Tug-Barge Couplers – Design & Construction
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.
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.
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.