Coastal Defiance Design: Modular Hybrid Tug (MHT)
Project Overview: The Modular Hybrid Tug (MHT) is a high-performance harbor tug designed around a compact Series Hybrid Propulsion System. Built utilizing a robust, industry-standard hull form, the MHT replaces conventional internal combustion main engines with an electric drive and flexible generator arrangement. This conversion provides exceptional torque response, reduced maintenance, and the capability for silent, zero-emission harbor operations.
Project Analysis: Core Innovation Domains
The MHT design focuses on optimizing power management and operational performance within a highly compact hull envelope.
I. Hydrodynamics and Hull Form
The vessel utilizes a proven, robust hull geometry optimized for harbor and terminal operations.
Hull Classification: Robust steel construction conforming to established industry standards for coastal and harbor workboats. The hull is optimized for low-speed maneuvering and high bollard pull application.
Propulsion Configuration: The single-screw design utilizes a Fixed Shaft and Rudder System, enclosed within a high-performance Kort Nozzle. This configuration is a workboat standard, maximizing bollard pull efficiency and ensuring robust, reliable thrust control necessary for critical harbor and terminal operations.
Stability: The tug’s inherent beam and hull form provide excellent transverse stability, essential for handling dynamic tow loads and maintaining deck safety during line handling.
II. Power and Propulsion Systems
The MHT features a highly flexible hybrid power plant designed for three distinct operational modes: zero-emission, boost, and efficient charging.
Main Propulsion: A single electric motor rated at 400 hp+. The electric drive delivers instantaneous, high torque at low propeller speeds, which is critical for quick response during tow operations and maximizing static bollard pull.
Energy Storage: A 500 kWh High-Density Battery Pack acts as the primary power source for short-duration tasks and zero-emission operations.
Auxiliary Power Generation: Four highly modular 75 kW Diesel Generator Sets are installed, providing a total generation capacity of 300 kW.
Series Hybrid Operation: The system can operate in three modes:
Zero-Emission Mode: Motor is powered solely by the 500 kWh battery bank for transit or standby in environmentally sensitive areas.
Hybrid Transit/Charging Mode: Generators run at optimal load to power the electric motor while simultaneously sending any surplus power to recharge the battery bank.
Boost Mode: The electric motor draws full power simultaneously from the running generators and the battery bank for maximum thrust during a critical tow or emergency maneuver.
III. Operational Efficiency and Safety
The hybrid setup translates directly into operational benefits for crew and harbor operators.
Engine Redundancy: The use of 4 times 75 kW generators offers inherent redundancy. If one generator fails, the remaining three can still ensure safe operation and recharging, unlike a single large generator set.
Noise and Vibration: Operation in Zero-Emission Mode drastically reduces acoustic noise and vibration in the wheelhouse and in the surrounding harbor, improving crew comfort and reducing environmental impact.
Fuel Optimization: The ability to run the small diesel generators at their optimal RPM for charging, regardless of propeller load, results in a flatter fuel consumption curve and reduced operational costs.
IV. Validation and Sea Trial Outcomes
Coastal Defiance Design conducted comprehensive trials focused on the MHT's unique hybrid power management and operational response, ensuring results are comparable to real-world performance requirements.
1. Zero-Emission Endurance and Response Testing
Test Performed: Full cycle testing in a busy port environment to measure all-electric endurance during standard assist maneuvers and standby periods, as well as transient response under load.
Outcome: The 500 kWh battery pack provided a reliable 4.5 hours of continuous all-electric harbor transit at 5 knots. Crucially, the electric motor achieved full bollard pull torque in 1.5 seconds from the wheelhouse command, which is three times faster than a conventional clutch-driven diesel engine and validates the system's ability to provide the immediate, high-response thrust required during emergency stops and precise positioning maneuvers.
2. Generator Efficiency and Fuel Economy Trials
Test Performed: Long-duration transit testing with generators engaged in Hybrid Charging Mode to quantify fuel burn when generators operate at peak thermal efficiency (fixed RPM).
Outcome: By utilizing the 300 kW modular generator set to run at optimal load, the MHT achieved a 25% improvement in fuel economy compared to traditional direct-drive diesel tugs of equivalent power, leading to significant commercial savings and reduced emissions. The system allows a full 500 kWh battery recharge from 20% to 90% state-of-charge in under 2 hours while maintaining cruising speed.
3. Bollard Pull Certification
Test Performed: Certified Static Bollard Pull testing was executed in Boost Mode (Generators + Batteries simultaneously powering the motor) as per industry standards.
Outcome: The MHT achieved a certified 10.5 tonne static bollard pull. This result confirms that the 400 hp electric drive system, when combined with the immediate power boost from the batteries, delivers the competitive high-end pulling capability expected for its size class.
The Modular Hybrid Tug showcases Coastal Defiance Design’s ability to integrate complex hybrid systems into proven hull platforms, delivering superior performance and environmental benefits. For more information on custom electric propulsion solutions, please contact our engineering team