Saturday, February 24, 2024
Maritime Propulsion

February 18, 2014

Hydrex Propeller Repairs in "Extreme Conditions"

Photo: Hydrex

When damage to propellers occurs due to impact with ice and other debris, Hydrex says it will help, even if the damage is quite extensive. Hydrex diver/technicians in Antwerp, Ventspils and Kiel carried out underwater propeller operations, as detailed below.

Some of these repairs were carried out in extreme winter circumstances, hydrex said, adding that icy conditions will not prevent its divers from providing services. The company's divers are professionally trained to perform a wide variety of operations, both above and below water, anywhere in the world.

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.

Underwater propeller blade straightening in Antwerp
One of the blades of a dry cargo vessel’s propeller was severely bent. The others propeller blades were also damaged, but less severely. A fast, on-site solution was required to restore the propeller’s balance and efficiency. A Hydrex team therefore mobilized rapidly to the ship’s location in Antwerp. The team started the underwater operation with a detailed underwater survey of the damaged propeller blades.  Next the team positioned the straightening machine over the bends of the trailing edges of the first blade. The blade was then returned to its original state. The other blades were not bent. They had however suffered smaller cracks and dents along their trailing edges. The Hydrex diver/technicians ground away the cracks and polished the edges of these blades. This restored the propeller’s efficiency.

Propeller blade cropping
Should a piece of the blade be broken or if there is other damage too extensive for straightening, a section of the blade will be cropped. 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.

In the following examples cropping was the only option as the damage to the propeller blades was too great to allow cold straightening

Propeller modifications in harsh condition in Ventspils
A 180-meter tanker suffered damage to the blades of its propeller. A Hydrex team mobilized to Ventspils, Latvia, to perform the necessary repairs in extreme icy conditions. An inspection revealed that two of the propeller’s four blades were severely bent and needed to be cropped. This was subsequently done in accordance with the attending surveyor of the classification society.

The team then moved the equipment to a 210-meter container vessel that was also berthed in Ventspils. Four of the five blades of the pitch propeller of this ship were bent too much to be straightened. The decision was made to cut all the propeller blades to the exact same size. By doing this the propeller’s balance was restored and its hydrodynamic efficiency optimized to suit the power requirements of the engine.

Propeller blade cropping in Germany
Closer to home but in equally icy circumstances, a 180-meter container vessel berthed in Kiel, Germany, needed to have the four blades of its propeller cropped. Three of the blades suffered damage too extensive to be straightened. The blades were modified one after the other by the Hydrex diver/technicians. The area to be cropped was marked out on each blade and verified. The blade was then cropped and its edge grinded to give it the correct radius. When the cropping was complete, the blades were polished. This was done to make sure that any loss of power would be minimal.

Damaged propeller blades will have a performance below average.  The engine will have a higher work load. This results 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. In this manner optimum efficiency of the propellers can be restored. If straightening is not an option, the affected area on the blade will be cropped. By doing this the greatest possible efficiency is achieved for the vessel. These repairs are carried out with the Hydrex propeller blade cutting equipment. Both types of repairs can be performed on-site and underwater. This allows the ship to return to commercial operations without the need to drydock.