Propeller Super Polishing
| Propellers should be maintained in tip top condition at all times and the main factors that deter the propellers from their optimum performance are fouling, marine growth, cavitation and physical damage. Any of these distortion from their original shape can cause imbalance and vibration which in turn causes increased cavitation, loss of thrust, drive shaft damage, wear and tear on bearings and increased fuel use due to decreased efficiency. The simplest form of maintenance performed on a propeller is to clean it. |
 |
 |
Cleaning and polishing involves the removal of any marine growth leaving a clean and highly polished surface. Removing marine growth in a rough manner willrender the surface of the blades look shiny, but the blades are deeply scratched and these scratches will impart a roughness that is beyond the 1.6 micron (CLA) Ra* tolerance required for a class I propeller. Therefore, the correct method and tools used is very vital as the level of finishing is desirable as its long-term effects on fouling build-up and engine wear more than compensate for the initial costs for the propeller polishing. |
| At Dive-Marine Services Pte Ltd, we perform propeller polishing using the hydraulic powered polishers with 3M marine stains removal pads for ultra gloss and smooth surfaces. Using the Ship Propellers Roughness Gauge to check against the condition of the propeller upon completion of the polishing works. |
 |
Propeller Damage Repairs
| Propellers are easily damaged if they strike a buoy, floating logs, debris or ice. The damage is usually located at the tip of the blade, which can become bent or chipped off. Physical damage of this nature commonly causes vibrations. The solution to solving the vibration problem is to trim the blades equally to remove the damage and achieve a proper balance and at the same time reduce excessive cavitation. The technique used requires extreme accurate measurement of the diameters of the individual blades to reduce a minimum the amount of material removed and to ensure a perfect balance of the propeller. |
 |
When trimming damaged blades, the nature and location of the damage dictate the type of repairs requires. Modification had to be made according to the desired effects on the rpm and thereby restore the RPM/MCR ratio. There are mainly three types of modification. Diameter reduction - Easily and inexpensively performed underwater, this is the usual method for increasing rpm and balancing the ratio. The blade tips are cropped and faired.
| Pitch reduction - This involves twisting the blades and can only be accurately done in a workshop as the blades need to be heated to prevent cracking. The twisting usually distorts the hub and requires machining to ensure proper re-fitting to the shaft. This is one of the most effective modifications as there is no loss of blade material and it ideally suitable for propeller blades smaller than 3500mm in diameter. |
 |
Trailing edge modification - It is performed by bending the trailing edges or by cutting them off. Either of them can be performed underwater and can achieve an effect on the rpm. In the process of bending the trailing edges of the damaged blades, the trailing edges are slightly modified without the loss of materials or strength of the blade. With cutting, a small amount of trailing edge material is removed and the edge re-ground to smoothen the cut edges. Templates are used to ensure accuracy.