Diesel & Gas Turbine Worldwide reported in the November 2009 issue about the fuel savings and reduced emissions offered by propeller optimization as discussed with Karsten Borneman, senior sales manager for medium-speed propellers and aft ship systems at MAN Diesel.
At the time, Borneman had indicated that the optimization of propellers and nozzles offers an advantage in retrofit projects, which are increasingly popular. As an example, he cited the Sassnitz RoPax vessel by Scandlines, on which MAN Diesel had fitted newly designed propeller blades.
Today, the efficiency improvement on the Sassnitz has been confirmed — with test documents indicating an increased efficiency of no less than 12%. In the meantime, the MAN Prime-Serv team in Frederikshavn, Denmark, carried out another propeller retrofit project on the fishing vessel Jette Kristine. The ship is based in Esbjerg, Denmark, and was built in 1986 by the Johs.
Kristensen Skibsbyggeri ApS shipyard. It has a 638 ton gross tonnage and is propelled by one MAN Diesel 8L23/30-D engine delivering 1080 kW at 825 r/min. The upgrade consisted of the replacement of the old blades with bollard pull-optimized blades and an upgrade of the propeller nozzle with the new MAN Diesel Alpha High Thrust (AHT) propeller nozzle. The technicians at MAN Diesel carried out a detailed comparison test, taking measures in a pretest
with the vessel in its original propeller and nozzle installation.
The physical replacement and upgrade operations took 14 days, thus two weeks later the test was repeated with the new propeller and nozzle arrangement, replicating exactly the same conditions the Jette Kristine with its engine at the same power output, same position in the
Frederikshavn’s harbor basin, same water depth below keel, same draft and trim of the vessel.
The pre-test produced a bollard pull of 19.1 metric tons, and the second run produced a bollard pull of 23.6 metric tons, for an increase in bollard pull force of 23.5%. The owner of the ship, Niels Arne Hounisen, reported on the reaction he and his crew had after the upgrade, “Plus 23.5% in bollard pull is remarkable, considering the fact that Jette Kristine was equipped with ordinary propeller equipment in good conditions. Nothing was outdated!” He added, “When steaming, it has given me approximately 1 kph extra top speed, and in trawling conditions, I
have experienced a clear difference with better control of my fishing gear. Most important is a reduction in fuel consumption of more than 15% recorded at trawling speed.”
There was also a remarkable improvement in onboard noise, as Hounisen said, “Regarding the onboard noise levels below deck and in the accommodation, my crew members have stated
that they experience much better conditions now.” MAN Diesel explained that propellers
designed more than 10 years ago normally offer great improvement potential in retrofit projects, where fuel consumption reductions of up to 12.5% for freerunning propeller upgrades have been reported. The company also said the investment is relatively small and has a short payback as well as a remarkable impact on fuel economy and emissions.
In the case with the Jette Kristine and in similar cases with other fishing trawlers, offshore vessels, tugs and dredgers, bollard pull is the key performance parameter. MAN Diesel offers upgrade solutions that span from bollard pull-optimized propeller blades alone, or in conjunction with a propeller nozzle upgrade.
According to the company, the propeller nozzle upgrade with the new AHT nozzle series has proven to have a significant impact on the performance improvement. MAN Diesel claimed
that bollard pull can be increased by 12% with the use of AHT nozzles, compared to solutions with 19A nozzles, which are currently the standard in the industry.