Small propellor defects can result in increased radiated noise
(Posted on 24/02/23)
The slightest deviation in the machining, polishing, and finishing of ships’ propeller blades could result in underwater radiated noise and cavitation, even if defects are within the maximum tolerance allowed by classification societies and the ISO 484-1 standard.
A Canada Transport-funded study on the impact of manufacturing tolerances on propeller performance – carried out by Memorial University of Newfoundland, DRDC Atlantic Research Centre, and propeller manufacturer Dominis Engineering – found the slightest change in propeller geometry resulted in “significant” cavitation, and much earlier than previously thought.
The behaviour of a section of propeller blade with leading edge defects of 94µm, 250µm and 500µm were studied using Computational Fluid Dynamics (CFD) at the DRDC-Atlantic Research Centre, and Memorial University of Newfoundland, in a three-year project that concluded last year.
Project lead, Dominis Engineering President Bodo Gospodnetic, said: “Experimental results show that current widely accepted propeller manufacturing tolerances as stated in the ISO standard need to be thoroughly evaluated and investigated further.”
The current tolerance for a defect to the leading edge of a propeller blade is 500µm (0.5mm).
Ship propellers are manufactured according to ISO 484-1, with the majority of propellers made from castings rough machined on CNC (Computer Numerically Controlled) mills and then finished using robotic and manual grinding. However, robotic and manual grinding of propeller surfaces introduces inaccuracies and deviations from the approved design, which can lead to cavitation, erosion, noise, vibration and loss of propeller efficiency.
“The leading-edge is a very challenging area to manufacture accurately yet it has a strong influence on sheet, streak and vortex cavitation,” said Gospodnetic.
Researchers found that a ship with “defective” propeller must travel at a given percentage slower than a vessel with a “correct” propeller to operate below the cavitation inception speed and remain quiet. For example, a ship with a propeller defect of 0.5mm would have to sail at 45% of the speed of a defect-free propeller to avoid cavitation noise. The smaller the defect, the less speed reduction is required to remain quiet.
“The 0.5mm defect tested is one of the tightest ISO 484-1 propeller manufacturing tolerances yet it has been demonstrated that it affects cavitation inception significantly and detrimentally. The rules need tightening up,” said Gospodnetic.
ISO 484-1:2015 has been a standard for propellers since 1982 and although the standard was reviewed in 2015 and 2022, the allowable tolerance and geometry remains unchanged.
“We know that 80% of underwater radiated noise comes from the propeller, but if ships are legislated to be quiet in sensitive habitats such as the Juan de Fuca Strait then they will have to limit their speed to below the cavitation inception speed,” said Gospodnetic.
While initial CFD studies show how very small defects can influence cavitation inception research partners are looking for funding to continue their investigation in second phase model tests in a cavitation tunnel.
Latest News
Damen shipbreaking pilot project to be made available for larger vessels
(Posted on 23/04/24)Damen Shipyards Group is launching a pilot project in which a small tug will be dismantled at Damen... Read more
John Sutch Cranes seeks collaboration to address travel restrictions challenges
(Posted on 18/04/24)Mobile crane hire and contract lifting specialist based in the North West of England, John Sutch Cranes... Read more
ClassNK awards AiP for Mitsui methanol fuel supply system
(Posted on 15/04/24)ClassNK has awarded an approval in principle (AiP) for a methanol fuel supply system developed by Mitsui... Read more
Bühler launches fully automatic bagging station with Premier Tech
(Posted on 15/04/24)Swiss technology group Bühler, in partnership with leading Canadian packaging equipment manufacturer... Read more
Groke unveils new situational awareness tool for ship managers
(Posted on 15/04/24)Groke Technologies, the Finnish technology company behind the Groke Pro Situational Awareness System... Read more
Pacific Basin leads dry bulk’s adoption of graphene-based coating
(Posted on 29/03/24)In a proactive move towards energy efficiency and environmental sustainability, Pacific Basin, one of... Read more
ClassNK grants endorsement to two MOL initiatives
(Posted on 29/03/24)ClassNK has granted its Innovation Endorsements for Products & Solutions*1 to two initiatives by... Read more
Marcor Stevedoring receives new LHM 800
(Posted on 25/03/24)Contributing to a greener bulk industry. And no Diesel engine is needed. The LHM 800 will do its work... Read more
Need for new safety rules for methanol fuelled vessels revealed
(Posted on 25/03/24)A new fire safety study by global Survival Technology solutions provider Survitec has revealed that... Read more
Cargill shares outcome of first wind-powered ocean vessel’s maiden voyage
(Posted on 18/03/24)Cargill has revealed exciting results of the six-month test period of the Pyxis Ocean, underscoring... Read more
