Marine Engines Save Fuel With Integrated Propeller-Rudder Design
“Look at the ships also: though they are so large and are driven by strong winds, they are guided by a very small rudder …”. Thus St. James remarked in the early years of the first millennium, and nothing much has changed since then except the power source and the addition of a propellor.
The interactive dynamic between those two appendages – rudder and propeller – in modern ships, and the part that plays in efficient and economic ship operation has been recognised by two long established Dutch/German rudder and propellor specialists who have recently joined hands to optimise design and manufacture. Van der Velden Marine Systems (VDV) and Mecklenburger Metallguss (MMG) name their solution the ‘Energy Saving Package’ which is intended to do ‘what it says on the box’.
In general terms, rudder and propeller designer both have one thing in common amongst a myriad of complexities: their design parameters are set by the mission profile of the vessel that occupies their attention. In the case in hand, the Energy Saving Package is aimed to benefit ocean going ships with fixed-pitch propellers.
Energy Saving Package: CAD impression courtesy of Van der Velden Marine
Energy Saving Package
The goal is to achieve a low effort maintenance design that provides fuel-efficiency, effective manoeuvrability with minimal cavitation and vibration.
Front Engineering Design (FEED), having collectively identified the ship’s operational profile with owner’s technical staff, naval architect, and shipbuilder, then employs the latest CAD technology to come up with the best possible solution for a specific vessel. That solution includes the combination of an optimised propeller design with an asymmetric, leading-edge rudder, propulsion bulb and adapted hub caps.
A feature of the package is VDV’s asymmetric rudder. Due to the rotation of the slipstream, conventional rudders constantly operate in an apparent angle of attack, increasing drag, which also results in cavitation on the rudder blade. The asymmetric rudder modifies the spatial arrangements of its components above and below the centreline of the propeller to expand the cavitation-free rudder angle and lessen that drag. Reduced rudder cavitation benefits the life-span of the rudder and the shaft bearing, with lower vibration and noise levels.
Equally, a well designed propeller from vastly experienced MMG, who have 60 years experience in the business, prevents tip cavitation, while the whole Energy Saving Package includes the Costa bulb, junction cap or boss cap fins to prevent hub vortex losses and further cavitation.
The manufacturers' strategic partnership informs that their the Energy Saving Package can also be provided for retrofits, doubtless having in mind propulsion modifications when shipowners envisage a change to long-term slow-steaming.
Checking Profile of Large Propellor: Photo courtesy of Mecklenburger Metallguss GmbH