LOGISTIC ENGINEERING

Logistic Engineering



Logistic Engineering

Introduction

The ABB order for the first ship was booked in 2011 and for the second vessel in the first quarter of 2012. The ships are the first in Royal Caribbean's new class of cruise ships, currently named 'Project Sunshine.' The 158,000-gt ships will have a capacity of more than 4,100 passengers; in addition to redesigned spaces to optimise capacity and fuel use while maintaining passenger comfort, RCL and Meyer Werft will incorporate various energy efficiency and environmental technologies on the ship. ABB will supply complete electrical systems for the new ships; the delivery for each ship includes power generation and distribution systems, thruster motors, and two 20.5MW propulsion systems including transformers, drives and two Azipod XO propulsion units. The Azipod propulsion is claimed to use less fuel than traditional systems, and to provide greater manoeuvrability in all operating conditions.

Azipod concept

In the traditional azimuth propulsion system the motor is inside the ship's hull and the propeller is driven through shafts and gearboxes. In the Azipod system the electric motor is inside the pod, and the propeller is connected directly to the motor shaft. By avoiding the use of a traditional propeller shaft, the propeller can be further below the stern of the ship in a clear flow of water providing greater hydrodynamic and mechanical efficiency.

Electric power for the Azipod motor is conducted through slip rings that allow the Azipod to rotate through 360 degrees. Because fixed pitch propellers are used in Azipods, power for an Azipod system is always fed through a variable-frequency drive or cycloconverter that allows speed and direction control of the propulsion motors.

Discussion

The propulsion efficiency of the Azipod propulsion, originally installed on the Carnival Cruise Lines Fantasy class cruise ships Elation and Paradise in the mid-1990s, improved by around 9% when compared through full scale measurements with earlier identical sister ships with traditional diesel-electric shaft line driven propellers. By changing the shape of the Azipod and hydro dynamically optimizing the positioning and angular placement of the pods when integrated with the hull, ABB Marine has since improved the system by another 9%, representing a total optimization of some 18% in propulsion efficiency over that of shaft lines in the mid-1990s.

ABB compared shaft lines with Azipod propulsion in model tests last year at MARIN (Maritime Research Institute Netherlands) and found that Azipod propulsion compared to latest fixed shaft line propulsion designs still had a 6% - 8% lead in propulsion efficiency. Factory workshop tests at the VTT Technical Research Centre of Finland, which were also conducted in 2010, focused on different types of thrust bearings, the sliding bearing intended primarily for the new XO pod and a roller bearing version of current type for comparison and retro?t purposes.

The two bearings were rigged against each other with a rotating shaft line in between and tested for full load, 1.6 times full load and almost 2.5 times the load expected in real operation. Rapid load changes were also applied to simulate changing operating conditions...