Propulsion System Upgrade From MAN Diesel & Turbo
By Jack Burke27 May 2016
MAN Diesel & Turbo said the Kappel propellers it will supply Danaos Shipping Co. Ltd. will be the largest fixed pitch Kappel propellers delivered to date.
Along with the Kappel propellers, MAN Diesel & Turbo will also supply propeller boss caps with fins and engine-power limitation for Danaos Shipping’s 8500 TEU container vessels CSCL Europe and CSCL America.
Both container vessels are powered by MAN B&W 12K98MC-C main engines rated 68.52 MW at 104 rpm. In connection with the propulsion upgrade the main engines will be limited to 44 MW at 89.7 rpm however; top speeds of more than 23 knots will still be available, the company said.
Along with the upgrade of their propulsion systems, MAN Diesel & Turbo said the vessels will also enter dock to rebuild their bulbous bows. Combined with the already installed Turbo Charger Cut Out these comprehensive upgrades are expected to reduce fuel consumption at the new optimization speed of 18 knots by a total of more than 15% compared to the vessels as they were delivered from the new building shipyard in 2004.
Most mid-size container vessels were often originally designed and build to operate at much higher speeds than it is the case today and accordingly, their propulsion characteristics can be optimized, the company said.
Man Diesel & Turbo said the design of the Kappel propeller, with its forwardly swept propeller blade tips, reduces the tip vortex and consequentially the drag of the blades trough the water. An additional effect of the Kappel design is lower pressure pulses induced to the hull allowing a smaller clearance between the hull and propeller blade tips. As a result of this the propeller diameter can be enlarged which increases the efficiency of the Kappel propeller even further. The Kappel propeller design concept was originally developed by the Danish inventor Jens Julius Kappel and after a decade of close cooperation overtaken by MAN Alpha at Mr. Kappel’s retirement. Combined with the knowledge from MAN Alphas more than 100 years of propeller design and refined to today’s concept the Kappel propeller design is among the most efficient propeller designs in the world.
With a diameter of app. 9 m, the 5-bladed propellers will be the largest fixed pitch Kappel propellers delivered to date, the company said. They will be manufactured by MAN Diesel & Turbo licensee, Zhenjiang Tongzhou Propeller Co. Ltd in China along with the new propeller boss caps with fins, which is an efficiency improving device for reducing the hub vortex and drag behind the propeller hub. The new Kappel propellers and propeller boss caps with fins contribute with an efficiency gain of 6% which can be directly transferred to reductions in fuel oil consumption and emission.
Man Diesel & Turbo said engine power limitation (EPL) is a simple way of reducing the power output of the engine by changing the governor settings. Indirectly, EPL has a fuel oil saving effect as a reduced power output can have a positive effect on others efficiency improving initiatives such as propeller upgrade and engine tuning.
As an example, the Kappel propellers in this upgrade have been designed for a reduced engine power of 44,000 kW at 89.7 rpm whereas a limitation of the power output is needed. By doing so, the Kappel propeller can be optimized better for the new optimization speed of 18 knots adding additional fuel oil saving to the upgrade package. Combining EPL with a propeller upgrade does however not only enable a better optimization of the propeller efficiency; it also allows weight reductions of the propellers and hence reduces both the propeller cost and the overall cost of the upgrade package.
Vessel and engine upgrades often have an impact on torsional vibration and NOX. When a low-load tuning method such as a Turbo Charger Cut Out or a propeller upgrade is installed, the torsional vibrations’ impact and the NOX level have to be taken into account to ensure that the vibrations’ impact is not harming the propulsion drive train and that the NOX level is in compliance with IMO regulations. All the required calculations and class approvals are included in the MAN Diesel & Turbo upgrade package.