Propeller polishing: Understanding roughness and the Rupert scale
Propeller roughness - causes and concerns
It is observed that after approximately 6 months out of dry-dock, a vessel’s fuel efficiency begins to decrease. There are several reasons attributed to this downslide, out of which propeller roughness is a prime factor.
As the propeller spins and produces thrust to drive the vessel forward, it is continually exposed to all types of underwater attacks. The assault is multifaceted and on-going; biofouling (marine growth), rusting/corrosion, electrolytic action and cavitation erosion, among other types of damage. This constant exposure contributes to the propeller’s surface roughness, which increases every passing day. Unprofessional, shoddy maintenance can also add to the deterioration.
An unmaintained, chafed propeller, clogged with incrustations or calcareous deposits, leads to several undesirable outcomes such as damaging the transmission axis, loss of thrust and diminished fuel efficiency. The end result is increased fuel cost, which decreases business competitiveness and ultimately impacts profitability.
Propeller clogged with incrustations and calcareous deposits
Polished propellers – more power, better performance
Propeller roughness has a direct bearing on vessel performance and fuel economy; indeed, a poorly maintained propeller can decrease speed and power by up to 5 %. Hence a shiny, clean and smoothly maintained propeller is crucial to achieving optimal fuel efficiency. Several studies conducted both on commercial vessels and military ships, have conclusively demonstrated that substantial savings can be achieved through professional propeller cleaning at frequent intervals.
Propeller after polishing
Roughness and the Rupert scale
The Rupert scale is the globally accepted standard for measuring and recording propeller blade roughness. The Rupert Scale ‘A’ grade, which roughly equates to a surface roughness of .65 microns, is apparently the highest quality finish that can be achieved by polishing and reconditioning the propeller blades.
KBAM – the propeller polishing experts
At KBA Marine, we have mastered the task of propeller polishing to a fine, proven technique. Our propeller polishing service is in consonance with best practices and the highest industry standards. KBAM divers are experienced professionals who are capable of achieving a surface finish of removing marine fouling including tenacious calcareous deposits, and polishing to approximately 2 Microns CLA. Our methodical polishing process leads to smooth, clean and dent-free propeller blades; as a ship owner/operator you not only end up with improved fuel efficacy but also reduce possible future maintenance costs by not having to dry-dock for serious repairs in the days to come.