200413 Gantry Crane Failure

13 Jan 2004 MARS

Gantry Crane Failure
MARS Report 200413

The Engine Room crane had burnt out its hoist motor in the previous dry dock and it was refitted by the dockyard staff. The crane had only been used once since then and that was only as a mobile platform to help fit some new cables. The crane was to be used for some main engine work and so was unlocked and positioned above the engine. The operator pushed the down button but was not looking at the hook block, he then heard a bang and looked up just in time to see the hook fall, bounce off part of the engine and land close to his feet, narrowly missing 3 cadets who were to help with the job. Subsequently it was found that the motor had been wired back-to-front so that when the lower button was pushed, the block went up and, because it should have been going down, the upper limit switch did not work and the block came up fast under the hoist drum and snapped the wire rope. We learnt the following lessons:

  1. Always watch the crane hook when it is being moved. Do not assume it will move in the correct direction or stop when asked to.
  2. Keep all unnecessary personnel clear of the area.
  3. Know how to isolate the crane power supply in an emergency.
  4. Always test equipment after dry dock repairs (the dry dock employees had been using it up for down and down for up).
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