International Shipbuilding Progress - Volume 31, issue 356

Authors: Stierman, E.J.

Article Type: Research Article

Abstract: Three different extrapolation methods for ships fitted with a ducted propeller are presented. A universal method is not found. For every nozzle arrangement a special method is recommended. An alternative method for scaling of the wake and thrust deduction is described, which seems to yield better results than the ITTC-78 method.

DOI: 10.3233/ISP-1984-3135601

Citation: International Shipbuilding Progress, vol. 31, no. 356, pp. 80-87, 1984

Authors: Ractliffe, A.T. | Mitchell, G.H.G.

Article Type: Research Article

Abstract: A floating dock consists essentially of a flat rectangular base stabilised in the submerged condition by means of a vertical wall each side. It has the virtue of being towable from one port to another but during such a voyage is subject to waves imposing longitudinal bending, shear and torsion. These loads may be the largest encountered during the life of the structure and are therefore significant for its design. The only information previously available on this topic was based on simplistic quasi-static theoretical models which do not account for either the water surging over the floor of the dock, …or the hydrodynamic forces resulting from pitch and heave. This paper describes a series of model experiments on a floating dock of representative proportions which is split in half transversely and fitted with straingauged straps measuring bending moment shear and torsion. The effects of draft, wave height, wave period and wave heading are investigated systematically and the results presented as families of non-dimensionalised curves. The effect of blocking the ends to prevent water surging through is also examined. The experimental bending moments are shown to be significantly lower than those obtained by quasi-static methods of analysis and non-linearities associated with free surface effects are found to be small enough to allow the use of a simple design formula. Show more

DOI: 10.3233/ISP-1984-3135602

Citation: International Shipbuilding Progress, vol. 31, no. 356, pp. 88-93, 1984

Authors: Slooff, J.W.

Article Type: Research Article

Abstract: A discussion is given of the physical mechanisms governing the hydrodynamics of sailing yacht keels and the parameters that, through these mechanisms, determine keel performance. It is concluded that due to the presence of the free water surface optimum keel shapes differ from optimum shapes for aircraft wings, a fact that does not seem to have been widely recognized. Utilizing computational fluid dynamic analysis and optimization methods it is found that the performance of conventional keels can be improved significantly by reducing taper or even applying inverse taper (‘upside down’ keel) and that dramatic improvements in performance can be realized …through keels with ‘winglets’ as utilized by the 1983 America’s Cup winner ‘Australia II’. Show more

DOI: 10.3233/ISP-1984-3135603

Citation: International Shipbuilding Progress, vol. 31, no. 356, pp. 94-102, 1984

Authors: Wind, J.

Article Type: Research Article

Abstract: The massive growth of arctic sea transport, planned for the coming years is associated with the application of unfamiliar propulsion equipment for icebreaking. The classical system with fixed pitch propellers, driven by electrically transmitted diesel – or steam – power, tends to make place for propulsion systems with new elements such as controllable pitch propellers and propeller nozzles. The introduction of these new elements in very large dimensions, means that more and rather vulnerable parts will be exposed to heavy iceloads. The advantages of this kind of new equipment can only safely be utilized if its behaviour under such …extreme loads can be sufficiently evaluated. Common knowledge at this stage is rather restricted, being based on the experience with a few number of installations in service. It is also clear that theoretical analysis can only partly answer the questions. Since in the near future a considerable number of new installations for icebreaking will be put into operation, it is expected that the coming years will provide an unknown feedback of practical experience. A better understanding of the main influencing factors finally will result in strong changes in the concept of icebreaking propulsion equipment, extrapolated to large powers. The paper describes the nature of iceloads and indicates methods to approximize the magnitude of ice impact on propeller blades and nozzles. The influence of power and propeller size is investigated. The resulting stresses are to be compared with allowable values both for a single static shock as well as dynamically in fatigue. Recommendations are given for the dimensioning of blade sections, the supporting points of nozzles and the way of determining their plate thickness. A comparison is made with the requirements of classification societies. Part 1. Historical events and future plans. Part 2. Discussion of Class requirements. Part 3. A method to determine blade strength for ice operation. Part 4. Ducted propehers in ice. Show more

DOI: 10.3233/ISP-1984-3135604

Citation: International Shipbuilding Progress, vol. 31, no. 356, pp. 105-117, 1984