction than high resistance barges. The reduction in cargo space with a low resistance stern is more than compensated for by the decrease in fuel consumption and the increase in speed.
In various studies concerning the use of skegs it was found that one skeg mounted on the centerline, or twin skegs mounted close to and parallel to the centerline were of little or no value. The two best methods reducing or eliminating yaw, it was found, are to affix twin single-plane skegs at proper angles (5 to 10 degrees) to the centerline and mounted as far to the sides as possible and to mount a pair of double-plane skegs—again as far to the sides as possible.
Barge construction today is almost entirely of steel rather than wood, and for very good reasons. Three principle advantages of metal over wood are: (1) lower cost of maintenance; it is noteworthy to add however, that well- built wooden barges with adequate preservation methods have been in existence for 30 to 40 years; (2) steel, being lighter has a greater deadweight capacity, hence a greater economic return; and (3) steel hulls offer less resistance when being towed.
Steel barge construction is done entirely by welding, rather than a combination of welding and riveting as is done in constructing ships. Construction of barges is on an individual basis, and the customer will confer very closely with the company selected to ensure the barge meets his desired requirements. Only after various plans have been considered and desired performance characteristics and practical performance characteristics are melded into one satisfactory design does construction begin. Barges are seldom, if ever, constructed and then placed upon the open market for sale, for the cost involved is prohibitive and customer preference and requirements are somewhat unpredictable.
Barge construction has been following the trend of ship construction in creating larger barges with more modern equipment. It is likely, too, that barges will continue to increase not only in size but also in the variety of purposes for which they are constructed. New techniques to decrease the cost of construction are constantly being tried and introduced, with the result that more and more businessmen are looking to this form of transportation.
A number of design trends have been observed in recent years. There has been an increasing use of model-basin studies, for various hull designs, skeg installations, and in support of the continuing refinement of the ends of the barges and the underwater form of the hull. The main emphasis, understandably, is on greater speed and good directional stability without a substantial loss in cargo-carrying capacity.
A recent study by the University of California at Berkeley on the feasibility of an oceangoing catamaran indicates that the catamaran concept offers sufficient reduction in resistance and an increase in stability for deck barges.
Another concept, proposed by a number of commercial concerns is that of a bargecarrying ship. Various proposals such as LASH (Lighter Aboard Ship), the Cargo Catamaran and the Lykes Sea Barge Clipper envision loading barges themselves aboard a ship for trans-oceanic movement. Such a craft could discharge her fully loaded barges, load a new cargo of loaded barges within a very short period of time, and cross the ocean at speeds unobtainable by barges in tow. The discharged barges would be moved by tugboats directly to various plants or terminals for unloading and subsequent reloading.
Lykes Steamship Line has proposed to contract for construction of three such Sea Barge Clippers during fiscal year 1967. Some of the characteristics of the Sea Barge Clipper are: over-all length—about 875 feet; beam, extreme—107 feet; draft, maximum—about 39 feet; and top cruising speed—21 knots. The Lykes Sea Barge Clipper will carry 38 barges, each of which will measure 97 feet by 35 feet and be capable of carrying 850 tons of cargo, or a total of 17,500 tons of dry cargo capacity. The total time required for discharge and loading of the entire cargo (76 barges) has been estimated as between 24 and 36 hours.
As more and more attention is given to the area of barge transportation, because of its obvious economic advantages, there will inevitably be produced new concepts, each aimed at achieving greater efficiency and use. The future outlook on barge construction looks promising.
Today, there are basically two methods for towing barges. In method A, the tugboat is secured alongside the barge and, by using a combination of pushing and pulling forces, moves the barge. Method B is the familiar use of a towline running from the stern of the tugboat to the bow of the barge.
Within the inland waterway system, reference is made to “tows,” which in reality are “pushes.” That is, the barges are being pushed by the towboat instead of being pulled or towed. This form of movement is excellent for relatively smooth surfaces, but is not suited to coastal and oceangoing traffic. It does however, allow for greater maneuverability in restricted areas and should be kept in mind as an excellent approach for work in areas with limited maneuvering space.
In using method B, early practice revealed that the attachment of the towline to the barge at a single point resulted in somewhat less than the desired amount of directional stability. Subsequent experimentation resulted in the use of a bridle attachment which, by virtue of the vectoring forces involved, tended to greatly increase the directional stability of the tow. From further experimentation with bridle lengths on a tow, was developed the normal practice to use a 45- foot bridle for coastal/harbor tows and a 60- foot bridle for ocean tows.
An excellent example of a multiple tow is found in a recent movement of five barges from the Army portion of the Military Ocean Terminal, Bay Area (MOTBA) in Oakland, California to Danang, Republic of Vietnam, by the Red Stack Towboat Company. The distance between each of the barges was about 600 feet, resulting in a total over-all length of over 4,000 feet for the tow. The average speed for the journey was approximately seven knots.
In a tandem or multiple tow, there are generally three types of yaw experienced by operators with the yaw in the multiple tow being less pronounced because of the dampening effect of the barges at the end of the towline. One type of yaw results when the first barge begins the movement and will yaw back and forth, while the after barge will remain on course. Another type of yaw results when the after barge yaws in the opposite cycle of the forward barge. That is to say, when the forward barge yaws to port the after barge will yaw to starboard. These two types of yaw are the most common experienced by operators. The third, and most interesting type of yaw, is where the motion of both barges are in harmony. Strangely enough, the speed of the two is increased by as much as 10 per cent when this type of yaw is experienced, provided that the amplitude and period of oscillation is not excessive. The various types of yaws associated with tandem or multiple towing may exist even when each of the barges in the tow can be towed individually with excellent directional stability.
It is prescribed practice not to man the barges while under tow except in unusual circumstances. Running lights are usually battery-operated and have sufficient power to operate as long as 60 to 90 days. If the barge has an anchor it may be released by radio signal. As might be expected, when this invention was first introduced there were a few instances where the anchor was released or the lights turned on by radio frequencies not initiated by the tugboat in charge of the tow.
As long as oceangoing barges are moved by means of a long wire towline, the size and displacement of the tugboat is an important factor in maintaining speed and control over the barge. A small tugboat is frequently forced to reduce power in bad weather in the interest of safety of the vessel and crew. A larger and more powerful vessel maintains power longer and her less lively movement permits a more steady strain on the towline, resulting in less chance of snapping the tow- line. In addition, the greater displacement of the larger vessel reduces the tendency of the barge to take charge under the influence of wind and large seas.
With one exception there has been no change in the method of connecting oceangoing tugboats and barges. This exception has been the recent introduction of serious research to develop a means whereby tugboats can push barges on the open seas instead of towing them on a line. Such a system would have many advantages beyond safety. Steering, for example, would be much more accurate, and directional stability would be greatly increased, reducing the need for skegs and directionally stable hulls. This would permit the hull of the barge to be designed for increased speed.
Such a device has been constructed and as of 1965 was being experimented with on the West Coast. This device (known as Sea Link) has successfully operated in waves as high as eight feet and, despite original structural failure, indications are that it is very feasible. A second prototype is currently being evaluated.
Western barge routes extend from Alaska to Mexico and westward to Hawaii and southeast Asia. But there is also a good deal of activity in tug-barge operations on the East Coast of the United States, with routes extending from Puerto Rico to the U. S. seaboard, and from the Gulf of Mexico to the Mediterranean Sea. The number of tugboats and barges in service has continually increased over the past ten years.
The basic reason a barge can provide cheaper transportation is the low manning level that is required. A tugboat and barge unit require substantially less men than a ship of the same deadweight capacity. On our West Coast, for example, a six-to-12- man crew is required for barge operations between Alaska and California. The crew of a 4,000 to 12,000-dwt-ton ship plying the same route will range from 25 to 45 men. Surprisingly, the biggest savings are not in wages and benefits, but in the initial cost of accommodations, subsistence, insurance, and medical claims. It should be mentioned, however, that recent developments in automation on board ship, especially tankers, have considerably narrowed the gap between the two methods of operation in this aspect.1
The capital required for construction of a 6,000-h.p.-tugboat and a 10,000-dwt-ton barge combination is roughly 50 per cent of a standard oceangoing freighter built in the United States. Obviously, the greater portion of this 50 per cent is expended on the tugboat. Thus, several barges and one tugboat may be purchased for the equivalent price of one oceangoing freighter.
For a company with a limited, but worthwhile, portion of its business concerned with water transportation of bulk cargoes, it is indeed worthwhile to use several barges in place of one ship. With one tugboat and three barges, a continuous operation of loading and unloading may take place while the tugboat and one barge are continually in transit. For smaller companies which cannot, or do not want to, operate a tugboat, the cost of renting (or hiring) a tugboat on a frequency-of-haul basis is economically feasible. In fact, some barge companies own a fleet of barges and rent or hire the tugboats as required, with a substantial reduction in costs.
Too, a barge may be used as a temporary floating warehouse without negating the power of the propulsion unit. One example of this is the recent decision by Connecticut Light and Power Company to shuttle coal between Jersey City and Connecticut ports. The barge can offer temporary storage. The coal need not be rehandled, thus reducing labor costs.
Another advantage of barge operations is that while a ship is of fixed design, such as a dry cargo freighter, a company may be able to construct two tank barges, one deck barge, and three dry cargo barges for the same cost as the freighter and yet achieve a greater versatility. This in turn will provide a greater economic potential as the barges can carry cargo that the freighter cannot. In addition, the tugboat is continually moving, which results in greater economic gain by making maximum use of the equipment.
Another advantage is the savings realized on maintenance. As most barges are unmanned there is no maintenance of facilities for personnel. The simple construction of the barge hull itself permits more economic upkeep and repairs. One fact not usually considered is the time delay involved with a loaded ship if a piece of propulsion machinery breaks down and renders the ship inoperative. In a tug-barge operation the tugboat can have necessary repairs accomplished while a second tugboat can proceed with the movement of the barge, without having to shift the cargo.
A final economic advantage is found in the shallow draft of a tug-barge combination, allowing it to proceed to areas of loading and unloading not available to ships. This is demonstrated every day on the inland waterway system.
The main disadvantage to barge operations is the low speeds involved. A barge tow is capable of between five and 12 knots, and very few oceangoing tows exceed nine knots. An oceangoing freighter will cruise at between 15 and 20 knots. While a barge can generally save time and money because of the advantages already mentioned, these advantages are more than offset by the speed with which a ship can travel the same distance. This factor becomes more important as the distance between the ports becomes greater. For limited coastal and harbor/river operations this is not an important factor because of the natural speed limitations involved.
A limited disadvantage is that certain cargoes requiring surveillance during transportation cannot be accompanied because of the fact that most barges are unmanned. However, as most of the oceangoing cargo is not of this nature, this is not a major disadvantage.
In the entire economic outlook for barges, the steady increase of economically potential inventions and developments is more than offsetting the setbacks encountered. The Lykes Sea Barge Clipper will enable barge operators and users to compete favorably, perhaps even to take the lead in the least total time required from loading the ship at one port to unloading at another. Economically, then, barges will continue to play a role of ever-increasing importance in the total transportation picture.
While this discussion deals with the commercial aspects of coastal and offshore barging operations, it is suggested that the recent improvements in this area of transportation not be overlooked by the Navy. The Sea Barge Carrier proposition of Lykes Steamship Lines, for example, offers immense strategic and logistic potential in the realm of amphibious operations. The fast-loading and discharge characteristics of this concept would certainly increase the operational responsiveness that is essential to our military commitments today.
Pericles
If they are kept off the sea by our superior strength, their want of practice will make them unskillful and their want of skill, timid.
1. See Verner R. Carlson, “Automation: the Bitter Pill,” U. S. Naval Institute Proceedings, November 1967, pp. 37-47.