An Experimental Study of the C-Start of a Mechanical Fish

The Northern Pike have recorded the highest accelerations for marine propulsors. The mean peak acceleration and velocity for a number of trials were found to be 120 ms-2 and 4 ms-1 respectively (Harper and Blake 1990) for live fish. Here, we emulate this fast-start motion and analyze the performance of the Northern Pike, using a mechanical fish. The mechanical fish was made of a PVC head attached to a spring steel frame with aluminum ribs and a plastic tail. A latex rubber sheet was used as the skin of the fish. The set-up used air bearings for frictionless motion with two degrees of freedom. The fish was bent to a C shape using servo motors. The two stages of the fast-start motion of a live fish with preparatory and propulsive strokes were closely replicated with this experimental set-up. The results showed that the acceleration profiles were qualitatively similar to that of the live fish. The objective of this project was to understand the mechanism by which the high acceleration is achieved in live fish. The designed mechanical fish was used to quantify the influence of the timing of each stroke and the shape and stiffness of the tail on the observed peak acceleration