International Shipbuilding Progress - Volume 15, issue 171

Authors: Ferdinande, V.

Article Type: Research Article

Abstract: Model tests in irregular head waves were analyzed with special emphasis on the slamming phenomena, endured by a cargo ship in the ballast condition. The conditions leading to slamming, i.e. the magnitude of vertical relative motions and relative velocities at the forward perpendicular, were evaluated. By means of theoretical computations of pitching and heaving motions and their phase angles in regular waves, relative motions and relative velocities could be evaluated at any station aft of the forward perpendicular. A distribution of the slamming decelerations, measured at a certain station near the bow, allowed one to determine the so-called “threshold velocity”, …figuring in the well-known probability formula, which lets one predict the occurrence of slamming. These “threshold velocities” are calculated for different stations along the ship length and for different levels of slamming severity. It is noticed that these “threshold velocities” are dependent on ship speed. The meaning of the conception “threshold velocity” is discussed. In order to predict slamming, as recognized on a ship in bad weather, an indication concerning accepted slamming severities is given. Estimating the number of slams in a hundred motion oscillations which is likely to be accepted by a ship’s master, the attainable speed in the here investigated sea state is determined. Show more

DOI: 10.3233/ISP-1968-1517101

Citation: International Shipbuilding Progress, vol. 15, no. 171, pp. 373-387, 1968

Authors: van Gunsteren, L.A.

Article Type: Research Article

Abstract: The costs and the engineering problems of the mechanism of any controllable pitch propeller are strongly dependent on the magnitude of the blade spindle torque. The blade spindle torque can be split into three parts: a hydrodynamic torque, a friction torque and an inertia torque due to the centrifugal force. The paper discusses the possibility of minimizing the hydrodynamic blade spindle torque by means of ventilation through holes on the face of the blade. The influence of the ventilation on the blade spindle torque is analysed by means of extended computer calculations. The two dimensional pressure distribution of …the ventilated sections is calculated with a linearized theory for lifting foils at zero cavitation number [9]. Blockage and interference effects in the ventilated condition are neglected. The distortion of the mean lines due to pitch setting is taken into account. The induced velocities by the free vortex system are calculated with a special lifting line theory, which has been adapted to heavy loadings by means of some empirical factors. As an example an existing c.p.p. of a trawler is analysed. It is concluded that ventilation is a promising tool for the realisation of c.p.p. designs with low blade spindle torque. Show more

DOI: 10.3233/ISP-1968-1517102

Citation: International Shipbuilding Progress, vol. 15, no. 171, pp. 388-398, 1968