The hydrex team regularly carries out cold straightenings, croppings and other propeller blade modifications on vessels around the world, specially during winter.
Winter months usually result in an increase in propeller repairs between January and March. Throughout the rest of the year, they also attend vessels for inspections of propeller blades that are broken or damaged by ice or debris
Returning bent blades to their original form
- For instance, they sent a team to Taranto, Italy, to inspect a 27,500dwt general cargo ship.
- Its engineers had reported excessive vibration from its five blade, 5m diameter propeller as the vessel returned from operations.
- The cause of the vibration was two bent propeller blades.
- The vessel deployed hydrex’s in-house developed cold straightening equipment and a dive team to repair the blades.
- This was done without disruption to cargo operations and the vessel’s ongoing schedule.
The Procedure
- After correctly positioning the cold straightening press over the propeller blades, it was bent back into shape.
- While their divers were repairing the propeller underwater, the team leader ashore monitored video links from underwater cameras on the divers’ equipment.
- This allowed them to communicate the exact dimensions and position of the damage between the divers and the technical team supervising the operation.
- This is essential because the calculations need to be perfectly accurate to achieve the best results in terms of propulsion efficiency.
- No sooner had the propeller been repaired or the dive team and cold straightener deployed to Togo, West Africa, to carry out a similar operation on a tanker whose propeller was vibrating due to a bent blade.
Cropping severely damaged blades
- These two call outs involved the repair of bent propeller blades.
- If straightening however is not an option, the damaged area of the blade can be cropped and grinded to restore hydrodynamic balance.
The Procedure
- This was done during an emergency operation on a tanker berthed in Antwerp.
- A doubler plate installed on the inside of the propeller nozzle had partially detached itself and had severely damaged the four blades.
- First a detailed underwater inspection was carried out by their divers to assess the extent of the damage and to calculate the ideal cutting line.
- The doubler plate was then removed to prevent it from causing further damage.\
- Next the four blades were cut underwater, grinded and polished using our patented blade repair tool.
Caution Points
If five-bladed propellers are damaged, the repair is more complex as extensive calculations have to be made to take the right amount off each blade to restore balance and prevent vibration.
An operation of this kind was carried out by one of their teams on a 184-meter container vessel in Singapore. Balance was restored to the propeller after all five damaged blades had been cropped.
They often encounter blades that have been severely damaged, chipped or almost completely broken off during ice navigation. In most instances, thesw can still be repaired on-site by grinding and cropping the blades.
Wide range of propeller modifications
- Luckily, the damage to the propeller blades is not always so extensive and a less comprehensive repair is required, as was the case for a 183-meter tanker in Tenerife.
- An underwater inspection revealed that two of its propeller blades had suffered smaller cracks and dents along their trailing edges.
- Because the damage to the blades was limited, the ship experienced no vibrations and only a small loss of performance.
- Their divers therefore grinded away the cracks and polished the edges of the blades. This gave the propeller back its original efficiency and prevented further cracking.
Other Services
Their teams can also provide prescriptive propeller maintenance. When a container ship suffered propeller damage after a particularly severe winter, the owner wanted to find a way of preventing ice-damage to propellers on other vessels in the fleet.
They strengthened the blades with modifications based on a specific design developed in cooperation with the original equipment manufacturer. The strengthening made them significantly less susceptible to ice-impact and debris, without decreasing the propellers’ performance.
Conclusion
Over forty years of experience with propeller repairs have given them the tools and know how to offer fast repair and modification services to vessels around the world. All types of operations can be carried out fast, fluently and efficiently and this afloat and underwater.
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Source: Hydrex
