Abstract:
A device that when fitted to a motor vessel&#39;s existing propulsion gear improves the performance and reduces potential damage and wear of underwater propeller shaft bearings, commonly referred to as “cutlass bearings” that are used on boats, ships, etc. Designed with radially mounted impeller blades around the periphery of the propeller shaft, the device creates a forced flow of water by centrifugal pumping action, which creates suction along the shaft abaft the cutlass bearing, thereby increasing the flow of water through the cutlass bearing. The device also greatly diminishes the probability that fouling around a propeller shaft will severely restrict water flow through the cutlass bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to provisional application Ser. No. 60/957,206, filed Aug. 22, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to devices and methods for marine propulsion and liquid pumping, and, more particularly, to such devices and methods for improving a performance of marine propulsion and pumping systems. 
         [0004]    2. Description of Related Art 
         [0005]    A cutlass bearing (common usage) is a special type of bearing used extensively in marine and industrial applications for bearings operating underwater or in other liquids. Cutlass bearings have no moving parts, and the bearing material is usually composed of a type of synthetic rubber and/or polymer, which supports the propeller shaft. Cutlass bearings are designed to utilize the lubricating properties of a hydraulic film of the surrounding water/fluid in which the bearing is operating. For this reason channels are designed within the bearing surface to promote the flow of liquids through the bearing, assuring proper lubrication while cooling the bearing and shaft surfaces at the same time. 
         [0006]    A common problem in propeller-driven vessels is fouling of the propeller and shaft with lines, rope, netting, plastic bags, etc. When propeller shafts are fouled, often the fouling material is wound around the shaft in the section between the cutlass bearing and propeller hub. When this happens, the flow of water through the cutlass bearing is restricted and, in some cases, is cut off entirely. A vessel operator is sometimes made aware of a fouling condition because of vibration in the propulsion gear and diminished performance. If he is aware of the fouling, the operator will usually attempt to clear it by reversing the propulsion gear in an attempt to release the wound-up fouling, or, when that is not successful, someone may go overboard to clear the fouled propulsion gear. Even a small amount of fouling right next to the cutlass bearing will severely impede the flow of lubricating water because the cross-sectional area of the water channels in the bearing is relatively small. Small amounts of fouling around a propeller shaft, however, often goes unnoticed for extended periods. In this situation, the cutlass bearing suffers premature wear because of starvation of lubricating water. Furthermore, it is fairly common to have the aft ends of bearings and bearing housings physically damaged and abraded when fouling materials are tightly wrapped around the propeller shaft for an extended period. 
         [0007]    Several devices have been designed and marketed for the purpose of preventing propeller and shaft fouling. They are generally based on rotary cutters that are attached to the shaft and act to cut the fouling materials as they begin to wrap around the shaft. Although some of these devices work well under the ideal conditions for which they were designed, they are not as effective in extreme conditions. These cutting devices generally require frequent repair and replacement in heavy use applications such as those experienced by vessels operating in the commercial sector. These devices also are not specifically designed to increase the flow of water through the cutlass bearing. 
         [0008]    Therefore, it would be beneficial to provide a simple, robust, and dependable device and method of manufacture and use for substantially preventing fouling of propellers, shafts, and cutlass bearings in marine vehicles. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is directed to a device that is mountable on a propeller shaft abaft (in back of) a cutlass bearing for improving a performance of a propeller-driven propulsion apparatus. The device comprises an annular collar affixable for rotation with and dimensioned for positioning about a shaft of a propeller in a longitudinal space between a propeller hub and a cutlass bearing. A plurality of impeller blades are affixed to and extend radially out from the collar in spaced-apart relation. Each impeller blade has a length sufficient to nearly span the longitudinal space between the propeller hub and the cutlass bearing, leaving a gap between forward ends of the blades and the cutlass bearing. 
         [0010]    An annular ring is affixed in spanning relation to the forward ends of the impeller blades. A bridging element extends from one of the annular ring and the cutlass bearing, and is positioned to longitudinally bridge the gap between the blades forward ends and the cutlass bearing, thereby substantially enclosing the gap. 
         [0011]    In use, the impeller blades rotate in conjunction with the propeller shaft, and in doing so they create a centrifugal flow of water outward from the shaft, which in turn creates suction along the shaft surface and abaft the cutlass bearing. The suction draws water through the water channels in the bearing surface. The pumping action of the impeller blades, along with the greatly increased discharge area for water around the periphery of the device, greatly decreases the likelihood that fouling around the propeller shaft can restrict the flow through the cutlass bearing. Additionally, the outside edges of the impeller blades help cut through and shear away the rotating fouling materials over time, making it much more likely that the fouling material eventually be cut and thrown off than it would when wound up on a relatively smooth shaft surface. 
         [0012]    The device can be easily attached to the existing propulsion gear of a vessel in order to improve the dependability and performance, and reduce the maintenance cost, of the propulsion gear. The invention can relate to that sector of vessels that utilize a propulsion system composed of an inboard engine that turns a drive shaft exiting through the hull to turn a propeller. This type of propulsion apparatus normally uses one or more cutlass bearings to support the shaft in its underwater section. 
         [0013]    The device of the present invention increases water flow through normal cutlass bearings and decreases the likelihood that the waterflow be severely impeded by propeller and shaft fouling. The device, even with fouling around the propeller shaft, lessens the likelihood of bearing damage owing to lack of water circulation. In order to achieve this, the device has multiple radially mounted blades that extend from the shaft surface outward. These blades act as an impeller to create centrifugal pumping action in the water when the shaft is rotated. The periphery of the device also creates a large area for fluid discharge, which makes severely flow restriction by fouling less likely. 
         [0014]    The present device, when mounted abaft a cutlass bearing, shield the bearing from physical damage and erosion from fouling materials that may become wrapped around the propeller shaft. The blades of the device mounted immediately abaft the bearing prevent fouling materials from reaching the after end of the bearing and bearing housing, thereby protecting the bearing and housing from direct abrasion. 
         [0015]    The present device is robust and durable, and is able to remain effective under extreme conditions and extended use. The device can be constructed of, for example, stainless steel or other corrosion-resistant metal alloys with welded or cast components and does not depend on sharp edges or close tolerances to remain effective. 
         [0016]    The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  (prior art) is a cross-sectional side view a propulsion setup for inboard engine vessel. 
           [0018]      FIG. 2  (prior art) cross-sectional end view of a propeller shaft, cutlass bearing, bearing housing, and water channel grooves. 
           [0019]      FIG. 3  is a cross-sectional side view of a device of the present invention mounted on a propeller shaft. 
           [0020]      FIG. 4  is an end view of the device of  FIG. 3 , illustrating a plurality of impeller blades equally spaced around the periphery. 
           [0021]      FIGS. 5A-5D  depict various impeller blade embodiments:  FIG. 5A , a flat plate blade of rectangular cross section with square outside edge;  FIG. 5B , a flat blade design with pointed ends;  FIG. 5C , a flat blade design with serrated edge;  FIG. 5D , a curved blade. 
           [0022]    FIGS.  6 A, 6 B are end views of two impeller blade placement embodiments:  FIG. 6A , a blade placed with its radial axis collinear with a radial axis of the shaft;  FIG. 6B , an impeller blade with a radial axis at an angle with respect to the shaft radial axis. 
           [0023]    FIGS.  7 A, 7 B, 7 C illustrate three embodiments varying in longitudinal placement of the impeller blades:  FIG. 7A , the longitudinal axis of the impeller blades parallel with the shaft longitudinal axis;  FIG. 7B , the longitudinal axis of the impeller blades at an angle with the shaft longitudinal axis;  FIG. 7C , the longitudinal axis of the impeller blades is curved downward in a forward direction. 
           [0024]      FIG. 8  illustrates another embodiment of the invention that includes a fairing and a different impeller profile. 
           [0025]      FIG. 9  illustrates an embodiment designed for intermediate shaft bearings. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    A description of the preferred embodiments of the present invention will now be presented with reference to  FIGS. 1-9 . 
         [0027]    In  FIGS. 1 and 2  are shown a typical marine vehicle arrangement of a propeller hub  101 , drive shaft  102 , cutlass bearings  103 , bearing housing  104 , water inlet  105 , and bearing-to-propeller dimension  106 . S 1  and S 2  are an aft strut and intermediate strut, respectively, which support the bearing housings  104 . Vessels with relatively short shafts generally use only one bearing S 1 . Intermediate struts S 2  and bearings  103  are typically used on vessels with longer shafts.  FIG. 2  further includes an illustration of the water channel grooves  107  in the cutlass bearing  103 . 
         [0028]      FIG. 3  shows a cross-sectional side view of a propulsion setup with an embodiment of a device  10  of the present invention mounted in the space  106  abaft the cutlass bearing  103  and before the propeller  100 . For this type of application the device  10  is manufactured to fit the available space  106 , with sufficient clearance to provide for some lateral and longitudinal movement of the shaft. A substantially annular collar  108  is dimensioned for placement over the propeller shaft  102  and extends approximately half the distance of the total length of the distance  106 . Multiple setscrews  109  in the collar  108  can be used to lock the device to the shaft  102 . An annular back-plate  110  is welded to the collar  108  and fits flush against the propeller hub  101  in this embodiment. As an alternative affixing means of locking the device to the shaft  102 , the device may be attached with multiple cap screws fastening the back-plate  110  to tapped holes in the propeller hub  101 . 
         [0029]    Multiple equally spaced impeller blades  111  are disposed radially around the device  10  and are welded to the collar  108  and back-plate  110 . A length  114  of the impeller blades  111  plus a width  115  of the backplate  110  nearly spans the distance  106 , leaving a gap  118  to allow for sufficient clearance between the impeller blades and bearing housing  104 . Forward ends  116  of the impeller blades  111  are welded to an annular ring  112 , which holds the forward ends  116  of the impeller blades  111  in place. The annular ring  112  extends a short distance  119  over an outside  117  of the bearing housing  104 , thereby covering the gap  118  between the impeller blades  111  and bearing housing  104 . 
         [0030]      FIG. 4  shows an end view of the device  10 , with a plurality of impeller blades  111  substantially equally spaced around the shaft  102 . 
         [0031]      FIGS. 5A-5D  depict various impeller blade cross-section embodiments that have been contemplated for use in the invention. although these are not intended as limitations. A simple design  111   a  ( FIG. 5A ) comprises a flat plate blade of rectangular cross section with square outside edge  120   a .  FIG. 5B  illustrates a flat blade design  111   b  with pointed outside edges  120   b .  FIG. 5C  illustrates a flat blade design  111   c  with serrated outside edges  120   c .  FIG. 5D  illustrates a curved blade  111   d  with a pointed outside edge  120   d.    
         [0032]    FIGS.  6 A, 6 B depict end views of two impeller blade placement embodiments  10   a , 10   b , with the embodiment  10   a  of  FIG. 6A  having a blade  111  placed with a radial axis  121  collinear with a radius  122  extending from the shaft axis  123 . In the embodiment  10   b  of  FIG. 6B , an impeller blade  111 ′ is placed with its radial axis  121 ′ at an angle  126  with respect to the radius  122  extending from the shaft axis  123 . The angle  126  can be in a range of 0 to 45 degrees, for example. 
         [0033]      FIGS. 7A-7C  depict embodiments  10   c , 10   d  in longitudinal placements of the impeller blades  111 ″, 111 ′″. The longitudinal axis  124 ″ of the impeller blades  111 ″ can be parallel to the collar axis  127 , which in use is collinear with the shaft axis  123 , as depicted in  FIG. 7A , or the longitudinal axis  124 ′″ can be placed at an angle  125  with respect to the collar axis  127 , as depicted in  FIG. 7B . Alternatively, the impeller blades  111 ″″ can be downwardly curved in a forward direction with respect to the shaft axis  123 , as depicted in  FIG. 7C . The longitudinal blade angle  125  can range between 0 and 30 degrees, for example. 
         [0034]    All the variations in blade cross section and placement depicted in  FIGS. 5A-7C  are capable of successfully achieving the objects of this invention. It is evident that the options in blade cross-section design and placement will only serve to enhance the performance of the invention and provide more options for particular applications. For example, it would seem reasonable that blades and annular rings with sharp and/or serrated edges will cut through fouling better, while curved blade sections will be better at creating pumping action. It is also evident that placing the blades at an angle to the longitudinal axis of the shaft, or having helical blades, may be used to create positive thrust with the device. The performance benefits of a certain blade design and placement scheme for a device can be weighed against the cost of its manufacture, durability, and maintenance. 
         [0035]    Also contemplated in the design of the device are various shaped fairings that may be fixed to the existing bearing housing forward of the device. The benefits of such fairings include that they (1) provide a better hydrodynamic profile, and lower resistance of the device, (2) improve the pumping ability of the invented device by serving as a volute of a pump, (3) help prevent fouling materials from jamming the device. 
         [0036]      FIG. 8  shows another embodiment  10   e  of the invention that includes a fairing and alternative impeller profile. The annular fairing ring  113  can be mounted to the bearing housing  104  with tapped screws. Forward annular ring  112   e  and impeller blades  111   e  are designed to fit the sleeker profile, as compared with the embodiment  10  of  FIG. 3 , with the annular ring  112   e  in this embodiment  10   e  not extending over the bearing housing  104 . 
         [0037]    For intermediate bearings S 2 , where there is no propeller behind the bearing S 2 , the device  10   f  can have a different profile.  FIG. 9  depicts one embodiment  10   f  of the invention designed for intermediate shaft bearings S 2 . A redesigned impeller profile  111   f  and the absence of a back plate present a more hydrodynamic profile, while other elements such as  112   f ,  113   f , and  109  remain similar to the embodiments shown above. The collar  108   f  can have a rounded rear edge  127  for improved hydrodynamic performance. 
         [0038]    It will be understood by one of skill in the art that the embodiment  10   f    FIG. 9  could also be used in concert with any type of shaft-borne bearing, for example, in a pump, for enhancing the lubrication thereof. The structure for this type of device would be substantially the same as that depicted in  FIG. 9 . 
       Design Theory 
       [0039]    The cross-sectional area of the water flow channels in traditional cutlass bearings is relatively small. For example, the height of the water channels in cutlass bearings measured from the shaft surface is less than one-half inch for shafts up to 4 in. thick. Therefore, when propeller shafts become fouled with lines, ropes, or other material behind the cutlass bearing, the water flow through the bearing is quickly blocked. Without a steady flow of water, the bearing and shaft surfaces are starved for lubrication, causing overheating and premature wear in the bearing and shaft surfaces. 
         [0040]    Conventional cutlass bearings depend only on the hydrodynamic force of the water flowing past them to provide water flow through the bearing. Many cutlass bearing housings have an inlet scoop designed on the forward end to promote positive water pressure on the forward side of the bearing. The amount of pressure developed at the forward end of the bearing is proportional to the speed of the water moving past the bearing. A slow-moving vessel, or one that is not moving, will therefore have much less water flowing through the bearing that would a vessel moving at high speed. 
         [0041]    With the use of the instant invention several key improvements are realized. 
         [0042]    1. The aft end of the bearing is shielded from external fouling by the placement of the impeller blades, which extend radially from the surface of the propeller shaft in the device. Restriction of water flow is therefore less likely and also direct wear damage to the bearing is less likely from fouling materials. 
         [0043]    2. The use of the device prevents bearing damage from water starvation even with fouling around the shaft and/or the device. This because the effective discharge area for water coming through the bearing and out of the invented device is about 100 times greater than it is without the device. 
         [0044]    3. The shaft-mounted impeller blades of the invented device cause centrifugal pumping action, which greatly increases the hydraulic force acting on the water that is fed through the cutlass bearing. That centrifugal force creates suction on the aft side of the bearing. The amount of hydraulic pressure imparted by the centrifugal action of the impeller blades is strictly dependent on shaft speed and not vessel speed. Therefore, the benefits of the invention for slower-moving vessels is even more significant. 
         [0045]    4. The sharp edges of rotating impeller blades make a much more hostile environment for fouling material that winds around the shaft than are the relatively smooth surfaces of the shaft and bearing housings found in traditional propulsion systems without the present device. Therefore, fouling is ripped apart by the rotating blades and does not remain in place as long when the device of the present invention is mounted to the propulsion gear. 
         [0046]    Finally, another potential advantage of the device is that the design of cutlass bearings can be improved because engineer-designers will have a new option of having forced water flow available instead of depending only on passive water flow as with conventional bearing designs. 
         [0047]    In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the embodiments of the apparatus illustrated and described herein are by way of example, and the scope of the invention is not limited to the exact details of construction. 
         [0048]    Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.