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The University of Southampton
Rifi An Enterprise Consultancy Unit

Case Study: Lifting analysis and load test of a hook foundation in a GRP vessel

Inflatable rescue craft
Inflatable rescue craft

Objective: Risk management of the largest ever davit boat launch.

Situation

  • RIfI was commissioned by the consultant naval architects Amgram Ltd.
  • New semi-rigid GRP (Glass Reinforced Polymer) inflatable rescue craft.
  • Largest ever boat to be considered for davit launch (18.8m long and 30.6 tonne).
  • A two point lift system was to be employed, each with a safe working load of 16 tonne.
  • For a davit launch a statutory safety factor of 6 was required.
  • Therefore, each lifting point must be able to withstand a load of 96 tonne.
  • What we did

  • Initially FEA (Finite Element Analysis) modelling was conducted on the lifting points.
  • This analysis highlighted that design changes were required: changes to the bolt detailing, local thickening of the hull, adding a backing plate to the outside of the hull and using spacer tubes to reduce the bearing stresses in the plywood bulkhead.
  • A bespoke test rig was designed and built at the University of Southampton to represent the hull lifting points and incorporated the design changes suggested by FEA.
  • The test showed the lifting points could withstand 96 tonnes and the lifting arrangement was fit for purpose.
  • Impact

  • Simulation and testing proved to be a powerful combination where FEA optimised the detailed design and the final design was proof tested before manufacture.
  • This mitigated against a potentially dangerous and costly accident during initial launching.
  • The craft has been successfully launched and recovered using the davit since 2005.
  • FEA model
    FEA model
    Bespoke test rig
    Bespoke test rig

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