Showing papers in "Naval Architect in 1978"

Towards a unified approach to ship structural safety

Abstract: A completely rational approach to primary safety is not possible at present. But two closely linked semi-probabilistic or second-moment methods which take some account of the statistical nature of the loading and collapse (or limit state) strengths may now commend themselves to designers, owners, and certifying authorities. These are the partial safety factor approach (closest to the conventional safety factor) and the safety index. The paper outlines them both but concentrates on the second concept which is applied to five naval designs varying in length from 91-154 m and for which measured strain records exist. The safety indices are compared with those for pseudo-merchant ships designed by rule and having the same lengths, and then with those for larger merchant ships having a length range 158-328 m. If one accepts the traditional design approach, in which comparisons are made with the best "successful" past designs then the heterogeneous nature of the results suggests two closely linked findings. First, that there are some obvious shortcomings in the conventional use of the safety factor. Secondly, notwithstanding the possible fatigue implications, it does seem that there is appreciable scope for better weight and cost compromises in both naval and merchant designs, and especially for the larger merchant ships. It would, perhaps, be premature to accept by itself either of these hybrid approaches to design until further statistical data are available. Nevertheless, the authors advocate a design policy which adopts one or both of these approaches in parallel with current methods. This would assist in building up a data bank of relevant information for future use. But even more important,it could provide a stimulus to rational design thinking and to the necessary further research.

Preliminary ship cost estimation

Abstract: The paper suggests a method for assessing the approximate capital cost of merchant ships in the very early stages of design. It is intended as a guide to ship designers, students and others concerned at the beginning of a new project who may wish to know the ship cost, and how it changes with alterations to principal design variables such as dimensions, weights, powering or carrying capacity. The method does not supplant more refined techniques used by professional cost estimators at later stages in the design, but it may be useful in circumstances where cost estimating expertise or actual shipyard costs are not immediately to hand. Simple worked examples are included to demonstrate the application of the method.

Wave slamming loads on horizontal circular elements of offshore structures

Abstract: Horizontal cylinders are subjected to impact loads when suddenly immersed. On offshore oil platforms and semisubmersibles these forces can contribute to eventual failure unless allowed for in the initial calculations. The paper describes a theoretical background to slamming and gives the results of a series of wave-tank experiments to establish the magnitude of the wave force slamming coefficient for a horizontal circular cylinder.

On the dynamics of slamming

Abstract: Symmetric slamming responses are estimated by the methods of linear dynamics. While the approach is a general one, suitable theories must be chosen for the purpose of computation. Here, the idealizations adopted in a previous paper by the authors have been used. The intensity, form and location of the slam itself are assumed to be given by theories due to Ochi and Motter and Kawakami et al, and also that of Leibowitz.

Parallel development of ship production facilities and information systems

Abstract: The paper deals principally with the Shipyard's initial efforts to organize a program for the development of Information and Control Systems and the evolution of an agreement with Kockums to use their Information Systems as a framework for development in Harlands. The development program for applying the systems used by Kockums to Harland and Wolff's Shipyard is described, including the means of achieving cooperation among all the people and departments involved. The resulting Harland Information System is described indicating the elements that are similar to Kockums and other elements that have been observed to work satisfactorily in the Swedish yard, but have not been fully implemented in the Belfast Yard.