The Effect of Course-stabilizing Fixed Fins on Manoeuvring Performance of a Water-jet Propelled Planing Boat

Abstract

Planing boats often lose course-keeping stability while planing at high speed. Course stability of a planing boat at high speed can be improved by attaching the course stabilizing fixed fins. In this research, course-keeping and manoeuvring performance have been investigated for a high speed planing boat with single water-jet propulsion whose length is 8.0 meter and weight is 3.0 ton. A 1/2.35 scaled model is used for a free running test to estimate the boat’s performance. The effects of fins on the boat’s course-keeping stability are investigated through course-keeping tests for fins with various area and aspect ratio at high speed, above 35 knots. Course-keeping stability is improved with increasing area or aspect ratio of fins. Fins also have significant effects on the turning performance of a planing boat. Turning tests are carried out with various water-jet nozzle angles at the speed of 20 to 30 knots. Initial transient and steady motionsin turning are compared with the variations of fin dimensions. In case of hard turns for a boat without fins, initially roll angle increases very rapidly together with high yaw rate and large drift angle. This so-called ‘side-slip’ can begreatly reduced by adding fins. In zig-zag tests, overshoot angles become smaller and the boat has better course-keepining and yaw checking ability as the area or aspect ratio of fins get larger. performance have been investigated for a high speed planing boat with single water-jet propulsion whose length is 8.0 meter and weight is 3.0 ton. A 1/2.35 scaled model is used for a free running test to estimate the boat’s performance. The effects of fins on the boat’s course-keeping stability are investigated through course-keeping tests for fins with various area and aspect ratio at high speed, above 35 knots. Course-keeping stability is improved with increasing area or aspect ratio of fins. Fins also have significant effects on the turning performance of a planing boat. Turning tests are carried out with various water-jet nozzle angles at the speed of 20 to 30 knots. Initial transient and steady motionsin turning are compared with the variations of fin dimensions. In case of hard turns for a boat without fins, initially roll angle increases very rapidly together with high yaw rate and large drift angle. This so-called ‘side-slip’ can begreatly reduced by adding fins. In zig-zag tests, overshoot angles become smaller and the boat has better course-keepining and yaw checking ability as the area or aspect ratio of fins get larger.