Abstract:
A method of integrating, optimizing and combining in a marine electric or hybrid system, the operation and safety of one or more energy storage units, a combination of one or more electric outboard(s) and ICE outboard(s) in a propulsion systems through use of an Energy Management Computer. One aspect of the invention involves the application of logic programming to automate the optimization and the operation of the Internal Combustion Engines (STANDARD OUTBOARD) so that whenever the system requires their usage, they are operated at optimum efficiency conditions. For a STANDARD OUTBOARD to operate at peak efficiency a combination of a large energy storage unit used as a buffer combined with electric outboard(s) is used.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Application No. 61/760,373, filed Feb. 4, 2013, the entire content of which is hereby expressly incorporated by reference. 
     
    
     FIELD OF THE INVENTIONS 
       [0002]    The present inventions generally relate to marine electric propulsion outboard motors. Some embodiments include electric outboard motors rated from 50 hp to 300 hp that use high voltage (240-600 volts) for operation as well as marine hybrid propulsion systems. Some embodiments include definition, programming, parameterization and safety systems of an electronic management device, such as a computer, to interface, integrate, optimize, automate and simplify the operation of one or more electric outboards and associated energy storage units. One or more of such electric outboard motors can also be used in combination with one or more ICE (Internal Combustion Engine) powered outboard propulsion systems. 
       BACKGROUND OF THE INVENTIONS 
       [0003]    With the advent of low weight energy dense permanent magnet brushless electric motors and the advances in ESU (Energy Storage Units), a new world of opportunity in optimizing the operation of inboard and outboard powered marine vessels has appeared. As in the automotive industry, the issues of ample electric energy storage is not yet resolved, whether due to cost, volume or weight. So in addition a relatively simple ICE replacement, there exist and will exist for some time a need for a combined approach of mixing both electric and ICE engines so that the restriction of inefficiencies of each can be reduced or eliminated by the use of the other. 
         [0004]    Electric inboard and outboard motors can be operated independently or in combination with standard internal combustion inboard or outboard motors to reduce the use of fossil fuel and to reduce or eliminate water and noise pollution. One of the difficulties in the development of high-powered (50 hp-300 hp) outboard engines, is that high voltage (240-600 volts) is more optimal for obtaining reasonable efficiencies, heat or current carrying reasons, creating a challenge to develop systems that are safe, reliable and cost effective. Another difficulty is the adoption of hybrid propulsion to the marine energy is the current use large ESUs with the inherent issues relating to their different technologies. However, anytime there is a large amount on energy stored, like fossil fuel, batteries or hydrogen, there is a risk of fire or explosion. A battery-initiated fire on a marine vessel can be as dangerous as a fire caused by fuel. 
       SUMMARY OF THE INVENTIONS 
       [0005]    One aspect of at least one of the inventions disclosed herein includes the utilization of automation to mix and match different technologies in a transparent fashion so that a normal unskilled user is able to operate a relatively complex marine vessel comprised of one or many electric inboard or outboards combined or not with one or many ICE propulsion engines, thereby reducing (or eliminating in certain regimes) the use of a conventional ICE powered marine outboard engine that uses petroleum products. Example of these are in low speed operations, fishing at low speed, navigation in rivers, harbors and speed restricted areas where an electric motor can supplement all propulsion needs for extended periods. Other uses include operations, or use in protected areas where noise and pollution are to be avoided at all cost. 
         [0006]    In instances where multi engines are included on one vessel, having at least one electric powered motor allows the advantages of electric only operation at low speeds. In case of an electric outboard engine, there is better increased acceleration to planning speed, at which point, the efficiency of ICE outboard greatly increases, this due to the inherent capability of Electric motors to apply very high torque even at very low RPM. Once efficient cruise speed is established, the electric motor can be shut down, put into low drag mode requiring very low power until needed again or used as a water generator thereby recharging the ESU (Energy Storage Unit) until needed again. 
         [0007]    To help a reader understand marine electric outboard engines and electric/ICE mixed outboard powered propulsion described herein, we may quickly define the different systems that we are going to refer to. In an electric outboard engine system, a large ESU (Energy Storage Unit) is used to power the electric motor, and the ESU is re-charged at the dock, via an onboard efficient AC or DC generators (ranger extender) or through the electric motor itself on multi engine configuration. More complex combined serial and parallel marine hybrid electric systems are fully described in U.S. patent application Ser. No. 13/240,107, the entire contents of which are hereby expressly incorporated by reference. 
         [0008]    We can understand the inherent inefficiencies of strictly standard ICE inboard and outboard motors. When a boat is operated at low speed, large quantities of petroleum products are used just to keep the engine turning even when producing little or no thrust. 
         [0009]    On the other side of the spectrum, where bursts of high power are required, such as acceleration in bad weather conditions with high sea, water ski operations or for operational reasons, electric motors are at their best because of the high initial torque and their relative high efficiency compared to ICEs. 
         [0010]    Also, having a larger energy storage unit on board allows much longer operation on battery power and through efficient DC/DC converter, the continuous operation of energy hungry devices like large sound systems, compared to ICE powered highly inefficient alternators 
         [0011]    Petroleum products are still the best way (in terms of price/volume/weight) to store energy and until the price of fossil fuels increase dramatically, and as long as extended range navigation or some form of shore power independence is required, petroleum products will still be used as a form of energy storage. 
         [0012]    To solve the issue of energy storage, like in the car industry, complex and sometime flammable chemistry are used in ESUs, Lithium, Cobalt, Manganese and other ion rich metal are used, and they like fuel and lead acid can (if mistreated) lead to high temperature and fire. The demand for high speed watercraft are even more demanding than the car industry due to the fact in a car, the energy needed to accelerate the heavier car can be in part compensated by re-generation when slowing down. In a high speed watercraft, the whole weight of the craft and of the ESU has to be lifted on the plane and maintained there. This poses very high power demands from the electric propulsion system and also requires a high level of stored energy, forcing the use of the highest possible energy density per volume and weight, with the associated risks. 
         [0013]    The term “lithium ion battery” for example is a generic term for an accumulator based on for which conventional nickel cadmium or nickel metal hydride accumulators would be too heavy or too large, for use in small watercraft. They are thermally stable and are not subject to a memory effect. Depending on the structure or the electrode materials used, Li ion accumulators are further subdivided into lithium polymer accumulators, lithium cobalt dioxide accumulators, lithium titanate accumulators, lithium air accumulators, lithium manganese accumulators, lithium iron phosphate accumulators and tin sulphur lithium ion accumulators. All thee energy storage devices suffer from on critical problem in the case of failure of the battery management system, manufacturing defect or other defect. They catch fire at elevated temperatures, posing a safety hazard to marine navigation. 
         [0014]    Thus, in accordance with some embodiments, a method for controlling the energy currents can include a device which controls the energy currents between electrochemical energy stored and in the process works towards the prevention or reduction of danger of overloading. The device for controlling the energy currents can include one or a plurality of sensors for measuring parameters of one or a plurality of energy stores, such as at least one of measuring voltages, terminal voltages of individual cells or batteries and/or temperatures, temperatures of current collectors and/or cooling means which exchange heat with an energy store and/or electric currents between the energy stores and/or between an energy store and an energy source or energy drain. 
         [0015]    Another aspect of at least some of the inventions disclosed herein includes ESU monitoring during operation of the hybrid system by the automation and optimization management system for a vessel equipped with electric motors, alone or in combination with ICE motors, and with an ESU. 
         [0016]    In accordance with at least some embodiments, some of which provide both efficiency and fuel saving obtained with an electric inboard or outboard motor with longer range or more power in certain weather or wave conditions, the present invention includes a system and method for use of both electric outboard and standard ICE outboard technologies in combination with an ESU, in order to optimize the operation of a modern boat powered by both one or many electric outboard motors(s) and one or many ICE powered outboard motor(s). 
         [0017]    To solve the issue of providing safety systems for the ESU in a marine environment, some embodiments disclosed herein take advantage that marine vessels operate on the water of inland lakes or oceans, and they have a ready source of water for cooling equipment, or even putting out a fire. Some embodiments include the containment of separate ESU in watertight enclosures that can be flooded with water in the event of an unsafe rise in temperature of the ESU. The ESU can be monitored for in range performance. If there is a system failure and the ESU temperature rises to a dangerous level, the defective part of the ESU can be flooded. 
         [0018]    Some embodiments disclosed herein relate to the automation and optimization of an energy management system for vessel equipped with electric outboard and/or electric inboard motors alone or in combination with ICE motors. This can involve the use of control software to integrate, optimize and combine in a marine electric system, the operation of one or more electric outboard motors with one or more standard outboard motors. This automation allows not only efficient operation, but safe operation by monitoring the ESU; in the event of an unsafe rise in temperature or if a fire were to start, the system with built in redundancy will open a valve to allow the defective module to be flooded with water, thereby cooling the hot cells before a run-away occurs or allowing the heat to dissipate and stop propagation to adjacent modules if a fire was to start. 
         [0019]    To optimize efficiency, heuristic algorithms based on fuel consumption versus kW produced at different loads and RPM can be used. Once an energy storage unit is coupled to an electric motor on a vessel, very accurate drag curves can be produced at different loads and sea condition thereby providing (when coupled to an accurate speed sensing device) very precise data for system optimization. On multi engine setups including a mix of ICE and electric, a complete 3D map can be produced of the combined efficiency of the different devices by measuring the actual kW produced for every gram of fuel or Amperes removed from the ESU at different RPM and torque over the whole speed range of the vessel. This information and the energy storage characteristics are then used by the software to determine which device (electric or ICE motor) (alone or in combination) to use, for the action to be performed. While the limitations of electric only, diesel only or gasoline only are well known, each of those has strong points and each has its disadvantages. Some of the present embodiments incorporate these disparate technologies and merge them into a unified computer controlled system, with the role of automatically optimizing these technologies in a transparent fashion for the boat operator and thus drastically increasing their combined efficiencies in accordance with the punctual loads demands. At the same time, the monitoring of all components of the system, including the ESU, allows for a safe operation and reduced risk of fire at sea because the ESU, a described in this invention, is enclosed in a container that can be flooded using water readily available to marine vessels. 
         [0020]    As an example of efficient energy usage, low power maneuvering and movement up to hull speed for a limited time are accomplished purely under electric. Should the demands of propulsion increase and be maintained; the standard ICE engine will start and provide propulsion power, until the demands decrease. In the final portion, should maximum power be required (rapid acceleration or peak speed), all the electric and ICE outboard(s) will can be combined to provide a mixture of electric and ICE power for maximum propulsion, irrespective of their nature, in an essentially transparent fashion for the boat operator. At all times during these different maneuvers, the ESU can be monitored for operation within the defined safe parameters for generation of heat and over-temperature. It is worth mentioning that the operator has no requirement to monitor the ESU, and required very little actual manipulation for this optimized switching, as the transitions in power demands are met by using the Energy Storage Unit and the electric motors. In this example, up to a momentary 300 kW of energy can be extracted from the ESU, and due to the inherent capabilities of state of the art motor controllers, through regeneration put some of the temporary excess energy back into the ESU to smooth out and optimize the transitions. 
         [0021]    Propeller sizing is also important to consider in a mixed configuration. Electric motors have inherently very high torque even at very low rpm due to the nature of the technology. ICE powered outboard(s) on the other hand have very low torque at low rpm but high static running loads making them very inefficient. On the other hand of the spectrum, due to the logarithmic nature of drag increase with speed, ICE powered outboards are normally sized for the maximum speed and are therefore ill suited for low power utilization. Maximum propeller load is normally not the most fuel efficient area of utilization of an ICE outboard motor either. By combining an electric motor and an ICE powered outboard motor, the very low power setting can be accomplished by the electric motor allowing all propellers to be pitched and surfaced to the most efficient point. It is also understood that at very high power, the Standard ICE outboard might not be able to achieve its top RPM because of the high pitch and surface of an optimized propeller, but when combined with electric outboard motor(s) the higher speed (RPM) can be achieved thereby further increasing the efficiency of the vessel, especially at normal cruise speed. 
         [0022]    Another aspect of at least one of the inventions disclosed herein includes the realization that the risks and dangers of a battery fire on board a vessel can be reduced if not eliminated by the use of state of the art electronics and software. 
         [0023]    In accordance with some embodiments, the system can include a hybrid EMC (Energy Management Computer) system. The EMC can include a human actuatable input device (Throttle(s) for example). One or many ESU(s) (Energy Storage Unit) are further included, the ESU(s) having a corresponding charge level. The ESU is contained in a water-proof container equipped with an overpressure vent and a separate valve that can in emergency allow water to enter the container. One or many electric motor(s) are included, the electric motor(s) operating in propulsion mode to turn attached propeller(s). One or many ICE outboard(s) are also included. An EMC can also be included, the EMC having a processor controlling the operation of the ICE outboard (s) and the electric motor(s) based at least in part on the ESU charge level and propulsion demands. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1 : is a simplified schematic view of an embodiment of an electric powered outboard including the electric motor, an ESU (Energy Storage Unit), an EMC (Energy Management Computer), and a throttle. 
           [0025]      FIG. 2  is a simplified schematic view of an embodiment of twin electric powered outboards including the electric motors, an ESU (Energy Storage Unit), an EMC (Energy Management Computer), and one or many throttles and/or a Joystick. 
           [0026]      FIG. 3  is a simplified view of an embodiment of an outboard powered vessel with at least two electric motors, an ESU (Energy Storage Unit), an EMC (Energy Management Computer), one or many throttles and/or a Joystick and equipped with independent steering of the outboard motors, so as to allow complete  3  axis maneuvering of the vessel through the  3  axis joystick and the EMC. 
           [0027]      FIG. 4  is a simplified view of an embodiment of a three outboards powered vessel comprised of two ICE engines, one electric, an ESU (Energy Storage Unit), an EMC (Energy Management Computer), one or many throttles and/or a Joystick. 
           [0028]      FIG. 5  is a simplified view of an embodiment of a three outboards powered vessel comprised of two Electric powered outboard motors, an ICE powered outboard, an ESU (Energy Storage Unit), an EMC (Energy Management Computer), one or many throttles and/or a Joystick. 
           [0029]      FIG. 6 . is a diagram of an energy storage unit (ESU) located in the hull of a boat. 
           [0030]      FIG. 7  is a diagram of one of many such ESUs, that are normally connected in series or parallel to each other to provide the necessary energy to the vessel. Each of these energy modules is equipped with a contactor rendering it inert unless it has a valid handshake from the EMC, a high speed fuse to cut current flow in case of a malfunction in the system, a Battery Management System that reports de individual state of each cells, the temperature in specific locations, performs equalization and controls either automatically or under the commands of the EMC functions like contactor and is one of the means to open safety water valve in case of an uncontrollable runaway. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0031]    Electric only operation is the most elegant, simple and economical, but until the energy storage issues are resolved, (cost and energy density), it may require recharging with a generator that uses petroleum products and/or with wind/water generators, solar panels, fuel cells or shore based power sources. This rapidly increases the cost and complexity of this type of system. 
         [0032]    Even if battery only electric propulsion is extremely efficient at low speed and for low speed maneuvering, a large part of the market still demands the capability to go at high speed (even if for limited time). Commercial, pleasure fishing and diving operators want to go at high speed to their temporary destination and revert to low speed for hours or days before coming back at high speed to offload their expensive and/or time sensitive cargo, so that they can do it all over again. 
         [0033]    Therefore, a way to automate the combination of the current technologies and greatly increase efficiency at a useful range of speeds is desirable. A transparent integration of the above can be achieved if proper automation is used, and it is possible to integrate all of these into a uniform and extremely efficient system. Some of the embodiments disclosed herein are directed to such systems, control, and operation, using state of the art components, electronics and logic. 
         [0034]    The systems of some of the embodiments disclosed herein can be programmed to operate efficiently in different modes for different situations, such as when at the dock and connected to shore power, or when at sea. 
         [0035]    For consumers to trust electric or hybrid electric marine vessels, better safety for the energy storage device is desirable, particularly in the case of high energy storage devices like lithium based ESUs. Fire protection of the ESU can be achieved through the use of a containment enclosure that can be flooded with water in the event of over temperature leading to fire hazard. For example, a system can include at least one temperature sensor configured to detect whether a temperature of an energy storage units for containment enclosure exceeds a threshold, and to automatically flood the containment enclosure if they detected temperature is above the threshold. Other types of ESU can also be protected in the same fashion. 
         [0036]    Now refereeing to  FIG. 1 , in some embodiments, the electric outboard can include the following components: the energy management computer (EMC) which communicates with the throttle, energy storage unit (ESU) and electric outboard motor via CANBUS communication. The electric outboard can be comprised of three or more components: the electric motor of 30-220 kW power, the motor controller, and the high voltage switching/safety box. The electric motor, motor controller, and water pump required to circulate cooling water can be contained within the outboard casing. The electric motor can be coupled to the lower unit of the motor. The high voltage switching box (not shown in  FIG. 1 ), may be contained within the engine casing, or it may be located outside the engine casing. 
         [0037]    Now referring to  FIG. 2  the system show a boat with a twin outboard motor. In this case each electric outboard motor contains an electric motor, motor controller and water pump, and the high voltage switching box is located either within each motor or a single high voltage switching box is located elsewhere in the boat. 
         [0038]    Now referring to  FIG. 3 , we see that in vessel with two electric motors, the EMC can be programmed in a way to allow the two motors to work with each other to control the position of the boat. The joy stick can be used for right translation, left translation, forward or reverse, left or right rotation and  3  axis movements. 
         [0039]    Now referring to  FIG. 4 , we see a configuration with two standard ICE outboard motors and a single electric outboard motor. The EMC is programmed to use the electric motor at low power, such as coming or out of port or when trolling (fishing). At higher power, as demanded by the throttle position, the EMC turns on the ICE engines in combination with the electric counterpart and standard mixes fuel/electric operation is used. An example of mixed operation would be low speed where only electric, acceleration is combined gas and electric, normal high speed cruise where the main power is derived from the gas engines and the electric is water regenerating the battery pack if required, and at extreme high speed all motors are combined with the assist of range extender generator if installed. When the ESU is depleted either an optional on board generator, shore power or high speed re-generation is used to replenish the energy level. 
         [0040]    Now referring to  FIG. 5 , we see two electric motors ( 1 ) that can be independently controlled in pitch and direction, we see a standard ICE (Internal Combustion Engine) ( 2 ) but controlled by electronics so that it can also be integrated into the EMC (Energy Management Computer) ( 3 ), the throttles ( 4 ), the 3 axis joystick ( 5 ) and the steering wheel ( 10 ) connected electronically to the EMC ( 3 ), the ESU (Energy Storage Unit) ( 6 ) that is electrically connected to the two electric motors ( 1 ) and electronically connected to the EMC ( 3 ), a petroleum storage tank ( 8 ) feeding the ICE engine, a shore charger ( 7 ) electrically connected to the ESU ( 6 ) and electronically connected to the EMC ( 3 ) so that the EMC can control and display the amount of power used by the device, and finally an optional range extender generator ( 9 ) that can be used to recharge the ESU ( 6 ) or used to provide a get home system should the ESU have reached its low energy limits. 
         [0041]    Also referring to  FIG. 5 , all low speed operation can be performed through the joystick ( 5 ) that sends commands to the EMC ( 3 ), the EMC has control of all propulsion motors ( 1 ) ( 2 ) in variable forward, reverse, direction and pitch, thus allowing full 3 axis movement of the vessel as described in  FIG. 3 ). The vessel can also be operated in a standard fashion through the normal throttles ( 4 ) sending thrust and pitch commands and the steering wheel ( 10 ) sending turn commands to the EMC ( 3 ). In normal operation, the EMC ( 3 ) will decide (based on ESU ( 6 ) status) and on the programmed efficiency maps witch of the propulsion device (electric or ICE) to use, alone or in combination to achieve the best efficiency for the requested operational demands . It can also be understood that in a setup like  FIG. 4 ), where low speed operation is done only through the use of the electric motor, acceleration to high planning speed is done by electronically combining (EMC  3 ) the electric and ICE motors, and once stabilized in normal cruise speed, the electric motor could be used as a water generator and recharge the ESU ( 6 ) until needed again. The optional on board generator ( FIG. 5  ( 9 )) can also be used to provide additional thrust when sustained high speeds are required. 
         [0042]    Now refereeing to  FIG. 6 , the diagram shows an ESU contained in a safety enclosure and located in the hull of the boat. Other locations for the ESU units may be under seats of small craft or in the engine rooms of larger vessels. 
         [0043]    Now referring to  FIG. 7 , this drawing represents a typical energy module composed of a combination of lithium cells in series and parallel combined to give us a nominal voltage of approximately 50 Volts and an energy of 5 to 7 kWh. The positive and negative terminals are finger proof shielded connectors with built-in safety switch to detect removal attempts and order system power down in such a case. By default, no voltage is applied to these terminals until all safety switches are closed, and a proper diagnostic/hand-shake is accomplished by the vessel&#39;s EMC (Energy Management Computer) through the canbus communication link. Therefore, the energy module incorporates a relay (high voltage and amperage contactor) controlled and sensed by the included BMS; a high speed fuse. Each module in a vessel has its own BMS (Battery Management System), that monitors individual lithium cell voltage, temperature, provides balancing/equalizing functions, monitors relays like contactor, and has the authority to open relays or the Water Ingress Valve should certain programmed limits be exceeded. 
         [0044]    Since anytime a large amount of energy is stored and used (charged/discharged), and sometime at high rates, a certain danger exists and the devices have to be controlled very accurately to operate within the prescribed limits. Should a fault develop, and the EMC unable to control it through normal voltage or amperage manipulation, there is the possibility of a thermal run-away. Even if this event is extremely unlikely, Lithium fires, like fuel, has the tendency to be very destructive: lithium will not explode as fuel, but lithium fires generate a lot of heat, the heat combines with neighbor cells and the fire goes out of control. In marine vessels, pulling on the side of the road is not an option, so an automated fires restraint system can be included in some embodiments. 
         [0045]    Again referring to  FIG. 7 , our innovative solution to protect from lithium fire take advantage of the operation of marine vessels on oceans or inland waters. Around marine vessels, the one thing that is clearly abundant is water, and water is one of the best moderators of lithium thermal runaway. In some of the embodiments disclosed herein, a water ingress port and valve can be used to allow water to enter this normally water tight (IP67) battery module. Additionally, a Pressure Relief Valve can be included, to allow water or steam to escape in case of an emergency requiring the injection of water in the battery module. This water ingress valve can be operated remotely by the EMC, locally by the onboard BMS or by temperature alone. Additionally, the system can be configured to activate an alarm, such as an audio alarm and/or a visual alarm, at any time there is water flow. For example, the system can be configured to activate such an alarm whenever the water pump is operated on emergency power. Other conditions can also be used for determining when the alarm should be activated. 
         [0046]    Additionally, in some embodiments, a method of operation of a system can be applied to an outboard motor comprised of a standard outboard lower end unit from an internal combustion engine powered outboard motor, with an electric motor mounted in place of the removed internal combustion engine such that an output shaft of the electric motor extends downwardly into the lower end unit in the same alignment as the crankshaft of the internal combustion engine was aligned. In such a method, the control system can be configured to operate the electric motor at a speed based on the built-in reduction ratio defined by the gears in the lower end unit, where were designed for internal combustion engine operating speeds and power outputs. Additionally, the propeller mounted to the lower end unit can be changed or modified to better match the resulting output of the electric motor as modified by the gear ration in the internal combustion engine designed lower end unit. Additionally, the built-in forward and reverse transmission is generally not required when the internal combusitno has been replaced with an electric motor. Thus, the forward and reverse transmission typically included in the lower end unit of internal combustion engine outboard motors can be modified to include only unidirectional gearing, and allow transmission operation despite the absence of a continuously turning ICE engine. Additionally, an electric outboard motor can include a built-in raw water impeller to provide cooling water to the electric motor and its controller&#39;s glycol heat exchanger. 
         [0047]    Additionally, some embodiments can include using standard AC or DC on board generators to supplement, assist or provide through the high power shore power or directly to the ESU charging and limited get home capability. 
         [0048]    Further, some embodiments can include, in reference to inherently inefficient fixed speed AC generators, through the use of the EMC, an automated way of optimizing the operation of such AC generator so that to limit its operation to its most efficient power producing point by electronically controlling the load demands of the ESU through the electronically managed shore charger for example. 
         [0049]    Further, some embodiments can include a system in a multi-engine mixed (ICE and Electric) configuration where each outboard is independently controlled in direction and pitch 
         [0050]    Further, some embodiments can include a system that will detect if a water craft is inverted and that will disable the electric propulsion system by opening all relays and contactors, thereby stopping the propulsion system and preventing any risk of dangerous electrical leakage. 
         [0051]    It will be appreciated by persons skilled in the art that the present inventions are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the inventions.