Patent Publication Number: US-11394255-B2

Title: Split electric machine for retrofit hybrid propulsion systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation Application of U.S. application Ser. No. 17/327,390, entitled, “Split Permanent Magnet Electric Machine for Retrofit Hybrid Propulsion Systems”, filed May 21, 2021, which is a Non-Provisional application claiming priority to U.S. Provisional Patent Application No. 63/029,089, entitled “Split Permanent Magnet Electric Machine for Retrofit Hybrid Propulsion Systems”, filed May 22, 2020, which is herein incorporated by reference. 
    
    
     FIELD 
     This disclosure relates generally to retrofit hybrid propulsion systems, and more specifically to split permanent magnet electric machines for retrofit hybrid propulsion systems for marine vessels. 
     INTRODUCTION 
     Hybrid technology is starting to become more and more accepted in the marine industry as a method of reducing the fuel consumption and the emissions associated with carrying out the industrial marine mission of a vessel. 
     A vessel&#39;s suitability to hybrid technology mainly depends on its duty cycle and operational profile. For example, an application that is typically well suited for hybrid propulsion is one in which the vessel design is based on a broad spectrum of power needs, yet a significant amount of the time is expected to be spent at low power. Vessels that may fit this profile include patrol boats, tug boats, work boats, offshore supply vessels (OSVs), platform supply vessels (PSVs), pilot vessels, research vessels, fishing boats, buoy tenders, ice breakers, navy vessels, and many more. 
     When a vessel is being considered for new construction, application of hybrid technology may not be considered difficult to integrate into the vessel design, and the additional capital expenditures may be offset by expected future savings (e.g. fuel expenses). The majority of the vessels that will operate over the next 30 years are already built, and except for a very small number of early adopters, these existing vessels are fitted with conventional power systems. 
     SUMMARY 
     The following introduction is provided to introduce the reader to the more detailed discussion to follow. The introduction is not intended to limit or define any claimed or as yet unclaimed invention. One or more inventions may reside in any combination or sub-combination of the elements or process steps disclosed in any part of this document. 
     There is a large opportunity for hybridization of existing vessels that have an operational profile that supports a hybrid design. There are only a few examples worldwide of successful conversion of existing vessels to hybrid power systems. This is in part due to challenges associated with any vessel conversion. Also, modification of propulsion shaft lines to integrate an electric motor into a conventional propulsion mechanical drive line is currently a disruptive and costly exercise. The associated loss of revenue for the vessel and cost of modification will typically remove the business case for hybrid conversion. Conventional electric motor design prevents the electric machine from being fitted in the propulsion system without interrupting the shaft line. 
     In the systems disclosed herein, a split permanent magnet electric machine design can be fitted to existing propulsion shaft lines without the need to interrupt or modify the existing shaft. This may lead to decreased installation time and/or costs for retrofitting existing vessels with hybrid power systems. For example, the split permanent magnet electric machine may be modular and/or scalable to facilitate its installation in a wide variety of vessel types. 
     Such split permanent magnet electric machines may help realize the environmental benefits that can be achieved by making the hybridization of existing vessels commercially viable. This has the potential to significantly reduce the environmental impact associated with marine operations in Canada and around the world. 
     In systems disclosed herein, a permanent magnet electric machine has a hollow rotor provided in at least two pieces, such that it can be positioned around, and coupled to, an existing propulsion shaft of a marine vessel without demounting and/or disassembling the propulsion shaft. The permanent magnet electric machine also has a stator provided in at least two pieces, such that it can be positioned around the rotor without demounting and/or disassembling the propulsion shaft. 
     It will be appreciated by a person skilled in the art that a method or apparatus disclosed herein may embody any one or more of the features contained herein and that the features may be used in any particular combination or sub-combination. 
     These and other aspects and features of various embodiments will be described in greater detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the described embodiments and to show more clearly how they may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
         FIG. 1  is an exploded perspective schematic view of an electric machine, in accordance with one embodiment; 
         FIG. 2  is a cross section view of the electric machine of  FIG. 1 ; 
         FIG. 3  is an perspective view of an electric machine coupled to an existing propulsion shaft via a motor mount, in accordance with one embodiment; 
         FIG. 4  is an isometric view of the rotor, stator, and motor mount of  FIG. 3 ; 
         FIG. 5  is an isometric view of the rotor, stator, stator housing, and motor mount of  FIG. 3 ; 
         FIG. 6  is an isometric view of the rotor, stator, stator housing, motor mount, and retaining rings of  FIG. 3 ; 
         FIG. 7  is a side view of the rotor, stator, and motor mount of  FIG. 4 ; 
         FIG. 8  is an exploded isometric view of an electric machine coupled to an existing propulsion shaft via a stator hub, in accordance with one embodiment; 
         FIG. 9  is an isometric view of the rotor, stator, and shaft adaptors of  FIG. 8 ; 
         FIG. 10  is an isometric view of the rotor, stator, stator housing, and shaft adaptors of  FIG. 8 ; 
         FIG. 11  is an isometric view of the rotor, stator, stator housing, and splined bearing of  FIG. 8 ; 
         FIG. 12  is an isometric view of the electric machine of  FIG. 8  coupled to an existing propulsion shaft; 
         FIG. 13  is a side view of the electric machine of  FIG. 12 ; 
         FIG. 14  is a schematic diagram of a hybrid propulsion system, in accordance with one embodiment; 
         FIG. 15  is a view of rotor shaft collar segments about a shaft, in accordance with an embodiment; 
         FIG. 16  is a view of the rotor shaft collar segments of  FIG. 15  as a rotor shaft collar, in accordance with an embodiment; 
         FIG. 17  is a view of rotor segments about the rotor shaft collar of  FIG. 16 , in accordance with an embodiment; 
         FIG. 18  is a view of the rotor segments of  FIG. 16  as a rotor, in accordance with an embodiment; 
         FIG. 19  is a view of end plates of the rotor of  FIG. 18 , in accordance with an embodiment; 
         FIG. 20  is a view of a rotor assembly, in accordance with an embodiment; 
         FIG. 21  is a view of bearings in conjunction with the rotor assembly of  FIG. 20 , in accordance with an embodiment; 
         FIG. 22  is a view of the bearings of  FIG. 21  as a bearing assembly, in accordance with an embodiment; 
         FIG. 23  is a view of a stator in conjunction with the rotor assembly of  FIG. 20 , in accordance with an embodiment; 
         FIG. 24  is a view of a fluid jacket in conjunction with the rotor assembly of  FIG. 20 , in accordance with an embodiment; 
         FIG. 25  is a view of a housing in conjunction with the rotor assembly of  FIG. 20 , in accordance with an embodiment; 
         FIG. 26  is a view of end plates of the housing of  FIG. 25 , in accordance with an embodiment; 
         FIG. 27  is a view of an electric motor assembly in conjunction with a frame, in accordance with an embodiment; 
         FIG. 28  is a view of mounting elements in conjunction with the electric motor assembly of  FIG. 27 , in accordance with an embodiment; and 
         FIG. 29  illustrates a method of assembly of an electric motor and its associated components about an existing shaft in accordance with an embodiment. 
     
    
    
     The drawings included herewith are for illustrating various examples of articles, methods, and apparatuses of the teaching of the present specification and are not intended to limit the scope of what is taught in any way. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Various apparatuses, methods and compositions are described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover apparatuses and methods that differ from those described below. The claimed inventions are not limited to apparatuses, methods and compositions having all of the features of any one apparatus, method or composition described below or to features common to multiple or all of the apparatuses, methods or compositions described below. It is possible that an apparatus, method or composition described below is not an embodiment of any claimed invention. Any invention disclosed in an apparatus, method or composition described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicant(s), inventor(s) and/or owner(s) do not intend to abandon, disclaim, or dedicate to the public any such invention by its disclosure in this document. 
     Furthermore, it will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the example embodiments described herein. However, it will be understood by those of ordinary skill in the art that the example embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the example embodiments described herein. Also, the description is not to be considered as limiting the scope of the example embodiments described herein. 
     While the apparatus and methods disclosed herein are described specifically in relation to and in use with marine vessels, it will be appreciated that the apparatus and methods may alternatively be used with other types of vehicles. 
       FIGS. 1 and 2  illustrate a schematic example of a permanent magnet electric machine, referred to generally as  100 . The electric machine includes a stator  140  and a hollow rotor  120  positioned interior of the stator that can be driven by the stator. Electrical power may be supplied to one or more stator windings to induce rotation of the rotor relative to the stator. 
     Stator  140  includes a plurality of windings (not shown) that may be made of copper, copper alloys, or other suitable materials. Stator windings may be arranged in any suitable configuration. For example, the windings may be arranged as a set of poly-phase multi-polar stator windings. Stator windings may be connected in star or delta configuration. 
     Rotor  120  includes a plurality of magnets (not shown) such as neodymium (NdFeB) magnets. The rotor magnets may be arranged in any suitable configuration. For example, rotor magnets may be polarized in a Halbach configuration. Other configurations (e.g. parallel, radial) may be used in one or more alternative embodiments. 
     Power control electronics (not shown) for the electric machine may be provided in any suitable location. For example, power control electronics may be provided within stator enclosure  160 . 
     Electric machine  100  preferably includes a stator enclosure  160 , which may be alternatively characterized as a stator housing  160 . In the illustrated example, stator enclosure  160  includes an annular casing positioned concentrically around stator  140 . 
       FIGS. 3 to 7  illustrate a schematic example of a ‘split’ electric machine  100 . In this example, two rotor segments  120   a ,  120   b  are provided that, when coupled together, form rotor  120 . While two rotor segments are shown, it will be appreciated that three or more rotor segments may be provided in alternative embodiments. 
     By assembling rotor  120  from two or more rotor segments, rotor  120  may be positioned around an existing propulsion shaft  10  (e.g. a drive shaft of a marine vessel) without disassembling and/or demounting shaft  10 . 
     In the example illustrated in  FIG. 3 , two stator segments  140   a ,  140   b  are provided that, when coupled together, form stator  140 . Also, two housing segments  160   a ,  160   b  are provided that, when coupled together, form housing  160 . While two stator segments and two housing segments are shown, it will be appreciated that three or more stator and/or housing segments may be provided in alternative embodiments. 
     Also, in  FIG. 3  the same number of rotor segments, stator segments, and housing segments are provided (i.e. two of each), it will be appreciated that this need not be the case. For example, four rotor segments may be provided to form rotor  120 , and six stator segments may be provided to form stator  140 . 
     To facilitate the ‘splitting’ of permanent magnet electric machine  100 , stator  140  is preferably wound with multiple parallel paths to reduce, minimize, or avoid effects of unbalanced magnetic pull (UMP), such as vibration, acoustic noise, and deformation. Additionally, or alternatively, the stator windings may be configured to maintain symmetry during splitting. 
     In the illustrated example, rotor  120  is coupled to shaft  10  via a splined coupling. Specifically, a pair of externally splined shaft adaptors  113   a ,  113   b  are positioned around shaft  10 , and may be secured to the shaft using any suitable method. A pair of internally splined shaft adaptors  115   a ,  115   b  are positioned around shaft adaptors  113   a ,  113   b , and may be secured to the shaft using any suitable method, e.g. via split bearing retaining rings  232   a ,  232   b  and  234   a ,  234   b . A two-piece rotor hub  110   a ,  110   b  is positioned around and engages shaft adaptors  115   a ,  115   b . Rotor segments  120   a ,  120   b  are secured to rotor hub  110   a ,  110   b.    
     Such an arrangement may have one or more advantages. For example, to accommodate shafts  10  with a range of possible diameters, some components (e.g. shaft adaptors  113 ,  115 ) may be fabricated to ‘custom’ dimensions for a specific vessel, while other components (e.g., electric machine  100 , rotor hub  110 ) of a ‘standard’ size may be used with two or more sizes of shaft  10 . 
     As illustrated, the center arms of rotor hub  110   a ,  110   b  may be slotted into groves in an outer surface of shaft adaptors  115   a ,  115   b . This may allow transmission of rotational torque while also allowing some axial movement/play of the propulsion shaft  10 . 
     In the illustrated example, a front retaining ring  222   a ,  222   b  and a rear retaining ring  224   a ,  224   b  are provided to axially secure and/or locate electric machine  100  to shaft  10 . 
     In the example illustrated in  FIGS. 3 to 7 , stator  140  of electric machine  100  is secured to the vessel via an annular machine mount. In the illustrated example, a two-piece machine mount  210   a ,  210   b  is used to secure the stator of electric machine  100  to the vessel. While two machine mount segments are shown, it will be appreciated that three or more segments may be provided in alternative embodiments. 
     Preferably, a flexible connection is provided between the machine mount and the vessel&#39;s hull, in order to reduce and preferably minimize unbalanced reactional forces applied to the motor assembly while transmitting the opposing full rotor torque to the vessel hull (directly or indirectly). 
       FIGS. 3 to 7  illustrate another schematic example of a ‘split’ electric machine  100 . In this example, the stator  140  is coupled to shaft  10  via a pair of two-piece stator hubs  312   a ,  312   b  and  314   a ,  314   b . While a total of four stator hub segments are shown, it will be appreciated that five or more segments may be provided in alternative embodiments. 
     In the illustrated example, each stator hub  312 ,  314  is coupled to shaft  10  via a splined coupling and a bearing. Specifically, a pair of externally splined shaft adaptors  332   a ,  332   b  are positioned around shaft  10 , and may be secured to the shaft using any suitable method. A pair of internally splined bearings  322   a ,  322   b  are positioned around shaft adaptors  332   a ,  332   b , allowing each stator hub  312 ,  314  to rotate relative to shaft  10 . The stator hubs  312 ,  314  may be coupled to each other directly, or indirectly (e.g. via stator housing  160 ) and secured to stator  140  using any suitable method. 
     Such an arrangement may have one or more advantages. For example, shaft  10  may bear some or all of the static weight of electric machine  100 , which may provide increased flexibility for connecting stator hubs  312 ,  314  to an interior of the vessel. For example, such a connection may only need to resist torque generated by electric machine  100 . Additionally, or alternatively, shaft bearings supporting the stator may be attached to the vessel&#39;s hull through one or more brackets (not shown) for providing additional support against a reaction torque. 
     As discussed above, the stator  140  and rotor  120  of electric machine  100  may be operated as an electric motor, where electrical power is applied to create mechanical torque on the rotor  120 . 
     Alternatively, the stator and rotor of electric machine  100  may be operated as an electric generator. For example, stator  140  may be operated to generate resistance to the rotation of rotor  120 . This may result in reduced net thrust provided by shaft  10 , leading to a reduction in the vessel&#39;s speed. This may also result in the generation of electrical power, which may be used e.g. to supply energy to one or more systems or components (e.g. electrochemical batteries or other service loads) on board the vessel. 
       FIG. 14  illustrates an example schematic configuration of a hybrid propulsion system. In the illustrated example, 75 kW split electric machines are positioned on drive shafts between 750 kW mechanical engines and thrusters for propelling the vessel. The 75 kW split electric machines can be split rotor or split stator permanent magnet motors able to be fitted to an existing shaft. The split electric machines are illustrated as being coupled to a switchboard, such as a direct current switchboard that may additionally be coupled to one or more pumps as well as a battery bank. Likewise, the DC switchboard as illustrated is coupled to an alternating current switchboard that itself may be coupled to one or more auxiliary generators, as additionally illustrated in  FIG. 14 . 
     As discussed above, a split design for the electric machine  100  can be fitted to existing propulsion shaft lines without the need to interrupt or modify the existing shaft. That is, typically to retrofit an electric motor to a vessel entails removal of a section of the existing shaft at a first location and a second location of the existing shaft  10 , installation of an electric machine with its own shaft disposed therein in the region between the first location and the second location, and coupling the shaft of the installed electric machine to the existing shaft  10  at the first location and second location via couplings to match the circumference of the shaft of the installed electric machine to the existing shaft. This process is costly and time consuming, as it includes the removal of a portion of the shaft  10  itself. However, utilization of the electric machine  100  described herein allows for decreased installation time and/or costs for retrofitting existing vessels with hybrid power systems, as they are, for example, gearless (which can allow for direct connection to a propeller of the vessel via the existing shaft  10 ) and because they are installed and implemented in-line with the existing shaft  10 . 
     Indeed, the electric machine  100  described herein may be modular and/or scalable to facilitate its installation in a wide variety of vessel types and can be disposed about existing propulsion shafts  10  having various circumferences. As described above, one technique to allow for the split electric machine to be coupled to a shaft includes the use of shaft adapters. However, additional techniques are envisioned to allow for a split electric machine to be coupled to various sided shafts  10 . 
       FIG. 15  illustrates rotor shaft collar segment  334  and rotor shaft collar segment  336  that can be directly coupled to one another about the shaft  10  to form the rotor shaft collar  338  of  FIG. 16 . As illustrated, the rotor shaft collar segment  334  and the rotor shaft collar segment  336  include a plurality of apertures  340  that align with guides  342  (e.g., pins or hollow members that accept fasteners such as bolts, screws, pins, and the like) from the corresponding rotor shaft collar segment  334  and the rotor shaft collar segment  336  so that apertures  340  and the guides  342  mate when the rotor shaft collar segment  334  and the rotor shaft collar segment  336  are brought into contact with one another to form the rotor shaft collar  338  of  FIG. 16 . It should be noted that other configurations for the rotor shaft collar  338  are envisioned, for example, having split flanges with through rods therethrough. 
     As illustrated in  FIG. 16 , the rotor shaft collar  338  circumferentially surrounds the shaft  10 . The rotor shaft collar  338  of  FIG. 16  can also include one or more apertures  344  that can operate to accept fasteners, such as bolts, screws, pins, and the like. In some embodiments, the apertures  344  may be equally spaced along a face of the rotor shaft collar  338 . Likewise, the rotor shaft collar  338  may have a generally cylindrical shape. However, in some embodiments, the outer portion of the rotor shaft collar  338  may include one or more alignment features  346  disposed about the outer portion of the rotor shaft collar  338 , for example, along the length  348  of the rotor shaft collar  338 . For example, the one or more alignment features  346  may be a groove or channel that can accept an alignment feature (e.g., a protrusion or projection) of a rotor segment disposed about the rotor shaft collar  338 . 
     In some embodiments, the rotor shaft collar  338  may have an inner circumference  350  that is sized to directly couple the rotor shaft collar  338  to the shaft  10 . This inner circumference  350  can be increased or decreased based on (i.e., to match) the circumference of the shaft  10 . Thus, in some embodiments where the shaft  10  has a first diameter and/or circumference, the inner circumference  350  of the rotor shaft collar  338  is machined to correspond to (e.g., match) the first circumference and/or diameter of the shaft  10 . Likewise, in other embodiments where the shaft  10  has a second circumference/diameter greater in size relative to the first circumference/diameter, the inner circumference  350  (and/the diameter) of the rotor shaft collar  338  is machined to correspond to (e.g., match) the second circumference/diameter of the shaft  10 . This allows the rotor shaft collar  338  to operate a spacer for a rotor assembly, so as to allow the rotor assembly to be mounted to shafts  10  each having a respective circumference to facilitate the electric machine  100  being scalable to facilitate its installation in a wide variety of vessel types having existing propulsion shafts  10  having various circumferences. This arrangement also has advantages in that to accommodate shafts  10  with a range of possible diameters and circumferences, some components (e.g. rotor shaft collar  338 ) may be fabricated to ‘custom’ dimensions for a specific vessel, while other components (e.g., the rotor, stator, housing, etc.) may be of a ‘standard’ size that may be used with two or more sizes of shaft  10 . 
     In other embodiments, one or more shims or other spacers (e.g., a hollow cylinder shaped spacer) can be generated from two (or more) shim segments coupled together. The one or more shims can be placed in direct contact with the inner circumference  350  of the rotor shaft collar segment  334  and the rotor shaft collar segment  336  and the one or more shims can also directly contact the shaft. This allows for the rotor shaft collar  338  to match a smaller diameter shaft  10  when the rotor shaft collar  338  is machined to a fixed inner diameter that is greater than the diameter of the shaft  10  (thus providing a rotor shaft collar  338  with a fixed inner diameter or inner circumference  350  to be matched to shafts  10  of various circumferences/diameters). 
       FIG. 17  illustrates rotor segment  352  and rotor segment  354  that can be coupled to one another about the shaft  10  to form the rotor  356  of  FIG. 18 . As illustrated, the rotor segment  352  and the rotor segment  354  each include an inner face  358  that directly contacts one another to form the rotor  356 . The rotor segment  352  and the rotor segment  354  each also include a rotor hub  360  that directly contacts and circumferentially surrounds the rotor shaft collar  338 . The rotor  356  further includes a plurality of magnets  364 , such as neodymium (NdFeB) magnets. The plurality of magnets  364  may be circumferentially disposed about the rotor hub  360  on each of the rotor segment  352  and the rotor segment  354  so that when the rotor segment  352  and the rotor segment  354  are directly coupled to form the rotor  356 , at least one magnet of the plurality of magnets  364  of the rotor segment  352  is disposed adjacent to at least one magnet of the plurality of magnets  364  of the rotor segment  354  to form a group of two magnets  366  that matches other groups of two magnets  368  of each of the rotor segment  352  and the rotor segment  354 . In this manner, similar to described above with respect to  FIG. 3 , the plurality of magnets  364  are disposed at a common distance from one another regardless of whether any two adjacent magnets are each in the rotor segment  352 , are each in the rotor segment  354 , or when one adjacent magnet is in the rotor segment  352  and the second adjacent magnet is in the rotor segment  354 . Thus, the rotor segment  352  and the rotor segment  354  combine to form a unitary rotor as the rotor  356  (e.g., a rotor  356  without intra-segment gaps). 
     The plurality of magnets  364  may be arranged in a number of orientations, for example, a flat web orientation, a flat simple orientation, a U-shaped orientation, a spoke magnet orientation, a V web orientation, a V simple orientation, or other orientations, which may be selected to tune torque or other performance characteristics of the electric machine  100 . In some embodiments, as rotor  356  rotates, the plurality of magnets  364  are retained in the lamination surrounding each magnet with the help of the lamination bridges, which may be designed so that the maximum stresses levels have been reduced to less than a determined value, such as 180 Megapascals. 
     As additionally illustrated in  FIG. 18 , the rotor  356  may include a plurality of apertures  370 . These apertures  370  align with guides  372  (e.g., pins or hollow members that accept fasteners such as bolts, screws, pins, and the like) from end plate segment  374  and end plate segment  376  of  FIG. 19  so that apertures  370  and the guides  372  mate when end plate segment  374  and end plate segment  376  are brought into contact with rotor segment  352  and rotor segment  354  to form the rotor assembly  378  of  FIG. 20 . Also illustrated are end plate segment  380  and end plate segment  382  which correspond to end plate segment  374  and end plate segment  376 . End plate segment  380  and end plate segment  382  include apertures  384  to receive the guides  372 . When the rotor segment  352  and the rotor segment  354  are coupled to the end plate segment  374  and end plate segment  376 , the end plate segment  374  and end plate segment  376  form a face  373  of the rotor assembly  378 . Likewise, when the rotor segment  352  and the rotor segment  354  are coupled to the end plate segment  380  and end plate segment  382 , the end plate segment  380  and end plate segment  382  form a face  383  of the rotor assembly  378  of the electric machine  100 . 
     Additionally, a bearing  386  and a bearing  388 , as illustrated in  FIG. 21 , which combine into a bearing assembly  390  of  FIG. 22 , can be utilized in conjunction with the electric machine  100 . The bearing  386  may be made up of a bearing segment  392  and a bearing segment  394  that may be affixed to one another via one or more fasteners, such as bolts, screws, pins, and the like. Similarly, the bearing  388  may be made up of a bearing segment  396  and a bearing segment  398  that may be affixed to one another via one or more fasteners, such as bolts, screws, pins, and the like. 
     The bearing  386  and the bearing  388 , when assembled about the shaft  10 , may be disposed at a distance  400  along the shaft  10  from the rotor assembly  378  of the electric machine  100 , as illustrated in  FIG. 22 . This distance  400  may be chosen based upon the size of the housing and/or fluid jacket of the electric machine. In some embodiments, the bearing  386  and the bearing  388  include ceramic rollers to isolate bearing currents. Additionally, the bearing  386  and the bearing  388  can each include an alignment feature  402  disposed about the outer portion of the bearing  386  and the bearing  388 , for example, circumferentially about the bearing  386  and the bearing  388 . The alignment feature  402  may be a groove or channel that can accept an end plate of the housing of the electric machine  100 . 
       FIG. 23  illustrates stator  404  as made up of stator segments  406  and  408  that, when directly coupled together, form stator  404 . Taken in conjunction, the stator  404  and the rotor assembly  378  form the electric machine  100 . Stator  404  is similar to stator  140  described above and stator  404  includes a plurality of windings  410  that may be made of copper, copper alloys, or other suitable materials. Stator windings  410  may be arranged in any suitable configuration. For example, the stator windings  410  may be arranged as a set of poly-phase multi-polar stator windings. Stator windings  410  may be connected in star or delta configuration). In some embodiments, the stator segments stator segments  406  and  408  when joined create a balanced polyphase source (i.e., a balanced polyphaser system). 
     Additionally, similar to described above with respect to  FIG. 3 , the plurality of stator windings  410  are disposed at a common distance from one another regardless of whether any two adjacent stator windings  410  are each in the stator segments  406 , are each in the stator segments  408 , or when one adjacent stator winding  410  is in the stator segments  406  and the second adjacent stator winding  410  is in the stator segments  408 . In some embodiments, the stator windings  410  maintain symmetry during splitting and the stator  404 . Likewise, when the stator segments  406  and the stator segments  408  are directly coupled to one another, the stator  404  comprises a unitary stator (e.g., a stator  404  without intra-segment gaps  FIG. 24  illustrates a fluid jacket  412  that may be disposed about the stator  404 . The fluid jacket  412 , as illustrated, is made up of fluid jacket segment  414  and fluid jacket segment  416  that, when coupled together, form the fluid jacket  412 . As illustrated, the fluid jacket segment  416  includes a plurality of apertures  418  that align with guides  420  (e.g., pins or hollow members that accept fasteners such as bolts, screws, pins, and the like) from the corresponding fluid jacket segment  414  so that apertures  418  and the guides  420  mate when the fluid jacket segment  414  and the fluid jacket segment  416  are brought into contact with one another to form the fluid jacket  412  of  FIG. 23 . It should be noted that the fluid jacket  412  represents one embodiment of a liquid cooling system as a cooling system for the stator  404 , however, other configurations for a cooling system (e.g., an air, liquid, or fluid cooling system) of the stator  404  are envisioned. For example, an air cooling system may include an integrated fan that operates to compress air and may, for example, include a fan coupled to the shaft  10  to utilize the rotations of the shaft  10  to propel the fan to compress air that is supplied to the stator  404  to cool the stator  404 . 
     The fluid jacket segment  414  and the fluid jacket segment  416  each include a face (e.g., an inner face) that is disposed circumferentially around the stator  404  when the fluid jacket segment  414  and the fluid jacket segment  416  are coupled. The fluid jacket segment  414  and the fluid jacket segment  416  each also include a face  422  (e.g., an outer face) that is disposed circumferentially around the above describe inner face of the fluid jacket segment  414  and the fluid jacket segment  416 . The face  422  for each fluid jacket segment  414  and fluid jacket segment  416  includes one or more cooling channels  424 . The one or more cooling channels  424  may provide improved thermal management for stator  404  and may operate to pass a fluid across the face  422  of the of the fluid jacket segment  414  and the fluid jacket segment  416  to operate as a heat exchanger to cool the stator  404 . Likewise, a groove or channel  426  may surround the one or more cooling channels  424  to interface with a protrusion of a housing segment that surrounds one or more cooling channels machined into its outer circumference, whereby the one or more cooling channels of the housing segment match the one or more cooling channels  424  of the fluid jacket  412 . Additionally, a gasket may be provided on each end of the fluid jacket  412  to be compressed by the housing when the housing segments are coupled to one another. 
       FIG. 25  illustrates an example of the housing  428  inclusive of a housing segment  430  and a housing segment  432  described above. As illustrated, the housing  428  includes an inlet  434  and an outlet  436 , whereby the inlet  434  transmits a liquid (e.g., water or the like) as a fluid at a first temperature into the one or more cooling channels  424  defined by the housing  428  and the fluid jacket  412  and the outlet  436  removes the liquid at second temperature higher than the first temperature to remove heat from the stator  404 . As illustrated, the fluid jacket segment  416  includes a plurality of apertures  418  that align with guides  420  (e.g., pins or hollow members that accept fasteners such as bolts, screws, pins, and the like) from the corresponding fluid jacket segment  414  so that apertures  418  and the guides  420  mate when the fluid jacket segment  414  and the fluid jacket segment  416  are brought into contact with one another to form the fluid jacket  412  of  FIG. 23 . 
     As additionally illustrated in  FIG. 25 , the housing  428  may include a plurality of apertures  438 . These apertures  438  align with guides  440  (e.g., pins or hollow members that accept fasteners such as bolts, screws, pins, and the like) from end plate segment  442  and end plate segment  444  of  FIG. 26  so that apertures  438  and the guides  440  mate when end plate segment  442  and end plate segment  444  are brought into contact with housing segment  430  and housing segment  432 . Also illustrated are end plate segment  446  and end plate segment  448 . End plate segment  446  and end plate segment  448  also include guides  440  that mate with when end plate segment  446  and end plate segment  448  are brought into contact with housing segment  430  and housing segment  432 . Once coupled, the end plate segment  442 , the end plate segment  444 , the end plate segment  446 , and the end plate segment  448  complete the housing  428 . Additionally, as previously noted, the end plate segment  442  and the end plate segment  444  can combine to form an end plate with an inner circumference that is disposed about a groove or channel of bearing  386 . Similarly, the end plate segment  446  and the end plate segment  448  can combine to form an end plate with an inner circumference that is disposed about a groove or channel of bearing  388 . 
     An electric motor assembly  450  inclusive of the electric machine  100 , the housing  428 , and the bearing assembly  390 , is illustrated in  FIG. 27 . Furthermore, as illustrated in  FIG. 27 , a frame  452  may be disposed beneath the electric motor assembly  450  and one or more fasteners of the housing  428  can couple the electric motor assembly  450  to the frame  452 . The electric motor assembly  450  can be designed and implemented in conjunction with a number of differing vessels, for example, as a 75 kilowatt, a 400 kilowatt, a 1 megawatt electric or another output electric motor. In this manner, the electric motor assembly  450  can have varying sizes and/or outputs for use with various vessels and each electric motor assembly  450  can accommodate a range of diameters/circumferences of shafts in line with the description above. Moreover, while the same number of rotor shaft collar segment  334  and rotor shaft collar segment  336 , rotor segment  352  and rotor segment  354 , bearing segment  392  and bearing segment  394 , bearing segment  396  and bearing segment  398 , stator segment  406  and stator segment  408 , fluid jacket segment  414  and fluid jacket segment  416 , housing segment  430  and  432  are provided (i.e. two of each), it will be appreciated that this need not be the case. For example, four rotor segments may be provided to form rotor  356 , and six stator segments may be provided to form stator  404 . Additionally, the electric motor assembly  450  may be implemented using various types of electric motors, such as an induction motor, a permanent magnet motor, or a reluctance motor (e.g., a motor having a stator coupled to the shaft  10  (either directly to or via a shim) with a rotor disposed about the stator) each separable, i.e., split, in the manner described herein to achieve the result detailed herein regarding installation about an existing shaft  10 . 
     Additionally, as illustrated in  FIG. 28 , the frame  452  may be coupled to or may include legs  454  and/or feet  456 . The legs  454  and/or the feet  456  may operate to support the weight of the electric motor assembly  450 . In some embodiments, the feet  456  may be directly coupled to a hull of the vessel. In other embodiments, a hull connection point may be connected to the hull of the vessel and the feet  456  are connected to the hull connection point via one or more fasteners  458  (e.g., a bolt or the like). In some embodiments, one or motor mounts may be disposed between the feet  456  and the hull or between the feet  456  and the hull connection point to dampen vibration, i.e., to isolate vibration of the shaft  10  from the hull and/or vice versa. 
       FIG. 29  illustrates an embodiment of a method  460  of assembly of an electric motor and its associated components about an existing shaft  10 . In step  462 , a rotor shaft collar  338  is assembled about an existing shaft  10  of a vessel, as illustrated, for example, in  FIGS. 15 and 16  and as described above. In step  464 , a rotor  356  and rotor assembly  378  are assembled about the existing shaft  10  of the vessel, as illustrated, for example, in  FIGS. 17, 18, 19, and 20  and as described above. In step  466 , a bearing assembly  390  is assembled about the existing shaft  10  of the vessel, as illustrated, for example, in  FIGS. 21 and 22  and as described above. In step  468 , a stator  404  is assembled about the existing shaft  10  of the vessel, as illustrated, for example, in  FIG. 23  and as described above. In step  470 , a housing  428 , which may be inclusive of a fluid jacket  412 , is assembled about the existing shaft  10  of the vessel, as illustrated, for example, in  FIGS. 24, 25, and 26  and as described above. Finally, in step  472 , an electric motor assembly  450  is mounted to a vessel about the existing shaft  10  of the vessel, as illustrated, for example, in  FIGS. 27 and 28  and as described above. It should be noted that one or more of the above described steps  462 ,  464 ,  466 ,  468 ,  470 , and  472  may be performed in a different order than listed above. 
     As used herein, the wording “and/or” is intended to represent an inclusive-or. That is, “X and/or Y” is intended to mean X or Y or both, for example. As a further example, “X, Y, and/or Z” is intended to mean X or Y or Z or any combination thereof. 
     While the above description describes features of example embodiments, it will be appreciated that some features and/or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. For example, the various characteristics which are described by means of the represented embodiments or examples may be selectively combined with each other. Accordingly, what has been described above is intended to be illustrative of the concept and non-limiting. It will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the invention, which should not be limited by the preferred embodiments and examples, but should be given the broadest interpretation consistent with the description as a whole.