Abstract

The full-rotation pod propeller is a new integrated marine electric propulsion device, which abandons the traditional ship propulsion system composed of main engine, shafting, steering gear and gearbox. It integrates the drive motor, propeller, sealing structure and cooling system inside a streamlined pod suspended under the hull. The pod can realize unrestricted 360° horizontal rotation. By changing the thrust direction of the propeller, it simultaneously completes the two core functions of ship propulsion and steering, greatly improving ship maneuverability, propulsion efficiency and energy-saving performance. This paper systematically elaborates on its structural composition, core working logic, operation modes and technical advantages.

I. Overall Structural Composition

The full-rotation pod propeller is mainly divided into three parts: hull-mounted rotary mechanism, pod cabin and propulsion execution unit.

1. Upper Rotary Mechanism

It is installed at the bottom of the ship's stern cabin, including rotary servo motor, rotary bearing, sealing assembly and conductive slip ring, which is the core component to realize full rotation of the pod. The slip ring ensures continuous power supply to the internal motor and CAN bus signal transmission during 360° rotation of the pod without cable winding. The high-load rotary bearing bears the horizontal thrust, vertical buoyancy and hydrodynamic impact generated by the propeller during navigation.

2. Streamlined Pod Cabin

It is a sealed waterproof metal shell suspended underwater, with a built-in permanent magnet synchronous drive motor. The cabin is equipped with an independent liquid cooling circulation system and pressure balance sealing structure to resist seawater corrosion and deep water pressure. The streamlined shape can reduce underwater flow resistance and suppress propeller cavitation.

3. Propulsion Execution Unit

It consists of low-noise high-efficiency propeller, propeller hub and shaft sealing components. The motor rotor is directly connected to the propeller hub, eliminating intermediate transmission links such as gearboxes and long drive shafts, which greatly reduces mechanical loss during power transmission.

II. Core Working Principle

The whole working process can be split into two independent and coordinated modules: electric propulsion drive and full-rotation steering adjustment.

2.1 Principle of Propulsion Power Generation

Alternating current output from shore power or shipborne generator set is converted into variable-frequency and variable-voltage power by the on-board frequency converter, and transmitted to the permanent magnet synchronous motor inside the pod through the slip ring.

After the motor is energized, the magnetic field drives the rotor to rotate directly and outputs torque to the propeller. When the propeller rotates continuously at the set speed, it continuously pushes seawater backward to generate equal and opposite forward thrust to propel the ship forward. Adjusting the output frequency of the frequency converter can steplessly change the motor speed, so as to control the thrust and realize acceleration and deceleration of the ship.

Different from the traditional diesel direct drive system, the pod adopts direct motor drive with fast torque response and stable low-speed output without idle fuel consumption of the main engine. Combined with the CAN communication protocol, the motion controller can accurately collect real-time parameters such as motor speed, operating current, winding temperature and fault code of the pod propeller to realize closed-loop power control.

2.2 Principle of 360° Full-Rotation Steering

The upper rotary servo system receives steering commands issued by the ship console, and the servo motor drives the rotary bearing to drive the entire pod cabin to rotate 360° horizontally.

The core steering logic is to change the horizontal direction of propeller thrust:

• Pod rotated 0° (propeller facing backward): The propeller pushes water horizontally backward, and the ship sails straight forward;

• Pod rotated 180° (propeller facing forward): The propeller pushes water horizontally forward to generate reverse thrust, enabling emergency reverse braking of the ship without reversing the motor;

• Pod rotated 90° to port or starboard: Thrust acts horizontally on the port or starboard side of the hull, allowing the ship to turn in place and move transversely;

• Rotation at any angle between 0° and 360° can synthesize oblique thrust to flexibly adjust the ship's track.

The rotary mechanism is equipped with an angle encoder to feed back the pod orientation in real time, and the motion controller forms closed-loop rotary control to ensure accurate thrust angle and avoid steering overshoot. Multiple pod propellers can work in linkage: by setting different rotation angles and thrust values for the left and right pods, the ship can complete actions such as zero-radius turning and transverse berthing that cannot be realized by traditional rudder-propeller systems.

2.3 Working Logic of Supporting Auxiliary Systems

To ensure long-term stable underwater operation, the pod is equipped with supporting auxiliary systems with independent working principles:

1. Liquid Cooling System: Circulating cooling liquid takes away heat generated by motor operation in the sealed cabin and exchanges heat with seawater through an external heat sink to prevent motor overheating failure under high load;

2. Multi-stage Sealing and Pressure Balance System: Combined mechanical sealing structure isolates seawater from internal electrical components, and the pressure balance chamber eliminates pressure difference inside and outside the cabin under different drafts to prevent seawater infiltration;

3. Real-time Monitoring System: Based on CAN bus communication, the pod can feed back operating parameters such as speed, current, temperature and fault information to the ship control terminal actively or on demand. It will automatically reduce power or lock rotation when faults such as over-temperature and over-current occur to realize equipment protection.

III. Typical Operation Modes of Full-Rotation Pod Propeller

Combined with rotation and power regulation characteristics, the equipment has three mainstream operation modes adapted to different navigation scenarios:

1. Fixed-Angle Continuous Propulsion Mode

   The pod locks the rotation angle, and the controller continuously outputs directional thrust at a fixed frequency. It is suitable for long-distance straight-line navigation of cargo ships, yachts and engineering vessels with stable propulsion efficiency and lower energy consumption.

2. 1Hz/10Hz Periodic Active Feedback Mode

   Without manual query, the pod automatically sends real-time speed and current data to the controller at a fixed frequency, facilitating shore remote monitoring and data collection for ship automatic navigation systems.

3. On-Demand Query Mode

   The pod does not actively upload data. The motion controller sends query commands only when necessary to obtain parameters such as temperature and fault codes, reducing bus data occupation during stable navigation.

IV. Technical Advantages Brought by Its Working Principle

• Ultra-High Maneuverability: 360° full rotation breaks the limitations of traditional rudders. Ships can turn in place and berth transversely without tugboat assistance, which is especially suitable for passenger ships, offshore wind farm operation vessels and port engineering ships;

• High Propulsion Efficiency: Direct motor drive eliminates transmission losses of shafting and gearboxes, and the streamlined pod reduces hydrodynamic resistance. The comprehensive energy consumption is reduced by 10%~20% compared with traditional propulsion schemes;

• Low Vibration and Low Noise: The motor is isolated in the underwater pod, cutting off the vibration transmission path to the hull without long shaft excitation, which greatly improves cabin comfort for passenger ships;

• High Safety and Easy Maintenance: Independent sealed pod structure, modular design of motor and rotary mechanism for convenient underwater inspection and replacement. The real-time monitoring system can give early warning of equipment faults to avoid navigation accidents.

V. Conclusion

The core innovation of the full-rotation pod propeller lies in the integrated design of electric drive and full-angle rotary steering. Relying on the coordination of underwater permanent magnet motor drive and upper rotary servo mechanism, it integrates propulsion and steering functions. Its unique working principle breaks through the performance bottleneck of traditional ship propulsion systems. With the development of marine electric intelligence, full-rotation pod propellers have become the preferred propulsion solution for new energy ships, offshore engineering equipment and luxury yachts. It will be further optimized in the directions of deep water pressure resistance, high-power output and intelligent coordinated control of multiple equipment in the future.