International Shipbuilding Progress - Volume 24, issue 277

Authors: Beek, G.H.M.

Article Type: Research Article

Abstract: The finite element approach for strength analysis of marine propeller blades is used to a growing extent. For the time being it is the proper method to be employed in order to obtain detailed and reliable information about the stress distribution over a propeller blade. The underlying article describes the application of a rather simple solid element type for static blade stress calculations. A solid element was preferred to plate or shell elements, because of the three-dimensional nature of the blade region near the hub. On the other hand it facilitates an extension of the considered structure into the …hub. Results of these calculations are presented in comparison with values obtained by means of strain gauge measurements on a separate full scale blade. Show more

DOI: 10.3233/ISP-1977-2427701

Citation: International Shipbuilding Progress, vol. 24, no. 277, pp. 225-232, 1977

Authors: Noordzij, L.

Article Type: Research Article

Abstract: A rule for scale effects on tip vortex cavitation inception is derived. With help of this rule full-size tip vortex cavitation inception can be predicted from model tests. The rule is illustrated by means of a few test results.

DOI: 10.3233/ISP-1977-2427702

Citation: International Shipbuilding Progress, vol. 24, no. 277, pp. 233-236, 1977

Authors: Tommasi, Giovanni B.

Article Type: Research Article

Abstract: The typical properties of the new stern shape provided with cochlea (helical) channels are displayed by the comparison of many model test results. The test and design methods of the new stern shape, not restricted solely to twin screw hulls, are thoroughly explained. The manipulation of the wake by means of the channel system leads to the following results: 1. a reduction of the thrust pulsation of the single propeller blades; 2. a drastic reduction in amplitude of the main frequency of the blade thrust, leading to its complete elimination; 3. a shift …to deeper sectors of the propeller disc of the reduced blade thrust maxima; 4. a counterpropeller effect generated by the vortex induced in the wake; 5. a limitation of the increase of the towing resistance due to the wake vortex and a possible reduction below the resistance of the corresponding traditional ship, provided with its unavoidable appendages; 6. a conveyance into the propeller disc of the (viscous) wake having lapped the surface of hulls provided with more than one propeller. Each one of the above contributions to the saving of propulsive power is not by itself of great significance, but their combined effect leads to a very substantial benefit. a reduction of the thrust pulsation of the single propeller blades; a drastic reduction in amplitude of the main frequency of the blade thrust, leading to its complete elimination; a shift to deeper sectors of the propeller disc of the reduced blade thrust maxima; a counterpropeller effect generated by the vortex induced in the wake; a limitation of the increase of the towing resistance due to the wake vortex and a possible reduction below the resistance of the corresponding traditional ship, provided with its unavoidable appendages; a conveyance into the propeller disc of the (viscous) wake having lapped the surface of hulls provided with more than one propeller. This explains how a power saving of the order of 25% could be achieved on comparative self-propulsion tests performed with a couple of twin-screw models, as well as the recorded drastic reduction of propeller induced hull vibrations. The available experimental data and criteria are shown, concerning the question to what extent similar benefits can be expected from the adoption of the cochlea channelled stern on any kind of ship. Show more

DOI: 10.3233/ISP-1977-2427703

Citation: International Shipbuilding Progress, vol. 24, no. 277, pp. 237-261, 1977