Abstract: An enhanced counter-rotating electric motor and an associate propulsion system for use with a water-vehicle includes a motor housing, a stator within the housing that rotates about a central axis in one direction, an armature within the stator that rotates about the central axis in an opposite direction from the stator, a first axel that is secured to the stator and extends out from the housing, a second axel that is secured to the armature and extends out from the housing, water-tight rotational seals about each of the two axels, a centrifugal-force-balancing electrical connection mechanism that supplies functioning electrical communication between the motor and external electrical circuitry while operating the motor, and a propeller secured to each said axel.

Abstract: An apparatus, system, and method are disclosed for an apparatus, system, and method to capture and store energy created as a result of a solid object moving through an electrolyte. The apparatus, in one embodiment includes a solid material, an electrolyte, a propulsion mechanism and an electrode. In certain embodiments the propulsion mechanism configured to produce a propulsive force to drive the solid material through the electrolyte at a rate sufficient to produce a net electrical charge on the solid material. The electrode may be connected to the solid material and configured to conduct the electrical charge away from the solid material.

Abstract: An outboard propulsion system is disclosed. In some embodiments, the outboard propulsion system includes a generator operable to produce a first electrical signal, an engine electrically coupled to the generator, an inverter electrically coupled with the generator to receive the first electrical signal, wherein the inverter is adapted to transform the first electrical signal into a second electrical signal, all electric motor electrically coupled to the inverter to receive the second electric signal, a shaft mechanically coupled to the electric motor and rotatable by the electric motor when the electric motor receives the second signal, and a thrust generation device mechanically coupled to the shaft. The engine is configured to operate the generator. The thrust generation device is adapted to rotate when the shaft rotates.

Abstract: There is provided a ship, in particular a cargo ship. It has a plurality of Magnus rotors, wherein associated with each of the plurality of Magnus rotors is an individually actuable electric motor (M) for rotating the Magnus rotor, wherein associated with each electric motor (M) is a converter (U) for controlling the rotary speed and/or the rotary direction of the electric motor (M).

Abstract: A marine vessel power generation system comprising a conventional machinery arrangement, such as an internal combustion engine (2) and a generator (3), a propulsion system, and a main switchboard (6). In order to provide an environmental friendly power generation system, when the marine vessel enters, leaves or is in port, said system is provided with an H2O operated power generation arrangement (8) for generating H2O from seawater in order to produce electrical energy.

Abstract: A watercraft propulsion system can be a hybrid type watercraft propulsion system including an engine and an electric motor both working as drive power sources for a propeller. When an operating lever instructs a speed reduction assist mode as a stopping mode, a controller can stop the engine and reverse the rotational direction of the electric motor to reversely rotate the propeller. The controller can determine whether the speed reduction assist mode is instructed or not based upon a mean movement speed of the operating lever and can control the electric motor based upon a speed of the watercraft. Alternatively, the controller can control the electric motor based upon instructions by the speed reduction assist lever.

Abstract: The invention relates to a marine-vessel transmission having an input-drive shaft (10), which extends along an input-drive shaft axis (A) and on which an input-drive shaft gearwheel (12) is arranged, a first pinion shaft (14), which extends coaxially with respect to the input-drive shaft (10) and on which a first pinion (16) is arranged, a second pinion shaft (24), which extends parallel to the input-drive shaft (10) and on which a pinion shaft gearwheel (28), which engages with the input-drive shaft gearwheel (12), and a second pinion (26) are arranged, an intermediate shaft (18), on which a spur gear (20), which engages with the first pinion (16) and the second pinion (26), and a bevel pinion (22) are arranged, and an output-drive shaft (30), which extends along an output-drive shaft axis (P) which runs at an angle (?) of more than 75° with respect to the input-drive shaft axis (A), and on which a spur bevel gear (31) is arranged, which forms a bevel drive with the bevel pinion (22).

Abstract: A transportable outboard drive for a boat has a head, a pylon, a shaft connecting the head and the pylon, an electric motor and a cable running inside the shaft. The shaft has at least two shaft sections and wherein the head, shaft and pylon can be arranged in a working configuration or in a transport configuration. In the working configuration, the head, the shaft and the pylon are rigidly connected to each other. In the working configuration and the transport configuration, the cable and shaft are differently positioned with respect to each other, whereas, in its transport configuration, the shaft sections are separated from each other.

Abstract: A marine vessel includes an exterior component fitted to a hull of the marine vessel and a propulsion module configured to be received by the exterior component. The propulsion module includes a power source configured to drive a propeller; a shaft configured to couple the power source and the propeller. The module includes a housing configured to store at least the power source and a portion of the shaft.

Abstract: An electrical linear motor for propelling a marine vessel comprises a thruster assembly disposed within a guide tube. Permanent magnets are attached to the thruster assembly and placed in close proximity to electrical coil windings, which are positioned outside of and parallel to the guide tube. Electrical current energizing the coil windings creates an electromagnetic field, which interacts with the magnetic field of the magnets to cause reciprocating linear motion of the thruster assembly with the guide tube. During the non-propelling back stroke, a check valve on the thruster assembly is in open position to allow free passage of water. The check valve is moved to a closed position during the working stroke of the thruster assembly, allowing the thruster assembly to propel the marine vessel.

Abstract: A boat propulsion unit includes an electric motor, a potentiometer arranged to detect the rotating angle of a throttle grip, a first stop mode sensor, a second stop mode sensor, and a controller including a CPU, and a disconnection and short detecting circuit. If the voltage signal fed by the disconnection and short detecting circuit is out of the specified range, the CPU detects the operation mode designated by the throttle grip based on the switching of the outputs from the first stop mode sensor and the second stop mode sensor. Then, the electric motor is driven in the forward operation mode and with the specified output power when the forward operation mode is designated, whereas, the electric motor is driven in the reverse operation mode and with the specified output power when the reverse operation mode is designated. Using this arrangement, the boat propulsion unit can obtain a minimum required boat operation as intended by the boat operator even when an abnormality has occurred in the controls.

Abstract: A motorized push pole device having a standard mounted to a raised poling platform on a boat. A housing is mounted to the standard wherein the housing is adapted to removably clamp around a push pole. A drive wheel is mounted under the housing, wherein a periphery of the drive wheel is in contact with the push pole and adapted to rotate in a first direction causing push pole to move in an extendable motion and the drive wheel adapted to rotate in an opposing second direction causing push pole to move in a retractable motion. An electrical switch is connected to a motor for controlling operation of the motor for rotating the drive wheel. The motor includes a rotating motor shaft terminating in a worm gear. The drive wheel further comprising a cog wheel for engaging the worm gear of the motor.

Abstract: A boat propulsion apparatus is constructed such that an operation mode can be switched to a reverse mode and an amount of an output can be set by an easy operation without a complicated structure and further in which a main body of the propulsion apparatus can be locked to a hull. The boat propulsion apparatus is provided with a main body and a locking mechanism. The main body of the propulsion apparatus is provided with an electric motor, a throttle grip, a potentiometer arranged to detect an indication by the throttle grip, a first controller arranged to control an operation mode and an output of the electric motor depending on an output of the potentiometer, and second controller arranged to control the locking mechanism depending on an indication provided by the throttle grip.

Abstract: A controller for an electric propulsion system for watercraft that provides for speed, steering and direction of propulsion with a single stick mechanism. The position of the joystick handle relative to the center position will define speed (deflection from center position), steering (angle position of the deflection relative to the stick access), and propulsion direction based upon the quadrant deflection in the angular position and the angle position of that deflection. The present control system includes an all electric wire connection between the controller and the electric motors eliminating any mechanical connections.

Abstract: A marine outdrive has a hydraulic vane motor with a spool shaped rotor eccentrically mounted in a fusiform shaped housing. The resulting increased vane area results in greater torque and speed.

Abstract: A watercraft (1) includes at least two oar handles (3a, 3b) which are designated to be actuated by a passenger of the watercraft in order to propel the same. A considerably expanded functionality is achieved in such a way that the oar handles (3a, 3b) are connected to a control unit which controls at least one power-actuated driving motor (6a, 6b; 7; 16a, 16b; 26a, 26b) of the watercraft depending on the actuation of the oar handles (3a, 3b).

Abstract: The methods and apparatuses of the present invention provides for powering and maneuvering (forward, reverse and steering) systems for amphibious vehicle, marine vessel or ground vehicle operation and control. An improved propulsion system may incorporate the use of electric motors combined with impellers which use positive and negative magnetic torque applications and allows for new control strategies when used in water or on the ground. More precise control of the motoring and steering forces is provided which is suitable for use in a variety of amphibious, marine vessels or ground vehicle applications. Various types of electric drive motor/generators may be incorporated for use therein. Intelligent motion control systems may provide for improved vehicle control that can provide motive force and braking force in a precisely controlled manner that significantly improves performance and has faster control dynamics incorporating a fully integrated electrical braking and maneuvering system.

Abstract: The invention relates to a pod ship propulsion System comprising a housing (3) connected to a ship hüll (2), an electric drive motor (8) mounted inside the housing at least one propeller (4) disposed outside the housing, wherein said electric drive motor is connected to the propeller by means a hydrodynamic gear (10).

Abstract: A system and a method for providing power to a marine vessel and, more particularly to a tugboat is disclosed. The system includes diesel engines and generators and batteries which can be charged using power supplied by the generators, shore power or regenerated power. The tugboat is operated utilizing battery power only and the generators are used to provide additional power if needed or to recharge the batteries.

Abstract: An assembly for retrofitting the hull of a watercraft is presented, which includes an elongated panel which defines a longitudinal channel and at least one console. The console defines at least one chamber extending through the panel and an upper chamber opening and a lower chamber opening. The panel is sized and configured to attach to the hull at an opening in the hull, and to form a seal between the panel and the hull at the hull opening. The console of the assembly is sized and configured to receive a detachably attached propulsion device. Also presented is a watercraft having integral thereto the assembly, and a method for retrofitting a watercraft to provide a location for detachable attachment of a propulsion device such as a trolling motor.

Abstract: A sports apparatus configured to support a rider upon the water surface is disclosed and may comprise either a compartment in the top surface configured to accept personal articles and a watertight cover to prevent damage and loss of personal articles or a propulsion source. The sports apparatus can have a V-shaped hull to add stability when used in the waves. The propulsion source is powered by either a combustion or electric motor that is controlled by a user interface on the board.

Abstract: A propulsion system for watercraft for personal enjoyment that incorporates human power with electric motor assistance, energy storage and optional solar power to achieve increased watercraft speeds and/or reduced pedaling effort. Control electronics enable operator-adjustable electric motor assistance to the propulsion, thereby providing flexible pedal cadences and efforts and enjoyment for a wide variety of operators. An optional photovoltaic solar panel augments the power generation to extend travel time with motor assistance, and recharges the energy storage system. This invention enables a pleasure watercraft that is simultaneously lightweight, low cost, low maintenance, environmentally friendly with zero pollution, ultra-low noise, and thrilling to operate, while simultaneously providing a means of enjoyable exercise for operators of nearly all abilities.

Abstract: A hybrid propulsion and energy management system for use in marine vessels and other variable demand propulsion applications monitors and draws energy from various energy sources dynamically to implement multiple operating modes and provide efficient system operation across a range of propulsive demands, altering the operation and output of various energy sources in response to propulsive load demands, hotel loads and auxiliary energy demands. The propulsion system incorporates at least two propulsive sources, including at least one main propulsive engine and at least one motor-generator unit arranged to drive a common output shaft, and the energy management system dynamically shifts operation of each of the two sources to satisfy propulsive demands. The main propulsive engine and the motor-generator unit are capable of driving the common output shaft both independently and simultaneously.

Abstract: An assembly for retrofitting the hull of a watercraft is presented, which includes an elongated panel which defines a longitudinal channel and at least one chamber housing. The chamber housing defines at least one chamber extending through the panel and an upper chamber opening and a lower chamber opening. The panel is sized and configured to attach to the hull at an opening in the hull, and to form a seal between the panel and the hull at the hull opening. The chamber housing of the assembly is sized and configured to receive a detachably attached propulsion device. Also presented is a watercraft having integral thereto the assembly, and a method for retrofitting a watercraft to provide a location for detachable attachment of a propulsion device such as a trolling motor.

Abstract: Disclosed is a power generation, distribution, and on-board power supply system for low-emission surface marine (navy) ships of different classes and sizes. The system is embodied as an equipment segment and includes at least one cruising speed drive unit, which can be supplied with electrical power from a DC network, and at least one auxiliary drive unit, e.g. a hydrojet, which can be supplied with electrical power from an AC network and can be connected as required. The DC network and the AC network are configured in such a way that power can be mutually transferred.

Abstract: A trolling motor control system includes plurality of modules that are connected to a communication bus to transmit and receive data used in controlling operation of a trolling motor. Based upon data transmitted over the bus, trolling motor speed, steering, and trim can be controlled. The modules can include motor controller modules, foot pedal modules, compass and GPS modules, RF modules for wireless control, battery metering modules, diagnostic modules, accessory device driver modules, power trim controller modules, and power steering controller modules.

Abstract: A watercraft includes a plurality of outboard motors. Each of the outboard motors has a generator and a rudder deflecting system driven by an electric motor. The outboard motors are turned by the rudder deflecting systems thereby steering the watercraft. Electric power can be supplied from the generators of others of the plurality of outboard motors to the rudder deflecting system of an arbitrary outboard motor among the plurality of the outboard motors. Using this arrangement it is possible to provide a watercraft in which electric power for operation is stably supplied to the rudder deflecting system without increasing the size of the generators.

Abstract: A boat control system includes trim tabs mounted on the lower transom of a boat, with an electric trolling motor attached to each tab. A user control provides commands to control positioning of the trim tabs and operation of the motors. Steering with the motors is provided by controlling the relative speed and propeller direction of the motors. The user control includes an input for generating a return-to-center command that causes the motors to be driven at the same speed and in the same direction.

Abstract: A watercraft includes a hull having a hull bottom with an opening and a trunk surrounding the opening. The watercraft also includes a propulsion device pivotally mounted to a portion of the hull other than the trunk. The propulsion device can include a transmission and a propeller on an end of the transmission, and can be movable between a deployed position and an onboard stowed position. In the deployed position, the transmission extends through the trunk and through the opening such that the propeller is positioned below the hull bottom. In the onboard stowed position, no portion of the transmission or the propeller is located within the trunk or below the hull bottom.

Abstract: Aspects of the invention relate to an electrical linear motor propulsion system and method for propelling an object through a medium. According to one aspect of the invention, the electrical linear motor comprises electrical windings and permanent magnets in close proximity so that electrical current energizing the coil windings creates an electromagnetic field which interacts with the magnetic field of the magnets to cause reciprocating linear motion of an movable linear motor thruster subassembly within a guide tube, the reciprocating linear motion comprising a fast back stroke when thruster subassembly check valve is open, and a working stroke, when a check valve is closed, that discharges the medium from the guide tube, thereby propelling the object (e.g., marine vessel, submarine, torpedo, etc.) through the medium. The linear motor(s) can be attached to the marine vessel, in multiple ways. For example, the electrical linear motor(s) can be disposed within the marine vessel.

Abstract: An energy producing device, for example a submersible vehicle for descending or ascending to different depths within water or ocean, is disclosed. The vehicle comprises a temperature-responsive material to which a hydraulic fluid is associated. A pressurized storage compartment stores the fluid as soon as the temperature-responsive material changes density. The storage compartment is connected with a hydraulic motor, and a valve allows fluid passage from the storage compartment to the hydraulic motor. An energy storage component, e.g. a battery, is connected with the hydraulic motor and is charged by the hydraulic motor when the hydraulic fluid passes through the hydraulic motor. Upon passage in the hydraulic motor, the fluid is stored in a further storage compartment and is then sent back to the area of the temperature-responsive material.

Abstract: An outboard motor adapted to be mounted on a stern of a boat and having a propeller to propel the boat, a power source which produces rotational output, a drive unit including a vertical shaft which transmits the rotational output of the power source to the propeller through a gear mechanism, and an interlock unit which detachably interlocks the power source to the drive unit. The changeable power source includes one of an internal combustion engine, an electric motor and a combination of the engine and the motor. The interlock unit interlocks one of the engine, the motor and the combination of the engine and the motor to the drive unit as the power source for propelling the boat, thereby enabling to freely change its power source as desired in accordance with a user's current needs and purposes.

Abstract: A watercraft propulsion system has a control lever for giving instructions regarding operating mode and output power from a source of driving force. A controller sets a propeller driving mode according to instructions given from the control lever. In an embodiment, an electric motor and an engine are included in the propulsion system, and the controller simultaneously controls both the engine and motor based on inputs from the control lever and sensed conditions.

Abstract: In an electrical power system of a diesel powered system having at least one diesel-fueled power generation unit, the electrical power system having a synchronous machine including a field winding being coupled to the diesel-fueled power generation unit, a battery for selectively providing a starting current during a starting mode of the electrical power system, and an inverter receiving the starting current for driving the synchronous machine and generating an inverter current, a circuit and method for reducing a voltage being developed across the field winding is described. The circuit includes a current conditioner for conditioning the inverter current and a parallel circuit interposed between the inverter and the current conditioner comprising a first branch including a resistance and a second branch including the field winding of the synchronous machine so that the parallel circuit is isolated from a voltage developed across the current conditioner during cranking.

Abstract: Improvements to electrically powered watercraft including kayaks are disclosed. The watercraft comprises a hull defining a cavity and a battery powered retractable propulsion unit. The retractable propulsion unit can be retracted into the cavity with powered or unpowered means. Various retractable propulsion units are disclosed, including propulsion units that are steerable wherein the thrust can be selectively directed. Specific embodiments to improve the steerability of electrically powered watercraft are disclosed. Mechanisms for disengaging the steering controls from the retractable propulsion units are also disclosed. Locking mechanisms for locking the retractable propulsion unit in an extended or fully retracted position are also disclosed.

Abstract: A marine propulsion device such as an outboard motor includes a submersible electric motor having a propeller connected directly with the drive shaft of the motor. The motor is an efficient brushless motor having symmetrical elliptical coils connected with a stator which generate magnetic flux when current is passed through the coils to rotate a rotor for driving the drive shaft. The motor is arranged in a housing having a nozzle connected with a rear portion thereof which surrounds the propeller to reduce cavitation. Cooling fins are provided on the outer surface of the housing to assist with cooling the motor and a motor controller arranged in the housing.

Abstract: An electric motor-driven water craft including a fuselage, on which a user can at least partially lie or stand. The fuselage has a flow channel with a screw that is driven by an electric motor and contains the electric motor and batteries, in addition to a control device for the electric motor and the screw, and those items are housed at least partially in the flow channel. This invention provides a higher power for motor-driven water craft of this type by locating the batteries in a water-tight housing. At least some sections of the batteries are in thermally conductive contact with the housing. The housing can be at least partially of a thermally conductive material and/or the electric motor is an internal-rotor motor. The stator is in thermal conductive contact with a housing of the electric motor by a heat conducting unit.

Abstract: An outboard drive has an electric motor that is electronically controlled from an inverter. The outboard drive includes a pylon, with the electric motor and inverter arranged in the pylon.

Abstract: Disclosed is a ship propulsion system comprising a synchronous machine (6) with an especially superconducting rotor winding that is to be subjected to intense cooling and a normally conducting stator winding (11) which is to be cooled. The stator winding (11) is disposed at least in part inside a support structure (14) encompassing a hollow cylindrical magnetically soft outer body (13) and web-type support teeth (21i) that extend in an axial and radial direction. A hollow cylindrical part (15a) of an exterior housing (15) encloses the outer body (13). In order to cool at least some areas of said housing part (15a), the stator winding (11) is thermally coupled to water as a cooling medium (K) via the support structure (14) and the housing part (15a).

Abstract: A frigate ship-type equipment system includes standard equipment segments, such as an energy generator, an energy distributor, a drive and an automation segment, also includes a hull which is adapted to the large and specific requirements of the frigate ship-type equipment system. In order to construct standard equipment segments for a frigate ship-type equipment system which is technically and constructively simple and economical in terms of cost, at least one of the standard-equipment segments, such as the energy generator and/or the energy distributor and/or the drive and/or the automation segment is constructed from the standard units or components which correspond to the requirements of the frigate ship-type equipment system and which are arranged in the hull of the ship and which can be built into the hull of the ship body according to equipping systems for various ship types.

Abstract: A propeller shield apparatus for mounting to a trolling motor having an exposed propeller with a horizontal axis includes a vertical fin and an arcuate propeller shield. The arcuate propeller shield is oriented concave downward and fixed to the vertical fin. The vertical fin is carried by the trolling motor. The vertical fin spaces the propeller shield above the propeller. A curved bracket is provided, connected to the vertical fin, and is clamped to the trolling motor. Angular fins can be provided at opposite ends of the propeller shield which extend substantially radially from the horizontal axis.

Abstract: A propulsion system for a marine vessel includes a first electric machine coupled to a first drive shaft configured to provide propulsion to the marine vessel, and a second electric machine coupled to a second drive shaft configured to provide propulsion to the marine vessel, in a first mode of propulsion system operation, the first electric machine is configured as a generator to supply power to the second electric machine. The second electric machine is configured as a motor to drive the second drive shaft. A method of operating the propulsion system and a vessel including the propulsion system are also described.

Abstract: A propulsion system for hybrid electric watercraft for personal enjoyment that incorporates human power with electric motor assistance, energy storage and optional solar power to achieve increased watercraft speeds and/or reduced pedaling effort. Control electronics enable operator-adjustable electric motor assistance to the propulsion, thereby providing flexible pedal cadences and efforts and enjoyment for a wide variety of operators. An optional photovoltaic solar panel augments the power generation to extend travel time with motor assistance, and recharges the energy storage system. This invention enables a pleasure watercraft that is simultaneously lightweight, low cost, low maintenance, environmentally friendly with zero pollution, ultra-low noise, and thrilling to operate, while simultaneously providing a means of enjoyable exercise for operators of nearly all abilities.

Abstract: A parent-child type boat having an electric power generating device, such as a fuel cell. The boat includes a parent boat and at least one child boat which is smaller than the parent boat. The parent boat is equipped with a generating device. The child boat is equipped with a battery and an electric propulsion device. When the child boat is docked with the parent boat and electrically connected thereto, power can be supplied to at least one of the battery and the electric propulsion device of the child boat from the generating device of the parent boat.

Abstract: A boat control system includes trim tabs mounted on the lower transom of a boat, with an electric trolling motor attached to each tab. A user control provides commands to control positioning of the trim tabs and operation of the motors. Steering with the motors is provided by controlling the relative speed and propeller direction of the motors. The user control includes an input for generating a return-to-center command that causes the motors to be driven at the same speed and in the same direction.

Abstract: An apparatus for releasably mounting a trolling motor on a watercraft and a trolling motor assembly which includes the inventive releasable mounting apparatus. The releasable mounting apparatus comprises a mounting bracket and a locking assembly which is releasably engageable with the mounting bracket at a first location and includes a cam structure which is rotatable for locking engagement with the mounting bracket at a second location.

Abstract: A method of generating electric power includes providing at least one open-winding generator having at least one winding, wherein the at least one winding has a first terminal and a second terminal. The method also includes electrically coupling the first terminal to a first electric power electronics apparatus via a first electric bus and electrically coupling the second electric terminal to a second electric power electronics apparatus via a second electric bus. The method further includes inducing and regulating a first voltage on the first electric bus and inducing and regulating a second voltage on the second electric bus.

Abstract: A propulsion system for watercraft for personal enjoyment that incorporates human power with electric motor assistance, energy storage and optional solar power to achieve increased watercraft speeds and/or reduced pedaling effort. Control electronics enable operator-adjustable electric motor assistance to the propulsion, thereby providing flexible pedal cadences and efforts and enjoyment for a wide variety of operators. An optional photovoltaic solar panel augments the power generation to extend travel time with motor assistance, and recharges the energy storage system. This invention enables a pleasure watercraft that is simultaneously lightweight, low cost, low maintenance, environmentally friendly with zero pollution, ultra-low noise, and thrilling to operate, while simultaneously providing a means of enjoyable exercise for operators of nearly all abilities.

Abstract: A boat control system includes trim tabs mounted on the lower transom of a boat, with an electric trolling motor attached to each tab. The control system controls positioning of the trim tabs within a trim range and within a troll range. If a main engine ignition switch changes from off to on while the trim tabs are within the troll range, the control system automatically moves trim tabs positions out of the troll range, and disables the trolling motors.

Abstract: In a hybrid outboard motor equipped with an internal combustion engine and electric motor as selective sources of power for driving the propeller and further provided with the first output shaft connected to the engine for transmitting its output to the propeller and the second output shaft connected to the motor for transmitting its output to the propeller, the first and second output shafts are disposed coaxially, so that the amount of space required for installing the shafts is smaller by the length of their coaxial portion relative to the prior art in which the shafts are simply connected in tandem. As a result, the size and weight of the outboard motors can be reduced, thereby enhancing its ease of operation and portability.