There are a number of systems available to connect a tug and barge at sea. They vary in experience from many years, to just a few months—from many applications, to just one application. We’d like to introduce you to the most commonly applied systems and some of the newer ones OT&BE has wide experience with many of these systems, and a full understanding of all.
The ARTUBAR system was the very first “axial” connection system. It is a single-degree-of-freedom system wherein the tug rolls with the barge, heaves with it at the connection point, but pitches independently. ARTUBAR utilizes a port and starboard, large diameter pin which is extended hydraulically from the tug hull. This pin is fixed in rotation relative to the tug hull, and it engages a pair of holes in the barge notch walls port and starboard. These holes are located approx. 7 feet apart vertically, and tend to be located at the loaded draft of the barge, the light draft, and the ballast draft. The barge holes are lined with bearing material such as Ultra-Poly or rubber. The large pin then rotates in this bearing material, relative to the barge, as the tug pitches. The pin does not bottom-out on the notch wall, and therefore, a small space is left between the tug and barge. Experience has shown that this space will allow the tug to slide back and forth and slam into the barge notch. Therefore, a recent modification of the system includes a set of pads port and starboard--aft of the pins--to fill this space and prevent such slamming.
This system is a Japanese invention designed to solve the shortcomings of ARTUBAR. It came about when a Japanese Artubar unit (the first built) suffered prototype pains, and a Japanese architect, (Mr. Takeo Yamaguchi) set out to improve the connection design. The result was ARTICOUPLE. The system is similar to ARTUBAR on the tug in that hydraulic rams actuate a pin outward from each side of the tug. However, this pin is in actuality a large ram which has a ball on the end of it. Affixed to this ball is a “helmet” with teeth. These teeth come hard against a vertical row of similar teeth on the barge notch walls. Thus, the tug is prevented from side to side motion allowed by ARTUBAR, and the multiple teeth up and down the notch wall allow connection at virtually any draft of tug or barge. Similar toothless arrangements in another type of ARTICOUPLE, replace the toothed helmet on the tug with a rubber-lined pressing shoe. This system is excellent for dump scows, or inshore AT/B’s.
The newer FRC series marries the pressing shoe and toothed engagement design to create a perfect system for AT/B’s where the tug remains connected but the barge changes draft while at sea. This is perfect for DP applications, shuttle AT/B’s lightering, dredges, etc. It is one of the connections chosen to be applied to our new PROVIDER Class AT/B OSV design.
The system can engage at any relative draft, and ballasting is not needed to line the tug up with the barge. The ball on the helmet allows a certain amount of angular misalignment as well, in heel. All side to side movement is halted because the helmet lands hard against the barge ladder. The systems allows only relative pitch. This is also the most widely applied system in the world, with the greatest experience in application, model testing, and operation. It is also available in the largest range of sizes and configurations of any tug to barge connection system. It is a product of Taisei Engineering, of Tokyo, Japan.
OT&BE has nine new AT/B’s under design with this system and has established a long-term relationship with Taisei Engineering to further the development of high-speed AT/B’s.
Articouple also produces a system known as the "TRIO-FIX" design, wherein three connection units are applied to the tug, to lock the vessel against pitch and obtain higher vessel speeds. A second set of connection ladders, aft of the main set, allows the tug to be moved back in the notch and thus be allowed to pitch - a large benefit in heavy weather to keep the wheels immersed.
The INTERCON system was developed by Robert Hill, working in concert with Intercontinental Engineering-Manufacturing in Kansas City, MO, to provide a U.S. alternative to the ARTICOUPLE, and solve the issues present in the ARTUBAR design.
The operation of the system is straightforward. The system is a single degree of freedom connection that like other systems, establishes a transverse, fixed axis between the tug and barge, around which the vessels are allowed free relative rotation, or pitch. All other movements such as yaw, roll, and heave are restrained. Thus the tug heaves and rolls with the gentler motion of the barge, and unlike systems that allow motions in more than one axis, the system forces are predictable.
In the system, the port and starboard sides of the notch wall are fitted with a vertical channel member with the open side facing the barge centerline. Notches, or teeth are incorporated on the fore and aft sides of the channel to eliminate vertical travel. The channel sides are tapered to provide a wider opening to ease connection, and the side taper is flat enough to minimize resultant thrust from higher bow to stern loads imparted on the barge by the tug. The notches lie on the taper of the sides and are of equal angle, peaked to balance forces and to minimize multi-angle planes of contact when engaged by the tug's connecting helmet. The vertical extent of these connection ladders is determined by the relative draft range desired for operation, and they can be supplied in a skeg module, prefabricated for installation as a unit into the barge. The machined steel connecting heads of the tug--which are inserted into the channels port and starboard to make the connection--are configured to match the channel tooth pattern. Each head is mounted on a spherical support to allow auto-alignment to the channel while retaining the greatest load carrying capacity in a minimal space. The ram is a heavy fabricated steel cylinder supported on the O.D. by a bronze bushing. The bushings are mounted in the I.D. of a "Load Box" structure which is a stress-relieved steel fabrication designed to transfer all structural loading, shaped to suit the tug and pre-fabricated and outfitted at Intercon with full lighting, access, wiring, piping etc. for insertion into the tug as a module. To extend or retract the head, the rams are moved along the horizontal axis by a large, male threaded shaft turning in the female boss on the inside of the ram. The threaded shaft is operated by electric motors through gearing mounted to the housing. Two drive motors are provided - one for low-torque high speed operation, the second for high-torque low speed operation. Emergency drives are also available, for use in the event of an electrical power failure.
Like ARTICOUPLE, INTERCON allows connection at multiple drafts. No ballasting is required. The system also is part of a large manufacturers product line, and as such enjoys solid engineering and service support. There is a large population of the units in existence with long experience. The system is built in pre-fabricated hull modules for ease of installation. The system has ABS and USCG approval and certification for dual-mode service. The gear/screw drive, prevents accidental retraction at sea, and allows for finer control of the units. Only this system provides a positive means to prevent retraction at sea. The unit is designed as well, to a very high safety factor.
Addendum: INTERCON has released a new, lighter weight connection system. Based on the current design’s general principles, the INTERCON-C features a simpler drive, lighter components, and a lower price. The trade-off comes in component life over longer time periods for the same loading. This new unit will need shorter overhaul periods, but that is based on operation continually in heavy seas, which most times is not required.
Intercon has also introduced a “lightering” type system, which used teeth in a wave form, welded on the barge connection ladder, to match a similar wave-type helmet, allowing the helmet to be slightly withdrawn during loading of a barge or discharge at sea, to change draft while the tug remains at a constant draft.
As co-inventors of the system, OT&BE has designed many newbuild AT/B tugs with this system, as well as multiple conversions, all of which have been successful.
This system operates by establishing a pivot, or relative pitch point about the bow of the tug. A clamp or caliper is deployed here, which attaches to a vertical bar at the head of the notch. Once gripped to the bar, the caliper is the pitching point. The tug has two sidepads at about midships, with either one or both moveable. The tug enters the notch with one pad retracted. The tug bow clamp is engaged and the pad(s) extended to fill the notch. The result is that the tug pitches about the bow clamp, with roll restrained by the moveable pads on the tug. The system has been in existence for many years, and BLUDWORTH-COOK is designing a new version that will eliminate many of the shortcomings found in the current design.
A simple system with light weight and easily retrofittable. The hydraulic components are fairly simple, and take up little space and power. Installation on the tug is straightforward and usually requires little in the way of structural changes and is among the least expensive to install on a tug. The system is sold and serviced by a reputable organization, and has a long history, with many applications.
Some operational flexibility is lost with this system as far as ordinary tug work is concerned. The tug’s bow unit holding the caliper can hole a barge easily if the tug comes alongside, or gets loose in the notch. The helmsman can’t see it in most cases, and it limits the tug to pushing in the notch, as opposed to working alongside, or approaching the barge from a tow in heavy weather. The system does have an 18 degree pitch limit, at which it will automatically disengage. The barge notch in the present system needs to meet very tight tolerances in construction which many yards have a difficult time meeting. The bar at the head of the notch also prevents other tugs from easily pushing the barge, and the longer notch needed as opposed to other systems, adds to barge cost. Bludworth is working on a bow unit adaptation that will allow full fendering, while retaining the functional capabilities of the system, mitigating many of the noted issues including automatic release. Note as well that this is among the most-applied systems in the marketplace. OT&BE has designed many AT/B tugs with this system, as well as multiple conversions, all of which have been successful.
This system is a mixing of a multiple-tooth engagement such as ARTICOUPLE and INTERCON, with the central hydraulic ram idea of the ARTUBAR. The teeth on the barge notch are individual weldments of 3 teeth each, installed in number as required on each notch wall. The main ram assembly is held in the tug with a chocking material such as Chockfast. Rotation of the tug in relative pitch, is via a bearing/axle on which the connection head rides, at the end of the ram. This system needs to be exactly aligned in the tug and barge. The system has worked quite well in the Great Lakes, though it has not been used or sold on the open sea or on the coast. The systems in use on the Lakes report good reliability, even in heavy seas on Lake Superior. The system is not manufactured by a large company. Each is custom-built. OT&BE has designed one AT/B tug with this system, the 7,200 HP DOROTHY ANN.
This system is the newest on the market and the list of applications has grown quickly, especially in smaller and medium-sized tugs. It marries some of the ideas of ARTUBAR with a unique approach to connection.
In this system, a pin on each side of the tug, self-aligns to a connecting hole as the tug enters the notch. This is done via wedges in the barge notch sidewalls directing the pin to the proper hole. The system is relatively light in weight. Like ARTUBAR, the pin does not bottom out on the receiving hole in the barge. The loads in this case are said to be much lower, by the builder, due to the reduced span/cantilever of the engaged pin, vs. other systems. The free space between tug and barge, like in ARTUBAR, needs to be filled to prevent movement of the tug back and forth across the notch.
Beacon’s web site forthrightly reported this in the maiden voyage of their first application, the KARA SEA. K-SEA, which owns the initial unit and later sisters, is planning further conversions to it and is happy with the cost and operation. Beacon has made continual improvements to their system. This system has potential, and is gaining experience. It has now sold to companies like Penn Maritime, Reinauer and others. It is a serious contender for retrofits due to it’s light weight, and newbuilds due to its cost. OT&BE is currently working in support of JAK applications for Penn Maritime, and others.