Underwater repairs company Hydrex are registering an increase in the number of vessels experiencing propeller damage.

Dave Bleyenberg, Hydrex Production Executive, explained: “While winter months usually result in an increase in propeller repairs, this normally occurs between January and March. But we have already attended a number of vessel inspections on propeller blades broken or damaged by ice or debris.”

In November, a Hydrex team was called out to Taranto, Italy, to inspect a 27,500dwt general cargo ship, whose 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.

To repair the bent blades, Hydrex deployed its cold straightening equipment and a dive team so as to repair the blades without disruption to cargo operations and the vessel’s ongoing schedule.

“After correctly positioning the cold straightening press over the propeller blade, they were bent back into shape,” said Bleyenberg. “While dive teams were in-situ repairing the propeller, Hydrex personnel ashore monitored video links from underwater cameras on the divers’ equipment. This allows us 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, the dive team and cold straightener deployed to Toga, West Africa, to carry out a similar operation to a tanker, whose propeller was vibrating due to a bent blade.

While these recent call outs have involved the repair of bent propeller blades, if straightening is not an option, the damaged area of the blade can be cropped and grinded to restore hydrodynamic balance. First a detailed underwater inspection is carried out to assess the extent of the damage and to calculate the ideal cutting line. The blade is then cut underwater, grinded and polished using Hydrex’s patented blade repair tool.

“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,” said Bleyenberg. “We often encounter blades that have been severely damaged, chipped or completely broken off during ice navigation. In most instances, they can still be repaired in-situ by grinding and cropping the blades.”

Hydrex can also provide prescriptive propeller maintenance. When a containership 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.

“We strengthened the blades with modifications based on a specific design developed in cooperation with the original equipment manufacturer,” said Bleyenberg. “The strengthening made them significantly less susceptible to ice-impact and debris, without detriment to propellers’ performance.”