A Study on Propeller-Guards for High Speed Small Crafts

Abstract

In the recent polluted condition on the inland waterways, high-speed small crafts have been suffering from propeller damages presumably caused by floating obstacles. A study has been made with the models in the circulating water channels at Tokyo University and Kawasaki Heavy Industries, Ltd. for the effective propller-guards as a countermeasure to collision of driftwoods with propeller blades. The model crafts used for the tests are a single-screw pilot boat and a twin-screw patrol boat shown in Figs. 1 and 2 and Figs. 3 and 4 respectively. Various types of guards were designed and tested with driftwood models thrown into the water. The configuration of the most effective one among a series of guard designs for the single-screw boat is shown in Fig. 10 and that for the twin-screw boat is the 11th scheme shown in Fig. 11. Employing these guards, the collision rate of the driftwood models and the index of damage of the propellers have been reduced almost down to 40 percent. The sea trials with the 15 meter twin-screw patrol boat fitted with the above-mentioned 11th guard proved that the guard did not cause any harm to the speed performance as well as the maneuvearabilty.