Modernization of Croatian Ferry Improves Course Keeping Stability and Speed

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Besides measures which maintain a vessel’s efficiency and performance, such as the necessary regular servicing thereof, changing its operational profile sometimes requires considerable modernization or retrofitting of the propulsion system. However, in some cases newly required thruster performance features can be achieved with the help of modifications which preserve most of the existing units.

Retrofitting a ferry for more challenging operating conditions
Earlier this year, the Croatian ferry Krk operated by the national Jadrolinija shipping company was retrofitted to cater for a new route with stronger winds and currents. For this purpose, the open propellers of the Krk’s thrusters were replaced with new optimized propellers and fitted with SCHOTTEL VarioDuct SDV45 nozzles. The thruster upgrade comprised a mixture of overhauls and modernizations in accordance with the time schedule of the vessel’s planned maintenance cycle.

Cost-effective retrofit completed between seasons
The entire retrofit process took place during the annual lay days between seasons. The thrusters were dismounted and reinstalled in Croatia by SCHOTTEL partner Alfa Marine. The conversion work on the thrusters themselves was carried out at the SCHOTTEL service workshop in Spay, Germany. A cost saving of around 50 percent was achieved by overhauling the existing thrusters – including the transportation costs to Germany – as opposed to purchasing new ones.

Results exceed expectations
The results of the Krk’s modernization exceed all of Jadrolinija’s expectations. The ferry is responding more accurately to steering manoeuvres and the autopilot makes fewer corrections thanks to the much-increased course-keeping stability. Hydrodynamical analyses from SCHOTTEL predicted the now realized top speed of 13 knots and various other advantages gained from using the SDV45 nozzle. In addition to the vessel’s increased course-keeping stability, the new nozzles also ensure smoother operation of the thrusters. Due to the much-improved thrust and performance values of the Krk, Jadrolinija is now able to tighten the ferry’s schedule.