Clean Sailing: Is Diesel Electric Propulsion the Right Choice?

Is Diesel Electric Propulsion the Right Choice?

For the global marine industry, it's crunch time.

Stringent requirements governing sulfur oxide (SOx) and nitrogen oxide (NOx) emissions in the newly defined Emissions Control Areas (EMAs) off the coasts of North America, Europe, Australia and Japan go into effect in January 2015 and 2016.

With these International Maritime Organization (IMO) regulations less than a year away, there's a heightened sense of urgency among shipbuilders seeking better ways to achieve fuel efficiency.

One option that is gaining traction is diesel electric propulsion. Advancements in control system reliability and improvements in variable frequency drive technology have made this a viable, cost-effective alternative to conventional mechanical propulsion systems.

But whether or not it's the right choice for a specific vessel is really a matter of physics – and the ship's operating profile.

Designed for power and speed, mechanical propulsion is characterized by separate diesel systems that run the propellers/thrusters and supply the ship's electric service. A typical setup may include five prime movers – two large engines dedicated to the propulsion system and three smaller units for the electric service.

For vessels that typically operate at full loads and high speeds, a conventional mechanical system – with prime movers continually dedicated to propulsion – is the only viable option.

But for supply ships and workboats that operate often at low loads and spend much of their time idling, mechanical systems are not ideal. Idling is not only inefficient from a fuel standpoint, but light-load operation stresses diesel engines and can cause maintenance issues.

When a ship has a low load or variable operating profile, a diesel electric propulsion system can be an optimal choice.

A diesel electric system utilizes the same engines for both propulsion and the ship's electric service. Using variable frequency drive technology, additional engines are brought on line and power is adjusted to meet propulsion/thruster load requirements.

Less power is used during idling. More during transport and offloading activities.

Not only does a diesel electric system improve fuel efficiency and reduce related emissions. It also decreases the number of prime movers required on many ships – and alleviates idling-related engine maintenance issues.

As oil, gas and mining operations venture into ever-deeper waters, the efficiency of the supply ships, Floating Production, Storage and Offloading (FPSO) vessels and workboats that support these operations will become increasingly important.

Diesel electric propulsion could be the cost-effective – and environmentally conscious – choice.

Learn how Rockwell Automation helps shipbuilders and operators meet today's challenges.

Michael Tangora
Posted November 25, 2014 By Michael Tangora, Market Development Manager, Rockwell Automation
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