Patent Publication Number: US-9889906-B2

Title: Towing system for a tugboat

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a towing system for a tugboat comprising a ring-shaped base for attachment to a ship&#39;s deck, and a circular turning ring that is displaceable along that base, which circular turning ring is provided with a winch, as well as a number of wheels for engagement with that base. 
     DESCRIPTION OF THE RELATED ART 
     Such a towing system is known from EP-1.208.035 B1 which describes in paragraphs [0003]-[0005] that: “During towing, there is a cable connection between the tugboat and the ship. On board the tugboat, this cable usually runs through a towing eyelet and is attached to a towing winch or towing hook. The towing eyelet is arranged as low as possible in the vertical direction on the tugboat, in order to minimize the tilting of the tugboat and to prevent the tugboat from capsizing. With respect to this towing eyelet, the towing cable can turn sideways through 90° or more in the horizontal plane, towards both boards. In the case of a towing winch, the cable length can be adapted to the desired towing length and maneuvering distance. In the case of a towing hook or attachment point, the towing cable length is fixed”. 
     This prior art European patent further describes that a discontinuous ring is attached to the deck of a vessel such as by welding and a further ring, displaceable on the base, is arranged around this ring, which is provided with a cable guide. Because of this, it is possible to expand the applications of the tugboat, especially by improving the maneuverability and stability. With this construction, the towing cable can be brought into any desired position with respect to the tugboat and can be fully loaded therein. 
     Such a construction is particularly successful. However, the costs for producing the towing system are relatively high. After all, both the ring arranged on the deck and the ring, displaceable along there, that do not necessarily have to be circularly shaped, must be accurately produced to enable proper adjoinment of the wheels lying there in between. Especially with large forces it is of importance to distribute these forces evenly over the wheels in such a way that these can be transmitted via the wheels into the stationary ring arranged on the ship&#39;s deck. 
     Moreover, it has appeared that during use small deformations can occur, as a result of which the true circularity of the two rings can no longer be guaranteed. 
     SUMMARY OF THE INVENTION 
     It is the aim of the present invention to avoid this disadvantage and to provide a towing system that can be produced cheaper and is less sensitive to the accuracy of two rings rotating with respect to each other. 
     This aim is achieved with a towing system as described above, in that those wheels are connected to the circular turning ring. 
     According to the present invention the wheels are no longer rigidly connected to the circular turning ring that is displaceable along the base. The wheels thereof can perform mutual displacements to absorb inaccuracies of the circular turning ring as well as the base. Because of this a more optimal force distribution over the wheels can take place and it is possible to suffice with a cheaper construction for the wheels. 
     The rings can be fully closed but can also just comprise a ring part. Moreover, the rings can be constructed circularly as well as elliptically. 
     The wheels may be arranged on auxiliary arms. Therein, a number of wheels can be arranged on an auxiliary arm and it is also possible to arrange a wheel/a set of wheels each time on an auxiliary arm. The different auxiliary arms can be hingeably arranged with respect to each other and can be connected to the circular turning ring via a further hinge construction and a main arm. 
     It shall be understood that the wheels are arranged especially at those places where the largest force is to be expected. The wheels shall be arranged depending on the construction of the base. The forces described above concern forces in diametrical direction of the base (ship&#39;s deck) as well as forces acting perpendicularly thereto, that occur when towing a vessel, wherein the point of engagement on the vessel lies much higher than the ship&#39;s deck. 
     The circular turning ring may preferably be constructed from a relatively stiff box part on which, for example, a winch is arranged. Connecting thereto a belt-like construction may be present that engages around the base for absorbing the diametrically acting forces. However, it is also possible to construct the circular turning ring as a box part that extends, just like the abovementioned box part, over a very limited part of the circumference of the base. However, with this embodiment the box part is not extended with a belt part or the like but provided with wheels that absorb the diametrically acting forces. These wheels then obviously engage the inner circumference of the base and not the outer circumference as in the abovementioned example. 
     According to an advantageous embodiment of the invention, springs are preferably arranged between the wheel connection and the circular turning ring. According to an advantageous embodiment such springs can comprise rubber springs. By means of example the use of cylindrical bushes is mentioned. Another possibility is to embody the springs as a rubber block. Depending on the application the actual rubber material will be selected. It is observed that neoprene rubber is a material that is especially suitable for most applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       As described above, preferably a winch is arranged on the box part of the circular turning ring. 
       The invention will be elucidated by way of exemplary embodiments shown in the accompanying drawings, in which: 
         FIG. 1  schematically shows a vessel provided with a towing system according to the invention; 
         FIG. 2  shows a top view of the towing system according to the invention; 
         FIG. 3  shows the close-up view III of  FIG. 2 ; 
         FIG. 4  shows the close-up view IV of  FIG. 2 ; 
         FIG. 5  perspectively shows a winch arranged on the towing system, and 
         FIG. 6  shows a variant of the embodiment as described above. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1  a vessel is indicated by  1 . This comprises a tugboat provided with a hull  2 , deck  3  and a towing system  4  arranged on the deck. This towing system  4  is rotatable around a pilot house  5  that is fixedly connected to the vessel. 
     As is apparent from  FIG. 2 , the towing system  4  consists of a stationary ring or ring-shaped base  6  that is fixedly attached to the deck of the vessel and a circular turning ring  7  rotatably arranged thereon. The circular turning ring  7  consists of a relatively stiff box part  8  and a belt part  9  connecting thereto. This belt can be embodied as a simple steel belt. However, it is also possible to provide it with reinforcements or to construct it, for example, as a chain. It is especially of importance that it is capable of absorbing the diametrically acting forces. Box part  8  and belt part  9  are externally arranged around the circular turning ring  7 . The box part  8  is provided with a platform  10  on which a winch  11  is arranged. Because of such a box a particularly high torsional stiffness is achieved, as a result of which the forces acting on the winch can be absorbed. 
     As is apparent from  FIG. 5  the winch  11  consists of a winch drum  12 , cable guides  13 , roll  14  and feed  15 . Feed  15  consists of a suitably rounded part for guiding the towing cable (not shown) along there. The winch according to the present invention is fixedly arranged on the platform and it has appeared that by proper dimensioning it is no longer necessary to arrange such a winch hingeably, with all associated disadvantages thereof. 
     The vertical forces will not reach the spool-up mechanism because the thread can move up and down freely in the spool-up mechanism between the upper and lower limit. 
     Transversal forces possibly acting on such a spool-up mechanism can be large and the forces can be absorbed by providing either two spool shafts, whether or not provided with cross thread, or spool shafts with normal screw thread and operation by a separate motor. 
     The forces acting on such a winch  11  respectively platform  10  can be large. One thing and another depend on the capacity of the tugboat  1 . These forces may vary from tens to hundreds of tons. This means that upon exerting such a tensional force on the circular turning ring  7  large forces have to be transmitted to the stationary ring  6 . For that purpose, according to the invention, wheels are present that are connected to the circular turning ring  7 . 
     In contrast with the prior art, such a connection is not a stiff connection but a resilient connection. According to the present invention, a spring is arranged between the wheel attachment and the circular turning ring  7  and more in particular a rubber spring. 
     The embodiment of this rubber spring depends on the position of the wheels. 
     In  FIG. 3  a set of wheels  28  is shown that is arranged on the belt part  9  of the circular turning ring  7 . An assembly is attached to the belt part  9 , indicated by  25 , comprising two spaced-apart plates  24  and  29 . Rubber spring  23 , embodied as a block, is vulcanized to these plates  24  and  29 . Plate  24  is attached with bolts  31  while plate  29  is attached to plate  30  with bolt  32 . On plate  30  attachment eyelets  33  are arranged in which a shaft  27  is inserted that is provided with wheels  28  on both sides. Possibly, the plates  24  and  29  can be provided with a cooperating guide for absorbing longitudinal forces. By constructing one or more of the wheels shown in  FIG. 2  in this manner the force distribution for transmitting forces from the circular turning ring  7  to the base part or stationary ring  6  can be effected in a relatively uniform manner. 
     The forces acting on the wheels  28  are diametrically directed. 
     Near the “front side”, i.e. the winch side of the circular turning ring  7 , different forces act for generating forces. These will particularly be directed upwards or downwards. For that purpose, the wheel attachment is constructed differently. This is apparent from  FIG. 4  that shows wheel assembly  21 . It is apparent that two spaced-apart wheels  38  are present that each rotate around a substantially horizontal shaft  37 . This shaft  37  is separated from outer bush  34  via a bush-shaped rubber spring  35  that is connected to the box part  8  in any way known from the prior art. By using two opposing wheels between which the rail is received upward respectively downward forces can be absorbed. With the present invention it is possible to reduce the peak load on each wheel. 
     Because of this, the wheels are loaded to a lesser extent, as well as the associated bearings. Peak loads of 40-50 tons/wheel are not unusual in the prior art. The present invention makes it possible to limit such forces considerably. 
     As a matter of course, the spring characteristic of the rubber spring will have to be adapted to the expected load. By means of example, a spring characteristic of 1-6 tons/mm is mentioned. It shall be understood that other loads are also conceivable and these will lead to a different construction of the spring. 
     In  FIG. 6  a variant of the construction as described above is shown, wherein a method different from a springy method is used that also acts in a force distributing manner. In this embodiment the box part and the platform are integrated into one part. Such a construction can also be used with the embodiment as described above. Fixed rails are indicated by  46  and wheels  47  are locked up between these rails. Pairs of wheels are each time connected to auxiliary arms  49  via rotational shafts  50 . Each auxiliary arm, near the middle thereof, is connected to a hinge  51  with a main arm  52 . In the example as shown, near each of the ends of main arm  52 , each time, such an auxiliary arm  49  is hingeably attached. In the middle the main arm  52  is connected to the box part  48  via a hinge  53 , on which a winch and the like can be arranged in the manner described above. In principle, one or more main arms can be used. 
     With the present invention, it is possible to realize a carrousel construction without particularly accurate working of the different parts and with parts that can be obtained relatively cheaply, which will promote the introduction thereof on different ships even more. 
     After reading the above, those skilled in the art will immediately be able to think of variants which are obvious and fall within the scope of the attached claims. Therein, rights are explicitly requested for the variants that are described in the dependent claims without combination with the main claim.