|Steyr's HDS hybrid diesels offer the speed and range of internal combustion plus the quiet and efficiency of electric.|
Contributing editor Lenny Rudow’s feature article in our March issue detailed how using a relatively simple set of solar panels, ordinary batteries and an electric trolling motor from a sporting goods store can save you fuel by allowing your boat to operate on electric power some of the time. It proved a point but also raised some limitations. Chief among them is the reliance upon a sunny day to recharge the batteries that drive the electric motor.
A good way to circumvent that dilemma is to install a generator to charge the batteries. A true hybrid system doesn't rely upon the sun. A combination of generators, engines and electric motors provides propulsion. How those components are configured determines what kind of hybrid system we’re talking about. There are three basic types of hybrid marine propulsion.
The first has been around for decades and probably at least sounds familiar: diesel electric. In a diesel-electric system, an internal combustion (IC) engine, which could be gas or diesel, is connected directly to an electrical generator. From this point on, the power in the system is transferred electrically to the propeller shaft via a motor controller and electric motor. The system may have multiple generators and multiple motors connected to a common electrical bus. Diesel-electric trains are common, and many large ships, such as the Queen Mary 2, also use diesel-electric power. By the strict definition this is not a hybrid, because there is no electric storage of energy — at least not enough to run the boat anyway.
The serial hybrid is similar to the diesel electric in that there’s no physical connection between the internal combustion engine and propeller shaft. The prop is turned by an electric motor, always. Serial hybrids do have a battery bank wired in to store energy that is generated, so you can stop the engine and use energy stored in the battery bank to drive the prop shafts. With large batteries you can have long periods of electric propulsion driving onboard electrical appliances without resorting to the generator.
The third type of hybrid is called parallel hybrid. The determining fact that makes a hybrid system parallel is that the internal combustion engine is directly coupled to the drive shaft in addition to the electric motor. This is accomplished by a set of gears that are sometimes called a power split. It’s a mechanical device that allows transfer of power between two sources. You can drive the propeller directly from the internal combustion engine. You can drive the propeller directly from the electric motor. You can also deliver power from both engines simultaneously. Finally, you can often disconnect the propeller from the internal combustion engine to create a stand-alone generator function. Parallel hybrids, such as the Steyr Hybrid Drive System, make the most sense for recreational boats. Here’s why.
|The electric motor and the generator are integral, saving space compared with hybrid systems requiring a separate generator.|