Abstract:
A quick change bearing holder apparatus for a rotating shaft including a shaft housing, a conical bearing holder and a bearing retainer element. The shaft housing has a conical socket. The conical bearing holder has an outer conical surface compatible with the conical socket of the shaft housing. The bearing retainer element mounts to the shaft housing to urge the bearing holder into the conical socket of the shaft housing. Lubrication feed lines and openings and drain lines and openings may be included in the shaft housing and conical bearing holder. Lubrication may further be facilitated using circumferential grooves in the shaft housing or the conical bearing holder. The outer conical surface of the conical bearing holder may have a taper angle that forms a self ejecting taper.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 12/565,041 entitled “WATERCRAFT PROPELLER PROPULSION SYSTEM HAVING A GIMBAL ASSEMBLY WITH AN EXTERNAL GIMBAL RING” by same inventor, now pending and issuing 1010812013 as U.S. Pat. No. 8,550,863, which itself claims the benefit of U.S. Provisional Application Ser. No. 61/099,820, filed on Sep. 24, 2008, which are both herein incorporated by reference for all intents and purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to watercraft, and more particularly to a quick change bearing holder apparatus for a rotating shaft. 
     2. Description of the Related Art 
     Various types of propulsion systems are known for watercraft. The present disclosure relates to screw propeller propulsion units that mount to a transom of a boat and are often referred to as “surface piercing drives” or “surface drives.”Surface drive propeller propulsion systems are typically provided on boats which operate at high speed and usually have a partially submerged propeller with at least one degree of articulation for tilt or steering adjustment. Conventional surface drive propulsion systems for boats commonly have a rotating propeller shaft coupled via a rotating Universal joint (U-joint) to the drive shaft of a boat motor or engine. The drive shaft, propeller shaft and Universal joint are housed within a non-rotating housing with an articulation joint that allows the drive system to have at least one degree of articulation for tilt or steering adjustment. Various types of articulation joints are known, such as a gimbal. Some conventional configurations do not use a gimbal, but rather use a ball or hollow sphere fitted into a hemispherical seat. The present disclosure, however, is directed towards a gimbal or gimbal assembly. 
     It is noted that the gimbal, although similar in appearance to a Universal joint, has entirely different function, stress analysis, and design constraints such that it warrants a different art classification. A Universal joint is a device used to transmit rotary power in the form of torque from a first rotating shaft to a second rotating shaft at a high rate of speed in which one shaft is allowed to move through various angular deflections relative to the other shaft. A gimbal, on the other hand, is a non-rotating device that is often used to house a Universal joint contained within to provide a guide to the Universal joint and to transmit axial load as common with conventional propeller propulsion systems. 
     A gimbal assembly includes three main components including a first gimbal end, a gimbal ring, and a second gimbal end. The first gimbal end is hingedly connected to the gimbal ring by a pair of gimbal pins to allow articulation about a first axis. The second gimbal end is also connected to the gimbal ring by a second pair of gimbal pins to allow articulation about a second axis. One conventional gimbal assembly includes a gimbal ring that is internal to one gimbal end and that is external to the other gimbal end. Another configuration includes a gimbal ring that is internal to both gimbal ends. Conventional propulsion units use standard rolling element bearings pressed onto the propeller shaft and bolted into the propeller shaft housing and are difficult to access and remove and/or replace. Conventional drive systems do not have a means to measure propeller thrust forces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The benefits, features, and advantages of the present invention will become better understood with regard to the following description, and accompanying drawings, in which: 
         FIG. 1  is an exploded view of the components between Match Line C-C and Match Line D-D of  FIG. 2 , depicting a gimbal assembly including a first gimbal end, a gimbal ring, and a second gimbal end. 
         FIG. 2  is a simplified and exploded view of the sequential relationship of adjacent elements of a watercraft propeller propulsion system having an articulation joint configured as a gimbal assembly with an external gimbal ring according to an exemplary embodiment as further detailed in remaining  FIGS. 1, 3 and 37 . 
         FIG. 3  is a phantom drawing of the gimbal assembly and shows a zigzag shaped gimbal ring in the center. 
         FIG. 4  is combination of an exploded view and a phantom view of the drive shaft housing located between Match Line D-D and Match Line E-E of  FIG. 2 . 
         FIG. 5  is a combination of an exploded view and shows a portion of the drive shaft housing located between Match Line E-E and Match Line F-F of  FIG. 2 . 
         FIG. 6  is a combination of an exploded view and a phantom view of the propeller shaft housing and enclosed propeller shaft located between Match Line C-C and Match Line B-B of  FIG. 2 . 
         FIG. 7  is a combination of an exploded view and a phantom view of the thrust bearing can and enclosed propeller shaft located between Match Line B-B and Match Line A-A of  FIG. 2 . 
         FIG. 8  is a simplified drawing of a conventional Universal joint that couples a drive shaft as shown on the right to a propeller shaft as shown on the left. 
         FIG. 9  is an end view of a bearing retainer plate located inside of the gimbal assembly and is used to secure a bearing holder in place inside of the shaft housing that protrudes into the gimbal end. 
         FIG. 10  is an end view of a seal retainer plate used inside of the gimbal assembly to secure a shaft seal in place. 
         FIG. 11  is a side view of the bearing retainer plate of  FIG. 9  and the seal retainer plate of  FIG. 10  and includes the clamping bolts to retain the plates. 
         FIG. 12  is a side sectional view of  FIG. 11  but rotated 90 degrees to show the relation of the drive shaft  422 , or alternately, propeller shaft  522 , and the bearing holder  622  and the shaft seal  625  and respective retaining plates. This view is a mirror image of  FIG. 11  as it represents the similar items but as located on the other end of the gimbal assembly. 
         FIG. 13  shows a side view of a retaining bolt that holds the gimbal assembly to either the drive shaft housing to the propeller shaft housing. 
         FIG. 14  shows a side view of the thrust collar that is connected to the drive shaft of  FIG. 5 . 
         FIG. 15  is an end view of the thrust collar of  FIG. 14  as mounted on the drive shaft. 
         FIG. 16  is an end view of the oil drain ring of  FIG. 5 . 
         FIG. 17  is an end view of the drive shaft input seal retainer plate of  FIG. 5 . 
         FIG. 18  is perspective view of the drive shaft input seal retainer plate of  FIG. 17 . 
         FIG. 19  is perspective view of the drive shaft forward thrust plate and bolts of  FIG. 5 . 
         FIG. 20  is perspective view of the drive shaft rearward thrust plate and bolts of  FIG. 5 . 
         FIG. 21  is perspective view of the drive shaft forward bearing holder retainer plate and bolts of  FIG. 5 . 
         FIG. 22  is an end view of the drive shaft rearward thrust bearing plate of  FIGS. 5 and 20 . 
         FIG. 23  is an end view of the drive shaft forward thrust bearing plate and bolts of  FIGS. 5 and 21 . 
         FIG. 24  is an enlarged sectional view of the propeller shaft annular thrust piston and propeller shaft annular thrust cylinder of  FIG. 7 . 
         FIG. 25  is a side view of the thrust bearing containment can of  FIG. 7 . 
         FIG. 26  is an end view of the thrust bearing containment can of  FIG. 25 . 
         FIG. 27  is a side view of propeller shaft rear bearing holder retainer plate of  FIG. 7 . 
         FIG. 28  is an end view of propeller shaft rear bearing holder retainer plate of  FIG. 27 . 
         FIG. 29  is a side view of propeller shaft rear seal retaining plate of  FIG. 7 . 
         FIG. 30  is an end view of propeller shaft rear seal retaining plate of  FIG. 29 . 
         FIG. 31  is an exploded assembly drawing shown as a perspective view of the bearing housing and seal parts at the rearward end of the propeller shaft as shown in  FIGS. 25-30  that are part of the bearing housing and seal of  FIG. 7 . 
         FIG. 32  is an enlarged sectional view of the bearing holder in relation to the drive shaft and the drive shaft housing of  FIG. 4 . 
         FIG. 33  is an end sectional view of the bearing holder and drive shaft housing as taken along Section Line  33 - 33  of  FIG. 32 . 
         FIG. 34  is another view of  FIG. 32  of a bearing holder fitted into a drive shaft housing including O-ring grooves and O-rings. 
         FIG. 35  is a view of a ball bearing held in bearing holder of  FIG. 32 . 
         FIG. 36  is a view of a tapered roller bearing held in bearing holder of  FIG. 32 . 
         FIG. 37  is a 360 degree view of the gimbal assembly of  FIG. 1  showing the cylindrical parts as though they were cut open and unwrapped to lay flat on a sheet of paper to illustrate the construction of the parts. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable one of ordinary skill in the art to make and use the present invention as provided within the context of a particular application and its requirements. Various modifications to the preferred embodiment will, however, be apparent to one skilled in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described herein, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed. 
     A watercraft propeller propulsion system as described herein is significantly more user friendly than conventional watercraft propeller propulsion systems. One embodiment relates to the construction of a gimbal assembly that connects the propeller shaft housing to the drive shaft housing that is connected to the boat. One embodiment relates to the quick-change journal bearing holders to support the propeller shaft. One embodiment relates to a thrust bearing assembly that is also used to measure propeller thrust forces. One embodiment relates to a bearing assembly with a lubricant impelling system and method. 
     The various embodiments provide any of one or more benefits as described herein. One benefit is that the propulsion unit may be designed to be more accessible for ease of maintenance of internal parts, and can be serviced with simpler tools. Another benefit is that the gimbal assembly uses an external gimbal ring, which permits ease of maintenance to the Universal joint located within, while still maintaining compact overall assembly dimensions. Another benefit is that the gimbal ring is designed in a zigzag configuration to permit the gimbal pins to be easily removable and installable. In one embodiment, for example, gimbal pins are clamped to the external gimbal ring using U bolts and corresponding nuts which are more easily accessible and removable with a single wrench. For example, the U bolt nuts may be loosened and tightened without a backup wrench. Also, the U bolt avoids a blind or threaded hole in the gimbal ring as is common for conventional gimbal assemblies. A zigzag shaped configuration allows the most compact gimbal ring because the clearance between the gimbal ring and the gimbal ends can be minimized since the area where the gimbal ring overlaps the gimbal end is at the same area where the two parts swivel parallel to each other. A compact gimbal ring has a smaller diameter than a conventional gimbal ring which allows the propeller shaft and drive shaft to be located as low as possible at the transom of a boat. Such configuration enables the propeller thrust vector to have a minimum vertical component, so that the thrust vector is more parallel to the direction of travel of the boat as compared to conventional gimbal assemblies which are larger and less compact. Furthermore, in conventional gimbal assembly configurations, a bellows is mounted around the Universal joint inside the larger conventional gimbal assembly to minimize exposure of the Universal joint to water, sand and other contaminants. A gimbal assembly with an external gimbal ring facilitates a more compact configuration so that the bellows may be mounted outside of the external gimbal ring. This enables quick change of the bellows without disassembly of the gimbal. 
     Another benefit is that the bearings that support the rotating shaft may be held in tapered holders for quick change from the stationary housing. This quick-change can be done by using simple hand tools. Another benefit is that the bearings may be configured with positive oil feed from a pressurized source for circulating cooled and filtered oil through the bearings. Another benefit is that the thrust load from the propeller may be constrained and transferred to the propeller shaft housing by a hydraulic or hydrostatic bearing that uses a pressurized oil source to levitate the thrust ring of the propeller shaft on a contained reservoir of oil to allow the frictional forces to be minimized. Another benefit is that the hydrostatic thrust bearing may be used as part of a remotely readable measure of the amount of thrust pushing the boat through the water at any given operating condition or speed. Alternately, the hydrostatic thrust bearing can be locked against rotation and used as a non-rotating load cell used for measuring axial load forces. Another benefit is to provide bearing assembly with an oil impelling means to circulate oil lubricant. 
       FIG. 2  is a simplified and exploded view of the sequential relationship of adjacent elements of a watercraft propeller propulsion system having an articulation joint configured as a gimbal assembly with an external gimbal ring according to an exemplary embodiment as further detailed in remaining  FIGS. 1, 3 and 37 .  FIG. 2  is a guide to the spatial relationship of adjacent elements of the total assembly, in which the propeller is shown on the left, the gimbal assembly is shown in the middle as a blank space, and the power input end is shown on the right and connects to a motor (not shown). Each figure includes Match Lines that delineate the sequential element from its neighboring element as the viewer goes from one end of the boat propulsion unit to the opposite end of the boat propulsion unit. The sequence of elements is shown in  FIG. 2  and shows the propeller on the left end of the figure near Match Line A-A, and shows the power input end at the right end of the figure near Match Line F-F. The two sections located on the left side between Match Line A-A and Match Line C-C depict the propeller shaft end of the system. The two sections located on the right side between Match Line D-D and Match Line F-F depict the drive shaft end of the system. The motor for the boat is connected at Match Line F-F. Match Lines may not have any structural meaning and may simply represent a convenient point on a larger detailed drawing where the components seem to end, but it is simply for convenience and clarity that the Match Lines are shown at the locations selected. The concept of an “exploded view” is used to depict the individual elements in relation to the adjacent elements and is commonly used in machine design and assembly drawing. The forward end of the boat propulsion unit is towards Match Line F-F where the motor is located, and the rearward end of the boat propulsion unit is towards Match Line A-A where the propeller is located. 
       FIG. 1  is an exploded view of the components between Match Line C-C and Match Line D-D of  FIG. 2  and depicts a gimbal assembly including a first generally cylindrical gimbal end, a gimbal ring, and a second generally cylindrical gimbal end. This assembly allows the propeller shaft housing located to the left of Match Line C-C to articulate relative to the drive shaft housing located to the right of Match Line D-D. The gimbal assembly is a non-rotating assembly that goes over the rotating Universal joint contained within, but not shown in this figure. Refer also to  FIG. 3  and  FIG. 37 . 
     The gimbal assembly has a novel arrangement of a gimbal ring  344  that is located externally to both gimbal ends. Gimbal assemblies are usually constructed from two end elements referred hereinafter as gimbal ends, plus a gimbal ring, and two pairs of gimbal pins. Conventional gimbal assemblies are constructed with the gimbal ring fitting in the radial space between the two gimbal ends. That is to say, in a conventional configuration, the gimbal ring is located both radially internal of one gimbal end and radially external of the other gimbal end, so that it is not an external gimbal ring. The gimbal ring  344  described herein is external since it is located radially external of both the first gimbal end  354  and located radially external of the second gimbal end  364 . Thus, the gimbal assembly includes a first gimbal end  354 , and a gimbal ring  344 , and a second gimbal end  364 , wherein said gimbal ring is located radially external to both the first gimbal end and located radially external to the second gimbal end. 
       FIG. 1  also shows another novel aspect in which the gimbal ring  344  is offset in a zigzag fashion such that the four individual gimbal pins  345  are located near the longitudinal faces of the gimbal ring wherein the adjacent gimbal pins, that are located 90 degrees away from each other, are near opposite longitudinal end faces, a first end face  396 , and a second end face  397 , of the gimbal ring, yet are aligned to be located on a single transverse plane. The plane of the gimbal pins is oriented to be transverse and perpendicular to the longitudinal axis of the gimbal assembly. External gimbal ring  344  is a generally cylindrical element and has ends that resemble a zigzag shape. The zigzag is intentional to allow the gimbal pins  345  to be mounted to the alternate faces of the gimbal ring at corresponding recesses  346  and secured with U-bolts  355  and nuts  356 . This is a face loaded gimbal ring. That is to say, in one embodiment the gimbal assembly includes a gimbal ring  344  in which the gimbal ring is generally cylindrical and has two pairs of gimbal pins  345  such that a first pair of gimbal pins are located diametrically opposite of each other on the gimbal ring, so that a second pair of gimbal pins are located diametrically opposite of each other on the same gimbal ring, and so that the first pair of gimbal pins form a first line and the second pair of gimbal pins from a second line and wherein the first line and second line intersect and form a plane in which the plane is generally transverse to the longitudinal axis of the gimbal ring, and in which the first pair of gimbal pins is located at a first longitudinal end face of the gimbal ring and the second pair of gimbal pins is located at a second longitudinal end face of the gimbal ring. The shape of the gimbal ring according to one embodiment is further explained in  FIG. 37 . 
     A first advantage to this zigzag ring configuration is that the gimbal pins can be placed in a common transverse plane relative to the centerline of the propulsion unit and the gimbal ring diameter can be minimized. This reduced diameter is possible because each transverse axis of the gimbal ring pivots about each opposite pair of gimbal pins  345  on opposite sides of a first gimbal end  354  and on opposite sides of a second gimbal end  364 , in closer clearance than would be possible with a gimbal ring that was symmetric about the common transverse plane of the gimbal pins. Thus, this is a space saving feature to allow a more compact overall diameter of the gimbal assembly. This is desirable in this application on boats because it is desirable to minimize the overall diameter of the gimbal assembly. 
     A second advantage to the zigzag configuration is that the radial clearance between the gimbal ring  344  and a gimbal end  354  is minimized to therefore minimize the bending moments on the gimbal pins  345  and also minimize the internal torsional stresses generated in the gimbal ring. 
     A third advantage to this zigzag shaped gimbal ring  344  is that the gimbal pins  345  can be secured to the faces of the gimbal ring with U-bolts  355  and nuts  356  to facilitate the ease of removal and replacement of the gimbal pins. The U-bolts and nuts are simply loosened and the gimbal pins are pulled out or reinserted to allow disassembly and reassembly of the gimbal assembly. Gimbal cross pins  348  prevent inserting the gimbal pins  345  too deeply into the grip of the U bolts  355 . This disassembly and reassembly of the gimbal unit is beneficial to gain access for removal and replacement of the rotating Universal joint  602  that is located inside the gimbal assembly. An exemplary Universal joint is shown in  FIG. 8 . 
     The term zigzag is used to figuratively describe the shape of the end faces of the gimbal ring  344  as can be seen clearly in  FIG. 37 . The end faces are undulated along the axis of the gimbal assembly and have two high and two low areas on each end face of the gimbal ring and are phased such that the general length of the gimbal ring is relatively uniform. Each end face of the gimbal ring is undulated with two highs and two lows per side. 
     The first gimbal end  354  is generally a cylinder shape and has two axial extensions commonly referred in the industry as first end yoke  398  that includes a pair of gimbal pin holes  349  to receive gimbal pins  345 . Similarly, the second gimbal end  364  is generally a cylinder shape and has two axial extensions common in the industry shown as second end yoke  399  that includes a pair of gimbal pin holes  349  to receive gimbal pins  345 . This arrangement is further explained in  FIG. 37 . 
       FIG. 3  is a phantom drawing of the gimbal assembly and shows a zigzag shaped gimbal ring  344  in the center and includes the gimbal pins  345 . In one embodiment, the gimbal ring appears as a zig-zag shaped cylinder. The figure also shows the corrugated bellows  375  on the outside to seal out water. The splined shaft  523  shown on the left is the input end of the propeller shaft and the splined shaft  423  shown on the right is the connecting end of the drive shaft. Not shown in this view is a rotating Universal joint that connects the spline of the rotating drive shaft to the spline of the rotating propeller shaft. 
       FIG. 3  is similar to  FIG. 1  but is more detailed to show adjacent parts of the boat propulsion system.  FIG. 3  is not an exploded diagram, but is generally a longitudinal section view along the centerline of the drive shaft spline  423  shown on the right side and the propeller shaft spline  523  shown on the left side. Drive shaft spline  423  is held in radial position relative to the gimbal assembly by the use of journal bearings mounted in a cone shaped bearing holder  622  having an outside diameter  427  with a defined angle of taper, or taper angle  620  ( FIG. 35 ). The bearing holder  622  is held into a mating tapered seat  425  of a drive shaft housing  424  ( FIG. 32 ) by a bearing retainer plate  623  and by retainer bolts  626  and nuts  356 . Shaft seal  625  is located outside of the bearing retainer plate by seal retainer plate  624  that is, in turn, clamped in position by bolts similar to retaining bolts  626 . A first gimbal end  354  is integral with a first gimbal flange  384 . The gimbal flange is typically circular and has bolt holes around the perimeter to accommodate bolting to the transom of the boat at Match Line DD. Other methods of fastening are contemplated. A second gimbal end  364  is likewise integral with a second gimbal flange  394 . The first gimbal end and first gimbal flange are generally identical to the second end, but are rotated 90 degrees relative to each other. Shaft splines  423  or  523 , bearing mounting and shaft sealing details of the drive shaft  422  and propeller shaft  522  within the gimbal assembly are very similar on either end. These details are shown and described in greater clarity in  FIGS. 9-12 . Alignment pins  311  are inserted temporarily into alignment pin holes  312  in first gimbal end  354  and second gimbal end  364  to keep the ends from flopping around when the gimbal assembly is being reassembled. Gimbal pin  345  has pull ring  347  and gimbal pin cross pin  348  that limits the insertion depth of the gimbal pin into the U bolt  355 . Bellows  375  is clamped to bellows ring  374  with bellows clamp  376 . Bellows ring has fill and drain holes  377  to flush and purge the enclosed space. Gimbal ends have access holes  366 , inspection holes  365 , and grease fittings  325  to pump sealant into the cracks between mating components. 
       FIG. 4  is combination of an exploded view and a phantom view of the drive shaft housing  424  located between Match Line D-D and Match Line E-E of  FIG. 2 . This portion of the propulsions unit is located where the drive shaft penetrates the transom  112  of the boat. The drive shaft housing flange  410  is integral with the drive shaft housing  424 . This is the portion of the propulsion system that pierces the transom  112  of the boat from the outside and is bolted in place by transom plate  417 , transom bolts  415 , and nuts  356 . The drive shaft  422  is located inside the center bore of the drive shaft housing  424  and is carried on a journal bearing mounted inside bearing holder  622  located on either end of the drive shaft housing  424 . Oil feed inlet  409  on the drive shaft housing provides a convenient point for introducing lubricating oil into an internally drilled longitudinal oil feed line  411 . Pressurized oil feeds in both directions to lubricate the bearings on either end of the drive shaft. Oil is returned via a similar internally drilled oil drain line  413  and drains out of the drive shaft housing via oil drain outlet  412  into a contained area defined by rubber reduction sleeve  495  and oil drain ring  490  and secured with hose clamps  376  including other oil containment parts in the adjacent portion of the drive shaft housing as shown in  FIG. 5 . U bolts  431  are shown separate from the housing but actually go into the crescent cuts  421  and are used to hold the adjacent parts in place in the drive shaft housing. The bellows  375  of  FIG. 3  are held in place with hose clamps  376 . 
       FIG. 5  is a combination of an exploded view and shows a portion of the drive shaft housing located between Match Line E-E and Match Line F-F as noted in  FIG. 2 . This portion of the propulsion system is located where the drive shaft connects to the inboard style boat engine or motor not shown, but located to the right side of the drawing. 
       FIG. 5  shows a continuation of  FIG. 4  between Match Lines E-E and Match Lines F-F and is shown as the input end of the drive shaft  422  where the drive shaft connects to the boat motor (not shown) via drive shaft input spline  499  on the right end of the drive shaft. The drive shaft is hollow and has a threaded rod  472  running down the center to the opposite end used to hold the Universal joint in place on the opposite end of the drive shaft. A drive shaft nut  471  with O-ring  473 , is tightened to pull the Universal joint tight onto the drive shaft output spline  423  shown in  FIG. 3 . Section Line  17 - 17  refers to  FIG. 17  where it is seen that the entire assembly is generally cylindrical. Chains  445  and screen door style spring  447  are tensioned and looped over and attach to bolts  439  to urge motor end seal retaining plate  438  to the left to secure shaft seal  625  against drive shaft forward thrust plate  482  to form a compression seal. Anti-rattle sleeves  448  are short pieces of loose fitting rubber hose slid onto the chain to prevent chain rattle. The shaft seal may be configured as a simple sheet of Teflon with a slightly undersized hole through the center to slip over the drive shaft. The Teflon seal is conformal and lends itself to quick and easy field repairs. 
     U bolts  433 ,  435 , and eyebolt  437  are shown at the top and bottom of  FIG. 5  to illustrate how these appear when properly installed adjacent to the drive shaft  422  in this figure. Bearing holder  622  is urged to the left by drive shaft forward bearing retainer plate  432  and held tight by U bolts  431  of  FIG. 4 . Bearing retainer plate  432  now provides an anchor point for U bolts  433  that is used to adjustably secure drive shaft rearward thrust plate  434  in correct axial position. U bolts  435  are secured to drive shaft rearward thrust plate  434  and bridge over the gap to a similar drive shaft forward thrust plate  482  discussed earlier. The drive shaft thrust bearing collar  440  is secured to the drive shaft and rides between a pair of drive shaft thrust bearing blocks  436  on either side of the thrust collar. Tie wires  443  hold thrust bearing blocks in place. The drive shaft thrust collar is detailed in  FIG. 14  and in  FIG. 15 . This thrust bearing assembly can be designed as a light weight assembly because only the inertial mass of the drive shaft and the Universal joint are carried by this assembly and none of the propeller thrust is carried here. 
     Lubricating oil is contained by rubber sleeve  496  and rubber sleeve  497  that are both secured to drive shaft oil drain ring  490  by using hose clamps  476 . The rubber sleeves are generally short pieces of large diameter hose. 
     Although other bolting and sealing methods may be used, it is desired to have a very field serviceable unit that can be repaired and adjusted using the simplest of hand tools and using captive bolts that swing aside after loosening the nuts, and U bolts to eliminate the need for a second wrench to hold the other end of the bolt, or to have blind or threaded holes in the drive shaft housing. 
       FIG. 6  is a combination of an exploded view and a phantom view of the propeller shaft housing  524  and enclosed propeller shaft  522  located between Match Line C-C and Match Line B-B of  FIG. 2 .  FIG. 6  is a side view similar to the others and shows a propeller shaft housing  524  between Match Line B-B and Match Line C-C as seen in  FIG. 2 . This end is similar to the drive shaft end of the propulsion system in that the propeller shaft housing is generally cylindrical with a hollow center and a propeller shaft  522  running down through the center. The rotating propeller shaft is carried by a journal bearing in a bearing holder  622  on each end of the propeller shaft. Lubricant input hole  510  feeds cleaned and cooled oil to the bearings in the bearing holders. Oil is fed via oil feed tube  511 . Oil drained out of the rearward bearing returns via the annular space between the propeller shaft and the propeller shaft housing and combines with oil in oil drain line  509  to ultimately exit via oil drain hole  512 . 
     Spring levers  549  with spring  547  and cable hook  548  exert a tension force on tension cable  545  to urge shaft seal  625  into place as shown on  FIG. 7 . Crescent cuts  521  provide a place to secure U bolts  531  to the propeller shaft housing in a fashion similar to that shown on the drive shaft end as shown in  FIG. 4  and  FIG. 5 . Oil inlet hole  512  feeds oil via oil lines  514  to the thrust bearing assembly of  FIG. 7 . Propeller shaft housing flange  510  is integral to propeller shaft housing  524  and further stiffened by braces  525 . U-bolt  313  are held in place by cover strips  524 , sealed by patch seals  527 , and all held in place by screw clamps  526 . 
       FIG. 7  is a combination of an exploded view and a phantom view of the thrust bearing can  534  and enclosed propeller shaft  522  located between Match Line B-B and Match Line A-A as noted in  FIG. 2 . A propeller  111  is shown to the left of Match Line A-A.  FIG. 7  is similar to  FIG. 5  in that it has a shaft bearing in bearing holder  622 , a thrust bearing assembly discussed below, and a shaft seal between the propeller shaft  522  and the thrust bearing containment can  534 . The propeller  111  slides onto propeller shaft spline  599 . 
     The thrust bearing assembly is much heavier on the propeller shaft than it is on the drive shaft because the entire thrust load from the propeller is carried in this assembly and is transferred to the propeller shaft housing  524  and ultimately through the gimbal assembly and to the boat hull at the transom. The thrust bearing assembly is comprised of an enlarged portion of the propeller shaft against which forward thrust collar  580  and rearward thrust collar  550  are abutted. The forward thrust collar  580  has impeller holes  581  drilled radially, plus others, to act as the impeller of a small oil pump to induce oil flow through the forward thrust bearing assembly located just to the right of the forward thrust collar. The forward thrust bearing assembly has a plurality of thrust bearing elements  557  located between a plurality of thrust bearing races  559 . The thrust bearing elements may be anti friction rolling elements or may be low friction Teflon washers. The thrust bearing assembly also has an annular thrust cylinder  537  and annular thrust piston  535  shown in an enlarged view in  FIG. 24 . The annular thrust cylinder is circular in shape and forms an annular space between the inner wall and outer wall of the thrust cylinder. In other words, the thrust cylinder looks like a square sided “U” shape that is rotated about the centerline of the propeller shaft. The annular thrust piston is circular in shape similar to a fat and thick washer and fits into the circular groove of the annular thrust cylinder. The annular thrust piston has at least one oil feed passage  505  drilled through it from front to rear. This oil feed passage allows high pressure oil to flow from a source forward of the annular thrust piston to the pressurized chamber formed behind the annular thrust piston and within the annular thrust cylinder. There is at least one bleed port  507  located near the rear portion of the inside wall of the annular thrust cylinder wherein the bleed port allows excess oil to flow out of the confined space between the head of the annular thrust piston and the bottom of the annular thrust cylinder. The annular thrust cylinder rotates along with the propeller shaft. The annular thrust piston is stationary relative to the propeller shaft housing. 
     This annular thrust piston and annular thrust cylinder serve two purposes. The first purpose is to provide a hydrostatic oil cushion between a rotating part, e.g., the annular thrust cylinder, and a stationary part, e.g., the annular thrust piston. The roles of these two components can be reversed. Thus, the combination forms a very low friction thrust bearing assembly. The second purpose is to provide a thrust force measuring system that is based on the prevailing oil pressure within the confined space of the annular thrust cylinder and annular thrust piston. An oil pump with a high pressure discharge is located at some convenient location on the boat. Somewhere on the discharge line of the pump is a metering orifice. Downstream of the metering orifice is located an oil pressure gauge and an oil line routed back to feed the metered oil to the oil feed passage through the thrust piston. As the thrust force of the propeller pushes the propeller shaft and annular thrust cylinder forward, the bleed port in the annular thrust cylinder is progressively covered more and more by the forward motion and the oil pressure builds to a higher and higher value because the bleed port is progressively covered more and more. Thus, the oil pressure gauge reads a progressively higher pressure proportionate to the thrust force of the propeller on the boat. The converse operation, wherein the propeller generates less and less thrust, allows the annular thrust cylinder to move rearward relative to the annular thrust piston and tends to uncover the bleed port in the annular thrust cylinder wall, hence, the pressure on the oil pressure gauge is decreased proportionate to the decrease in the thrust force of the propeller on the boat. In this embodiment, metered oil is fed through a passage in bearing holder  622  and into the forward face of the annular thrust piston  535 . Other means of oil feed can be used Annular thrust piston and annular thrust cylinder can be replaced with electronic load cells of similar annular shape, for example, “Large I.D. Through Hole Load Cell LC8213-200-5K” sold by Omega Engineering. 
     Rearward thrust collar  550  and rearward thrust bearings  536  push against thrust bearing containment can  534  when the propeller generates rearward thrust. Rear thrust bearings can be needle type or Teflon washers including shims for axial position adjustments. 
     Thrust bearing containment can  534  is in the shape of a cylinder with a full diameter hole at one end and an axial hole in the other end where the propeller shaft  522  exits. U bolts  533  and nuts  356  hold the thrust bearing containment can tight against bearing retainer plate  532 . Bearing retainer plate is held in place against the propeller shaft housing by U bolts  531  and nuts  356 . 
     Shaft seal  625  can be a sheet of Teflon with a tight fit over the propeller shaft  522  and is held tight against the rear face of the thrust bearing containment can  534  by means of rear propeller shaft seal holder plate  538  and is urged forward by tension cables  545  and cable hooks  548  shown in  FIG. 6 . Rear propeller shaft seal holder plate  538  has string cutters  560  with sharp edges to cut any fishing line wound around the propeller shaft. String cutters are also known as line cutters. Cable grommets  539  prevent chafing of tension cables  545  and preserve rotational alignment. 
     The propeller  111  is mounted to the propeller shaft in the ordinary way by use of propeller shaft splines  599 . Forward motion of the propeller is limited by a propeller thrust washer  710  that has an internally tapered shoulder and fits on a complimentary tapered shoulder near the end of the propeller shaft  522 . Propeller thrust washer  710  has rotating string cutters  712  with sharp edges to cut any fishing line wound around the propeller shaft. String cutters are also known as line cutters. 
       FIG. 8  is a simplified drawing of a conventional Universal joint  602  that couples a drive shaft  422  as shown on the right to a propeller shaft  522  as shown on the left. The universal joint is located within the confines of the gimbal assembly of  FIG. 1  and  FIG. 3 . The illustrated Universal joint  602  is market available and typical of a double yoke Cardan style. These Universal joints are also referred to as “three piece Universal joints” comprising an input section  642 , a center section  672 , and an output section  652 . Not shown, but common to all these Universal joints is a cross piece that is inserted into bearing holes  662  in each of the three sections. The Universal joint is located inside of the gimbal assembly of  FIG. 1  and  FIG. 3 , but is not shown in those views to prevent clutter. The input section  642  is connected to drive shaft spline  423  and the output section  652  is connected to the propeller shaft spline  523  with a sliding fit. Universal joint center section  672  is located between the input section and the output section. The input section is secured to the drive shaft by a bolt  472  and washer  402  to prevent axial motion between the drive shaft and the input section. The drive shaft thrust bearing assembly of  FIG. 5  is adjusted to correctly locate the Universal joint center section to be longitudinally centered within the gimbal assembly of  FIG. 1  and  FIG. 3 . That is to say, the center plane of the Universal joint center section  672  is longitudinally centered at the same plane as the gimbal pins  345  of the gimbal assembly of  FIG. 1  and  FIG. 3 . Slight longitudinal displacement can be tolerated, but it is not desirable. 
       FIG. 9  is an end view of a bearing retainer plate  623  located inside of the gimbal assembly and is used to secure a bearing holder in place inside of the shaft housing that protrudes into the gimbal end. The bearing retainer plate  623  is viewed along Section Line  9 - 9  of  FIG. 3 . Second gimbal end  364 , or alternately, first gimbal end  354 , are shown as cross hatched and access holes  366  allow access to bolts and nuts inside. Slots at the top and bottom of the bearing retainer plate are for U bolts  626  shown in  FIG. 11 . 
       FIG. 10  is an end view of seal retainer plate  624  as viewed along Section Line  10 - 10  of  FIG. 3 , in which the seal retainer plate used inside of the gimbal assembly to secure a shaft seal in place. Second gimbal end  364 , or alternately, first gimbal end  354 , are shown as cross hatched and access holes  366  allow access to bolts and nuts inside. Slots at the top and bottom of the seal retainer plate are for receiving swing bolts  627  shown in  FIG. 11 . 
       FIG. 11  is a side view of the bearing retainer plate of  FIG. 9  and the seal retainer plate of  FIG. 10  and includes the clamping bolts to retain the plates.  FIG. 11  is a top view of an enlarged portion of  FIG. 3  as viewed along Section Line  11 - 11 . This view straddles Match Line C-C and shows how the U bolt  626  secures the bearing retainer plate  623  with nuts  356 . Also shown is the seal retainer plate  624  held in place by swing bolt  627  and nut  356 . The swing bolt is configured as an eye bolt fitted onto the square U bolt  626  and both are inserted into gimbal plate  394  or ( 384 ) before it is bolted to propeller shaft housing plate  510  or (drive shaft housing plate  410 ). This construction of using captive bolts allows both the U bolt and the swing bolt to be tightened or loosened with a single wrench and swung aside for removal of the respective retainer plates without loosing either the nuts or the bolts. 
       FIG. 12  is a side view of  FIG. 11  and is taken along Section Line  12 - 12  of  FIG. 3 , but is rotated 90 degrees to show the relation of the drive shaft  422 , or alternately, propeller shaft  522 , and the bearing holder  622  and the shaft seal  625  and respective retaining plates. This view is a mirror image of  FIG. 11  as it represents the similar items but as located on the other end of the gimbal assembly. This view shows how the bearing retainer plate  623  holds the bearing holder  622  into place in the drive shaft housing  424 , or alternately in the propeller shaft housing  524 . Shaft seal  625  is held by shaft seal retainer plate  624 . Bearing retainer plate  623  is held in position by U bolts  626  and nuts  356  that can be loosened and swung away for removal of the bearing holder. Shaft seal retainer plate  624  is held in place by eye bolt  627  and nuts  356  that can be loosened and swung away for removal of the shaft seal  625 . 
       FIG. 13  shows a side view of a retaining bolt  313  that holds the gimbal assembly to either the drive shaft housing, or alternatively, to the propeller shaft housing.  FIG. 13  is a view of clamping U bolt  313  and nuts  310  that hold second gimbal flange  394 , or alternately first gimbal flange  384 , together against propeller shaft housing flange  510  or drive shaft housing flange  410  as seen in  FIG. 3  and  FIG. 6 , or  FIG. 3  and  FIG. 4 , respectively. 
       FIG. 14  is a side view of drive shaft thrust collar  440  mounted on drive shaft  422  as viewed in  FIG. 5 . Drive shaft thrust collar takes on the appearance of a V belt pulley with flat faces and has the small diameter of the pulley groove cut away at two locations to allow the buckle portion of a pair of collar clamps  480  to intrude into a groove cut into the drive shaft. Thus, the thrust collar is easily removed and replaced without any loose part by simply loosening the collar clamps to slide the drive shaft thrust collar off the end of the drive shaft. An ordinary hose clamp can be used as a collar clamp. However, a pair of hose clamps connected nose to tail to each other is better because it ensures symmetry such that rotating balance is preserved. 
       FIG. 15  is an end view of the thrust collar  440  as mounted on the drive shaft  422  of  FIG. 14  taken along Section Line  15 - 15  and shows the detail of the buckle portion of the collar clamps  480  actually intruding into the groove in drive shaft  422 . 
       FIG. 16  is an end view of oil drain ring  490  as shown in Section Line  16 - 16  of  FIG. 4  and similarly in  FIG. 5 . Oil drain ring is made of rigid material, usually metal, that has drain holes  492  for hose fitting to return oil to a reservoir not shown. Hose clamps  376  hold hose  496  and hose  497 , as shown in  FIG. 5 , in place to prevent leakage. 
       FIG. 17  is an end view of drive shaft oil seal retainer ring  438  as viewed in Section Line  17 - 17  of  FIG. 5 . Bolts  439  are secured with nuts  356  and provide an attachment point for chain  445  used to tension drive shaft oil seal retainer plate against shaft seal  625  shown in  FIG. 5 . 
       FIG. 18  is a perspective view of drive shaft oil seal retainer ring  438  shown in  FIG. 17  and  FIG. 5 . Bolts  439 , with nuts  356 , provide an attachment point for chain. 
       FIG. 19  is a perspective view of drive shaft forward thrust plate  482  as shown in  FIG. 5 . Location for U bolts  435 , eye bolts  437 , and nuts  356  are shown. 
       FIG. 20  is a perspective view of drive shaft rearward thrust bearing plate  434  as shown in  FIG. 5 . Locations for U bolts  433 , and nuts  356 , are shown. 
       FIG. 21  is a perspective view of drive shaft forward end bearing retainer plate  432  as shown in  FIG. 5 . Locations for U bolts  431 , and nuts  356 , are shown. 
       FIG. 22  is an end view of drive shaft rearward thrust bearing plate  434  as shown in  FIG. 5  and  FIG. 20  but is shown to illustrate the approximate layout required for machining of the bolt holes and slots. 
       FIG. 23  is an end view of drive shaft forward bearing retainer plate  432  as shown in  FIG. 5  and  FIG. 21  but is shown to illustrate the approximate layout required for machining of the bolt holes and slots. 
       FIG. 24  is an enlarged and detailed side sectional view of an annular thrust cylinder  537  and an annular thrust piston  535  as seen in  FIG. 7  on propeller shaft  522 . Details of the oil bleed port  507  through the annular thrust cylinder and oil feed passage  505  drilled through annular thrust piston are shown. This is configured as an annular piston that fits inside an annular cylinder that are filled from a high pressure oil source through the oil feed passages to cause the oil to push the annular cylinder towards the rearward position and away from the annular piston. Propeller thrust forces in the forward direction cause the annular cylinder to be pushed forward towards the annular piston. As the propeller thrust forward forces increase, the oil bleed port is progressively closed by the closing motion of the annular piston into the annular cylinder, thus raising the oil pressure as read by the remote gauge. Thus, the trapped oil causes the annular piston to assume an equilibrium position in the annular cylinder. As the propeller thrust decreases, the annular cylinder moves rearward by a small amount thus allowing more of the trapped oil to flow out of the oil bleed port and the system comes to a new equilibrium position. The pressure of the oil trapped in the cylinder is proportional to the forward thrust force of the propeller. This pressure is read by a remote gauge located at the drivers convenience to monitor the propeller thrust. This combination of an annular cylinder and an annular piston also serve as a hydraulic bearing that is a hydrostatic bearing. This is different from a hydrodynamic bearing such as a Kingsbury thrust bearing or a journal sleeve bearing which operate by a skiing action of a moving shaft against a stationary bearing causing the oil to be swept into a thin wedge shaped film of oil separating the two mating machine parts. One of the embodiments of this invention is the oil filled annular cylinder with an annular piston that serve either as a hydraulic thrust bearing, or as a hydraulic thrust force sensor. 
       FIG. 25  is a side view of thrust bearing containment can  534  as shown in  FIG. 7 . This figure also shows details of an oil return hole  570  as drilled diagonally into a threaded hole  572  for an oil drain fitting that is piped back to an oil reservoir on the boat. 
       FIG. 26  is an end view of thrust bearing containment can  534  as shown in  FIG. 25  as viewed along Section Line  26 - 26 . Various holes are shown for U bolts  533  and tension cables  545  shown in  FIG. 31 . Oil return hole  570  and threaded hole  572  of  FIG. 25  are shown. 
       FIG. 27  is a side view of propeller shaft rear bearing retainer plate  532  as shown in  FIG. 7 . 
       FIG. 28  is an end view of propeller shaft rear bearing retainer plate  532  as shown in  FIG. 27  as viewed along Section Line  28 - 28 . Holes for bolts and slots for cables are shown for machining layout. 
       FIG. 29  is a side view of propeller shaft seal retainer plate  538  as shown in  FIG. 7 . Tension cable  545  is shown passing through cable grommets  539  and includes sharp edged string cutters  560 . String cutters are also called line cutters. 
       FIG. 30  is an end view of propeller shaft seal retainer plate  538  as shown in Section Line  30 - 30  in  FIG. 29 . Cable grommets  539  and sharp edged string cutters  560  are also shown. String cutters are also called line cutters. 
       FIG. 31  is a perspective of an exploded view of the propeller shaft thrust containment can  534  including U bolts  531 , and U bolts  533 , and nuts  356  that holds the propeller shaft thrust containment can against propeller shaft bearing retainer plate  532  which is in turn held against bearing holder  622  forced into the propeller shaft housing  524 , both shown in  FIG. 7  by U bolts  531 . Also shown is propeller shaft seal retainer plate  538  with string cutters  560  and cable grommets  539  that hold it in place around the propeller shaft by means of tension cables  545 . All of which can be seen in  FIG. 7 . 
       FIG. 32  is a side sectional view of bearing holder  622  as seen in  FIG. 3  near Match Line D-D. Drive shaft housing  424  has the tapered seat  425  to receive the tapered outside diameter  427  of the bearing holder, the tapered seat in non-deformable  622 . Oil supply drilled hole  411 , shown in  FIG. 4 , supplies pressurized oil from a remote oil reservoir not shown. Oil return drilled hole  413  provides a drain path away from the bearing as seen in  FIG. 4 . Oil supply drilled hole communicates with a first circumferential groove  931  that allows the bearing holder to be inserted in any angular orientation and still ensure that oil will feed into bearing holder oil feed passages  911  into an internal annular groove  951  to feed lubricating oil into sleeve bearings  922 . Similarly, oil return drilled hole  413  aligns with a second circumferential groove  933  that allows the lubricating oil that seeps out of the end of the sleeve bearings to slide down into face groove  953  and pass through drilled drain holes  913  and to oil return drilled hole  413  to ultimately return to a reservoir located on the boat. Bearing holder  622  has a recessed face area  952  to allow clearance for the return oil to flow radially from the drive shaft outward to annular face groove  953 . As stated before, bearing retainer plate  623  urges bearing holder  622  into the mating tapered seat  425  of the drive shaft housing  424 . The location of the shaft seal  625  is shown. Circumferential O-ring grooves  944  are located on the tapered outside diameter  427  and on the end face of the bearing holder  622 . Drive shaft housing has an inside bore diameter  963  greater than the diameter of the shaft  422  with sufficient clearance for a drain path  965  for excess oil. The inside diameter of the bearing  922  is the point where the shaft is in contact with the bearing. The slope of a taper angle  420  of the drive shaft housing  424  is greater than the critical self-ejecting taper angle as determined from machinery design handbooks. Taper angle  420  is a self ejecting taper such that the tangent of the taper angle is greater than the coefficient of friction between the two mating materials. The outside diameter  427  of the bearing holder  622  has taper angle  620  that is generally equal to the mating taper angle  420  of the taper seat  425  ( FIG. 35 ) of the drive shaft housing  424 . The same is true for the propeller shaft housing  524 . 
       FIG. 33  is an end view of  FIG. 32  as taken along Section Line  33 - 33 . Oil supply drilled hole  411  and oil return drilled hole  413  are shown in drive shaft housing  424 . Sleeve bearing  922  supports drive shaft  422 . The inside of the drive shaft housing  424  has an inside bore diameter  963  greater than the drive shaft  422 . The inside diameter of the shaft bearing  922  is the point where the shaft is in contact with the bearing. 
       FIG. 34  is a side sectional view of bearing holder  622  similar to  FIG. 32 . Alternate embodiments of the oil supply channels and oil drain channels include circumferential supply grooves  932  and circumferential drain grooves  934  to be cut into the drive shaft housing  424 . Other features of bearing holder  622  remain the same. Resilient O-rings  945  are placed in the circumferential O-ring grooves  944 . 
       FIG. 35  shows an alternate style of bearings common in the industry thus mounted in bearing holder  622 . Ball bearing  923  is held in place by the bearing retainer plate  623 . The inner race is commonly secured to the rotating drive shaft  422  by set screws or press fit as common in machine practice. Mounting and retaining these bearings is common knowledge. Other features of the bearing holder and shaft housing are the same as  FIG. 32 . Taper angle  620  of the bearing holder  622  is equal to the taper angle  420  of the drive shaft housing  424 . 
       FIG. 36  shows an alternate style of bearings common in the industry thus mounted in bearing holder  622 . Tapered roller bearing  924  is held in place by the bearing retainer plate  623 . The inner race is commonly secured to the rotating drive shaft  422  by set screws or press fit as common in machine practice. Mounting and retaining these bearings is common knowledge. Other features of the bearing holder and shaft housing are the same as  FIG. 32 . 
     All of the above described features in  FIG. 32 ,  FIG. 33 ,  FIG. 34 ,  FIG. 35 , and  FIG. 36  also apply to the bearing holder of the propeller shaft housing  524 . Although the tapered section is generated from a single geometric cone, it is contemplated to use multiple geometric cones to accommodate other design constraints. The single geometric cone is usually sufficient and is the easiest to manufacture. 
       FIG. 37  is a view of  FIG. 1 , but shows what the cylindrically shaped gimbal assembly would look like if it was cut open and laid out flat on a sheet of paper. This view emphasizes the zigzag nature of the gimbal ring  344  showing how the gimbal pins  345  are mounted to the face of the gimbal ring by use of U bolts  355  and nuts  356 . Gimbal pins form a common flat plane transverse to the axis of the gimbal assembly. This is a face loaded gimbal ring. Although it is possible to axially offset one pair of gimbal pins relative to the other pair of gimbal pins, there is no real advantage and it is poor machine design practice because it will cause improper operation of the Universal joint contained within the gimbal assembly similar to that caused by improper axial alignment. Improper axial alignment causes excessive vibration and wear. The gimbal ring  344  has a first ring edge  396  facing towards a first gimbal end  354 . The gimbal ring has a second ring edge  397  facing towards a second gimbal end  364 . Both the first ring edge and the second ring edge are generally parallel to each other and have a zigzag shape that is undulated from one gimbal pin  345  to the next gimbal pin. However, the gimbal pins are arranged to form a single transverse plane across the gimbal ring. The first gimbal end  354  has a pair of first end gimbal yokes  398  that are longitudinal extensions of the cylindrical form of the first gimbal end. These gimbal yokes have holes located on opposite sides of the cylindrical form to receive gimbal pins  345 . The second gimbal end  364  has a pair of second end gimbal yokes  399  that are longitudinal extensions of the cylindrical form of the second gimbal end. These gimbal yokes have holes located on opposite sides of the cylindrical form to receive gimbal pins  345 . In this layout, gimbal ring  344  appears longer than first gimbal end  354  or second gimbal end  364 . That is to be expected because the gimbal ring has a larger diameter, hence a larger circumference, than first gimbal end or second gimbal end. The gimbal pins are separable from the gimbal yokes. 
     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions and variations are possible and contemplated. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of the present invention without departing from the spirit and scope of the invention as defined by the appended claims.