What is a Hybrid?
Understanding the core differences between conventional diesel, diesel-electric, serial hybrid, and parallel hybrid marine propulsion systems.
The Basic Concept
A hybrid vehicle achieves propulsion using either a fuelled power source or a stored energy source.
Fuelled Power Sources
- Internal Combustion Engine (Diesel, Petrol, Gas)
- External Combustion Engine (Stirling, Steam)
Stored Energy Sources
- Traction Battery Bank (Lithium, AGM)
- Flywheel / Hydraulic Reservoir / Supercapacitor
The vast majority of marine hybrid installations combine a marine diesel engine with a high-capacity battery bank driving an electric propulsion motor.
Comparing Marine Propulsion Architectures
1. Conventional Diesel
This is a standard single-engine mechanical installation. A diesel engine (e.g., 100 hp) connects directly to a marine mechanical gearbox, which turns the shaft and propeller.
Mechanical gearbox efficiency losses typically average ~6%. Therefore, roughly 94% of the engine's peak power is delivered directly to the propeller.
2. Diesel-Electric
Replacing the mechanical gearbox with an engine-driven generator, motor controller, and electric motor creates a Diesel-Electric drive.
All power transmission is converted from mechanical to electrical power and back to mechanical power at the shaft. Because energy passes through multiple conversion stages (Generator → Controller → Electric Motor), cumulative electrical transmission losses occur before reaching the propeller.
3. Serial Hybrid
Adding a propulsion battery bank to a Diesel-Electric setup creates a Serial Hybrid.
The propeller is always driven electrically by the motor. Energy comes either from the battery bank (engine off for silent cruising) or from the generator running to supply electrical power. All propulsion power passes through the electrical driveline regardless of mode.
4. Parallel Hybrid
A Parallel Hybrid establishes two independent, parallel transmission paths to the shaft:
- Path A (Direct Mechanical): Engine → Gearbox → Shaft for efficient, full-power open-water motoring without conversion losses.
- Path B (Electric Drive): Battery Bank → Controller → Electric Motor for silent, zero-emission electric cruising.
A mechanical power split device couples the electric motor to the shaft. When underway under diesel power, the electric unit acts as a high-output generator to charge the battery bank.
Explore the component integration and operational modes of our parallel system.
How Our Hybrids Work →