An Application of Course Stabilizing Fins for Coasters

Abstract

This report relates the results of study on improving the course stability of two small cargo boats by means of a pair of fins attached at the stern. Fig. 1 shows the arrangement of fins for Ship A. Provided a pair of fins, Ship A was perfectly stabilized. In case of Ship B, similar kind of fins named F_1 were fitted referring to the former experience but they were found to have quite a poor effect on the original purpose as compared with Ship A. Then, an experimental research on more effective fins was carried out with radiocontrolled model. We obtained the conclusions that : 1) It is an useful way to fit the course stabilizing fin of the present type on course unstable ships. 2) Even for unstable ships, the zig-zag test and its quasi-linear analysis are still applicable as well as for stable ships. 3) Models are generally much more stable on course than actual ships, as may be seen in Fig. 3. The difference of course stability between models and actual ships should be considered due to the scale effect on manoeuvering tests, and it is strongly desired to develop the research on the scale effect in manoeuvering tests.