Core Differences Between Berthing with Rim‑Driven Side Thrusters and Conventional Propellers

Ship berthing is the highest‑risk and most challenging operation in shipping. Narrow port waters, complex currents and wind interference place high demands on vessel maneuverability, positioning accuracy and stability. Two mainstream berthing modes are currently adopted. One is the combined solution of conventional shaft‑driven propeller + rudder + auxiliary side thruster, widely used for merchant and cargo ships. The other is the innovative rim‑driven shaft‑less thruster with omnidirectional side‑thrust capability, applied to new‑energy vessels, port workboats, research ships and high‑end official vessels. Significant gaps exist in power principle, control logic, berthing workflow, safety performance and operating costs, directly determining berthing efficiency and safety. This article analyzes their core differences based on real‑world port operating scenarios.

1. Power Principle: Rigid Shaft Transmission vs. Shaft‑Less Omnidirectional Vector Thrust

Conventional propulsion systems rely on shaft‑driven propellers and rudders as prime movers, assisted by bow/stern side thrusters for berthing. Power is transmitted via through‑hull stern shafts, gearboxes and main engines. Forward and reverse motion is achieved by propeller rotation, while course alteration depends on rudder deflection. Thrust works in fixed directions with no independent lateral force. Rudder efficiency drops sharply at low speed, requiring frequent main‑engine start‑stop cycles plus side‑thruster correction. Its power output follows an “oriented, delayed and segmented” transmission pattern.

The rim‑driven thruster is a shaft‑less annular electric propulsion unit. It eliminates complex traditional components including stern shafts, rudders and gearboxes. Motor rotors are integrated into the thruster rim with blades mounted inside the annular rotor. The rotating ring drives blades to generate thrust. It delivers 360‑degree omnidirectional vector thrust without rudders. Electronic control instantly adjusts thrust magnitude and direction for forward, reverse, lateral and diagonal force, realizing genuine all‑azimuth maneuverability and reshaping the fundamental logic of ship berthing.

2. Berthing Control & Workflow: Step‑by‑Step Correction vs. One‑Step Precise Docking

Berthing with Conventional Propellers: Cumbersome Process, Experience‑Dependent, Low Fault Tolerance

Conventional ship berthing requires complicated iterative adjustments heavily dependent on crew experience and equipment coordination. When vessels reduce speed entering port, rudder effectiveness declines rapidly and maneuverability deteriorates, making fine speed and heading control difficult. Approaching the pier, bow and stern side thrusters must be activated together with intermittent astern engine bursts and repeated rudder tuning to counteract current and wind drift.

Multi‑position collaboration among captain, helmsman and engineer is mandatory. Frequent adjustments to engine RPM, rudder angle and side‑thruster power cause delayed responses. In constrained harbours, strong winds or swift currents, operational difficulty rises exponentially. Hull offset and improper berthing angles frequently occur, requiring tugboat support for safe docking. The whole workflow is lengthy, labour‑intensive and inefficient.

Berthing with Rim‑Driven Side Thrusters: Omnidirectional Maneuver, Simplified Control, Autonomous Docking

Vessels fitted with rim‑driven thrusters adopt a revolutionary berthing philosophy. Benefiting from 360° all‑direction thrust, ships can perform stationary turning, sideways translation and ultra‑low‑speed precision positioning. Frequent main‑engine cycling and repeated rudder corrections are unnecessary, nor do side thrusters need continuous operation. Ships may proceed at constant ultra‑low speed while electronic vector‑thrust compensation counteracts wind, wave and current disturbances to maintain stable hull attitude.

Vessels can move sideways directly against berths with zero approach angles without tugboats. A single operator completes core manoeuvres. Overall berthing procedures are greatly streamlined with over 50 % faster control response, eliminating low‑speed steering failure and attitude instability typical of conventional systems. It suits inland narrow waterways, high‑density harbours and complex offshore coastal conditions.

3. Berthing Safety & Environmental Adaptability: Passive Disturbance Rejection vs. Active Attitude Stabilization

Berthing hazards mainly originate from poor low‑speed handling, offset caused by external loads and delayed power responses. Conventional propulsion has inherent limitations: rudders barely function at slow speeds. Faced with cross‑winds and transverse currents, crews can only counter disturbances reactively by tuning power and heading. The hull tends to sway, drift and tilt, raising risks of pier collision and scraping. Furthermore, exposed conventional propellers easily get entangled with mooring ropes and underwater debris near berths, resulting in blade damage and extra operational hazards.

Rim‑driven thrusters feature active attitude stabilization and omnidirectional disturbance resistance. The fully‑enclosed shaft‑less design removes exposed propeller blades and prevents rope or debris entanglement for superior physical safety. Modular electric thrust delivers millisecond‑level response, dynamically offsetting wind, wave and current forces and keeping the hull steady. Even under strong winds, rapid currents, confined berths and dense vessel traffic, accurate, smooth and safe berthing is achievable. The risk of collision, grounding and hull scraping drops substantially with significantly higher fault tolerance.

4. Energy Consumption, Noise & Water‑Body Impact: High‑Disturbance Operation vs. Low‑Impact Green Performance

During conventional‑propeller berthing, repeated main‑engine start‑stop and speed shifting increase fuel burn and exhaust emissions. High‑speed propeller rotation generates intense jet streams and cavitation that scour quay walls, stir up bottom sediment and cloud harbour water. Loud mechanical noise and vibration also harm aquatic ecosystems. Shaft‑transmission vibration causes noticeable hull shaking throughout berthing.

Rim‑driven thrusters run purely on electricity with zero fuel consumption and exhaust gas during berthing, complying with green‑port standards. The enclosed annular propulsor produces smooth water flow without violent jet streams or cavitation. It avoids berth erosion and seabed disturbance to better preserve aquatic environments. Removing shafts and gearboxes eliminates major vibration sources for low‑noise, low‑vibration and smooth berthing, delivering truly low‑carbon, quiet and eco‑friendly harbour operations.

5. Equipment Maintenance & Operating Costs: Complex High‑Cost System vs. Streamlined Long‑Lifespan Solution

Conventional propulsion consists of numerous precision mechanical parts: main engine, stern shaft, gearbox, shaft seals, rudders and multiple side thrusters. Frequent start‑stop and speed changes during berthing accelerate wear‑and‑tear and failure rates. Regular professional inspections, servicing and component replacement generate heavy long‑term maintenance expenditure. Tugboat fees for each berthing manoeuvre further raise cumulative operational costs.

The rim‑driven thruster adopts modular integrated shaft‑less architecture. Few moving mechanical parts reduce wear and failure probability for high reliability and infrequent servicing. Inspection and overhaul are straightforward without complicated shaft disassembly, cutting labour and spare‑part expenses. Redundant isolated electrical modules ensure continued operation even if individual units malfunction. Tugboat assistance is no longer required, removing substantial tug hire charges and lowering overall port‑berthing expenditure.

Summary

Conventional‑propeller berthing represents a “mechanical transmission, passive correction, experience‑reliant, high‑cost & low‑agility” legacy workflow adequate for open‑water standard harbour tasks yet showing obvious weaknesses for complex‑water and high‑precision docking scenarios with hard‑to‑improve safety and efficiency limits. In contrast, rim‑driven side‑thruster berthing is an advanced solution characterised by “electronic vector control, active stabilisation, full‑azimuth manoeuvring, green efficiency”. Thanks to omnidirectional thrust, precise handling, safe low‑disturbance behaviour and economical maintenance, it matches demands for modern refined, eco‑friendly and intelligent port operations and constitutes the mainstream technical upgrade direction for future ship berthing. With growth in inland waterway transport, coastal harbours and new‑energy vessels, rim‑driven thrusters will progressively replace conventional propulsion systems as core power equipment for harbour‑ship berthing.