TABLE OF CONTENTS The most frequent collisions i.e., contacts between offshore supply vessels and the platform to which they are delivering supplies, generally cause only minor damage, although significant impacts have been reported in rare cases. Impact from external, non-platform related vessels is probably the most location dependent hazard. This is however, not reflected in general design criteria, which are not related to impact from non-offshore traffic. When it is considered that the level of this hazard may vary considerably, it is primarily the collision probability which will be location dependent, whereas the consequences are not. In addition, the collision probability is also more or less (but not entirely) independent of the concept that is chosen.
In addition to design requirements against progressive collapse due to an impact load, any structure will have to fulfil a number of other requirements. These may govern the dimensions and the design of the platform. This means that the platform may have quite extensive additional capacity with respect to collision impact, compared to the minimum design limits and thus it may have a substantial over-capacity to resist collisions. This over-capacity is concept dependent and may vary significantly even for seemingly similar concepts.
According to the WOAD database, (DNV, 1998a) there have been six cases of total loss of a platform since 1980 due to collision or 'contact' (impact by vessel in close attention):
Two jacket structures in US Gulf of Mexico have been lost due...
