Tug-Barge Couplers – Design & Construction

Design

The Intercon Coupler System ram assembly is equipped with a cast steel interface head (helmet) which incorporates a multi-tooth profile. The helmet is mounted on a forged steel spherical support (ball) which is designed to allow automatic alignment during engagement yet retain the greatest load bearing capacity in a minimum space. Rotation, caused by tug pitch, is transmitted to the ram by anti-rotation pins that connect the helmet and ball. Ram rotation is carried by a either a bronze or an Orkot® bushing which is installed in the cylindrical ram housing. All other relative motions are restricted. The extension and retraction of the ram assembly is accomplished by an alloy threaded shaft turning in a bronze threaded boss incorporated into the inboard end of the ram assembly. The screw is actuated by electric motors driving through gear reduction mounted on the interior end of the housing assembly. The screw can be actuated in both high speed and low speed modes. In low speed mode, extension force exceeds 260,000 lbs. on each ram. Auxiliary hydraulic drive motors are optionally available. The transverse thrust from the actuator screw assembly is carried by a roller type thrust bearing rated in excess of the worst condition athwartship loads revealed in model tank tests. A load cell is incorporated into the bearing housing to monitor thrust forces.

Model Tests

The Intercon Coupler System has been designed to meet severe operating conditions. These criteria and operating load parameters were tested by computer simulation, and dynamic tank testing at the Netherlands Ship Model Basin. These initial tank tests utilized models of a 260,000 barrel capacity barge pushed by a 6000 HP class tug equipped with lateral connecting rams simulating the Intercon design. Load tests were conducted in 22 ft. mean seas, and included various wave heights in the spectrum. Substantial data was generated by wave heights, periods, and directions; these results guided the final engineering phase of the Intercon System. Subsequent to the initial testing – continued model testing has been conducted to verify coupler sizing on new applications. Upon review of the design and NSMB test data, the U.S. Coast Guard approved the Intercon Coupler System for Dual Mode tug-barge service as defined by USCG NAVIC 2-81.

Construction

The rotating ram components are comprised of rolled steel and structural plate, all fabricated and machined as a one-piece cylinder. The outside diameter of the ram is clad with corrosion resistant stainless steel. The ram housing is fabricated and machined as a single weldment. The housing is provided with circumferential flanges and longitudinal ribs spaced to accommodate design loads. The ram housings are incorporated into complete “load box” modules – port and starboard – which become part of the hull structure. The load box weldments are thermally stress relieved, and machined to receive all coupler components. All mechanical and electrical assembly is completed and tested at Intercon’s plant prior to shipment. Load box modules are designed and fabricated to match exactly with surrounding hull structure, allowing the Intercon System to be easily adapted for both retrofit and new construction.

Tug-Barge Couplers – Installation

As a part of the Intercon Coupler System, customers are furnished ladder members for installation in the barge notch walls. Alternatively, skeg modules can be fabricated at Intercon, with the complete ladder section incorporated. The ladder members provide a continuous tooth pattern on the fore and aft sides of the section, designed to engage the ram’s helmet, and thereby lock the tug’s vertical motion relative to the barge. The side taper is relatively flat to minimize resultant thrust from bow to stern sway loads. The tooth profiles are of equal angle, and peaked to balance forces and minimize multi-angle planes of contact when connected. Ladder vertical length can vary from 15 ft. to 50 ft., eliminating the need for ballasting either vessel when entering the notch. When engaged, the Intercon Coupler System fully eliminates hull to hull contact between tug and barge, permitting the tug to pitch freely relative to the barge. Crew fatigue is lessened given smoother tug motions afforded by the pitchline being aligned with living areas. With the ability to retract the interface heads within the hull envelope, the Intercon System avoids dangerous, fixed projections on both the tug and barge. This feature also preserves fleet interchangeability. Tugs equipped with the Intercon Coupler System can conventionally push or tow non-System barges, and conversely, non-Intercon Coupler System tugs can work with ladder equipped barges. Each vessel retains its ability to operate as any vessel in its respective class.

Tug-Barge Couplers – System Operations

The Intercon Coupler System is typically monitored and controlled from the upper wheelhouse using a touch screen controller. A secondary touch screen controller as well as auxiliary manual controls are located in the coupler room. When engaged, the Intercon Coupler System fully eliminates hull to hull contact between tug and barge, permitting the tug to pitch freely relative to the barge. The ram axis is typically aligned with crew living areas to provide smoother motion which lessens crew fatigue. With the ability to retract the interface heads within the hull envelope, the Intercon Coupler System avoids dangerous, fixed projections on both the tug and barge. This feature also preserves fleet interchangeability. Tugs equipped with the Intercon Coupler System can conventionally push or tow non-System barges, and conversely, non-Intercon Coupler System tugs can work with ladder equipped barges. Each vessel retains its ability to operate as any vessel in its respective class.

Tug-Barge Couplers – Advantages

The favorable economics of the Intercon Coupler System result from several factors, but essentially center on speed. This Coupler can produce speed advantages of 35% compared to towed units in average conditions. The ability to pitch maintains propeller and steering efficiency in any sea direction and condition so the tug can stay safely in the notch – pushing – while other units are towing or weatherbound. The Intercon Tug-Barge Coupler is the result of thorough analysis of today’s tug-barge operations. The demands of the application, as well as the limitations of alternate linkage technology, were all considered in the development of this System.

A summary of the Intercon advantages:

• Permits pushing in a wide range of sea conditions
• Increases speeds 35-40% over towed units
• Fuel savings enhanced by wheel and rudder efficiencies
• Fully eliminates hull contact between tug and barge
• Fail-safe mechanical connection with force monitoring
• Engagement allowed regardless of draft or trim
• Fabricated construction allows retrofit on existing conventional tugs and barges
• Mechanical drive with engagement safeguards – not vulnerable to hydraulic or pneumatic system failures
• Engaged and disengaged without crew on deck
• Eliminates expense and hazards of hawsers, headlines, and cables
• Comfortable ride resulting in less crew fatigue
• Fleet interchangeability due to flush mounted components
• Unmatched maneuverability at sea, and in port
• USCG approved for Dual Mode under NAVIC 2-81
• Worldwide product support from Intercon’s service facilities
• Designed and manufactured in America by one of the leading names in marine equipment

The Intercon Coupler not only provides the economies of pushing, but offers flexibility, speed capabilities, improved transit predictability, and a degree of safety in operation not found in traditional tug-barge operations.

Tug-Barge Couplers – Vessel List

Intercon Coupler Systems Reference