Developing A Better Way To Repair Damaged Propellers
There are a variety of reasons that a ship’s propeller can get damaged. The common factor in most of these situations is an external mechanical impact that results in a damaged or bent propeller blade. “This happens when the propeller strikes a hard object such as a large tree trunk, a block of ice, an anchor chain or buoy, or even the seabed,” explains Martin Pauwels from Underwater Propulsion Engineers (UPE).
The consequences of such a collision may be directly noticeable on board the ship. “Of course, if the impact is big enough, the crew might have actually felt the impact. Or maybe the impact has caused the whole propulsion train to become misaligned. If this is the case, then this could cause vibrations throughout the ship,” Martin continues.
On the other hand, it is possible that a propeller strike goes unnoticed by the crew. However, this doesn’t mean that there is nothing wrong. Propeller design is the result of a finely tuned engineering process; even the smallest of deviations can result in reduced performance. “This means that the main engines will have to work harder – and burn more fuel – to get the same output,” he adds. “This can be observed by an increase in temperature of the exhaust gases.” An efficient propeller, therefore, is not only beneficial to the state of the ship’s engines, it also leads to optimised (and therefore more sustainable) levels of fuel consumption.
For decades the most frequently used solution to a bent propeller has been to simply remove the damaged section in a relatively straightforward process called cropping. However, the finely balanced nature of a propeller means that the opposite undamaged blade(s) also has to be cropped in order to maintain the functional integrity. This leads to an even greater reduction in performance. This is why, as Martin says, “cropping is not a solution”.
Not satisfied with this inefficient and short-term technique, UPE joined forces with propeller specialist Plug en De Boer to develop something better. UPE drew on its extensive experience in underwater maintenance and repairs of thrusters, propulsion systems and stern tube seals (using its team of specially trained divers); Plug en De Boer utilised its 20+ years of experience of propeller service and repairs.
Their solution is a submerged hydraulic press that bends back damaged propeller blades. “This piece of equipment is all about restoring the operational efficiency of the propeller,” says Martin. “We can use this new apparatus out of the water too, but the real added value is that our divers can carry out propeller repairs underwater. This is so much faster than dry-docking, and far better than cropping.”
This horseshoe-shaped hydraulic press developed and produced by the UPE/Plug en De Boer collaboration is operated by a team of two divers who are supported and guided from the surface. After an initial inspection and damage assessment, the divers put the hydraulic press into the correct position on the propeller blade, and then communicate with the operators on the surface to monitor the amount of hydraulic power provided to slowly bend the blade into position. Once the work is completed, the ship is taken out on a test run to verify levels of performance and to check for possible vibrations.
UPE and Plug en De Boer have two sizes of hydraulic press available. The larger has 100 tonnes of power, the smaller has 75 tonnes of power. To date, they have used them on several propeller repair jobs. All these jobs have been Class-accepted and – most notably – also in different locations. “This is because we can transport this equipment to wherever our client needs us. This is especially important if the ship is loaded with cargo; it is crucial to keep the downtime to an absolute minimum. The client – and the client’s client – doesn’t want to be kept waiting.”
When asked about the financial benefits of using this submerged hydraulic press, Martin is understandably cautious. “This is a simple question with a complicated answer,” he smiles. “There are lots of factors to take into consideration. What type of ship is it? What is its day rate? How bad is the damage? Is it carrying cargo? How far away is the nearest dry-dock? Because every situation is different, we do our best to inform the client of their options so that they can make a well-informed decision.”
For AEGIR-Marine, the added service of UPE and Plug en De Boer’s submerged hydraulic press marks an expansion of an already broad portfolio of combined services. “We have worked closely as partners with AEGIR for years now. We have different specialties, but with an overlapping core business,” Martin says. “They contact us when they need underwater support. And we contact them when we need help with stern tube seals or propulsion systems.”
The close relationship between UPE and AEGIR-Marine is one of the reasons why UPE and Plug en De Boer decided to send a submerged hydraulic press permanently to Panama, the location of one of AEGIR-Marine’s global service hubs. “It is also a very strategic location for the shipping industry, with lots of ships coming through the canal, and the conditions for diving are very good,” says Martin. “Together with another local company, we plan to continue working as partners with AEGIR-Marine in Panama.”
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