Experimental Investigation on Bulbous Stern Ship

Abstract

The term "Bulbous Stern" has the same meaning as "Hogner Stern" which was originated with Hogner. The purpose of our investigation is to find out whether or not it is possible to decrease propeller horse power of the bulbous stern ship compared with that of ordinary sterns by improving propulsive efficiency, even though her resistance inevitably increases. This report deals with experiments carrid out on 8 bulbous stern ships (3 tankers and 5 cargo ships) which were so designed that the principal dimensions of ship, the position of propeller, and sectional area curve were changed as least as possible. Flow patterns around the sterns and wake distributions have- also been investigated. Analizing the results of these experiments, we reached the following qualitative conclusions. (1) The total resistance of the bulbous stern ships is about 5-20 % higher than that of ordinary ships. (2) There may be some possibility to decrease propeller horsepower by a few per cent by providing a suitable shape and an appropriate position of the "Bulb" is designed. (3) To make the wake distribution of the bulbous stern ship uniform in the circumferential direction of propeller circle, it is preferable to make the "Bulb" somewhat virtically longer in the transverse section. (4) The most important of all the problems in designing the bulbous stern ship is to make the augmented resistance due to the "Bulb" as least as possible. It is relatively easy to improve the wake of the bulbous stern and its distribution, but it will be the most difficult problem to design the "Bulb" with the minimum augmented resistance.