Observed Storm Stability of Jackup Boats (Liftboats)

A rational approach to establishing overturning loads for liftboats is presented. Resistance to overturning as a consequence of geotechnical forces is shown to be significant contributing factor to the elevated stability of liftboats. The same calculation techniques can be used also for jack-ups. Observed conditions in Hurricane Juan where some liftboats failed by overturning, some liftboats had legs broken off but the hulls survived afloat, and some lifeboats survived without damage are presented. A general procedure for determining ultimate overturning resistance for liftboats accounting conservatively for pad rotational stiffness is defined.