Abstract:
The main propulsion and drive system of a merchant vessel such as a freighter or tank vessel, or a military vessel is supplemented by an auxiliary propulsion and drive system that includes at least one, but preferably a pair of auxiliary propellers that flank the main propeller at port and starboard positions and each of which are attached via a drive shaft through a gear train, which can optionally include a clutch mechanism, to an auxiliary motor or motors. In order to reduce the drag when the main propeller is disabled, segments of a wake field modifying propeller duct are mounted for repositioning to form at least a partial housing or cowling that diverts the water over the exterior surface of the duct and minimizes contact with the stationary blades of the main propeller as the vessel moves through the sea when powered by the auxiliary propulsion system.

Description:
RELATED APPLICATIONS 
       [0001]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to vessel propulsion systems, and more particularly to an auxiliary vessel propulsion system employing one or more controllable pitch propellers. 
         [0004]    2. Description of Related Art 
         [0005]    Propellers have been the primary mode of propulsion for merchant marine and military vessels since they replaced paddle-wheel and wind-driven sailing vessels in the early 20 th  century. While the scale, materials of construction, shape and engines have developed substantially over the past 100 years, the configuration of choice has essentially remained constant—single engine/single propeller design. 
         [0006]    The tremendous scale and complexity of primary drive engines requires scheduled and unscheduled maintenance for optimum operation. For proper service, the vessel should be anchored or drifting. Additionally, engine failure is a problem which, while not necessarily very common, can yield disastrous consequences. For instance, in January 2007, the Vindu cargo vessel experienced engine failure, and came dangerously close to colliding with gas platforms and pipelines in the North Sea. Even when imminent danger is not a concern, the economic impact caused by a vessel that is anchored or adrift can be substantial, and cargo delays can cost resellers and/or sellers substantial sums of money in penalties, damaged business relationships, or result in useless goods such as perishables or seasonal merchandise. 
         [0007]    Supertankers and container vessels have propulsion engines that can produce over 100,000 horsepower to turn the vessel&#39;s propeller and move the vessel through the water. This primary drive engine and other engines for driving electrical generators to provide power for the vessel&#39;s electrical systems are located in an engine room. While there is convenience in a single engine room for routine service and maintenance, in the event of damage, fire, attack or other disaster impacting the engine room, the vessel can be halted or set adrift. 
         [0008]    Different types of auxiliary propellers on marine vessels have been described in the patent literature. For instance, U.S. Pat. No. 1,577,101 describes a system having a main propulsion propeller and two auxiliary propellers used as generators. The generators can be disabled by means of clutches between auxiliary shafts. However, when the vessel is operated by the main propulsion propeller, the turning of the auxiliary propellers creates hydrodynamic drag, lowering the efficiency of the propulsion system. In addition, the main propeller and the auxiliary propellers are operably interrelated, so the auxiliary propellers are essentially rendered useless in the event that the main propeller system fails. 
         [0009]    U.S. Pat. No. 3,993,912 discloses a marine propulsion system that includes a gas turbine, a generator, a three-phase AC electric motor and a fixed pitch propeller. In the normal ahead and astern directions, the motor operates synchronously; in the slow ahead and astern directions, the motor is operated asynchronously with the gas turbine operating at its idle setting. Means are also provided to break the propeller before astern torque is applied when the power propulsion lever is rapidly moved from the normal ahead setting to the normal astern setting by operating the motor as a generator. However, there is no consideration given to propelling the vessel when the motor and/or the gas turbine fail or requires maintenance. 
         [0010]    U.S. Pat. No. 4,668,197 discloses a retractable auxiliary and emergency propulsion device for small craft. The device includes a hydraulic motor with its own propeller powered by a hydraulic pump, coupled with either a dedicated motor installed on the craft or existing motors on the boat for purposes other than propulsion. The hydraulic motor slides on inclined guides located in the stern of the craft so as to be dropped into the sea when necessary, or raised up and placed in a suitable storage space in the boat. However, this device is intended for small watercraft, and is not suitable as a backup propulsion system for large merchant vessels. 
         [0011]    Therefore, a need exists for a reliable, fail-safe system for minimizing vessel delays and loss of control in merchant and military vessels during a period of time that the main propulsion drive system fails or is shut down for scheduled or unscheduled maintenance at sea. 
         [0012]    Accordingly, it is an object of the present invention to provide an auxiliary propulsion system for vessels that does not interfere with the routine operation of the main propulsion and drive system. 
         [0013]    It is another object of the present invention to provide a system for auxiliary propulsion that optionally provides the additional benefit of power generation. 
       SUMMARY OF THE INVENTION 
       [0014]    The above objects and further advantages are provided by the apparatus, system and method of the invention in which the main propulsion and drive system of a merchant vessel such as a freighter or tank vessel, or a military vessel is supplemented by an auxiliary propulsion and drive system that includes at least one, but preferably a pair of propellers which flank the main propeller and which are attached via a drive shaft, through a gear train, which can optionally include a clutch mechanism, to an auxiliary motor or motors. It will be understood by one of ordinary skill in the art that use of a single auxiliary propeller, positioned either port or starboard of the main propeller will require the rudder to be turned in order to maintain a straight ahead course. This positioning of the rudder creates a certain amount of hydrodynamic drag. Use of two auxiliary propellers eliminates this use of the rudder. 
         [0015]    In the following description, when reference is made to a propeller in the singular form, it will be understood that the description is equally applicable to the preferred embodiment in which two auxiliary propellers are utilized. 
         [0016]    In the interest of simplicity and clarity, the invention will be described with reference to a vessel having a single main drive engine and, in any event, it will be assumed that the vessel is without an operable main propeller. 
         [0017]    In a preferred embodiment, when no power is being applied to the auxiliary propeller(s), the pitch of the blades are adjustable to one or more predetermined positions, one of which positions reduces the hydrodynamic drag, and therefore the tendency to cause the auxiliary propeller to rotate as the vessel is propelled through the sea by the main propeller. This will be referred to as feathering the propeller, or to a feathered propeller. 
         [0018]    As used herein, the term “feathering” includes any movement of the propeller blades that has the effect of reducing the propeller&#39;s hydrodynamic drag on the vessel as it moves through the water. 
         [0019]    In another particularly preferred embodiment, the pitch of the blades of the auxiliary propeller can be adjusted to cause the auxiliary propeller to rotate the drive shaft at a rate that is optimum to turn an electrical generator located aboard the vessel which can be used to power vessel systems and/or to charge storage batteries. 
         [0020]    When the auxiliary propellers are not being used to operate the electrical generator(s), the blades are preferably feathered and the propeller drive shaft is disengaged via a clutch or other gear train mechanism so that the propeller is free-wheeling with the minimum number of on-board components in the drive train moving in order to minimize frictional drag forces in bearings and the like. 
         [0021]    As will be understood by one of ordinary skill in the art, the size of the auxiliary motor(s) must be sufficient to drive the auxiliary propellers at a speed that will produce a propelling force sufficient to provide headway that will allow the vessel controls, which may be limited to the rudder, and perhaps bow thrusters, to direct the movement of the vessel and prevent it from being carried into a broaching or other hazardous position as a result of the action of currents and/or waves, or the vessel&#39;s own momentum. Although the determination of the power output, e.g., horsepower of the auxiliary motor(s) is readily determined, such calculations must take into consideration the vessel&#39;s maximum load capacity, as well as the worse case scenario for adverse conditions of the weather and seas through which the vessel can be expected to ply. For example, if a vessel&#39;s main engine is capable of generating up to 100,000 horsepower which enables it to safely navigate based upon its size, maximum load and foreseeable weather and sea conditions, it may be possible to control the vessel in order to maintain a safe course using an auxiliary power source of as little as 2,000 horsepower. A reasonable design parameter is presently believed to be an auxiliary motor that has from about 5% to about 15% of the horsepower of the main engine. 
         [0022]    A pair of propellers flanking the main propeller can be powered by a single auxiliary motor with an appropriate gear train and drive shafts in accordance with any of a number of mechanical arrangements that will be readily apparent to one of ordinary skill in the art. In addition, the speed of each of the auxiliary propellers can also be controlled independently by means of an automatic power transmission device associated with each drive shaft, the transmission or gear boxes being located in the respective drive trains. Thus, by varying the relative speed of the auxiliary propellers, the course of the vessel may be directed, at least to some extent, and the rudder can be used to a lesser extent. 
         [0023]    Assuming that each auxiliary propeller is powered by a separate auxiliary motor, the speed of each of the auxiliary propellers can be controlled by adjusting the speed of the motors independently and/or the use of automatic transmission devices or adjustable gear boxes. Likewise, the direction of rotation of each of the auxiliary propellers can be reversed in order to facilitate a more rapid change in course or to assist in docking the vessel. 
         [0024]    As will be apparent to one of ordinary skill in the art, only a single auxiliary propeller is mounted to the port or starboard side of the main propeller, the energy required to maintain the vessel on course and making sufficient headway will have to be increased due to the drag effect of controlling the forward direction using the vessel&#39;s rudder. 
         [0025]    In order to maximize the efficient operation of a vessel at sea that is relying solely on the auxiliary propellers, in a preferred embodiment of the invention, the main propeller is disengaged from the drive shaft and any gear train stemming to the main engine. In a particularly preferred embodiment, the pitch of the blades of the main propeller is adjustable to a position that minimizes the hydrodynamic drag of the water moving across the blades. 
         [0026]    In order to reduce the drag when the main propeller is disabled, in a particularly preferred embodiment, a series of efficiency fins mounted forward of a fitted propeller duct are rotated 90°, and preferably folded in the aft direction, to form at least a partial housing or cowling that diverts the water over the duct and out of contact with the stationary blades of the main propeller. 
         [0027]    In another preferred embodiment, a duct or vane having movable segments defining a water channel is installed between the vessel&#39;s hull and the forward portion of the main propeller and surrounds the main propeller drive shaft, and is maintained in a first open position while the main engine is used to propel the vessel. In the event that the main propeller stops while the vessel is underway, the moveable segments forming the walls of the vane or duct are reoriented and moved toward each other to thereby form a cone having its larger open end in proximity to the stationary main propeller blades and the forward end proximate the main drive shaft, thereby reducing the drag force that would otherwise be created by water contacting the surfaces of the stationary propeller. The cone is of a truncated configuration and can be formed from two opposing curvilinear sections that in the open position serve to channel water passing from the vessel&#39;s hull toward the propeller into a more efficient slip stream. Alternatively, the cone can be formed from more than two segments, each of which segments can be of a flat or curvilinear configuration. The movement of the cone segments can be controlled by hydraulic supporting struts or rams and/or other mechanisms known in the field of marine engineering and architecture. 
         [0028]    In one embodiment, the auxiliary propulsion and drive system of the invention is only intended to be activated during what would be considered emergency conditions when the main propeller has ceased to operate while the vessel was underway at sea or in other port locations where one of more tugboats or other similar vessels cannot provide immediate assistance to prevent damage to the vessel and/or the surrounding facilities. 
         [0029]    It should also be understood that the orientation of the blades of the propeller can be adjusted relative to the drive shaft in order to attain more efficient operation, for example, to increase power when initiating movement from a stopped position, i.e., high torque and lower RPM, or to increase speed, i.e., low torque and relatively higher RPM when the vessel is underway. 
         [0030]    It is known in the art to install a generally tubular stationary duct between the propeller and the vessel&#39;s stern to modify the wake field of full-form vessels such as tankers in order to improve fuel efficiency. In accordance with a further embodiment of the invention, a two-part moveable duct is mounted co-axially with the main propeller drive shaft between the propeller and the stern to provide in a first position, an open body formed of curvilinear segments to modify the wake form when the vessel is being powered by the main propeller, and in a second position, a truncated conical surface, with the smaller end forward towards the hull and relatively closer to the drive shaft, and the aft end defining an opening adjacent to the path circumscribed by the rotation of the ends of the main propeller blades. In the second position the conical surface serves to deflect the water outwardly to thereby by-pass the stationary blades of the main propeller and reduce the hydrodynamic drag on the vessel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The invention will be described in further detail below and with reference to the attached drawings in which the same or similar elements are referred to by the same number, and where: 
           [0032]      FIG. 1  is a schematic diagram of a propulsion system according to the present invention; 
           [0033]      FIGS. 2A and 2B  are enlarged depictions showing in more detail the operational positions of a preferred embodiment of the apparatus of  FIG. 1 ; 
           [0034]      FIG. 3  is a view taken along line  3 - 3  of  FIG. 1 ; and 
           [0035]      FIG. 4  is a flow chart of an embodiment of the method of the invention. 
       
    
    
       [0036]    In the interest of clarity and to facilitate the depiction of the inventive features, the vessel&#39;s rudder has been omitted from the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    Referring to  FIG. 1 , a propulsion system  10  for a merchant vessel or the like is schematically depicted, including a main propulsion and drive subsystem  12  and a pair of auxiliary propulsion drive subsystems  14   a  and  14   b , collectively referred to as  14 , that can be operated independently of the main propulsion and drive subsystem  12 . Generally, the main propulsion and drive subsystem  12  propels the vessel under normal operating conditions in accordance with known and conventional practices. According to the present invention, if the main propulsion drive subsystem  12  fails, or when the main propulsion drive subsystem  12  must be shut down for routine or unscheduled maintenance while at sea, the auxiliary propulsion drive subsystem  14  is used to propel the vessel, thereby offering reliable back-up propulsion. As will be understood by one of ordinary skill in the art, in a preferred embodiment the pair of auxiliary systems  14   a  and  14   b  flank the main drive system  12  at corresponding port and starboard positions in order to provide a balanced power source, and also to facilitate navigation by independently controlling subsystems  14   a  and  14   b , e.g. by running the two propellers in opposing rotational directions. However, the method and system of the present invention comprehends the use of a single auxiliary propulsion drive system which, in conjunction with the vessel&#39;s rudder, can be used to achieve the goals and benefits described. 
         [0038]    More particularly, and still referring to  FIG. 1 , the main propulsion drive subsystem  12  includes a main engine  16  selectively coupled to a fixed propeller  18  via a driveshaft  17 . The main engine  16  is connected to the fixed propeller  18  through a clutch system  20 . 
         [0039]    The auxiliary propulsion drive subsystem  14  includes an auxiliary motor  24  selectively coupled to an auxiliary controllable pitch propeller  26  via a driveshaft  25 . The auxiliary motor  24  is connected to the auxiliary propeller  26  through an optional clutch system  28 . In certain embodiments, the auxiliary propulsion drive subsystem  14  also includes a gear train and generator apparatus  30  intermediate the clutch system  28  and the controllable pitch propeller  26  for operating the auxiliary propulsion drive subsystem  14  in a power generation mode. In general, the auxiliary motor  24  has substantially less horsepower then the main engine  16 . For example, where the main engine  16  is rated at from 30,000 to greater than 100,000 horsepower for a merchant vessel, the auxiliary motor can have a rating that is about 5% to about 15% of the horsepower of the main engine  16 . 
         [0040]    The auxiliary motor  24  can be an electric motor powered by an electrical system of the marine vessel, or powered by dedicated electrical storage batteries. In the latter configuration, the auxiliary propulsion drive subsystem  14  provides a fail-safe back-up or emergency drive power source, even if the vessel&#39;s entire main propulsion and drive subsystem  12  and its associated electrical system fails. 
         [0041]    Alternatively, the auxiliary motor  24  can be an internal combustion engine. The internal combustion engine can be a diesel engine or a gasoline engine. Preferably, even if the type of fuel for the main engine  16  and the auxiliary motor  24  is the same, the fuel for the auxiliary motor  24  is stored separately and is isolated from the fuel for the main engine  16 . Since most large vessels utilize bunker oil as fuel, the smaller auxiliary motor  24  can be more efficiently powered by diesel or gasoline. 
         [0042]    In a propulsion mode of the main propulsion drive subsystem  12 , the clutch system  20  of the main propulsion drive subsystem  12  engages the main driveshaft  17  to allow the engine  16  to turn the propeller  18 , and the fixed vane cone  22  is in an open configuration to allow water to flow through and the rotation of the propeller  18  functions to move the vessel forward. While the main propulsion subsystem  12  is operating in its normal propulsion mode, the clutch system  28  is of the auxiliary propulsion drive subsystem  14  is disengaged from the auxiliary motor  24  thereby preventing rotation of the controllable pitch propeller  26  by the auxiliary motor  24 . 
         [0043]    In certain embodiments, the gear and generator apparatus  30  can be selectively engaged with the controllable pitch propeller  26 . Accordingly, in the propulsion mode of the main propulsion drive subsystem  12 , while the vessel is being driven through the water by power from the main engine  16 , the blades of the trailing controllable pitch propeller  26  are pitched to maximize hydrodynamic forces to cause rotation of the propeller  26 , and the rotational forces are transmitted through the driveshaft  25  to the gear and generator apparatus  30 . The generator apparatus  30  can be electrically coupled to one or more electrical storage batteries, to one or more electrical loads on the vessel directly or through an electrical distribution system, or to both the storage batteries and the electrical loads. As is conventional in power generation apparatus, the electrical output from the generator can be coupled to the batteries and/or other loads through one or more suitable power conditioners, such as AC-DC inverters and/or voltage converters. 
         [0044]    During a disengaged mode of operation of the main propulsion drive subsystem  12 , e.g., corresponding to periods of engine failure or shut down for maintenance, the clutch system  20  and the driveshaft  17  are disengaged from the engine. In addition, the fixed vane cone  22  is moved to a closed configuration to divert water flow past the stationary propeller  18  and prevent its rotation while it is disengaged from the engine  16 . 
         [0045]    When the main propulsion drive subsystem  12  is disengaged, the auxiliary propulsion drive subsystem  14  can be activated to operate in the propulsion mode. The auxiliary controllable pitch propeller  26  is adjusted to a drive configuration to provide forward propulsion force to the vessel. In the propulsion mode of the auxiliary propulsion drive subsystem  14 , the clutch system  28  is engaged to couple to the auxiliary motor  24  and rotate the controllable pitch propeller  26 . 
         [0046]    As will be apparent to one of ordinary skill in the art, a control system for switching to the auxiliary mode electronically can be provided using an appropriately programmed processor/controller that is responsive to an emergency shut-down of the main engine or unexpected failure. For example, the control system can be programmed to automatically initiate the change-over to the auxiliary power system, or to provide an alarm so that vessel&#39;s personnel can make the decision to manually initiate the action. The back-up or emergency control system can be connected to the storage batteries or emergency power generation system in the event that the main power fails 
         [0047]    When operating in the propulsion mode, the auxiliary propeller  26  provides the propulsion force to allow the vessel to move through the water, even while the main engine  16  is undergoing repairs and/or maintenance. By disengaging the main engine from propeller  18  via the clutch system  20  as described above, and when the fixed vane cone  22  is in the closed position, the hydrodynamic drag forces on the main fixed blade propeller  18  is minimized as the vessel moves under power of the auxiliary propulsion drive subsystem  14 . 
         [0048]    If the main propeller has controllable pitch blades, the blades are adjusted to minimize the drag of the stationary blades. While the auxiliary propulsion drive subsystem  14  is not intended to provide horsepower that is comparable to the main propulsion drive subsystem  12 , the engine(s) or motor(s) are selected to provide sufficient power to propel the vessel at a speed that will permit the use of the rudder to control the vessel&#39;s direction to avoid collisions, and make headway while the main engine  16  or other components of the main propulsion drive subsystem  12  are being repaired or serviced. 
         [0049]    In order to adjust the pitch of the controllable pitch propeller, a suitable feathering apparatus (not shown) is also incorporated in the auxiliary propulsion drive subsystem  14 . Controllable pitch propellers are well known in the art, as are the mechanisms for changing the pitch of the blades to two or more predetermined positions. These mechanical systems and their components form no part of the present invention. 
         [0050]    For instance, in one embodiment, a mechanical subsystem for feathering the propeller is provided that moves the propeller blades to minimize the hydrodynamic drag forces when the vessel is moving under the main power system. 
         [0051]    In another embodiment, a mechanical subsystem for feathering the propeller is provided that moves the blades of the propeller to a position in which the edges of the blades are in line with a direction of marine traverse during the disengaged mode of operation, and to a water-contacting position during the engaged mode of operation. 
         [0052]    Also as shown in  FIG. 1  generally, and in more detail in  FIGS. 2A ,  2 B and  3 , an optional, but preferred embodiment is shown in which a vane or duct  50  with moveable segments is installed axially about the driveshaft  17  between the vessels stern and the main propeller  18  to modify water flow patterns in the region of the main propeller. 
         [0053]    With reference to the embodiment schematically illustrated in  FIGS. 2A and 2B , the vessel is provided with a vane or duct  50  having moveable elements  50 A and  50 B. As shown in  FIG. 2A , the elements are in the open position and assist in reducing the turbulence in the water following the stern of the hull, thereby improving the efficiency of the main propeller. 
         [0054]    Referring now to  FIG. 2B , the forward ends of segments  50 A and  50 B are moved toward the main drive shaft  17  to form a truncated conical surface. In this position, the duct  50  provides a streamlined surface in the form of a housing that directs the water outwardly to minimize direct impingement on the stationary blades of the main propeller when it is out of operation. Thus, when the vane or duct segments  50 A and  50 B are moved to the enclosing position shown in  FIG. 2B , they form a surface that minimizes turbulence and produces a laminar flow, to the extent possible, as determined by limitations of spacing and configuration of the vessel&#39;s hull, location and range of movement of the vessel&#39;s rudder and overall spacial relations that will be apparent to one of ordinary skill in the art. During ordinary operation of the main propeller, the segments of the duct or vane are moved to stationary positions in which the individual segments themselves present minimum hydrodynamic drag and also serve to channel the water trailing the adjacent lower hull portion at the vessel&#39;s stern. 
         [0055]    Referring to  FIG. 3 , a view aft from the hull position shows the segments  50 A and  50 B in their open configuration during normal propulsion of the vessel by the main propeller  18 , with the auxiliary propellers  25 P and  25 S stationary, and preferably feathered to minimize their hydrodynamic drag on the vessel. 
         [0056]    With continuing reference to  FIGS. 2A ,  2 B and  3 , a supporting member  52  is, illustratively, mounted around drive shaft  17  and includes a cross-member  53  to which the aft portions of segments  50 A and  50 B are mounted at pivot points  56 . Other mechanical arrangements and details for supporting the segments comprising the duct  50  and the related elements for adjoining its position will be apparent to those of ordinary skill in the art. 
         [0057]    As previously noted, the segments  50 A and  50 B in this open configuration modify the wake field of the water streaming from the vessel&#39;s hull at the stern end to reduce turbulence before the propeller. 
         [0058]    This step-wise practice of the method of the invention will be further described with reference to the flowchart of  FIG. 5 . With the main engine stopped,  100 , due to an emergency or predetermined maintenance requirement, the main propeller blades or optionally feather  102 . If present, the wake field control duct is adjusted from its open position to its closed conical position  104 . 
         [0059]    If provided and operational, the electrical generator is disengaged from the auxiliary propeller(s)  110 . 
         [0060]    With the main engine stopped and the auxiliary propellers moved from an optional feathered position to the operational position  106 , the auxiliary drive motor(s) are activated  120  and the drive shaft(s) for the auxiliary drive propeller(s) are engaged  122 . 
         [0061]    During continuing operation of the auxiliary propulsion system, the speed and direction of rotation of the auxiliary drive motor(s) are adjusted  124  to maintain the desired speed, and optionally the course of the vessel. 
         [0062]    As previously noted, the above steps can be undertaken by the vessel&#39;s personnel, or essentially automatically in accordance with an appropriately programmed computer processor and controller. 
         [0063]    It will also be understood from the above description, the steps identified as optional, e.g.,  102 ,  104 ,  106  and  110 , are designated as such because the particular feature may not be present on the vessel, because it was not engaged at the time that the main engine stopped. For example, retrofitting an existing vessel with a controllable-pitch main propeller for use with the auxiliary propulsion system of the invention may not be commercially practical. 
         [0064]    In summary, the principal aspects of the preferred embodiments of the present invention comprise an auxiliary propulsion drive subsystem that includes a disengaged mode, a power generation mode and a propulsion mode, in which the propeller blades are adjustable to at least three corresponding pitches to provide the most efficient and effective operation. Additional pitch configurations can be provided to provide high torque/low RPM and low torque/high RPM operation of the auxiliary power system. 
         [0065]    The method, apparatus and system of the present invention have been described in detail above and in the attached drawings; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.