A recent full-scale bollard pull test on the Esbjerg-based fishing vessel Jette Kristine showed an increase in bollard pull performance of an impressive 23.5%.
The vessel had just undergone a great propulsion upgrade at MAN Diesel Frederikshavn. The bollard pull test before the upgrade measured 19.1 metric tonnes, and after measured 23.6 metric tonnes. This corresponds to an increase of 23.5%.
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 free running propeller upgrades have been reported – simply by exchanging the existing propeller blades to today's optimised and advanced designs.
MAN Diesel says that this is a relatively small investment with short payback time and radical impact on the ships' future operational economy, fuel consumption and exhaust gas emissions. The green impact and environmental benefit of lower consumption are also not to be neglected.
In this case with Jette Kristine and in similar cases with other fishing trawlers, bollard pull is the key performance parameter. MAN Diesel's upgrade solutions can include bollard pull optimised propeller blades alone, or bollard pull optimised blades in connection with a propeller nozzle upgrade.
Optimised propeller blade profiles applied together with the newly designed high-efficient AHT (Alpha High Thrust) nozzle is the ultimate solution, says MAN Diesel.
Advanced CFD tools (Computated Fluid Dynamics) were used to develop MAN Diesel's new AHT propeller nozzle series. According to the company, the nozzle shows superior performance compared to the standard "19A" propeller nozzles, which are common standard in the marine industry today.
The increased bollard pull achieved when using the AHT nozzle is not only a result of the optimised nozzle profile, which is double-curved on both the inner and outer diameter. Other contributing factors are the nozzle length/diameter ratio, nozzle support, aft ship lines, and tilting and azimuthing of the nozzle, among others.
The addressing of all these topics has been refined by MAN Diesel into a new systematic method, whereby the bollard pull can be increased by more than 12% compared to solutions with 19A nozzles. The achievements have been demonstrated both in various model tests and in full scale.
After two fishing trips, evaluating how the propeller and nozzle upgrade performed in real life operational conditions, the owner of Jette Kristine, Niels Arne Hounisen, expressed his satisfaction: “MAN Diesel has fulfilled my request for more pulling power, and they have delivered more than promised. Plus 23.5% is remarkable, considering the fact that Jette Kristine was equipped with ordinary propeller equipment in good condition – nothing outdated!
“When steaming, it has given me approximately 0.5 knot 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. Regarding the onboard noise levels below deck and in the accommodation, my crew members have stated that they experience much better conditions now – and this is not something they say just to please me”, concludes Mr Hounisen.
The physical replacement and upgrade operation was performed over 14 days at MAN Diesel's slipway in Frederikshavn.
