How Our Hybrids Work

The image below shows the business end of a single motor hybrid. Start by looking at the component parts

Hybrid parts

Item	Description
A	Standard marine gearbox (in this case a PRM 150). On the right hand side this connects via bell housing "B" to the engine "C" (engine not shown). On the left hand side the output flange of the gearbox connects to a soft coupling and the propeller shaft
B	Gearbox bell housing
C	Marine engine,
D	Oil cooler for gearbox
E	A liquid cooled, brushless, motor/generator, the heart of the hybrid. This sits above the gearbox and connects to the output flange of the box via a pulley/belt arrangement.
F	Motor/generator mounting bracket fixes the assembly to gearbox and bell housing
G	A pulley is inserted between the gearbox output flange and the shaft coupling. This pulley then connects, via a toothed belt, to a pulley on the motor/generator.
H	Belt guard
I	Shaft Clutch. Allows the shaft to be disconnected from the gearbox so the hybrid can run as a stand alone generator without turning the propeller. This is an optional extra and is not required on some systems (for example canal boat hybrids replace this with a boost alternator)

System Overview

Below is a simplified diagram of the main hybrid components.

Basic operation

With the engine turned off and the gearbox in neutral, the electric motor can drive the propeller using energy from the battery bank. Speed and direction are set by the controller.

When the batteries run down, (or high propulsion power is required), the engine is started and the gearbox put into drive. At this time, the controller senses the engine is running and switches the motor to generate mode. So the engine now drives the propeller, and the motor acts as a generator to recharge the batteries.

When the batteries are recharged, you can stop the engine. The controller senses the engine has stopped and automatically switches back to electric drive mode.

The engine does not need to run all the time, and when it is on, it is substantially loaded by the propeller + generator. The engine running at higher loads gives us greater efficiency; see Hybrid Efficiency section.

The six operating modes of a Hybrid

There are six basic operating modes for a hybrid (sometimes referred to as power flows), these are:

How the Hybrid Marine System provides the six modes of operation

Mode 1 – Engine drive

Conventional propulsion with hybrid is completely disabled. The engine can drive through the gearbox to the shaft. It does not require any hybrid components to enable propulsion.

Mode 2 – Electric drive

The engine is off, and the motor is driving the propeller with energy from the battery bank.

Mode 3 – Engine + electric drive (boost mode)

Both the engine and electric motor drive the propeller. This is used to good effect in automotive applications but has limited advantage for a marine hybrid. For automotive applications, the maximum power requirements are during acceleration. Once a car has achieved cruising speed, the power required drops off. Having a motor boost the engine for short periods of acceleration means you can downsize the engine.

A marine application is quite different. Power demand is constant and determined by a vessel's speed. Acceleration is not so relevant unless it is a fast planning craft. Therefore, a motor boost must be present for much longer periods to be effective. Battery banks would need to be large to provide sufficient energy for a prolonged boost and would then add extra weight (requiring more propulsion power). You would need to set the propeller to absorb the power of the motor plus the engine. When your batteries eventually run down, you are back to the engine only. However, now your propeller is too big and overloading the engine when it does not have a motor boost.

Although motor boost is theoretically possible, we do not implement it in most of our applications. General advice is to size the engine for maximum power requirements and to have the motor/generator in generating mode whenever the engine is running.

Mode 4 – Engine drive and electrical generation

The engine is driving the propeller shaft via the gearbox in the conventional way. At the same time, the generator is engaged and provides an extra load on the engine. Energy is extracted and stored in the battery bank. The controller can provide multi-region charging of the battery bank (this patented technology) and accommodate any battery technology. When the propeller starts to substantially load the engine at higher engine speeds, the hybrid generator backs off so as not to overload the engine. At very high loads, the hybrid generator turns off completely, allowing the engine to supply its full power to the propeller.

Mode 5 – Stand-alone generator

The shaft clutch is open, and the propeller is disconnected.

The engine and hybrid generator can now operate in stand-alone mode. Useful if at anchor or in the harbour and the generator is required. In some cases (inland barges) it is better to achieve stand-alone operation with a boost alternator bank. This can run with the gearbox in neutral and will boost hybrid generation when underway and at low engine speeds.

Mode 6 – Regeneration

Applicable only to sailing craft (see Regeneration section). When under canvas, the propeller can be allowed to free the wheel.

The controller can then have the generator extract energy from the spinning propeller to provide a charge back to the battery bank.

Why Buy a Hybrid? >