THE INVESTIGATION OF THE EFFECT OF THE BULBOUS BOW SHAPE TO THE WAVE DRAG OF A 28.3 m TRAWLER / PURSE SEINER

Abstract

Bulbous bow (or bulb at the bow) is designed below the water line to modify the flow of water around the hull, probably will cancel out or reduce the bow pressure wave systems. The aim of this project is to investigate the effect of the bulbous bow shape to the wave drag of a 28.3m Trawler/Purse Seiner. The prediction of resistance was conducted using CFD simulation by using SHIPFLOW CFD code developed by of FLOWTECH International AB. In order to find the optimized design of the bulbous bow shape, there are three parameters were laid out and studied by using Kratch (1978) design bulb approaches. The three parameters are the protruding length, LPR, bulb breadth, BB, and bulb height, ZB. The aim of the study is to improvise the bulbous bow shape design by changing the parameters to get the minimum resistance result, and quantify the resistance of the trawler upon the installation of bulbous bow in model and full scale. There were 8 different bulbous bow shape configurations. All the 8 different configurations were compared in terms of its resistance in model and full scale. All the 8 difference configurations were simulated using full RANS equations for speed of 7 to 15 knots. The free surface of the water was modelled using panel and volume of fluid (VOF) method. A grid dependence study was conducted to determine the best grid cell resolution and it was chosen at a total of 2469746 cells. The bare hull resistance of trawler was validated with experiment data from UTM’s towing tank results. All the bulbous bow shape designs were modelled using Maxsurf and Rhinoceros 3D software, and settings in SHIPFLOW. The best and worst bulbous bow design was selected in judging its minimum drag, largest percentage reduction, wave elevations and hull pressure distribution. It was found that the bulbous bow design TR1 by CFD is the most optimized configuration in terms of its performance criteria as mentioned earlier and TR2 is the worst bulbous bow design.