Recently teams of Hydrex diver/technicians performed propeller blade croppings on several vessels across Europe. In Kalundborg, Denmark the four propeller blades of a 170-meter bulk carrier were cropped. A similar operation was carried out on a 330-meter cruise vessel in Dubrovnik, Croatia.
Having developed different procedures for different kinds of damage, Hydrex is equipped and trained to make the best out of a bent or broken propeller. Ideally, the in-house developed cold straightening technique is used. This procedure enables Hydrex to straighten damaged blades in-water, allowing commercial operations to continue without the need to drydock.
In the following examples cropping was the only option as the damage to the propeller blades was too great to allow cold straightening. This kind of repair is carried out with the propeller blade cutting equipment developed by the Hydrex research department. In cases where there is an even number of blades an identical piece will be cropped from the opposite blade to restore the hydrodynamic stability of the propeller. By doing so, the best possible efficiency is obtained.
Underwater blade cropping in Kalundborg
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.
The four blades of a bulk carrier’s propeller were severely bent. A fast, on-site solution was needed 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 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 the four blades were bent over angles of 90 degrees or more. 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. 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.
Hydrex plans operation around cruise vessel’s strict schedule
A 330-meter cruise vessel needed all five blades of both its propellers cropped, ten in total. At the same time both the ship’s stern thrusters needed to be inspected. This had to be done without interrupting the ship’s sailing schedule. As a consequence only a very short time frame was available when the ship was berthed in Dubrovnik. For this reason the Hydrex technical department proposed to carry out the operation in two parts.
During a first stop in Dubrovnik, three of the five blades of the starboard side propeller were cropped. Both stern thrusters were inspected during this part of the operation. This revealed several cracks on the grids and blades of the two thrusters.
When the cruise vessel returned to the same location two weeks later, a Hydrex diver/technician team was ready in Dubrovnik for the second part of the operation. The remaining two blades of the starboard side propeller and all five blades of the portside propeller were cropped. Simultaneously the cracks that had been found on the thrusters were ground.
Both parts of the operation were finished before the cruise ship had to leave for the next stop with its passengers.
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Press Release, June 17, 2013