Shaft generator retrofits
Sven Schemmink, Renk Group, Rheine; Robert Banek, Renk Group, Hamburg
The IMO has set challenging decarbonisation targets for the maritime industry. In addition to the long-term goal of a net CO2-neutral maritime industry by 2050, the timeline for the maritime energy transition is a challenge in itself. The short and medium-term decarbonisation targets cannot realistically be achieved by newbuildings alone, but also depend heavily on retrofitting solutions for the existing global fleet.
While long-term solutions could be based on the three pillars of (i) carbon-neutral energy sources,
(ii) on-board carbon capture and (iii) improved energy efficiency, retrofit solutions are mainly based on improved energy efficiency, due to the availability of carbon-neutral energy sources.
For the on-bord power supply of oceangoing 2-stroke driven vessels, shaft generators have developed into a standard for improved energy efficiency for newbuild vessels. While some years ago only 3% of all 2-stroke newbuildings were equipped with a shaft generator, these figures have increased to two-digit percentages in the last years (source: Clarksons World Fleet Register). Though this development shows the effectiveness and attractiveness of shaft generators as part of vessel decarbonization, only very few shaft generator retrofit projects were conducted up to now. It is obvious that this is due in particular to the great installation effort required for such a retrofit. Until now, retrofitting required the installation of large systems in the propeller shaft. These machines had to be laboriously brought into the engine room via large cut-aways in the hull. A new, separate foundation already had to be prepared there. The foundations for the system were laid in the dry dock. Only then could the propeller shaft be returned to its original position and installed. A realignment of the drive train was a necessary consequence of this complex procedure. All of this led to long docking times. In addition to the fact that many existing ships do not have the necessary space in the aft ship, retrofitting was costly and rarely a business case.
The market for retrofit shaft generator installations opens again now, as different suppliers developed front-end mounted shaft generator systems. These systems are characterised by the fact that they do not require a separate foundation but are flanged directly to the free front-end of the main engine. There is no need for time-consuming installation with the necessary realignment of the propeller shaft. Instead, smaller parts have to be installed in the engine room, leaving the propeller shaft untouched. Drydock periods are significantly reduced and larger parts of installation can be conducted at the pier. Two different types of front-end mounted shaft generators are currently in the market. While the first relies on a low-speed generator that is integrated directly into the engine's flywheel, the second convinces through the consistent use of a reduction stage and the associated small and lightweight construction.
As part of the presentation we show the applicability of a front-end mounted shaft generator for retrofits and demonstrate first successful retrofit projects, which were conducted on VLOC bulk carriers with this rather new technology. Furthermore the saving potential of shaft generator retrofits will be evaluated and the electrical engineering challenges will be addressed.
