NOVEMBER 7, 2012 — Hydrex diver/technician teams have recently carried out a wide range of underwater propeller operations on tankers around the world. Jobs have included a spinner cone (Propeller Boss Cap Fin –PBCF) replacement on a 110-meter vessel in Singapore, a propeller blade straightening on a 248-meter ship in Algeciras, Spain, and a blade cropping on a 183-meter vessel in Flushing, the Netherlands.

Underwater spinner cone (PBCF) replacement in Singapore

Hydrex was contacted to install two new spinner cones (PBCF) during a LPG tanker's scheduled stop in Singapore.

After arriving at the vessel's location, team member started the operation with a full inspection of both propellers. Next the diver/technicians removed the port side propeller spinner cone (PBCF) and hoisted it on board the vessel. After they had cleaned the area under the spinner cone (PBCF), the team lowered the new cone into the water and positioned it on the propeller. When this was done, grease was inserted in the space underneath the propeller cone for lubrication and the bolts were put on torque and secured with wire, finishing the replacement of the first spinner cone (PBCF).

The divers then repeated this procedure with the starboard side propeller.

The PBCF alignment was monitored on an underwater CCTV camera and supervised by the manufacturer's specialist from the diving boat. The manafacturer told Hydrex that this was the first installation of a PBCF underwater.

The Hydrex team worked around the clock. No gas freeing operations were required, saving time for the owners of the LPG tanker.

Underwater propeller blade straightening in Spain

With three of the four blades of its propeller severely bent, a 248-meter tanker needed a fast, on-site solution to restore the propeller's balance and efficiency. A Hydrex team was rapidly mobilized to the ship's location close to the Hydrex office in Algeciras, Spain, to perform a cold straightening of the blades.

After the equipment arrived at the vessel's location with one of the Hydrex workboats the team started the underwater operation with a detailed underwater survey of the damaged propeller blades. The inspection revealed that the three blades had suffered deformations along the trailing edges.

The team then carefully positioned the straightening machine over the bends of the trailing edges of the first blade and, in close communication with the team leader on the work boat, applied pressure to return the bent blade to its original state. This procedure was then successfully repeated for the other damaged blades, restoring the propeller's efficiency.

Underwater cropping of damaged propeller blades in the Netherlands

In September, Hydrex mobilized a diver/technician team to carry out a detailed inspection and necessary repair to the damaged propeller blades of a 183-meter tanker during the ship's stop in Flushing.

To make a full assessment of the damage, the team first performed an underwater inspection. This revealed that all four blades had been damaged. The affected areas of the blades therefore needed to be cropped to restore the propeller's balance. 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 propeller blades. The area to be cropped was marked out on the four blades and verified. Next the divers cropped the blades one by one 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.

Damaged propeller blades will have a performance below average. The engine will thus have a higher work load, resulting in increased fuel consumption and added stress. By taking advantage of Hydrex's in-house developed cold straightening technique, damaged blades can be straightened underwater and optimum efficiency of the propellers can be restored. If straightening is not an option, the affected area on the blade will be cropped to restore the hydrodynamic balance. This is done to achieve the greatest possible efficiency for the vessel. This kind of repair is carried out with propeller blade cutting equipment developed by the Hydrex research department. Both types of repairs can be carried out on-site and underwater, allowing the ship to return to commercial operations without the need to drydock.

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