Case study: safety of mechanised landing craft

Questions had arisen about the structural integrity of the mechanised landing craft on board the Royal New Zealand Navy’s vessel, HMNZS Canterbury.

A project was set up to specify and resolve two problems.

  1. Was there excessive strain on the lifting lugs of the landing craft?
  2. Why had cracks developed at the hinges of the bow ramp doors?

By using Finite Element Analysis (FEA) to make a 3D model of affected landing craft parts, taking into account the material it was made from and the forces it might be loaded with in a worst-case scenario, we were able to establish where problems might occur.

Finite Element Analysis modelling can also be used to check the accuracy of proposed solutions and quickly analyse a range of loading scenarios.

In the case of the lifting lugs, the in-service loading was found to be very sensitive to misalignment of fittings. The forces were acting at slightly different angles placing extra strain on the lugs beyond what was originally anticipated by the designers.

The proximity of other structure to the lifting lugs was also a problem, concentrating loads within the lifting lugs.

Non-destructive testing and inspection of the parts revealed some cracking was starting to appear in the areas predicted by FEA. We used FEA technology to develop an alternative design that overcame these problems.