The dual crane lifting capacity of the semisub:nersible crane vessel Hennod was during winter refit of 1985-86 increased from 5000 sh.t to 9000 sh.t. How this was achieved is described and commented upon with emphasis placed on changes and roodifications of hull fonn, upgrading of cranes and the enhancement of the dynamic ballasting systen of the vessel.
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.
Since the design of ships always involves compromise between various desired characteristics, it is necessary to find ways to develop hull forms in which reduced wave-making resistance is incorporated in that compromise. Some way is needed to take hull forms which fulfill the other reqv.irements placed on them and then modify, them in such a way as to reduce their wave-making resistance. The method of steep descent appears suitable for this purpose. A hull form generated by fifty-five sources placed on the center line plane of a hull in five horizontal rows is modified using this method so that its wave-making resistance is decreased U5 percent while the shape of the water line plane and the hull volume are, to first order, held constant. INTRODUCTION AND DESCRIPTION OF THE METHOD .The design of ship hulls is controlled by a great many factors other than the need to reduce the wave-making resistance. Therefore a most desirable technique for reducing wave-making resistance is to start with a hull form which meets these other requirements and then modify it continuously in such a way as to reduce the wave-making resistance. When the change has gone as far as possible without making the hull incompatible with the other requirements placed on it, then the change must be stopped.In 1956, Hogner published a paper which took the first step toward developing a method of this sort. He promised a sequel which apparently was never published. It turns out, however, that the necessary mathematical machinery to finish the development of his method has been brought forth in the past few years, and is known as the method of steep descent. This is not to be confused with the saddle-point method of the same name which has been used for a long time. The method of steep descent referred to here requires that we describe the resistance of the ship as a function »f a finite number of variables. The hull form is also described in terms of these variables. Then if we consider each of these variables to represent a coordinate in a finite-dimensional vector space, we may find the gradient of the resistance in this vector space. If, next, we change our defining variables In a direction as nearly parallel as possible to this gradient vector, then we will decrease the resistance as rapidly as possible for a given amount of motion through the vector space.Note: Because of corrections made to the tabulated functions on which this paper's calculations were based, it was necessary to recalculate the results which were presented at the Seminar. Although the first set of calculations were performed with a slide rule, those presented in this version of the paper were performed on an LdM 1620 computer, J155- MIM»QMM«p« ■■■■■■■■■■■■■■■■■MM -4^6-If it is desired to hold some quantity fixed --the hull volume, for example -then it is possible to constrain the trajectory through the vector space so that it is orthogonal to the gradient of that quantity. This can be done by rotating coordinates so that the vector space is spanned by a set of basi...
The problem has been treated of determining deflections and bending moments of the barge hull and independent cargo tanks combination as these occur in Class I and Class II barges during grounding. The method of solution is that of the initial parameters, which is here developed by means of operational calculus. The solution is closed and exact within the limitations of the Euler-Bernoulli beam theory.
A general method for obtaining the stability criteria of a grillage is presented. Axial loads in both sets of intersecting beams are considered. Properties and arrangements of beams are fairly arbitrary, as are permissible boundary conditions. However, the analysis is restricted to include only initially straight compression members.
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