Wärtsilä has signed a major contract with the A.P. Moller Maersk Group (APMM) for the installation of slow steaming upgrade kits to 34 more of the company's large container vessels, following the successful installation and testing on one of the fleet's sister vessels in late 2009.

The 34 ships to be fitted are powered by Wartsila RT-flex96C and RTA96C main engines with 10, 11 and 12 cylinders. Applied to the ow-speed main engines, the kits will produce major savings in the ships' fuel consumption while also cutting CO2 emissions. The upgrade kits will be fitted as fully engineered solutions, with the company supplying all necessary material, labor, ship-specific engineering and full project management.

It is anticipated that as a result, these vessels will achieve fuel savings of between 3 percent and 7 percent with the engine running at low load, according to Wartsila. These savings are in addition to those attained through reducing speed to slow steaming operation.

The fuel savings are achieved by cutting out one of the engine's turbochargers at engine loads of less than about 60 percent (this figure is valid for engines with three turbochargers), thereby providing greater scavenge air pressure for better combustion and optimal engine component temperatures. This cut out is controlled and fully automated.

In addition to the fuel savings, the solution provides full flexibility - with unrestricted operation from 10 percent to 100 percent load. The engine is not permanently derated, but retains full flexibility so that it can be operated at any time up to its full installed power for full sea speed. It also decreases the risk of engine fouling and excessive component temperatures.

The upgrade kit involves fitting shut-off valves in the engine's exhaust duct before the turbocharger turbine, and in the scavenge air duct after the compressor. The valves are remotely operated by a control system included in the upgrade kit.

The upgrade is available for most Wartsila RTA and RT-flex engines with multiple turbochargers. The achievable break specific fuel consumption (BSFC) figures are strongly dependent on the final NOX emission balances over the whole load range. For ships that must comply with the IMO NOX emissions regulations, the restrictions imposed by the emissions limits will be evaluated in each case and a customized turnkey package is then offered.

Since its introduction in 2009, Wartsila said it has received orders for slow steaming upgrade kits for 47 vessels.