Propeller repair and modification
A ship with bent or cracked propeller blades might experience severe vibrations while sailing. The classification society might demand a repair before the vessel is allowed to sail on. By straightening the blades or cropping them, Hydrex can restore the propeller’s balance, resulting in a green light from the class for the vessel.
A propeller modification can easily be combined with any other maintenance or repair operation that needs to be carried out on the vessel, as was the case with several of the examples that can be found below. Thanks to the flexibility of the Hydrex teams this allows a vessel to keep to its schedule.
Prior to a propeller repair, a detailed underwater inspection is carried out by Hydrex diver/technicians. They are certified to make a full assessment of the condition of the propeller. The exact dimensions and position of the damage can then be communicated to the Hydrex technical department supervising the operation. This is essential because the calculations need to be perfectly accurate to achieve an ideal result with the repair. Hydrex team members are not only divers, but have experience in dealing with all kinds of different situations and circumstances. They are trained to think with the people in the technical department. As diver/technician experts, they can assist in working out the best solution and have the skill and experience needed to implement the theoretical solutions that have been worked out.
By taking advantage of the in-house developed cold straightening technique, damaged blades can be straightened underwater, allowing the ship to return to commercial operations without the need to drydock. Optimum efficiency of the propellers can be restored by bringing the blades back close to their original form. The cold straightening machine has been in use for quite some time now but the Hydrex research department has been looking into ways to enhance the technique even further to improve our services. A new model of the straightening machine was recently put into service. It is compatible with the existing model and is used to restore more severely bent propeller blades.
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 the propeller blade cutting equipment that was also developed by the Hydrex research department. First a detailed underwater inspection is performed by a Hydrex diver/technician team to obtain the exact parameters of the damage which are then used for a detailed calculation of the ideal cutting line. This allows the customer to know in advance what the result of the operation will be. He can then make an informed decision.
Restoring optimum propeller performance
Both cropping and straightening are done to restore the propeller’s performance to as close to its optimum condition as possible and to balance it. This can help a vessel that is suffering loss of speed due to an out-of-balance propeller. Propeller optimization is sometimes also done to restore the performance even if no real damage has occurred, as after some years of service an engine sometimes loses some of its performance. By calculating the possibilities of a propeller optimization the performance can be restored. Hydrex has been cropping propellers since 1985 and straightening them since 2000.
On some occasions an entire blade has to be replaced on a variable pitch propeller. This work can also be carried out by our divers who are trained to perform a wide variety of operations, both above and below the waterline, anywhere in the world and sometimes even in the most extreme conditions.
Hydrex not only offers repair services, but can also help customers when they have the need for preventive or other special custom projects. At the end of 2010, for example, preventive modifications were made in Bremerhaven to the blades of three ice-going sister vessels. When several of this customer’s vessels suffered damage and the propellers needed cropping after the 2009-2010 winter, the owner wanted to find a way to prevent this from occurring to his other container vessels. When the 2010-2011 winter promised to be equally harsh, he wanted to give the blades extra strength and make them less susceptible to damage from ice or other debris. This was done by modifying the blades to a very specific design that made them less prone to damage while keeping the performance of the propeller as close to optimum as possible. The operation was performed in close communication with the manufacturer of the propellers.
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