Propulsion Plant for “Clean Ship”

Wärtsilä has received an order for a complete ship power plant and propulsion system for a new Norwegian Coastal Express ship built by the Norwegian shipyard Kleven Verft AS. The requirements for the ship's power plant and propulsion system were demanding. Apart from the usual matters such as fuel economy and reliability, they include environmental performance, flexibility in matching ship speed and economy, manoeuvrability, and low noise and vibration in the accommodation.

The "Finnmarken" will break new ground in her environmental characteristics. She will be the first vessel of this type to receive the Clean Design class notation of Det Norske Veritas (DNV). The rules for this notation affect many aspects in the design of the ship and its equipment which together reduce and control the environmental impact from exhaust emissions, discharges to the sea and deliveries to shore.

Among its various requirements, the Clean Design notation of DNV calls for NOx emissions 40 per cent less than the limit set by the IMO regulation (MARPOL 73/78 Convention, Annex VI). This is met by equipping all four Wärtsilä 32-type engines with direct water injection. Thus there is no need for installing catalyst units to comply with the emissions requirements. To ensure the least possible SOx emissions, the engines will burn marine special distillate, a type of marine diesel oil (MDO).

The ship power system is designed for optimum performance with regards to noise and efficiency for a wide ship speed range. The machinery is arranged in a "father-and-son" configuration, with the twin CP propellers. A variable-frequency generator/motor is connected to a power take-off/power take-in gear in each gearbox. The frequency control system allows propeller speeds from 110 to 155 rev/min.
Particular attention has been given to the design of the propulsion system to achieve low noise and vibration levels. Thus, the Wärtsilä NSD propellers will be of the highly-skewed type and are designed for lower propeller-induced pressure impulses against the hull. The PropacRudders will further reduce propeller-excited vibration by reducing propeller cavitation and tip vortices. The PropacRudders will also make an important contribution to reducing fuel consumption.