⎯propeller boss cap fin is one of the efforts to increase efficiency, especially in the field of ship propulsion. boss cap fins propeller or commonly called PBCF is one of the technologies that replace the boss cap propeller technology that first exists. Increasing efficiency can certainly have an impact on fuel consumption. This study will describe changes in efficiency, thrust, torque and the phenomenon of flow in the propeller after changes in span to chord ratio of fins with a fin form in the form of NACA foil. This research begins with determining the dimensions of the propeller and its model. The next step is to design and draw the boss cap fins propeller by modifying the span to chord ratio of the fins. The final step is analyzing propeller performance with software based on fluid dynamic computation. It is believed that changes in the PBCF span to chord ratio can improve efficiency, thrust, propeller torque, and minimize the hub vortex Simulations are carried out on four variations of the span to chord ratio, namely 0.17, 0.23, 0.29 and 0.34. From this study, it can be concluded that the propeller boss cap fins can increase thrust, torque, and efficiency, but the changes of span to chord ratio PBCF have not much effect on thrust, torque, and propeller efficiency. Increasing the PBCF span to chord ratio can reduce the hub vortex on the propeller. Keywords⎯ computational fluid dynamic, propeller boss cap fins, span to chord ratio.

Singing is one of the problems that occurs in the propeller. However, singing will not happen to every propeller. Singing occurs a lot in high-speed propellers and on propellers with wide and thin blade sizes. One of the ships that have high speed and wide propeller is fast patrol boat. To overcome this problem, modifying the trailing edge is one of the most commonly used methods. Sharpening the trailing edge is a way to reduce vortex shedding. However, modifying the trailing edge of the propeller will change the shape of the propeller, which can affect the performance of the propeller. Therefore, this study discussed about the effect of trailing edge modification as anti-singing on propeller performance. Propeller performance analysed with open water test simulation assisted by computational fluid dynamic based software. There are three sharpening model in this study, where the sharpening size in this study refers to Van Lammeren anti-singing design. The size of sharpening are 20 mm, 25 mm, and 30 mm, where 20 mm sharpening is the best modification to overcome singing according to flow analysis. The open water test simulation result shows that the modification of trailing edge as anti-singing can increase the average thrust coefficient 8.96%, average torque coefficient 7.88%, and average open water efficiency 1.29%.