Lifting Analysis and Load Test of a Hook Foundation in a GRP

Research Institute for Industry

nCATS research Group

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 to represent the hull lifting points and incorporated the design changes suggested by FEA.
• The test showed that 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 system since 2005 .