Search

The effect of the radial load distribution of the screw blades on the performance of shrouded propellers have been examined, in particular with respect to separation of the flow at the nozzle, to clearance between blade tips and nozzle wall, to efficiency and cavitation. Design diagrams have been developed for the “optimum” solution of the “screw + nozzle” combination, which can be recommended for practical purposes.

In Part IIIresults are presented of open water tests with geometrically similar models of a Victory wake-adapted screw to six different scales, ranging from scale 50 to scale 6. An analysis of these results was made according to Lerbs’ method of the equivalent radius of the screw. This analysts enabled conclusions to be drawn about the effect of Reynolds number on the open water test results of this type of screw. In Part IVthe results of self-propulsion tests with Victory models to scale 6, 18, 23, 30, 40 and 50 at self-propulsion point of model are analysed on the basis of the results of open water propeller tests. The analysis is made both according to the methods of thrust identity and torque identity. Tabulated values are given for all the propulsive components at speeds corresponding to 10–17 knots for the ship. Mean values of these components are represented in diagrams on basis of model scale. A method is introduced for plotting thrust-deduction as a function of thrust.

In this experimental research the effect of type of screw blade, type of stern arrangement, power absorption, draft and number of blades has been investigated for a single screw tanker with a block coefficient of 0.77. The dynamic thrust, torque and bending moments, excited by the propeller in the shaft have been analysed.

The boom in high-powered tanker-building after the last war led to many cases of vibration troubles and cavitation-erosion damage on the propeller blades. For this reason an extensive systematical investigation into the effect of shape of afterbody on propulsion has been carried out at the NSMB. The basic ship type was a 39,000 ton deadweight tanker, the maximum size that can pass the Suez Canal in loaded condition. The variations in afterbody which were studied follow: I–Optimum shape from an efficiency point of view, based on statistical data of the NSMB (moderately U-shaped sections). II–Extremely V-shaped sections. III–Extremely U-shaped sections. IV–Cigar-shaped stern with Mariner rudder arrangement (Hogner afterbody). V–Extremely U-shaped sections combined with a screw in a nozzle. VI–Extremely U-shaped sections combined with two screws, each fitted in a nozzle, one above the other. VII–A twin-screw arrangement. Resistance and self-propulsion tests were carried out with four- and five-bladed propellers in the loaded and ballast condition. Wake measurements with pitot tubes and flow observations with tufts have been made. Cavitation tests in the tunnel with adjustable frow were carried out. Finally the variations in the propeller thrust and torque during one revolution were recorded and analyzed.

The properties of the propeller, which have to be known for an investigation of the “crankshaft – thrustblock – propellershaft – propeller” system, are briefly discussed. The description of an apparatus for measuring dynamical thrust and torque on propeller models and the electronic part of the measuring system already in use is given. In addition a new system which has been developed at the N.S.M.B. is given. By applying the new system an improvement in the natural frequency and an increased reliability of the recordings has been achieved.

In this paper the results are discussed of wake measurements behind seven Victory models on scales varying from 50 to 18 and behind the Victory model boat D.C. Endert Jr.on scale 6. The scale effect in the circumferential inequality of the wake distribution is examined. The mean wake fractions of the models and the frictional wake fractions for a propeller placed behind a flat plate show a close analogy to the skin friction extrapolation diagram when plotted on a Reynolds number base.

After a short introduction the present publication deals with the vortex system of the “screw + nozzle” propeller. The results obtained from systematic experiments with propellers in nozzles in which the length-diameter ratio of the nozzle, the number of blades and the blade-area ratio of the propeller have been varied are discussed. In addition the results of experiments carried out for determining the optimum diameter of the nozzle system behind the ship are described. Explanatory comments on nozzle design are given, including diagrams for determining the radial inequality of the axial velocities in the nozzle and for making computations with regard to cavitation and strength. The influence of the clearance between blade tip and nozzle wall is discussed.

This paper presents the results of an extensive research into model test technique and the extrapolation problem in shallow water. These results enable us to examine the necessity for the use. of a method of three-dimensional extrapolation for shallow water. Experimental data on wall effect have been obtained by carrying out tests according to the method of images in a pressure-tight shallow-water basin. With the aid of a three-dimensional extrapolator the wall effect has been divided into effects on frictional and on wave-making model resistance. The results of the wall-effect tests were compared with the Kreitner theory and the influence of slots between tank walls and an adjustable bottom was analyzed. The results of propulsion and overload tests are given. Finally the correlation between model tests in shallow water and full-scale trials on a lake and the river Rhine has been discussed.

After a brief description of the velocity field induced by a propeller, the results obtained from open-water tests with systematically varied contra-rotating propellers of the B3-65 type are discussed. The results of these experiments are given in a Bp−δdiagram. With the aid of this diagram it is possible to derive a satisfactory survey of the efficiencies of contra-rotating propeller systems. This diagram also supplies data concerning the optimum diameters and the pitch ratios of the front and rear propellers. An analysis with the aid of circulation theory of the results of the experiments shows that with a distance of 0.37Dbetween front and rear propellers the axial induced velocity generated by the rear propeller is, in way of the front propeller, about 20 per cent. of the value it has infinitely far downstream of the rear propeller. Finally, a method based on circulation theory is developed by which contra-rotating propellers can be rapidly designed, provided they are of optimum diameter.

This paper deals with the resistance- and thrust-measurements on a series of nine geometricall similar Victory ship models, ranging in scale from 160 to 18, and on a Victory model boat of scale 6. The first part of the paper gives a description of the ship, the propeller, the models, the test apparatus, the test performance, the instrument calibration and the necessary corrections. The measured resistance and thrust values of the model boat are correlated with the results of the tests with the models using three methods, i.e. the Schoenherr, the Hughes, and the Lap-Troost extrapolators. The results of experiments for the determination of the wall-interference are given. These experiments are on the principle of the “image method”. An attempt is made to analyse the thrust deduction factors as a function of the Reynolds number. Conclusions and a programme for the continuation of the tests are presented at the end of the paper.

A general introduction is given about wake and thrust-deduction. Several theories about the nature of thrust deduction are dealt with. It appears that the part of the thrust deduction, arising from circumferential inequality of the velocity field, consists mainly of frictional thrust deduction. A new concept, the local thrust deduction coefficient, is introduced and a formula is given with which it is possible to calculate the radial distribution of the local thrust deduction over the screw disc. It appears from calculations that the relation between local and total thrust deduction and wake coefficients can approximately be given by the formula: 1−t′1−t=1−w′1−w14

The paper deals first with the deficiencies in the theory of wake-adapted ship screws. Next, a method of design for these screws is discussed which, by starting from the available data of the circulation theory, has been developed with the aid of experimental data in such a way that the screw design satisfies the requirements with regard to correct pitch and cavitation properties. Using this method of design, a series of 4-bladed wake-adapted screws has been calculated. The appropriate design charts are provided, and a numerical example given. For readers not acquainted with the fundamentals of the circulation theory a brief review of the screw design according to this theory is given in the appendix.

This paper deals with open-water tests with propellers of the B 4-55 series in nozzles of systematically varied form. The results of the open-water tests with the “screw plus nozzle” combination are given for each form of nozzle in a Ks– Km– λ-diagram, as is usual with systematically varied series of screws [1, 2]. By means of these diagrams the optimum “screw plus nozzle” combination for the nozzle form under consideration can immediately be determined, while it is also possible to compare the efficiency with that of the screw without nozzle. A method is discussed for determining the translational velocity in the nozzle in the vicinity of the screw. The influence of the various parameters, decisive for the open-water “screw plus nozzle” combination, are examined as regards their importance. Finally, attention is devoted to the framing of a condition of minimum loss of energy for the “screw plus nozzle” combination, and at the same time directions are given for cavitation-free design of the screw in the nozzle according to the vortex theory.

In this paper the results of research into the effect of propeller cavitation on ship-propeller interaction and on vibratory forces induced by the propeller are reviewed. A motivation for the need of a large depressurized towing tank is given. The areas of research in which an experimental penetration by application of such a ‘vacutank’ is possible. are discussed.

In this paper the application of non-conventional propulsion devices and the motives thereof with respect to merchant ships are considered. This is done from the viewpoints of efficiency, cavitation, vibrations, stopping, manoeuvring, safety and economics. The propulsion devices considered are: -controllable pitch propellers,-overlapping propellers,-contra-rotating propellers,-ducted propellers,-vertical axis propellers and-high speed propulsion devices, including air propulsion.The main part of this paper has been presented at the 2nd Symposium on Marine Propellers, The Society of Naval Architects of Japan, Tokyo, 24–25 November, 1971. The illustrations have been compiled from available N.S.M.B.-material; the bibliography is of an international character. controllable pitch propellers, overlapping propellers, contra-rotating propellers, ducted propellers, vertical axis propellers and high speed propulsion devices, including air propulsion.

This paper presents the results of open-water tests with a systematic series of contra-rotating propellers, consisting of a four bladed forward screw and a five bladed aft screw. Based on the open-water test results, contra-rotating propeller systems were designed for a tanker and a cargo liner. Comparative tests have been carried out with the tanker and the cargo liner both equipped with contra-rotating propellers and with a conventional screw. The propulsive efficiencies, the cavitation characteristics, the propeller induced vibratory forces and the stopping abilities are dealt with.

The stopping abilities of a 100,000 tons d.w. tanker equipped with different propeller types have been derived from model test results with the aid of a quasi-stationary method. Four propeller types have been examined i.e. a.a conventional screw propeller.b.a screw and nozzle system (ducted propeller).c.a contra-rotating propeller system.d.a controllable pitch propeller. a conventional screw propeller. a screw and nozzle system (ducted propeller). a contra-rotating propeller system. a controllable pitch propeller.

This report gives a review of recent research activities at the Netherlands Ship Model Basin (N.S.M.B.). The aim of this paper is to give the naval architect in a nutshell an overall impression of the progress made during the last few years. The main research items described are: Systematic test series on various propeller types, propeller excited vibratory forces, cavitation, ships’ in waves and the application of electronic computers in naval architecture.

Sparenberg’s lifting surface theory for ship screws was programmed for the digital computer X 1 of the Netherlands Ship Model Basin. The results of systematic calculations for symmetric blades and pressure distributions can be interpreted as “lifting line to lifting surface correction” factors. These factors were plotted in a diagram for different pitch ratios, numbers of blades, blade area ratios and three types of radial load distributions. Also the effect of skew back and asymmetric chordwise pressure distributions has been considered.

A quasi-stationary analysis is given for the cavitation phenomena, which occur when a propeller blade passes the stern of a ship. The camber induced by the flow leads to a camber decrease when the blade leaves the wake peak. This explains the inception of bubbles midchord, which grow towards the trailing edge. A simultaneous collapse of these bubbles at the trailing edge, when the induced camber disappears and the stagnation pressure becomes effective, is the cause of damage to the trailing edge. Some qualitative recommendations are given to prevent these troubles.

A theory has been formulated for calculating the properties of large hub to diameter ratio propellers with cyclic pitch control. In addition experimental results have been given for the efficiency and manoeuvring characteristics of such a device.

REPORT OF A CASE De B., a soldier 19 years of age, was sent to the ophthalmic department of the military hospital in The Hague because of decreased vision in the left eye, which could not be corrected by glasses. The young man did not remember whether he had ever been able to see well with this eye.The left eye deviated to a slightly divergent position. The vision was nearly ¼ (Snellen) ; there was no improvement with lenses. Skiascopy without cycloplegia revealed apparent low hyperopic refraction, which later could not be verified. The pupillary reactions were intact. In the anterior segment of the eye no abnormalities could be seen with the slit lamp. There were no evidences of past inflammation or signs of a persistent pupillary membrane. A little pointlike opacity on the posterior surface of the lens, somewhat to the nasal side and below the center, possibly marked