The Semi-Submersible Crane Vessel "Balder"

Abstract The extreme weather and sea conditions of the Northern North Sea and the consequential generally low performance rate of crane ships and barges in general, particularly during the winter months, has led to the concept design and construction of the very large semi-submersible crane vessels which are now being brought into service. This paper describes the important features of the S.S.C.V. 'Balder' with emphasis placed on its functions as a floating foundation of heavy lift cranes. Some details of an analysis of the workability rate of the Balder is given. A comparison of this rate with that of a conventional crane ship clearly indicates the operational advantage of the vessel. Introduction During the past 7 – 8 years we have witnessed a rather astounding increase in the lifting capacity of the offshore derrick. This development has run parallel with the call for equipment capable of lifting ever-increasing loads. The largest offshore crane in use today can handle a maximum of 3000 short tons. Any further increase in crane size can only be expected to give a negligibly small improvement in the performance of the crane ship. The principal reasons for this are the relatively large motion responses of the crane ship to the seaway and the stringent limitations on motions imposed by the cranes. Thus, the crane ship or crane barge is one of the most weather bound vessels employed in offshore construction. One therefore arrives at the conclusion that to substantially improve the efficiency of the crane vessel, one needs to look for a different crane support base than that offered by the conventional barge or ship. The incentive to do so becomes even more evident when considering the critical aspects in terms of costs and time which the installation of production facilities in hostile waters represent.