Hydrex Performs Underwater Propeller Blade Straightening

In April, a diver/technician team performed propeller blade straightening operations on two vessels at anchorage in Kalundborg, Denmark. First the bent blades of a 225–meter bulk carrier were restored. The team then straightened the damaged blades of 158-meter reefer in the same location.

By taking advantage of the in-house developed cold straightening technique, damaged blades can be straightened underwater. This allows a ship to return to commercial operations without the need to drydock. Optimum efficiency of the propellers can be restored by bringing the blades back to their original form.

The Kalundborg Fjord is a perfect location to carry out repair work. Vessels at anchorage there are sheltered from the current. This makes it ideal for underwater repair work to be performed – a nice change for the Hydrex diver/technicians from the sometimes harsh conditions they are faced with during their travels around the world.

With three of the five blades of its propeller severely bent, a bulk carrier needed a fast, on-site solution to restore the propeller’s balance and efficiency. Hydrex diver/technicians are trained to carry out repairs underwater in the shortest possible time frame. A team was therefore rapidly mobilized to the ship’s location in Kalundborg to restore the damaged blades to as close to their original condition as possible.

After the equipment arrived at the vessel’s location the team started the underwater operation with a detailed survey of the affected propeller blades. The inspection revealed that two blades were damaged too severely to be straightened and needed to be cropped, but that a third one could be straightened. The other two blades were unaffected.

The team positioned the straightening machine underwater over the bend in the trailing edge of the first blade. In close communication with the team leader in the monitoring station on-shore, the divers returned the bent blade to its original state. The team then used the information acquired during the inspection to calculate and determine the correct measurements needed to modify the trailing edges of the other propeller blades. Next the divers cropped the blades and ground their edges to give them the correct radius. When the cropping was complete, the Hydrex technicians polished the blades to make sure that any remaining loss of efficiency would be minimal.

After they had completed the repair, the team stayed in Kalundborg until the reefer arrived the next day. Two of the four blades of the propeller of this ship were severely bent. They could both be straightened. The other two blades were not damaged.

After the divers had restored the bent blades with the new generation cold straightening machine, they also performed a hull repair on the same vessel. The team installed a 300 x 300 mm doubler plate over a small hole in the hull plating of the ship. Performing both repairs during one operation saved the owner of the reefer from having to take his vessel to drydock.

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