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Underwater Propeller Blade Straightening – Cold Static Loading

Case Study

Underwater Propeller Blade Straightening – Cold Static Loading

Abstract

Did you know your vessel’s propeller blades can be straightened underwater? SGS has the equipment, procedures, and expertise to straighten large deflections in propeller blades at your vessel’s next port call during cargo operations with no off-hire time. This is even true for propeller blades with bends greater than 180 degrees.

The SGS Solution

SGS has developed state-of-the-art underwater propeller blade press equipment designed to straighten deflections up to 600 mm from the blade edge with section thickness up to 50 mm and deflection angles over 180 degrees. The time requirement for repair and restorations is minimal. In many cases blades can be restored in less than one hour, even propellers with complex deflections on all blades are usually restored in under 12 hours.  Underwater propeller blade straightening by cold static loading is approved by Class as a permanent repair with no requirement for post repair heat treatment for NiAlBr propellers, the most common modern propeller alloy (Class Reference: Rules for Survey After Construction, Part7, Section 10 – 1.9.2 (b)). Propellers cast from other alloys can still be repaired by cold static loading as a temporary repair which can subsequently be considered a permanent repair after heat treatment at the next scheduled dry docking.

Conclusion

As the alloy of the propeller blades shown in the images above was NiAlBr, post repair heat treatment was not required as per class rules. This propeller was released and considered safe for continued use without operational restrictions until the vessel’s next scheduled dry docking at which time SGS would recommend a detailed inspection supported by dye penetrant to ensure the propeller is free of latent defects. With our underwater propeller blade straightening process you have the better option to keep your vessel’s propeller in one piece!

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