Static and Fatigue Behaviour of the Main Section of a Fast Patrol Boat

Abstract

This paper analyses the static resistance, as well as the fatigue resistance, of the main section of a fast patrol boat designed and manufactured in Portugal. The ship under study is a high-speed lightweight craft that was mainly fabricated with two types of aluminium series alloys, namely the 5083-H111 and the 6082-T6 alloys, which are commonly used in shipbuilding. The structural response of the critical section of the ship was obtained using the Finite Element Method (FEM), when the structure was submitted to different loading conditions, such as the hydrodynamic and hydrostatic sea loads, the longitudinal sagging or hogging, or the loads on fuel oil tanks. Results obtained for the load cases considered showed that the Von Mises equivalent stresses do not exceed the Yield Strength of the aluminium alloys used in the manufacturing of the ship. In addition, strain gages were placed on the main ship's bulkhead, near a structural detail in its bottom, and real-time acquisition strain data was collected using a computer code routine written in LabView. The Rainflow cycle counting method was applied to load spectrum gathered in order to obtain the Rainflow matrix and to predict the fatigue life of the critical main section of the ship.