One of the challenges is to estimate how much effect the modified building method has on other than direct purchase and installation cost.
Some of these indirect costs are:
・ Cost of the total purchasing process of shaft lines and related equipment, including factory acceptance tests and negotiations.
・ Cost of design of the propulsion machinery
・ Cost of logistics, storage and handling of the equipment at the shipyard
After analyzing the whole chain of the shipyard processes related to delivering the vessel to the owner the real cost comparisons can be made. Naturally a reliable calculation can be made by the shipyard itself.
4.7.1 Challenges to the shipyard and shipowner
The challenges the shipyard and the ship operator are me as with facing when using the CRP podded concept are same as with electric propulsion systems in general. New tasks for the ship owner are training of the staff and crew to the new systems as well as familiarizing them with the maintenance and day to day operations. The shipyard must adapt the current design and building processes to the new concept to be able to utilize the advantages in full.
4.8 Case study of a fast RoPax vessel
A case study was made to evaluate the economical and technical effect of applying the podded CRP concept. As the base case a vessel with the following characteristics was selected:
Lpp
176,00 m
B
25,00 m
T
6,40 m
Service Speed
27.5 kn
Gross tonnage
28 000 t
Deadweight
4 600 t
Trailer lanes, total
1 600 m
Private cars
170 pcs
The base case has a machinery consisting of two shaft lines, with two medium speed diesel engines each, driving CP-propellers through a reduction gear. A shaft generator is connected to each gearbox.
The auxiliary machinery consists of three medium speed diesel generator sets.
The vessel is also equipped with two forward bow thrusters and one stern thruster. The following figure shows the machinery configuration and power levels.
4.8.1 Ropax vessel machinery arrangement with a twin shaftline
The base case is compared with a vessel having the same main dimensions and the following machinery:
Two medium speed diesel engines drive one CP-propeller through reduction gear. Auxiliary power is generated by three medium speed diesel generator sets. This power is also used to drive the single Azipod unit located behind the main propeller. Due to the pod, the stem thruster has been removed. The bow thrusters are the same as in the base case.
The machinery concept with power levels is shown in Fig.3
Fig. 3 Twin shaft RoPax machinery
4.8.2 RoPax vessel with the podded CRP concept
The comparison was made for a vessel operating in the Baltic on the route between Helsinki and Rostock, a route that includes both full speed operation in the open sea as well as maneuvering in narrow channels and in the harbors. The selected service speed gave the ship a roundtrip time of 48 hours.
The study focused on determining the required passenger ticket rate, when the freight rates were considered the same for each alternative.
Experience from earlier CRP tests and theoretical studies conclude that the single shaftline CRP Azipod arrangement requires 10-15% less power to achieve the same speed as the fully mechanical twin shaftline CP-propeller configuration. On this specific route, the annual fuel saving, taking into account the different power transmission efficiencies is 12%, giving an annual fuel cost saving of $1 million in favor of the CRP Azipod alternative.
