International Shipbuilding Progress - Volume 17, issue 196

Authors: Ferdinande, Y. | De Lembre, R.

Article Type: Research Article

Abstract: The present analysis of performance data, gathered on the car-ferry m.s. ROI BAUDOUIN, has been largely based on the properties of the apparent slip. The assumption of invariability of wake in this special case of a twin-screw vessel enables the authors to map out a generalized power diagram, that remains unaffected by fouling of the hull. All available performance data, gathered by only one experimenter on board, and thus not quite simultaneous, could be converted to values related to a standard condition of loading and hull surface. These values are used to map the iso-weather curves in the delivered horsepower/ship …speed diagram. For that purpose, however, an ‘equivalent Beaufort number’ had to be introduced, i.e. an index of total influence on added power at a given ship speed by wave height and wind strength, which actually are not simply related to each other in coastal waters. Seakeeping qualities have been investigated also. Waves, pitching and heaving motions, vertical and transversal accelerations, maindeck stresses amidships have been measured. Responses of ship motions, vertical accelerations, relative vertical motions and velocities, bending moments to regular headwaves have been computed theoretically and, on the basis of the measured spectra, the statistical values calculated. The agreement with the measured values is satisfactory, except for vertical bow accelerations. The theoretical responses, though, were considered as being sufficiently accurate to investigate the seakeeping in severe sea states. A prediction of excessive bow accelerations, slamming, shipping of water, propeller racing and main deck stresses was attempted. It could be concluded that excessive vertical accelerations at the fore-end of the garage is the main cause of voluntary speed reduction. A criterion of maximum allowable bow acceleration, by which the attainable speed can be determined in severe head seas is suggested. In this way, it is pointed out that for this car-ferry no voluntary speed reduction is necessary up to a sea state Beaufort 7-8 in the coastal waters under consideration. Show more

DOI: 10.3233/ISP-1970-1719601

Citation: International Shipbuilding Progress, vol. 17, no. 196, pp. 361-394, 1970

Authors: de Jong, B.

Article Type: Research Article

Abstract: In the present report expressions are derived for the hydrodynamic coefficients of two identical rigidly connected parallel cylinders of infinite length which perform harmonic oscillations in the free fluid surface. The cylinders are supposed to have only connections above the free surface. The method applied in this report is in fact an extension of Ursell’s method for the corresponding problem of one cylinder.

DOI: 10.3233/ISP-1970-1719602

Citation: International Shipbuilding Progress, vol. 17, no. 196, pp. 395-409, 1970