The IMO published a proposal for what is called ‘second generation intact stability criteria’ (IMO, 2013). A specific part of this proposal is devoted to crane vessels stating stability criteria during loss of load events. This is based on the accidental drop of load stability criteria from (DNV, 2013). The criteria state that the area under the GZ curve from the new equilibrium to first flooding angle is at least 40% in excess of the potential energy represented by the area under the GZ curve from initial angle to new equilibrium due to loss of load, i.e. an area ratio of 1.40 is required. This paper presents a study of the impact of this proposed rule on operations with heavy lift vessels and the safety margin regarding survivability is studied. BigLift's vessel Happy Sky is used as a benchmark case.
The study shows that an area ratio of 1.00 is inherently safe. In addition, a proposal is made for operations in unsheltered waters. It is proposed to correct the flooding angle with maximum allowed roll amplitude during the operation at hand.