International Shipbuilding Progress - Volume 14, issue 157

Authors: Broersma, G. | Tasseron, K.

Article Type: Research Article

Abstract: In general, efficient running of ships has not yet arrived at the state of affairs as exists in airline transportation, but in an increasing number of cases, there is a directed attempt of cost concious owners to maintain ships at optimum running conditions. Efficient running of main and auxiliary machinery, and maintaining the hull in a state of cleanliness, is applied in general. However, maintaining the efficiency of the propeller has come under scrutiny only since recent time. It is true, and especially in Germany, that propeller efficiency as a function of its condition has been studied for some …decades already. But the practical experience of specialist propeller manufacturers has induced them to establish a reconditioning and maintenance service to keep with the need for dependable and efficient use of the propeller. No macroscopic changes in form and spacing occurring, it is only the increasing roughness of the propeller which causes decreasing efficiency in service. Parameters influencing the character of the surface are summarized; and in this respect it is recommended to study actual surface characteristics as in production engineering of high class gears. Additionally, one might introduce the definition of permissible undulation of a surface, as used in gear technology. In the case of propeller manufacture, this is of prime importance to limit, or even to exclude, the possibility of cavitation due to discreet jumps in the location of the centre of curvature of the blade surface. Show more

DOI: 10.3233/ISP-1967-1415701

Citation: International Shipbuilding Progress, vol. 14, no. 157, pp. 347-356, 1967

Authors: van Gunsteren, L.A.

Article Type: Research Article

Abstract: Using an electronic computer, one should apply other rules of integration for the calculation of statical and inertial moments than for the approximation of areas. Requiring an exact result for polynomials of first and second order, this leads to the two-points – and three-points-rules given in this paper.

DOI: 10.3233/ISP-1967-1415702

Citation: International Shipbuilding Progress, vol. 14, no. 157, pp. 357-364, 1967

Authors: Remmelts, J.

Article Type: Research Article

Abstract: Technological investigations are described in which a laboratory set-up simulates conditions of practice when blast cleaning steel plate as well as possible. The rate of cleaning is found to increase when more abrasive per unit of time is discharged. This means that high pressure, a large nozzle and a wide valve for metering the abrasive flow are advantageous, bur the actual setting of these variables should be mutually adjusted. The optimum blasting angle for removing millscale is about 45°, and the optimum nozzle to work distance 55–75 cm. The smaller the abrasive grains, the quicker the cleaning process. Air …consumption decreases as, under otherwise constant conditions, the abrasive transport is increased. High cleaning rates are advantageous, because they lead to lower costs per m2 for labour and power, whilst costs for abrasive hardly go up. Show more

DOI: 10.3233/ISP-1967-1415703

Citation: International Shipbuilding Progress, vol. 14, no. 157, pp. 365-377, 1967