International Shipbuilding Progress - Volume 51, issue 4

Authors: Pinkster, J.A.

Article Type: Research Article

Abstract: Ships moored in harbours are subjected to hydrodynamic forces due to other ships passing nearby. These hydrodynamic forces induce motions of the moored ship which may hinder loading/discharging operations or cause damage to the mooring system. These low frequency forces, sometimes known as suction forces, are associated with the primary pressure system around the sailing vessel which acts upon the moored ship. These effects are not to be confused with forces due to the secondary wave …system, or wash waves, of t he passi ng ship. T he latter are a relatively high f requency phenomenon and will not be treated here. This paper adresses two methods to predict the low frequency forces due to a passing ship, the first of which is based on implementation of the so-called 'double-body' flow method introduced by other authors. Double-body flow methods have been shown to be effective in predicting passing ship forces on a ship moored in open water. However, ships are rarely moored in open water but rather in harbours with a more or less complex geometry which is orders larger that the ships involved. Ships passing through harbours besides generating forces on moored ships also generate long-wave activity or seiches in harbours. These are due to the discontinuities in the harbour geometry which are almost always present. The second method treated in this paper is concerned with prediction of passing ship effects which take into account the generation of seiches due to the passing ship and the forces these exert on the moored ship. Results of both methods are compared with results of model tests for the case of a ship moored in open water. Both methods are subsequently applied to cases involving a complex harbour geometry. Results of comparisons of predicted horizontal forces on a moored ship show the additional effects due to such seiches. Show more

Citation: International Shipbuilding Progress, vol. 51, no. 4, pp. 313-338, 2004

Authors: Belmont,, M.R. | Bogsjö, K. | Horwood, J.M.K. | Thurley, R.W.F.

Article Type: Research Article

Abstract: Simulations of deterministic sea wave prediction provide empirical evidence of the dependence of prediction accuracy on the degree of statistical dependence present in wave models. This issue is examined and to arise from the effect of local coherence on the estimation of spectral coefficients used in prediction models. Coherence within the phase spectrum is found to be particularly important in this respect. The consequences of these findings are discussed in terms of applying prediction to real …seas and this raises the issue of coherence in actual wave systems. Show more

Citation: International Shipbuilding Progress, vol. 51, no. 4, pp. 339-351, 2004

Authors: Dang, J.

Article Type: Research Article

Abstract: Major problems in modern propeller designs for commercial vessels are discussed. New blade sections and their application in tackling those problems are investigated. Two designs and applications of propellers with new blade sections have been presented which exhibit a much wider cavitation bucket than conventional profiles. Thus, it is possible to reduce cavity volume, prevent leading edge vortex separation and its related cavitation erosion and reduce the pressure pulse levels as well as prevent broadband excitation …of cavitating propellers. Show more

Citation: International Shipbuilding Progress, vol. 51, no. 4, pp. 353-376, 2004

Authors: Millward, A.

Article Type: Research Article

Abstract: An investigation has been made into the effect of channel width and depth on the resistance of a high speed hull in the Froude number range F_n from 0.3 to 1.0 using experimental results from tests on two different sized models of the NPL 100A hull and also theoretical work using Wigley hulls as representative of a suitable high speed hull. The results of the investigation showed that for there to be no significant effect from …the boundaries of a channel or towing tank the model size should be approximately not more than half the width of the channel nor more than the depth of water in the channel. This result is in broad agreement with the guidance resulting from larger towing tanks given in the published literature which is generally for lower speed ships. The results also showed that using linear wave theory on a simpler hull shape, modified for the effect of a transom on the real hull, gave reasonable guidance of the magnitude of the correction for data from tests on larger hulls to allow for channel effects. Show more

Citation: International Shipbuilding Progress, vol. 51, no. 4, pp. 377-394, 2004