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er or longer boat of the same form. The most successful design, then, is where the form is such that the most efficient length corresponds with the length required and, in the case of sailing vessels, that the wind veloc- ity corresponding to this length will be the actual wind velocity encoun- tered at the time of racing. This accounts for one of the reasons why certain yachts are faster or slower than competitors under varying wind conditions. Other reasons are that the righting moment increases with size faster than the heeling moment, allowing the larger vessel to carry sail with less relative heel than the smaller vessel and hence with less re- sistance. Also some vessels sail dif- ferently on the wind than before the wind. While the writer is keenly aware of the many limitations as to dimen- sions usually imposed upon the naval architect due to stability, cost, draft, or yacht racing rules, never- theless, there are occasions where a simple expansion of dimensions weuld result in decreased power and increased deadweight capacity. Itc is, therefore, hoped that this ex- tended use of tank test results of models may prove of interest and value. This paper contains many dia- grams and a number of tables. Ex- amples are also given showing the application of his model test analy- sis to a fire boat and a cargo and passenger steamer. + + * 4 Recent Developments in Pro- » peller Design, by Karl E. Schoenherr, Dr. Eng., member. The foreword to this paper which follows in full is a clear explanation of its scope: The first successful screw propel- lers were patented by Francis Pettit Smith and John Ericsson in 1836. These inventions were rapidly devel- oped and applied, so that by 1850 screw propellers and screw wheels were in common use for ship propul- sion on both sides of the Atlantic. In the early days progress in propel- ler design was achieved mainly through the imagination of inventors and by the method of trial and er- ror, because neither an adequate propeller theory nor the means to carry out experiments otherwise than on the ship itself were available. With the introduction of model basins, however, the situation changed. Apparatus was developed to test and study propeller perform- ance by means of small-scale mod- els. By this powerful method the influence of the different variables was determined, so that soon it be- came possible to select the most ef- ficient propeller for any given set of conditions. While thus the practical side of the problem had been solved in a 12 fairly satisfactory manner, the theo- retical side had lagged behind. The early theories by Rankine (1865) modified by R. E. Froude in 1889, by W. Froude (1878) and by Green- hill (1888) taken together had laid a firm foundation, but were quite in- complete and incapable of account- ing for all the phenomena of pro- peller action. The subsequent work by D. W. Taylor and the theories by Lorenz (1905) and Guembel and Reissner (1910) filled in many of the existing gaps. It was not, how- ever, until Grammel (1916) and Foettinger (1918) had introduced an entirely new viewpoint, by tak- ing account of the vortices in the slip stream of the propeller, that the ground was prepared for a satisfac- tory propeller theory. This was final- ly developed in the next ten years by Betz, Prandtl, Helmbold, Pistolesi, Bienen, v. Karman, Glauert, Kuchar- ski, and others. The purpose of the present paper is to present to the members of this society the salient points of this latest theory and to show how it can be applied in practical design work. In the first part of the paper the theory is presented essentially as developed by Betz, Prandtl and Helmbold, worked up from the sources given in the bibliography. In the second part a simple method is given by which the application of the theory to practical design work is greatly facilitated. This method is one that was developed by us some five years ago and used repeatedly in practice, To illustrate its use, an example has been worked through. Finally, the advantages of the new method are discussed, and it is shown that by means of it substan- tial improvements in propeller effi- ciency can be obtained. The author is connected with the United States experimental model basin, Washington. This appears to be a valuable contribution to the practical design of propellers, and the author is of the opinion that the method developed is capable of giv- ing results which compare favorably with those obtained by any other de- sign method, and that this fact com- bined with the other advantages of the method, some cof which are unique, will undoubtedly gain many adherents for it in the future. 5 Measurement of Propeller » Thrust on Shipboard, by Com- mander H. E. Saunders (CC), U.S.N., council member. This paper, which is 29 pages in length, with numerous illustrations, begins with the following statement: Although measurements of pro- peller thrust were first made not long after the general introduction of the screw propeller, so little was known of the behavior and character- MARINE REVIEW—December, 1934 istics of the propeller and of the in- teraction between propeller and ship that a determination of thrust meant little to the designer or builder of the vessel and her machinery and still less to the owner and operator of the ship. If the power plant could develop the specified horse- power, and the ship make the re- quired speed, all hands were satis- fied, and they continued to be satis- fied throughout a long period of de- velopment in the design of the pro- peller, during which a decrease in power or an increase in speed con- tinued to represent the primary goals to be attained. Until after the beginning of the present century, the power developed by the reciprocating steam engine of a ship was measured by indicators applied to its cylinders. It was not until engines of this type were em- ployed extensively for driving elec- trical generators ashore that engi- neers began to inquire as to the horsepower actually delivered at their shafts, Similarly, it was not until the extended use of the steam turbine, with its more or less uni- form turning movement, made pos- sible the development of a simple torsionmeter, that shaft horsepower instead of indicated horsepower be- came the measure of the output of a ship’s propelling machinery. In the meantime, however, a few inquisitive minds endeavored to de- termine how much of the _ shaft horsepower was being turned into useful work by the propeller, and how efficiently the propeller was de- veloping the thrust necessary to drive the ship through the water. Includ- ed among these few were experi- menters who devoted their time largely to research problems on re- sistance and propulsion which they hoped to solve by the use of models. The elder Froude, a renowned pio- neer in model research, developed a dynamometer for measuring’ the thrust of a propeller, but it has not been possible for the author to un- earth a description or drawing of this device. Most of the investigators made only sporadic attempts at the development of a reliable and serv- iceable thrustmeter for use on ship- board, limiting their efforts to a sin- gle type or design. Bauer, on the other hand, tackled the problem in comprehensive and systematic fash- ion in Germany, and it is to be re- gretted that, largely through circum- stances over which he had no con- trol, his efforts were not rewarded with the complete success which they deserved. In concluding this paper, which is a very complete treatise on the sub- ject, including summaries of the more important attempts made to measure propeller thrust, the author states that he regrets that his survey did not enable him to present a more optimistic view of the thrustmeter situation, and he hopes that the read-