Dredge shows big fuel savings after propeller and nozzle switch

DECEMBER 5, 2012 — A sand and gravel dredge owned by Scandinavian construction giant NCC is reporting a 14 percent improvement in fuel efficiency following an exchange and modernization of its propeller blades and propeller nozzle. The fuel savings mean the payback time for the upgrade will be just 18 months

MAN Diesel & Turbo’s PrimeServ division in Frederikshavn, Denmark, carried out the upgrade to the M/V Baltic, a 900 cu.m sand and gravel dredge that is one of five in the NCC fleet that, together, annually recover about two million tonnes of raw materials from the seabed around Denmark. The materials are subsequently processed for use in the concrete and asphalt industries

In connection with a fleet energy-optimizing project, NCC contacted MAN PrimeServ at the beginning of 2012 with an enquiry regarding upgrade possibilities for an existing vessel’s propeller and nozzle. NCC was, as a starting point for the project, interested in the upgrade of the Baltic. The vessel, which was built in 1983, had – over many years of operation – suffered from propeller and aft-ship vibrations resulting in high noise levels in the accommodations. Eventually the nozzle broke loose from the hull.

In January 2012, the PrimeServ retrofit department in Frederikshavn started discussions with NCC Chief Superintendent, John Jeppesen, on the design of new propeller blades and a new, customized propeller nozzle. The priority was increased propulsion efficiency and fuel savings. The propeller-blade design chosen was a medium-skew blade profile for ducted operation with a MAN Alpha AHT nozzle – customized with a length/diameter ratio of 0.5. The new nozzle and blades were installed in April 2012 while the vessel was docked at Svendborg Shipyard, Denmark.

The ship has been in operation with the new propulsion equipment since April and the feedback from the Chief Engineer and the operational crew clearly indicates a much improved performance.

Chief Superintendent Jeppesen confirms: “The measured fuel consumption reduction is 14 percent and the noise level in the accommodations is reduced by 10 dB together with an effective reduction of vibrations. Also, the ship’s maneuverability in harbours has been improved.”

MAN Alpha propellers cover a power range from 4 to 40 MW with fixed pitch and controllable pitch propellers in four and five-bladed executions. The propellers are designed and optimized for a large number of vessels of different design and applications, from cargo vessels, ferries, cruise ships, offshore vessels, tugs and work boats to fishery and navy vessels.

Previous examples of high-end MAN Alpha propeller installations include some of the world’s largest dredges – Cristobal Colon and Leiv Eiriksson, both 46,000 cu.m and with the dredging capacity to a water depth of 155 m – operated by Jan de Null. Another notable reference is the world’s largest RoPax ferry – the 78,300 bhp M/F Tanit– recently started in service for CTN between Marseilles and Tunis. To date, the MAN Alpha brand has produced more than 7,000 propellers since the first Alpha CP Propeller design was supplied in 1902 and patented in 1903.