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Monday, February 4, 2019 

Recently, two teams of Hydrex diver/technicians undertook underwater propeller blade repairs, one on a 246m cruise ship in Tenerife, while another team cropped the heavily bent blades of a 200m vehicle carrier in Antwerp.

In both cases the solution offered to the customer was to restore the propeller’s efficiency as closely as possible to the original condition.

The crews of both ships had noticed overheating of the main engine, with reduced performance and higher fuel consumption resulting from the propeller damage.

Hydrex says that its in-house developed cold straightening technique enables damaged blades to be straightened underwater. This allows a ship with a damaged propeller 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, as carried out on the cruise ship.

The four starboard side propeller blades of the cruise ship were bent. Hydrex started the operation with a detailed survey of the ship’s two propellers, which revealed that the port side propeller blades were in good condition but the starboard propeller required repair. The team positioned the straightening machine over the bend in the trailing edge of the first damaged blade. In close communication with the team leader in the monitoring station on-shore, the divers returned the bent blade to its original state. When the straightening was complete, the technicians cleaned the blade to make sure that any remaining loss of efficiency would be minimal. The same procedure was then repeated on the other three blades.

Hydrex says that if straightening is not an option, the affected area on the blade will be cropped, to achieve the greatest possible efficiency, as was carried out on the vehicle carrier. With all four blades of the ship’s propeller severely damaged, the engine was overloading, so Hydrex was asked to restore the propeller’s balance.

After the equipment arrived at the vessel’s location, and the team had undertaken a detailed survey, Hydrex calculated the correct measurements needed to crop the propeller blades. Next the divers cropped the blades, followed by cleaning.

Hydrex says it often encounters blades that have been severely damaged, chipped or almost completely broken off during ice navigation. In most instances, they can still be repaired on-site by grinding and cropping the blades. Its R&D department has recently developed enhanced models of straightening and cutting machines, which allow straightening blades that could previously only be cropped, and to crop extremely damaged blades with only a minimal loss of efficiency for the propeller. 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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