Shaft generator

As a complement to auxiliary engines, the auxiliary power can be generated by a shaft generator on the main engine.

Applicability and assumptions

3D illustration shaft generator system, Source: Wärtsilä SAM Electronics

Shaft generator is applicable for vessels with diesel mechanic propulsion, for all ages.

Smaller 4-stroke auxiliary engines compared to larger 2-stroke main engines are generally less efficient, having a higher fuel consumption resulting in more expensive operations and higher emissions. There are many different types and configurations of auxiliary- and main engines on vessels, but the vast majority sail with large 2-stroke engines in combination with smaller auxiliaries. Installing a shaft generator on this more efficient engine can be done directly to the main propulsion shaft, or with a gear box to the main shaft. As a redundancy or booster for the main engine there are also shaft generators that can be used as an electric motor driven by auxiliary engine power.

The latest shaft generator configurations can be used independently of shaft speed and maintain a stable voltage and frequency output; this makes it possible to optimize each route with parallel auxiliary operation. Use of shaft generators can reduce the maintenance costs and lubrication costs for the auxiliary engines. The number of auxiliary engines or the size of the auxiliary engines can also be reduced. Using shaft generators rather than auxiliary engine for electric power generation typically also reduces noise and vibration levels.

Installing a shaft generator on the typical main engine is by itself more efficient than producing the same power via a smaller and less efficient auxiliary, but for many cases the shaft generator would in addition increase the total load of the main engine closer to the optimum load point with minimum specific fuel oil consumption.

Shaft generator is an option for many types of vessels, especially those in need of a larger amount of power for heating or cooling, and sailing long transits.

Additional measures advised include new torsional vibration calculations.

Cost of implementation

A typical shaft generator will cost around $400 (USD) per kW. Depending on the required power output and vessel type it is estimated that the cost of implementation will be in the range of $240,000 to $600,000 (USD).

Reduction potential

The reduction potential is 2% to 5% of total ship fuel consumption.

Other References

1. MAN Diesel & Turbo / Shaft Generators for Low Speed Main Engines
2. Wärtsilä Technical Journal / Shaft Generators: propelling vessels toward leaner, greener power generation