Danaos opts for MAN Diesel & Turbo upgrades

The 9 m diameter five-bladed propellers for the Danaos ships will be the largest fixed pitch Kappel propellers delivered to date

MAY 26, 2016 — MAN Diesel & Turbo is to upgrade the propulsion system of two 8,500 TEU Danaos Shipping containerships, CSCL Europe and CSCL America.

The upgrades will include Engine-Power Limitation (EPL) and the fitting of fixed pitch Kappel propellers, propeller boss caps with fins.

“Our R&D Department has conducted very thorough investigations before concluding what the right upgrade solutions for these vessels are and we are confident that the vessels will be highly competitive in the market once upgraded,” says Mr. Dimitrios Vastarouchas, Technical Director & Deputy Chief Operating Officer of  Piraeus- headquartered Danaos.

Both ships are powered by MAN B&W 12K98MC-C main engines rated at 68,520 kW at 104 RPM. The main engines will now be limited to 44,000 kW at 89.7 RPM, but top speeds of more than 23 knots will still be available.

Along with the upgrade of their propulsion systems, the vessels will also enter dock to rebuild their bulbous bows.

Combined with previously 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’ consumption when delivered from the newbuilding shipyard in 2004.

The upgrade packages will make the Danaos container vessels among the most competitive mid-size container vessels in the market.

Vessel & Engine Specific Study

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.

MAN PrimeServ’s Retrofit & Upgrade Departments in Copenhagen and Frederikshavn, Denmark, began a Vessel & Engine Specific Study of the Danaos ships in 2015 that researched 12 different potential solutions for optimizing propulsion using various MAN Diesel & Turbo technologies and products individually and in combinations. At the same time, Danaos ran some 35 concept studies on the optimization of its vessels at its in-house R&D department before concluding on how to proceed.

Before the final choice of solution was made, exhaustive CFD-simulations and model tank tests were carried out at the Krylov State Research Center (KSRC) in St. Petersburg, Russia.

Besides verifying the performance of the new Kappel propellers and the new bulbous bow design, a primary reason for carrying out model tests was also to ensure that the new propellers for the CSCL Europe and CSCL America would have the correct light running margin (LRM). A temptation with optimization projects can be to deliberately reduce the LRM below the optimal in order to give the propellers a slightly higher efficiency. Ultimately, a propeller layout with a reduced LRM will come at the expense of the engine’s SFOC and the full potential of the propulsion upgrade will not be exploited in full scale. The philosophy at MAN Diesel & Turbo is to avoid looking at individual components alone and to look at the complete propulsion drive train in a holistic fashion, viewing components in terms of the mutual influence they have on each other.

Kappel propeller

The unique 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 further increases the efficiency of the Kappel propeller.

The concept was originally developed by the Danish inventor Jens Julius Kappel. After a decade of close cooperation, it was acquired by MAN Alpha when Mr. Kappel retired. Combined with the knowledge from MAN Alpha’s more than 100 years of propeller design and refined to today’s concept, the Kappel propeller design is among the most efficient in the world.

With a diameter of app. 9 meters the 5-bladed propellers for the Danaos ships will be the largest fixed pitch Kappel propellers delivered to date. 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 – 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 deliver an efficiency gain of 6% which can be directly transferred to reductions in fuel oil consumption and emission.

Kjartan Ross, Business Development Manager of MAN Diesel & Turbo said: “I started my carrier in the maritime industry in 2004 – same year as these vessels were delivered. Taking the fairly high top speed of more than 23 knots still available after the upgrade into consideration I am continuously impressed by how much technology has leaped forward in the maritime industry just during these last 12 years.”

The propellers will be delivered directly to the shipyard where installations of the new propellers and bulbous bows have already been tentatively scheduled for July and September 2016.

Engine Power Limitation

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 other efficiency improving initiatives such as propeller upgrade and engine tuning.

The Kappel propellers in this upgrade have been designed for a reduced engine power of 44,000 kW at 89.7 RPM, requiring a limitation of  power output to enable them to be better optimized for the new optimization speed of 18 knots, adding additional fuel oil saving to the upgrade package.

Combining EPL with a propeller upgrade, not only enables a better optimization of the propeller efficiency but also allows weight reductions of the propellers, reducing both the propeller cost and the overall cost of the upgrade package.

Propulsion Drive Train

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.

Nose job, too

Apart from the new Kappel propeller and propeller boss cap with fins – both designed for the reduced engine output – the container vessels will also, while in dock, have a “nose job,” altering their bulbous bows to a design that better matches their future operation profile. 

Vessel type     Fully cellular container vessel
Cargo capacity     8,500 TEU
Length overall     333.99 m
Breadth     42.80 m
Design draft     13.00
Main Engine     12K98MC-C6
Engine power and propeller speed     68,520 kW @ 104.0 RPM
Engine power after upgrade     44,000 kW @ 89.7 RPM
Max. ship speed after upgrade     +23 knots
Service speed after upgrade     18.0 knots
Kappel propeller diameter     8,900 mm
Number of propeller blades     5