This invention relates to a coupling mechanism between a pusher tug and a barge.
Methods are known for pushing a barge not provided with any propeller by a powered tug. Among various prior art coupling mechanisms between a pusher tug and a barge are included the single push rod--two wire system, the plural push rods--two wire system, the V notch system, and the V notch--pin system. These systems are not always satisfactory. More particularly, as shown in FIGS. 1A and 1B, in the single push rod--two wire system, an arcuate push rod 2 is secured to the bow of a tug 1 for engaging a thrust receiver 4 at the stern of a barge 3. The tug 1 and the barge 3 are tightly connected together by riggings 6 with one end pulled by a winch 5. This method of coupling prevents relative movement between the tug and barge in the fore and aft direction and in the left and right directions as well as relative swinging motion, but permits rolling, pitching and relative vertical movement. As shown in FIGS. 2A and 2B, in the plural push rod--two wire system two push rods 2 are secured to the bow of the pusher tug 1a for engaging a vertical surface 7 at the stern of a barge 3a. The tug and barge are coupled together by riggings 6 and winches 5 mounted on the pusher tug 1a. With this system the relative movements in the fore and aft, left and right and swinging in a horizontal plane are substantially precluded, but relative vertical motion, rolling and pitching are relatively free. Furthermore, in the V notch system shown in FIGS. 3A and 3B, the bow 8 of the pusher tug 1B is received in a V shaped notch 9 at the stern of a barge 3b with motor car tires or other cushion members 9 interposed therebetween. The tug and barge are connected together by riggings 6b made of nylon or other material that can elongate and contract to some extent. With this method of coupling, fore and aft, left and right and swing as well as rolling are prevented, whereas pitching and vertical relative movement are permitted. According to the V notch and pin system shown in FIGS. 4A and 4B the bow is received in the V shaped notch 9 but riggings and winch 5 shown in FIGS. 3A and 3B are not used. Lateral pins 10 projecting from the opposite sides of the tug are received in openings 10a on both sides of the V shaped notch 9 for interconnecting the tug and the barge. This method of coupling prevents relative movements of fore and aft, left and right, up and down, swinging and rolling but permits one component of the rotary movement caused by pitching.
The relative motions between the tug and the barge can be analyzed into six motions comprising three displacements of fore and aft, left and right and up and down and three rotational displacements of rolling, pitching and swinging, such analysis being possible depending upon which one of the six displacement movements is arrested. While no displacement occurs in the arrested direction, it is necessary to apply a substantial force to effect such arrest. Generally speaking, the force increases with the number of arrests. In the method of coupling utilizing connecting riggings as shown in FIGS. 1A to 3B it is troublesome to connect the riggings and with the increase in the size of the barge it becomes necessary to use strong riggings due to increased tension applied thereto. While the coupling system shown in FIGS. 2A and 2B, has a large freedom as above described, durability to waves is poor because no positive expedient has been made for permitting relative movement. The prior art coupling mechanisms described above conform to the prior art coupling systems described above and are subject to excessive force while they are maintained in a state of preventing specific relative movements between the tug and the barge. Some of them require the use of connecting riggings requiring troublesome connecting operation. For example, it has been proposed in U.S. Pat. No. 2,870,743 to steer a pusher tug and a barge to always sail them with their longitudinal axis aligned by detecting the deflection angle between them. However, it is necessary to provide riggings between both sides of two ships, thus not only complicating the construction but also requiring much time to engage and disengage the coupling mechanism. Where the barge is large, riggings having a large diameter are necessary which are difficult to handle.