UMC CARRY OUT UNDERWATER PROPELLER
BLADE CHANGEOUT
UMC Rotterdam carries out underwater propeller blade changeout on a 37,048 dwt oil tanker at Rotterdam Port.
Earlier this year, UMC Rotterdam were called upon to carry out an underwater CCTV inspection of the four-blade propeller, under the direction of the attending propeller manufacturer and DNV surveyor in order to determine the condition of a previously-reported crack and cavitation damage to the propeller blades.
Once the inspection report had been verified, the UMC dive team would then perform an underwater changeout to a blade that had already been reported as damaged with cavitation of up to 25mm deep.
Some heavy-duty equipment including pneumatic cycles and hammers had to be employed in order to remove the unyielding blade bolts and then a small section of the rope guard outer edge in-between the 10 and 2 o’clock position was cut off in order to make way for the new blade to be installed.
During the underwater inspection, the UMC dive team were also tasked to carry out grinding repairs on reported crack to a second blade and arrange for NDT testing.
The first ACFM crack examination, non-destructive test (NDT) on the grinded areas did not pass muster and UMC divers were asked to polish the rough edges of the crack.
Jean-Paul Engels, UMC Continental Manager said, “We were able to use our specialist underwater propeller polishing equipment to achieve a smooth surface finish, we can use abrasive sizes down to 360 grade grit to produce a finish of 0.5-microns CLA (0.5m Ra). After our polish the ACFM test was successfully completed and no cracks detected after the grinding work anywhere on the blade area in way of the grinded out crack,” he concluded.
Next, the new blade was lowered into the water and divers, using hydraulic tools, tightened the bolts whilst maintaining torque pressure. The propeller was then turned 180 degrees and divers used compressed air to remove all water from inside the bolt holes. After closing the bolt heads the propeller was again turned 180 degrees in order to gain a 12 o’clock position. Divers then covered all securing bolts and locking bars with a two-compound steel epoxy. Once the blade plugs were secured, UMC were then instructed to polish the propeller before a final DNV Class inspection was carried out.
The underwater work took five days to complete and once the vessel departed the owner was able to report that there were no signs of vibration and the propeller was performing well.
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