Underwater Propeller Blade Straightening

With all five blades of its propeller severely bent, a 290-meter container vessel 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 and a team was therefore mobilized to the ship’s location in Diego Garcia in the British Indian Ocean Territory to perform a cold straightening of the blades.

After the equipment arrived at the vessel’s location, the divers installed a monitoring station on a workboat and made all the required preparations. The workboat was then positioned next to the vessel and the team leader went on board to discuss the details of the operation with the captain and the chief engineer of the ship and to go over the safety procedures.

Next the team started the underwater operation with a detailed underwater survey of the damaged propeller blades. Because fouling was present on the blades, the divers carried out a polishing to be able to inspect the blades for stress fractures and cracks. The inspection revealed that the five blades had suffered multiple deformations along the trailing edges and that there were stress fractures and nicks in the same areas. Cracks were also found up to 15 mm deep.

Part of the team started the repair part of the underwater operation with grinding work on the blades to remove the cracks. Once this was done the locations were smoothed to create a hydrodynamic profile on the trailing edges. Meanwhile, the rest of the team also entered the water and prepared the in-house developed hydraulic cold straightening machine for the straightening operation. The divers carefully positioned the 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 four blades.

When the divers had also completed all grinding and polishing repairs on all identified cracks and gouges of the blades, they made a full inspection of the newly modified condition of the blades for the attending ABS surveyor and the captain of the vessel. With all parties involved satisfied, the divers demobilized their equipment and returned home.

The operation restored the balance and the efficiency of the propeller. By carrying out the straightening on-site and underwater, Hydrex avoided a costly and time consuming drydock visit for the owner of the vessel.